The Diminishing Returns of Adding Insulation

A look at the numbers behind this oft-heard expression

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If you’re building a house and want to have a really good building enclosure, you need it to be airtight, handle moisture properly, and have a good amount of insulation. Ideally, you’d also consider the effects of solar radiation on the home, but for now let’s just focus on the insulation. What exactly is “a good amount” anyway?

Insulation is like alcohol

If you’re a practical person, I’m sure you realize that life has a tendency to make you aware of certain limits. After the first few drinks in an evening, for example, further libations have less and less of an effect. Well, less and less of a positive effect anyway. Unfortunately, diminishing faculties obscure the diminishing returns, and you wake up the next day wondering how your head got in that vise. (Not that I know anything about that. I take all things in moderation, including moderation.)

The same is true with insulation. Below we’ll take a look at what happens as you keep increasing the R-value in a wall. If you just want to understand the concept of diminishing returns, you can skip ahead to the text below the graph. For the building science geeks out there, though, I need to tell how I generated the numbers for the graphs.

Calculating heat flow

The equation to calculate heat flow over a heating season is Q = U x A x HDD x 24. The result is the total number of BTUs of heat that flow through the wall under those conditions. The only thing that varies in the graph below is the R-value.

U = 1/R
A = 1,000 square feet
HDD = 4,400

A is the wall area, and I chose 1,000 square feet as a representative value. HDD is the number of heating degree days using a base temperature of 65°F, and, for four of the graphs below I chose a city in IECC climate zone 4, such as Portland, Oregon, Asheville, North Carolina, or Louisville, Kentucky.

For the other example I used Atlanta, which has 3,000 HDD. For all of the graphs, I divided the result of the calculation by 1 million and plotted MMBTU (million BTU) instead of having all those unwieldy zeroes on the axis.

OK, now we’ve got those details out of the way. Let’s see what it means.

Getting less and less from more and more

First, here’s what everyone knows already. As you keep adding more and more insulation, you keep reducing the heat flow through the wall more and more. The blue line in all the graphs below shows the heat flow through the wall, and the red columns show either the stepwise or cumulative reduction in heat flow compared to what it was with an R-2, R-11, or R-16 wall.

An uninsulated standard 2×4 wood-frame wall has an R-value of about 3, so our starting point of R-2 in the first graphs is close to that of an uninsulated wall.

This first graph shows cumulative reduction in heat flow. Notice carefully how it grows.

If you can see what’s really happening here, you don’t need the next graph. The important effect here is that most of the reduction in heat flow happens early on. With each addition of R-2 to the insulation level, the reduction declines.

An easier way to see that is with the graph below. Here I’ve plotted only the reduction achieved for a given step of R-2. Once you get out to about R-14 or so, at least on the scale shown here, the additional insulation results in pretty small reductions in heat flow.

From this we can draw our first conclusion:

Important Lesson: Adding any insulation to uninsulated homes can save more energy than adding more insulation to already-insulated homes.

Where the curve is more vertical is where most of the action occurs. Once it starts flattening out, you get less and less from more and more. That’s what is meant by the term “diminishing returns.”

In fact, this whole exercise harkens back to my “Flat or Lumpy?” article, in which I wrote about the importance of not missing areas that need to be insulated and getting a uniform coverage. My friend Mike MacFarland helped make this connection for me last night when he texted, “This is why it’s so critically important to use building performance equipment to locate and fix all of those areas in homes where the vertical part of the graph exists.” Indeed!

The previous graph helps understand how important it is to fix uninsulated homes, but it could lead to the wrong lesson when it comes to designing new homes. If you’re designing a new home and trying to find out how much energy you might save by adding more insulation, you’ve got to choose a more reasonable starting point.

In Atlanta, for example, you’ve got to put a minimum of R-13 insulation in your above-grade exterior walls. Factoring in the effect of all that lower R-value wood in a standard 2×4 wall (with studs 16 inches on center), the whole-wall R-value is about R-11, so that’s our starting point.

If you’re framing with 2x4s, you could go with a higher density R-15 insulation and get a whole wall R-value of 13 in the same space. You could also build thicker walls or add exterior insulation or both, with the result of higher R-values. However you do it, we get a similar graph of cumulative heat flow reduction as our first graph above, shown in the graph below.

The graph below shows the stepwise reduction in heat flow when you go from R-11 up to R-40 walls (adjusting the calculation for Atlanta’s 3000 HDD). Each red column shows the reduction in heat flow for just that step (e.g., R-11 to R-13 or R-30 to R-35). As before, with each step up in R-value, the potential savings decrease for each unit of R-value.

The key is to figure out how much it’s going to cost you to get those savings. Going from R-11 to R-13 just involves using a different insulation, but going from R-13 to R-15 (the whole-wall R-value for 2×6 walls) requires going from 2×4 to 2×6 walls and thus more insulation, more lumber, and doors and windows with wider jambs. That means going from R-11 to R-13 is has a much higher potential of being cost-effective than going from R-13 to R-15.

What if you were to insulate your walls to R-19 in the climate zone 4 cities I used for the first graph? When you put R-19 insulation in the cavities and mix in 2×6 framing that’s only R-7, the whole-wall R-value is about R-16, our starting point in this case. The same pattern as before holds in this case, as you can see in the graph below.

And the returns still diminish, as you can see in the stepwise reductions shown in the graph below.

Too much is never enough

The debate over how much insulation to use is an important one. There’s no clear-cut answer. I can’t tell you, “Use this much in Climate Zone 4 and this much in Climate Zone 5” because there are multiple variables involved. Here are the main ones:

• Climate zone
• Type of heating and cooling system
• Fuel used for heating
• Utility costs
• Photovoltaic (solar electric) system costs
• Comfort
• Your interests and goals: utility bills, carbon footprint…

In my Mastering Building Science course, which begins on October 27, 2014, I’ll dive into these variables and show how you might decide what’s the optimal amount of insulation to use. You’ll also get my spreadsheets if you sign up.

Take heating system types, for example. The graphs above show the amount of heat moving through that 1,000-square-foot wall, but the amount of heat you pay for may be different from what’s flowing through the wall. If you’re heating with a furnace that’s 80% efficient, you’ll have to buy 25% more BTUs than you lose through the wall. If instead you use electric resistance heat, you buy the same number of BTUs you lose, but with a different fuel and at a different cost. All that and more factors into the decision.

I’ve had this topic on my list for a long time, and finally got spurred to write about it because of the debate over the Passive House program and the insulation levels required to meet the requirement for the annual space heating demand to be no higher than 4,750 BTU/sf, no matter what climate you’re in.

Martin Holladay, the Energy Nerd here at Green Building Advisor, had a great article about it last week: It’s Not About Space Heating. He reported on a recent presentation by Marc Rosenbaum, and the issue of the diminishing returns of adding insulation played a big role (although that term didn’t appear). Rosenbaum’s main point is that spending a lot of extra money on the building enclosure to chase those last BTUs is probably not the best way to go. Go read the article. And be sure to read Rosenbaum’s comment (#2), too.

How far you should go depends on all those variables above, including your goals. If you want to build a net-zero-energy home, you’ll go further than someone who wants only comfort and reasonably low energy bills, who will go further than someone who wants the lowest upfront cost.

Some people look at the graphs above, especially the second one, and conclude that it’s silly to go beyond the first few steps since you’ve already gotten most of the reduction you’re going to get. That is a mistake. First of all, you have to make sure you’re choosing the correct point for comparison. The first two graphs use a starting point of an uninsulated wall.

If you’re designing for new construction, you have to choose a starting point that is at least at the level required by your local code. As you can see in my R-13 and R-19 examples, the returns don’t diminish nearly as quickly when you start higher. That may sound odd, but it’s true. That doesn’t mean all those higher levels of insulation are cost-effective, though. You’ve got to do the calculations to find where your optimum is.

The bottom line is that although you can certainly put R-40 insulation under your slab or R-80 insulation in your walls, it may not be the smartest thing to do. Take a look at the bigger picture and see whether you might be better served by reducing the size of the home, finding ways to save on water heating, appliances, and plug loads, or investing in photovoltaics. Whether you’re trying to reduce power plant emissions or just save money, at a certain point, it becomes wiser to stop with the insulation and spend your money on the stuff that, dollar for dollar, will yield better results.

Allison Bailes of Decatur, Georgia, is a speaker, writer, energy consultant, RESNET-certified trainer, and the author of the Energy Vanguard Blog. Check out his in-depth course, Mastering Building Science at Heatspring Learning Institute, and follow him on Twitter at @EnergyVanguard.

1. GBA Editor
| | #1

Great article
Allison,
Thanks for doing a great job covering this topic.

My two mantras (which you covered) are these:

1. Every time you double the insulation thickness, you cut the rate of heat flow in half. (This rule never changes.)

2. Any comparison has to start with a code-minimum assembly, not a tent.

Plenty of spray foam contractors who talk about "diminishing returns" forget Principle #2. In a climate zone that calls for a minimum of R-38 roof insulation, they compare R-2 assemblies to illegal assemblies like R-4 assemblies and R-8 assemblies and R-16 assemblies -- all of which are irrelevant.

2. | | #2

How does the cost scale?
Thanks for this review of an essential basic principle. As you note, it's easier to understand the way the heat flow changes with the insulation value than it is to understand how the cost scales. If you are starting with a 2x4 wall and adding polyiso to the outside, each increment of more polyiso is expensive in terms of material; it also adds some difficulty to the installation although that's harder to quantify. On the other hand, if you are making a double wall with cellulose between the walls, you've already bought the expensive part--the materials and labor in the two walls--and adding cellulose is cheap. So with that construction approach once you've bought pretty good, the extra cost for great can be small.

It's also worth noting other benefits of a good envelope.
* You save money on the heating system because it can be smaller.
* You get more uniform temperatures for improved comfort and the ability to use fewer heat sources.
* You get fewer heating degree days because the base temperature at which you need to start heating goes down, so the need for purposeful heat supplied can go down by a bigger factor than the heat flow through the walls goes down.

3. | | #3

Insulation "Cost Effectiveness" - a poor decision making tool.
Thanks Charlie Sullivan for mentioning other benefits to consider!

It is very tempting to oversimplify design criteria. We need to be careful to distinguish between efficiency and laziness.

In my mind optimizing efficiency is considering important connections and drawing lines effectively. Laziness is drawing those lines so they exclude critical issues. Simplistic design thinkers ignore critically important connected issues when making decisions which leads to harming clients.

Designing for delta T cost effectiveness seems to elevate air temperature and optimizing energy loss through surfaces as a primary design consideration.

Instead of designing insulation levels for optimal temperature delta t cost effectiveness don't we want to consider energy replacement, dew point control, humidity control, and mean radiant opportunities?

Isn't it likely that considering these issues will allow for lower air temperatures, smaller equipment, longer equipment run cycles under all conditions, better humidity levels, and better control - all of which combine to mean significantly less capital expense, energy use while providing better comfort, control, and environmental health?

4. | | #4

Good article
Insulation values to the zone with a very tight envelope is key. I found using mostly picture windows (within code) helps with cost and air tightness as well. Extreme homes help us understand building science better. A balance is created from those examples and helps us all.

In an ideal world it be nice if insulation came with a air sealed whole wall effeciency number instead of r values.

5. | | #5

The graph looks a whole lot different if you start at R-5
I've seen this graph many times before, frequently to justify paying for expensive insulation options. I have often thought it deceptive because it suggests that uninsulated framed walls perform at R-0. I've heard Michael Blasnik lecture several times about the shortcomings of energy modeling and his data suggests that uninsulated walls perform pretty close to R-5. This curve of this graph looks much different if it starts at R-5--which well illustrates both of Martin's mantras in comment #1. I feel that this graph adds unnecessary confusion and detracts from a key message--that most builders can choose better assemblies which are cost-neutral to build and cost-effective to operate.

6. GBA Editor
| | #6

Response to Dan Lutz
Although you don't say, I'm assuming the graph you are referring to is either of the first two, the ones that are embedded in the text. If you will look closely, you'll see that they both start at R-2, not R-0, and that I said in the text that an uninsulated wall is about R-3, which isn't too far from R-5.

If you read the rest of the article, you'll see also that I looked at the two cases of starting from a wall built with R-13 insulation and a wall built with R-19 insulation. The graphs for those cases are at the bottom of the article.

I'm not sure, though, whether you're arguing for more insulation or less, Dan. You say the first graphs starting at R-2 are used "to justify paying for expensive insulation options" and that it's better to start at R-5. But the higher your starting point, the easier it is to justify more insulation. Again, see the part about starting with R-13 or R-19.

7. | | #7

Looking Outside In
Good discussion here and we’d just like to reinforce the point made that the building envelope can play a significant role in achieving energy efficiency goals. Wall studs, both wood and metal, are poor insulators — when they come in contact with the exterior cladding, they allow heat to pass through them (thermal bridging). Since these studs represent up to 25 percent of the wall surface of an average home, it’s like having an entire exterior wall with no insulation at all. One solution is insulated siding, which is included in the 2015 International Energy Conservation Code among the materials that can be used as continuous insulation outside of the building framing to provide the required total wall R-value for buildings in the coldest climate zones. It provides continuous insulation over the studs, reducing thermal bridging and improving a home’s energy efficiency.

8. | | #8

I've given more thought to this. The technical side of things is fine, but the article inadvertently changes the dialog in a direction that could be detrimental to both the client and the practitioner.

Clients want problems solved. In a new home they want problems with their old home solved. If we change their focus too much towards cost effectiveness it is a dangerous path. Residential energy efficiency is rarely 'cost effective'. The SIRs on my projects (granted they are retrofit and more expensive) run in the .4 to .6 range, meaning that about half the project will pay for itself within the predicted lifespan of the improvements.

If we move the focus much towards cost effectiveness, the likelihood of disappointment from both the client and the practitioner goes up substantially. If we instead focus on extreme comfort, excellent IAQ, good Indoor Environmental Quality, and the like, that is more likely to lead to a happy client.

Those are emotional things. Our homes are emotional things. If we focus too much on the rational it can be a slippery slope.

Allison, I know you prefer to think comprehensively, so this is more of a commentary than any kind of shot. It was bugging me.

9. | | #9

Whole-wall U-value
Allison, Thanks for a clear and careful explanation. Two concerns:

One, I think your critical point – that it’s a mistake to look only at the first two graphs and think high levels of insulation are not cost effective – is easy to miss by being near the end of the article and with only the first two graphs positioned in-line with the text. (I know you didn't format the page…) The additional graphs were the most interesting and compelling, and I almost missed them and their discussion.

Second, in encouraging us to look at the bigger picture, windows are omitted from the list of measures to address. The insulation discussion is often framed as “extra insulation vs. photovoltaics” (as in the photo caption) but I think this misses the point. It’s helpful to understand solid wall performance before adding other variables, but people keep putting windows in those nice walls. Once we have an initial wall insulation goal, the next key step might be analyzing the window performance and it’s effect on the whole-envelope U-value. I think the return on wall insulation is hard to understand without studying the interaction of window performance.

10. GBA Editor
| | #10

Thanks for the suggestion. I've asked Martin to insert the other graphs into the text as well.

And yes, you make an excellent point about windows. They definitely should be included in the discussion because when you start talking about improving walls, you can't avoid the windows. That R-13 insulated wall in Atlanta has R-3 windows, so it's possible to save a considerable amount of energy there, as well as helping with the mean radiant temperature indoors.

11. GBA Editor
| | #11

Perhaps I didn't do as good a job framing the issue as I should have. This is not changing a conversation but adding to one that's been going on here at GBA and other places for years. People who want lots of insulation (e.g., the superinsulation/Passive House crowd) have discussed this for a long time, and everyone needs to know that there's a way to figure out when is a good point to stop adding more insulation and instead spend the extra money on windows (there you go, david posada!), PV, or a heat pump water heater.

I'm not arguing that energy conservation is the most important goal or that comfort doesn't matter. And I'm not saying every expense has to meet some cost effectiveness metric. What I'm trying to do is help people who want a really energy efficient house and have a certain budget to work with understand that just adding more and more and more insulation isn't the smartest way to get there.

This is exactly what the Passive House Institute US (PHIUS) has been going through recently as the technical committee has worked to recommend moving from the fixed standard (4750 BTU/sf/yr) to one that works for different climates. (See the discussion of this in my recent article here, Highlights from the North American Passive House Conference.)

12. | | #12

Banging the retrofit drum
Great article.

I'd love to see a similar average cost per installed BTU load reduction for the retrofit situation. GBA is an amazing site but often takes a very energy high-end new approach when much of the construction in the US is either commodity building or cost-sensitive energy refurbishment. An article (or tool) that helped address where money is more cost effectively spent would be a great tool. You might think you could get this information out of hvac contractors, window salesman, insulation installers, or even energy raters but only if you haven't talked to those folks as a residential customer.

An example: In my area, there are many prototypical home that have an 80% efficient furnace, R-11 walls, single pane aluminum windows with storms, an uninsulated attic hatch, ducts in the exterior walls, R-13 to R-19 in the attic, a vented uninsulated soil crawl under the uninsulated floor, and a 55% efficient atmospherically drafted hot water heater. I'm a new owner and have \$X to spend. Do I get PV? Windows? Furnace? New siding and foam board insulation? etc.

You might suggest that an energy audit would help with this. Maybe it does sometimes but that hasn't been my experience.

It seems like a decision tree type tool would not be that hard.

13. | | #13

Keith:
would not be hard to list ...but nearly impossible to target.
Just way too many possibilities.

I agree with Dan when he says that we need to find better build systems to lower the cost/performance ratio.
As i mentioned in another thread, i firmly believe that half of what keeps higher efficient designs to get economical is better building strategies.

Pre-fab might be the best solution for high performance/price ratio .
Pre-fab wall sections with engineered systems and labor optimized designs to monimize both labor time and errors.

There are many types of buildings to consider here,
but don't believe you can sell efficiency to the mass.

The only way we can make a difference in the buildings energy consumption is through quantity,
and the only way to build quantity with economical sense is manufacturing.

If you wait for the next owner to ask for efficiency, you will be building half-assed, low quantity buildings that will have no impact on environmental problems.

One needs to step up, work harder on design and planning, build according to design and goals,
and invest on larger housing projects .

Performance always sells itself , no marketing required.

In my area, 90% of builders are afraid of the investment and risk, because they have no passion and build boring buildings with no attributes that are just like the 100's next ones and then complain about the lack of potential buyers.
So they then revert back to building owners requests only, which ends up as inefficient buildings with nice cliche looks and impossible roof trusses and fake chimneys .

It is difficult to explain how one can save using recent LED lighting to more than 90% of people i tried . ( i tested it hard and many times )
Even with paybacks in the 2-3years with recent prices.
Imagine, we are talking about investments in the ~10-100\$ here, not thousands.

Finally, as mr Bailes pointed out, there are soo many other factors to consider than solely heat transfer/economy when designing buildings, combinations seem limitless.

14. GBA Editor
| | #14

Response to Keith H
Keith,
It's worth investing in an energy audit. A good auditor or home energy rater should be able to provide a prioritized list of suggested energy retrofit measures, beginning with the most cost-effective measure.

I was going to make a stab at guessing which measures might make sense for the house you were describing, until I realized that you forgot to tell us (a) your climate zone, and (b) your fuel type or fuel cost. These omissions point to the larger issue that Jin raised -- there are too many variables to make generalizations.

15. | | #15

Heat flow goes both ways...
I've often wondered why we only look at HDD rather than looking at both HDD and CDD.... after all, we need to use energy to cool a home, too. Accounting for this would push the cost-effectiveness point for wall and ceiling insulation up and lower that for the slab.

16. | | #16

Dustin :
Most of the time, heating is more expensive than cooling .
( larger temperature in most of USA/CANADA zones )
And cooling with recent heat pump systems is usually much efficient .

Then, north people tend to see only heating as we do not need much cooling or do not care because of its low impact;
and south folks without any real heating needs can't be blame for thinking about cooling and latent loads.

It's a matter of perspective and interests.

But, you might see more heating dominated climate users here because,
heating in zone 5-8 costs much more than cooling in southern climates, thus
economics of climate and heat loss gain importance with the larger HDD
up to where they drive everything in situations like Alaska and north Canada .

The heatloss formulas works both ways, so you can just add the heatloss together to get an idea of the impact.

17. | | #17

Dustin, I hear you and agree.
Dustin, I hear you and agree. In warmer climates wall and ceiling insulation are much more important than floor insulation. A point that is little recognized so I'm glad you did. Hopefully that is one of the things that the USPHG will be working on in their climate specific guidelines. It's important. I also wish there was at least one person who regularly contributes blogs and articles on this excellent web site known as GBA that hails from a western, warm, non-humid climate. Is that too much to ask?

18. GBA Editor
| | #18

Response to Eric Habegger
Eric,
I could assemble a list of articles (and case studies) on the GBA site that were written by Western authors, but I imagine that isn't necessary. I understand your point. Now is probably a good time to say that GBA welcomes submissions and guest blogs from our readers, especially from readers who live in regions where our coverage is relatively weak.

So, if you live west of the Rocky Mountains, plus submit articles to GBA!

19. | | #19

divide by zero error
I'm glad someone finally posted one of those graphs with an
identifiable baseline. "R-0" is really pretty meaningless
unless you're trying to live in a single-wall box made of
sheet copper and painted matte black.

_H*

20. | | #20

Insulation, savings in the longer term.

Surely the starting point must be, how long will this home be used, lived in?
World wide, we have people living in buildings that are hundreds of years old. Their building costs long ago become totally insignificant. The same applies here, build today, with insulation in place to Passive House standard and the heating and cooling costs amount to perhaps one tenth of that of the code built home next door, and this saving goes on day after day – for years.
That over the top insulation, will be working night and day summer and winter 24/7 for perhaps one to four hundred years. In that time that installed heating and cooling equipment will be replaced many times and those heating and cooling, bills will still be thought significant by future generations. The home next door will have spent several fortunes on heating and cooling.......surely we can see the benefit of more effective insulation over the long term.....the pay back continues for years.

21. | | #21

Roger :
15 years ago one might have thought so,
but never forget that we are always 1 discovery from very cheap and green energy.

As discussed in other recent threads, with the current prices and efficiency of PV,
it might be sooner than we think that energy will drop in price substantially,
which will affect all of predictions.

Also we might invent or discover new ways for thermal regulation of buildings, which might have great effects on the energy spent.

The goal for now should be to reduce depence on all fuels,especially those coming from outside North America.

22. | | #22

It's worth investing in an energy audit. A good auditor or home energy rater should be able to provide a prioritized list of suggested energy retrofit measures, beginning with the most cost-effective measure."

That is what a SALESPERSON might do (see the MacFarland case study), but that is absolutely NOT what a good auditor will do!

Martin, this is a really important concept I hope you can get:

-- Home performance is not individual measures - it's bringing systems that are out of balance into balance.

-- Home Performance is not like replacing a light bulb or buying a refrigerator. Those are systems unto themselves.

-- Home Performance is not picking from an a-la-carte menu of items that then save you the prescribed amount of money.

Perpetuating that simplistic thinking is HARMFUL to consumers, and I don't think that is your objective. (Nothing get's me more upset than when I see people who I think have high integrity cavalierly giving people bad advice, it makes me think I'm a bad judge of character.)

A GOOD AUDITOR WILL help you figure out your problems. He will then help you figure out a budget to address these problems, in the proper order which is NOT determined by cost effectiveness. Based upon your budget a good auditor will put together a plan for TO DO NOW items and possibly TO DO LATER items, and hopefully they will address your PROBLEMS, not what will "save" an extra \$5 per month in theory - but not in practice.

The first job I helped Nate with was his very first furnace sale. These people had recently DONE the "most cost effective item" and replaced their furnace. The had a very nice two stage ecm driven furnace. Practically brand new - 3 years old in perfect shape. They replaced it with another brand new two stage ecm driven furnace. \$5000 in the toilet because of "low hanging fruit" thinking.

Please please please take a moment to think about this. Be open to having your schema's changed because you can either really help consumers with guidance that helps them think differently, or you can really harm them by confirming they should continue to think about things the wrong way.

23. | | #23

First off, in no way do I
First off, in no way do I support any use of my name or case studies to disrespect anyone or for any purpose other than to inspire home performance pros and the public to what is possible. I appreciate and respect Martin and all of his work here at GBA, and hope that we will continue to see it for years to come. Even if he does think ductless mini splits are the best choices for EE homes- we can't all be perfect.

Interestingly, I've yet to meet a home energy rater that can provide a list of improvements that will solve real problems in a home. And we've used an independent rater for years that I would consider to be "very good". But he's very good at ensuring compliance with minimum code standards and barely-passing work. And he's very good at giving a score to a home that means absolutely nothing and creates no savings for a client. And he's very good at invoicing and showing up when I need him, to make very good pay for looking at gauges and punching numbers into a computer. And he's very ethical and smart. He just has never data logged anything and used that data to do better work. And he's never dug into our best ASHRAE engineering and adapted it to his work as an installer. And he's never challenged conventional wisdom and discovered how to take brand new stuff apart and optimize it to work best in his climate.

Yes, any rater will show you the results of imaginary modeling and what programs like Energy Amateur will demonstrate for savings. But since he's never correlated his modeling to reality, it's not anything that should be shared with a potential client who wants real solutions. Customers should always ask for real data and proof of results from past projects, and what the contractors actual realization rate is. If he can't supply real data, they should move on until they find someone who can.

Once the public demands data, we will raise the industry from "barely pathetic" to "passing" and better. They just need to know why they need to require it, and that's the role that great sites like GBA can play a huge part in.

24. | | #24

Reply to Martin And Ted Kidd
Martin: I was speaking generically about the value of a software tool to drive better decision making while being consumer accessible rather than talking about my own needs.

Martin and Ted:
My own experience as a residential homeowner with an energy audit (yes, I've had one) was pretty poor. Despite multiple attempts to reach out to the audit company, I never got anything actionable. Only once I had a manual D/J and started using a usb camera to look in walls for thermal envelope badness did I start understanding why the house performed so poorly.

There are a lot of folks who need a generic starting point so they can call the right person or have starting points of knowledge for when they first contact HVAC contractors. Seems like software (ie a website) could provide an expert rule system for that first point of contact.

25. GBA Editor
| | #25

Response to Ted Kidd and Mike MacFarland
Ted and Mike,
You have both (in different ways) challenged me for advising GBA readers with old houses to get an energy audit, and to implement the most cost-effective measures first.

Before I respond to this challenge, I'd like to make some stipulations:

1. Ever since I was the editor of Energy Design Update, I have been reporting the results of research studies showing that actual energy savings from energy retrofit work are less than predicted. Many studies have shown this to be true, and these studies' findings are consistent.

2. Many energy experts (notably Michael Blasnik) have been pointing this out for years, and as an editor I have provided a platform for Michael and others to explain this phenomenon to interested readers.

3. I have reported for years on the cost and results associated with so-called "deep energy retrofits," and along with Paul Eldrenkamp have concluded that this approach is extremely expensive and yields energy savings that will never justify the cost of the work.

OK. I'm glad we got these stipulations out of the way.

Concerning Ted's insistence that homeowners can afford to borrow money from a lender for \$20,000 to \$30,000 of home performance work: it's a silly argument. Some homeowners can afford this type of work, while others can't. If you are in the business of doing this type of work, it's in your interest to locate the type of homeowner who can afford this type of work and convince them that it's worthwhile to borrow the money.

I live in a leaky, poorly insulated house. (I built it, but that's another story.) If you came to me and suggested that I go to a bank and borrow \$25,000 for home improvements that aren't cost-effective, I wouldn't do it. Call me an ass if you want, but I don't want to take on that kind of debt. To my way of thinking, I can't afford it. Others can.

I see three approaches to these problems:

1. Traditional weatherization work -- one day of blower-door-directed air sealing and some extra cellulose for the attic, at a cost of \$3,000 to \$5,000.

2. The Nate Adams approach: convincing homeowners to borrow \$20,000 to \$30,000 for home performance work, while explaining to the homeowners that the expected energy savings will be less than their monthly loan payments.

3. A full-on deep-energy retrofit costing \$100,000 to \$150,000, as performed by Paul Eldrenkamp -- an approach that even Paul Eldrenkamp doesn't really endorse.

In the meantime, as we ponder these three options, owners of old, leaky houses write to GBA every day, asking, "What should I do?" I advise them to hire an energy auditor or home energy rater to evaluate their house with a blower door and an infrared camera, in order to obtain a prioritized list of possible energy retrofit improvements. Both of you (Ted and Mike) are ridiculing that approach. I understand why. Of course it makes no sense to buy a brand new 80,000 Btuh furnace as your first measure, when air sealing work and better insulation could lower your design heating load. I get that. You have to think.

I know that there is a shortage of good energy auditors who can provide comprehensive advice. We try to fill in the information gap here at GBA. Energy audits aren't perfect. But there are millions of homeowners who could benefit from air sealing work and a new layer of cellulose in their attic. I will continue to do my best at advising people with high energy bills, even though my solution isn't perfect.

The \$30,000 solution isn't perfect either. It's a boutique program for one category of homeowner, the ones for whom comfort trumps low energy bills. Lots of working-class families are just getting by right now, and they don't want to take on new debt.

26. GBA Editor
| | #26

One more point for Ted and Mike
Ted and Mike,
It seems that the two of you (and also Nate Adams) have concluded that traditional residential energy retrofit work isn't cost-effective. In the light of the many research studies that show that energy savings associated with this type of work are dependably less than predicted, you may be right.

That's why those of us who have worked in this field for decades are challenged by the fact that energy savings associated with the installation of a PV system are generally (to quote Mona Lisa from My Cousin Vinny) "dead-on balls accurate." You want a cost-effective energy saving measure? In many regions of the U.S., the best approach is to install a PV system.

But of course, saying that on an energy-efficiency forum is politically incorrect.

27. | | #27

Bravo Mike MacFarland and this blog Allison and Martin
Very good topic. I like the Mike methods and think it should be the norm.

What I like about this blog is the idea that one should find the low R areas of a home and investigate the cost of increasing the R there as it is the most worthy... the graphs show such. Air sealing is number one as an air hole is R 0! Great way to sell air sealing to one self and to a customer.

Air sealing of R 0 is best shown with the first graph so all the graphs have their place in my mind in fact the graph starting at 0 is to me the obvious most important graph. Old homes need air sealing priority number one.

28. | | #28

Martin,

Martin,

Please lower your guard as I'm not arguing with you or teamed up with any other commenters, but rather agreeing and simply adding clarifications to your solid advice.

My point was that the public should be advised to ask for an audit from someone with real credentials, and the best credentials are data gathered from prior projects (test out and utility data for a year minimum). Additionally, the public should ask for realization rates and how much energy the auditor has promised versus saved prior clients, measured by actual utility bill data. They should know whether the auditor guarantees anything, and to what extent.

I have never intentionally challenged the cost effectiveness of home performance, and only supported it with case studies of deep energy retrofit projects.

Your experience and wisdom isn't being challenged by me, and I'm only offerring further advice to help your readers request information that will ensure that when they pay their hard earned money for an audit, they know that it will hold tremendous value potential. The request for data will transform the conversation from theoretical to actual, and eliminate the issues between the dependable return of PV you mentioned, and get people measuring their work.

All very good outcomes, right?

29. GBA Editor
| | #29

Response to Mike MacFarland
Mike,

I love data and verified results! Let's trumpet the contractors who can provide both.

30. | | #30

Response to Martin #25 and #26
If energy retrofits aren't cost effective and energy results are consistently disappointing, wouldn't it be good to admit that as an industry for honesty's sake? Once those admissions are behind us, we can move on to real problems, which usually aren't saving clients \$300-1000/year in utilities, which is typical. We can fix comfort and ice dam and asthma and allergies and moisture problems, which are always underneath the \$ requests, but we have to dig.

If I thought we could get there without 'comprehensive' but not deep energy retrofits, I'd be all for it. I've been down that road. It doesn't work.

Comprehensive, in my mind, means getting enough control over heat, air, and moisture flows in a home to be able to have full control over them with the HVAC system. Most houses aren't there. But \$10-20K in shell work, plus a new HVAC system which will need to be bought in the next 15 years, will fix most houses. Mike MacFarland goes further than this.

The full DER in my mind is nuts, and is not a market solution, particularly in places like Cleveland where \$200K will buy you a 3000 sf older home in many towns. There just isn't enough home value. If we could get \$10K of that \$20-30K to stay with the house through On-Bill, and that keeps utility costs where they are (i.e. \$50 energy savings for a \$50 loan), then we're talking a much smaller bite.

Homeowners plop \$20-50K down on kitchens, for \$10-20K, or \$75-150/mo, they can fix their homes from a comfort, health & safety, durability, and efficiency standpoints. Boom. Done. Loads usually get reduced to between 2 and 3 ton heat pumps, which gives us nice equipment choices. Now they can slap those 'dead nuts' panels on the roof (I LOVE My Cousin Vinny) and push towards Net Zero. Or power an electric car - hey, does that sound like a consumer solution to climate change? (I am working on a post with that title.)

As far as dead nuts goes, BTW, MacFarland is THERE. He guarantees energy costs. If someone buys a TV, he notices it. I think we could get there as an industry, but we need to go far enough to gain control over heat, air, and moisture flows so that we have some certainty of outcome. And that doesn't take a \$100-150K DER. That accuracy needs to be rewarded, though, which is a major result of One Knob. Those that are accurate rise to the top. I've made some educated guesses this year, we'll see how they work out - I want to be on the top of that list!

What we are doing isn't working. The only people in HP I know of making good money are attached to a program, sell equipment, or (maybe) are in the publishing business. =) One HP job gets done for every 1000 HVAC jobs. We have failed miserably as an industry. It's time to try something radically different. Half measures lead to quarter results. Let's help educate homeowners on full measures.

Does that give you some more insight into our thinking?

31. | | #31

Nate, I think you are being
Nate, I think you are being injudicious by taking such a hard line on Martin's observation that often there IS low hanging energy conservation fruit in many homes. You are coming to the conversation from the standpoint of your failed business model based on small jobs that used government energy conservation programs. You explained very well in your article why that did not work for both yourself and also your customers. What I don't think you are getting is that those reimbursed government programs mostly are a one-size-fits-all thing. They don't actually address the real problems that stand out in many homes. In other words, those government programs don't really apply to "low hanging fruit". They are generic fixes.

I think the whole conversation is geared to this paradigm shift thing that you are promoting. I think it does a disservice to Martin and many readers here. People here, especially Martin and the other contributers here, are very sophisticated about what works and what does not work. Of course sometimes a house is such a mess, http://vimeo.com/108391422 such as the home in Redding Ca. that there are no easy fixes. However, after watching that video I'm not convinced that previous work that caused the problems encountered was not done by incompetent HVAC guys. Perhaps the construction of the house, as integrated with the HVAC system, was the problem.

So OK, we get it. It wasn't an easy fix. That doesn't mean it wasn't an easily identifiable problem. You are conflating those two things by introducing the low hanging fruit thing. Again, I think that's a false analogy created by your bad experience working with government subsidy programs for increasing energy efficiency in homes. I know Martin doesn't need my help here but it seems you guys, you in particular, are ganging up on him just because of your preferred usage of language.

32. | | #32

RE: MacFarland on “Asset Ratings”

“Yes, any rater will show you the results of imaginary modeling and what programs like Energy Amateur will demonstrate for savings. But since he's never correlated his modeling to reality, it's not anything that should be shared with a potential client who wants real solutions. Customers should always ask for real data and proof of results from past projects, and what the contractors actual realization rate is. If he can't supply real data, they should move on until they find someone who can.
Once the public demands data, we will raise the industry from "barely pathetic" to "passing" and better. They just need to know why they need to require it, and that's the role that great sites like GBA can play a huge part in.”

HERE HERE!!

In theory I’m a billionaire. What frustrates me about that is in reality it doesn’t put a Tesla in my garage. I think when home performance becomes about reality we will see market transformation. People really love getting their homes fixed, they just lack confidence they will get what they want. When they open the garage we need to be sure the Tesla will be there.

The one place Mike and I deviate is I believe it is the PROGRAM responsibility to track results. First, there is no incentive. Second, I have as much confidence in the data as I do in referenced - where are the clients that HATE you? Third, the idea you can get contractors to be good and home performance AND be data dorks is absurd. These characteristics are such polar opposites I don’t think one in a million is capable. Forth, tracking should have standardization and public access.

That doesn’t happen when the data lives in my or Mike’s or Nate’s silo.

33. | | #33

RE: Response to Ted and Mike.
Martin, you are like a hair in a biscuit!! Thank you for hanging in! By your language it’s seems you are starting put aside conventional thinking and see this as we see it.

The purpose - the reason people have us to their homes in the first place - isn’t to save energy for the sake of saving energy. The purpose is fix existing problems. Often a consequence of these problems is wasted energy. Using creativity and building science we do this and leave a home using less energy where other often solve problems by using more energy.

Energy is not why we get called, there are ALWAYS other issues.

1. Yes they are less. Without feedback, accountability, or reward why would they be accurate? When energy programs have pass/fail “minimum savings” this encourages exaggeration, what do you THINK you are likely to get? The final step is “OK, how do I game this model to show this project is cost effective.”

2. Shallow thinking about the “why” leads to the presumption accuracy is impossible. Financial bias can also cause people to see only what they want to see. How about creating incentive and accountability for accuracy - let’s try that for a while and see what happens.

3. Experiments are useful because they push the envelope and a lot is learned. Does anyone presume DER at that level is scalable?

“ \$20,000 to \$30,000 is more than most can afford”

Again, those are the job sizes we are seeing, not the job size we need to get vertical on the sigmoid (http://bit.ly/NateLowHangingFruitFallacy and http://bit.ly/sigmoidalbum - where results and energy savings go geometric) If you are looking for the tipping point, in our climate and energy prices our confidence in accuracy and precision get’s strong around \$13,000. The customer net ends up being under \$50 a month.

As we all have seen, spending \$3000-\$4000 with the “Poke and Hope” or “this seems to be your low hanging fruit” or “lets see what sticks” approach is, often as not, as effective as flushing the money down the toilet. A lot of our clients are tired of flushing.

It would be nice not to have to remove all the crap people have thrown on the walls.

“I live in a leaky, poorly insulated house. (I built it, but that's another story.) If you came to me and suggested that I go to a bank and borrow \$25,000 for home improvements that aren't cost-effective, I wouldn't do it.”

But if I came to you and lied about the savings, you’d do the work and that would be OK? No thanks.

Look, if you aren’t to the point you mind living in a crappy house, or your house just isn’t that crappy, I don’t WANT to work for you. You aren’t going to be ecstatic about my saving you \$400 a year even if it DOES cost justify. YOU ARE NOT THE TARGET CONSUMER! I’d say you shouldn’t get work done and if you DO you are an ass, not if you don’t!

I don't think you have an obligation to save energy just for the sake of saving energy. Being judgemental about how others spend their money is not my job.

34. | | #34

RE: Martin: Three Approaches
1. THIS IS WEATHERIZATION - Often creates more problems than it solves. Energy savings occurs over large populations but has high likelihood of NOT occurring case by case. Works for Utilities because they save energy over a large population and make like they are trying. Works for consumer because they get the work done for free.

BAD IDEA TO SELL THIS AS "HOME PERFORMANCE" because it is not - and if consumers pay for the work they are often unhappy. Gives Home Performance a bad name: http://bit.ly/esoConfessions

2. COMPREHENSIVE HOME PERFORMANCE - No convincing required. They have problems they want fixed and need to attach a budget. If the budget is enough to solve their problems, great! If not, we help them understand what to expect with the resources they have.

On-Bill recovery and low income assistance makes “can’t afford it” a lie. If people are lying to you you've done it wrong. They either don't trust, aren't bothered enough, or have something else going on that they haven’t disclosed.

3. DER - Science Experiments. We prefer helping everyday people and trying to push for Market Transformation

35. GBA Editor
| | #35

Response to Ted Kidd
Ted,
I can assure you, I am completely serious when I tell you that I don't want to take on \$20,000 to \$30,000 of debt. Although you didn't call me an ass this time, it seems that you are calling me myopic. (Do you have a bag full of adjectives for people like me?)

I can also assure you that my house is not yet falling down around me. Fortunately, if it ever does start to collapse, I have some screw jacks, long levers, and a few come-alongs so that I can pull my house back up. I hope.

And no, I didn't buy my house all at once. I'm still picking away at it, slowly, on weekends. Just like the working class people who perform their energy retrofit work a little bit at a time, as they can afford it.

36. | | #36

RE: One More Point - Solar
"a PV system are generally (to quote Mona Lisa from My Cousin Vinny) "dead-on balls accurate." You want a cost-effective energy saving measure? In many regions of the U.S., the best approach is to install a PV system.

But of course, saying that on an energy-efficiency forum is politically incorrect."

Martin, I'm an environmentalist and an Economist. I love solar and I love optimizing opportunity.

Absolutely shake things up in EE forums about this. If the house isn't broken, why fix it? I don't think we want to fix houses just to save energy. If it costs \$2 to save what you can produce on your roof with \$1, I'll step into your side of whatever ring you need me in.

In fact if it’s \$1 to \$1 and there are no “non economic benefits” available to the homeowner from EE, I’m still on your side. Put in Solar!!!

37. | | #37

“WHAT SHOULD MARTIN DO"?
Absolutely recommend energy audits with blower door tests. I don't believe anyone is suggesting that is bad advice.

The bad advice comes when you suggest people should "pick the cost effective items". That's prescribing. Stop telling people what improvements to choose. I'd like to see you change your recommendation regarding the decision making process.

Instead of suggesting people make decisions based upon “what pays for itself and what doesn’t” how about suggesting they collaboratively develop solutions to their problems that they can afford?

Home Performance is a custom tailored suit, not an a-la-carte menu. I think you are seeing this.

“Take on debt” Argument? REALLY?!

That is so myopic. Simplistic. Do you pay your energy bill for the next 30 years up front? Do you buy your house all at once?

Will you let it fall down around you because you “don't want more debt?”

You demean yourself and us with these dumb examples of stupid people that are incredibly rare in the wild. We just don't run into stupid people very often! These hypothesis of what people can afford and how stupid they are are fallacy of excluded middle.

We can fix houses but we can't fix stupid. On the rare occasion that we run into it, as quickly and politely as possible we get the hell out.

38. | | #38

Never done it - but you are an expert?
Martin, you've already said you are not a prospect for home performance. Why do you keep talking about what you can't imagine spending to fix a house that doesn't need fixing?

I'm sorry you haven't the imagination to understand that other people want their houses fixed, and they understand that even if they get things right the energy savings is unlikely to pay for the fix. These people exist in abundance. If there were confidence in results, there would be a supply problem.

That you can't imagine spending \$50 a month to solve comfort, durability, health, or energy problems at your house tells me you either don't have these problems, you aren't confident they can be solved (and want to bury your head about them), or the thought of spending the money is more painful than the the thought of living with the problem(s).

This is not typical thinking that drives people to have an energy audit, this is the thinking that keeps them from having one. Folks, if this is how you think, don't have an energy audit!

But that inability to empathize, to understand people situations and preferences are not all just like yours that prevents you from seeing that people solve problems with money. The bigger the problem the more they will pay to solve it. Rich and poor - this is a hard fact.

I get that some people have a fixation on EE paying for itself. That it needs to be a great investment. Sorry, residential scale and cheap energy make it a very rare event. Maybe you should switch fields, get into giving investment advice. Might be more suited to the way you think about things.

39. | | #39

Ted, Ted, Ted
To quote AJbuilder... Is there really a need to act quite this negative towards someone who obviously knows his stuff? By "obviously" I mean to anyone who has spent time reading his advice and interesting blogs here. It makes me wonder if you just started looking at GBA because you latched onto Martin's thoughts on EE and now that he disagrees on that subject with you, you then have to impugn his vast knowledge. I just hope you aren't from California, because I am also and I wouldn't want people to jump to wrong conclusion about all of us.

40. GBA Editor
| | #40

You got me, Martin...
"I can also assure you that my house is not yet falling down around me. Fortunately, if it ever does start to collapse, I have some screw jacks, long levers, and a few come-alongs so that I can pull my house back up. I hope."

Thanks for keeping it real, Martin! If you need some help cranking those come-alongs, just let me know.

41. | | #41

Response to Eric Habegger
"I think the whole conversation is geared to this paradigm shift thing that you are promoting. I think it does a disservice to Martin and many readers here. People here, especially Martin and the other contributers here, are very sophisticated about what works and what does not work."

The curse here is one that I was guilty of too until recently. Do you have measured results you can share? As an industry, we say we know what saves energy, but very, very few of us measure after the fact to find out what worked and didn't work. Do you have any results you can share?

Energy Upgrade California has a 34% realization rate. If that's good for you, can I borrow a million bucks? I'll pay you back \$340,000 tomorrow in full... That what happens when we don't go far enough. That is what happens when we don't really know what saves energy.

For better or for worse, we have to go further to deliver the results clients ask us for. I understand your hesitation, that was me not long ago. Ted is correct, somewhere in the \$13-15K range you get close enough to a tipping point to change the character of a home.

Finally, I didn't work with a gov't program, but a utility rebate program similar to Energy Upgrade California or NYSERDA or other program. Do you work with something similar? What do you do for a living?

I did dabble in low income weatherization (great training), but program design holding job sizes down to where I couldn't make a living and deliver the results I wanted to ultimately doomed me, amongst my other shortcomings.

By the way, this isn't a game of gang up on Martin. Yes, we hope for a conversation change, though. As an industry, we are an utter failure. We can drastically improve the health of society and reduce energy use to the point that the earth won't cook from home energy use, but we only do 1 job to the HVAC industry's 1000 jobs. What we're doing ain't workin'. So we propose another path. One that aims for, measures, and delivers results.

42. | | #42

Looking forward to the next articles
It's important to understand about diminishing returns. Allison's six charts and associated text explain that well, in relation to insulation, with examples for zone 4 and for Atlanta. It's also important to understand that heat flow vs. insulation is a linear relationship, as Martin emphasizes in comment 1.

Costs and cost effectiveness are alluded to many times in the article and the comments. Diminishing returns are covered well here, without any concrete connections to costs. I'm looking forward to future articles that give some basis for thinking about the costs of varying insulation level choices.

I agree that it is challenging to move from the simple mathematical relationships shown in Allison's charts to something useful about houses, insulation levels, and costs. The real world has a lot of variables. But GBA repeatedly tackles the challenges of providing useful guidance for addressing real world problems, and does so with success.

Let's not turn away too quickly from important problems that have a lot of variables. Complexity can be tractable. If we could put together a decision tree, as Keith H mentions, of six questions, each having three ranges (high, medium, and low, or the equivalent), that would let us address 729 different types, varieties, and categories of houses or systems. Add a level for the major US climate zones, and we could be looking at thousands of meaningful answers for different houses and scenarios, differentiated by seven simple questions.

Creating a useful decision tree isn't trivial, nor is a decision tree applicable to every problem. However, my point is, that it is often possible to handle multiple variables and a great deal of variety within fairly simple analysis structures. This can produce tools and information that professionals and homeowners can use to solve real world problems.

43. | | #43

eric, eric, eric...
So, if I write about golf that will that make me a scratch golfer? Maybe I could write about health care and that will make me a doctor! Oh, I know, I'll write about airplanes and simple folk like you will think me a fighter pilot!!

"Knows his stuff?" What stuff would you call Martin expert in? By his own admission he hasn't even done Comprehensive Home Performance on his own house! If you start elevating his expertise you do him injustice.

Is Martin expert in Home Performance? Is he expert in Energy Audits? Is he expert in saving energy? Be careful conflating expertise where it doesn't exist - I doubt he considers himself expert in these things.

I don't know Martin, but I know Mike and Nate. They are experts in a field where a lot claim to know things, but most never perform due diligence. Most hit their drive off the tee, then claim "hole in one" and turn their back before the ball even lands. Is that good enough for you Eric? Would you call them all experts?

I believe the reason Mike and Nate are putting considerable effort into this discussion is they think Martin is a good writer and smart guy who needs slight course correction. That his intellect is large enough, and ego small enough that he can see new things and understand his current perspective flaws and their potential harm to homeowners and the industry, and make the slight adjustments necessary to be truly helpful advocate of Home Performance.

Mike and Nate follow up. They have high integrity. They don't make fictional promises with no intent to follow up. They find out where their balls land and continuously improve their game.

Mike and Nate are very smart and very knowledgeable, and if they feel Martin is worth this effort, that Martin isn't so stuck in his mindset that he can't learn a new way of thinking, I'm in. It should be obvious that I've put a lot of time into this discussion when I could have been out mountain biking.

44. | | #44

Lets do more numbers
Lets do more numbers, R1 - 0%, R2 - 50%, R4 - 75%, R8 - 87%, R16 - 93%, R32 - 96%, R64 - 98%, R128 - 99%. Note that going from R64 to R128 reduces the heat flow rate less then 1% (0.78%). The old roof standard of R30 - 96%, new R38 - 97%. It always seems to me that R16 at 93% should be good enough, so why did code require R30, my best guess was that when the code was written, FB was the insulation used 99% of the time, and it was installed so poorly, that you needed R30 to get into the low 90s for the typical install. Not sure why they think that moving the standard from R30 to R38 will make that much difference. I find it interesting that the BSC hot box testing showed that 2x6 FB wall performed worst then 2x4 cellulose or cc foam in the worst case, and that was with a HERS grade 1 FB install, not how it install in the real world. Since the same study showed that all the insulation performed about the same when there no air movement, maybe there should be different R values for walls and attics depending on the shell air flow rate @ 50 pa. Maybe the same could also be done depending on the HERS grade rating of the FB install, HERS grade 1 is code, HERS grade 3 (typical) requires 25% more insulation. This would require builders who build using the cheapest FB installs to either use thicker FB, or have it inspected, either way, it would greatly improve the insulation of the average home.

45. GBA Editor
| | #45

Response to Carl Fosler
Carl,
You're using the wrong starting point. Who cares how much is saved compared to an R-1 assembly? R-1 assemblies are both illegal and irrelevant.

There is a reason that building codes require (for instance) R-15 walls and R-38 ceilings (or whatever). These are the minimum starting points for any building.

If I'm being paid \$7.25 an hour, and my boss tells me that I'm making 725 times more money than workers who are paid 1 cent an hour, I'm not impressed. It's illegal to pay workers 1 cent an hour.

46. | | #46

this blog and Bruce Brownell
To me this blog shines a bright light on Bruce's 50 year old design methods. His design eliminates R-0 to R-10 on all 6 to 7 sides of the home.

4" of continuous insulation well sealed, R-0 is air leaks. R<10 is losses from insulated framing instead of continuous.

50 years prior to GBA and the German's PH program.

47. | | #47

Insulation/Radiant Barrier Effect of Solar Panels
New subscriber so pardon my ignorance of previous answers. I have an 8kw solar system covering about 90% of my south roof, 4 inch gap between panels and roof, in Central Texas. My cost savings exceed my production and I think that the barrier effect of the panels may explain it. I also have a solar attic fan. Any thoughts? Also, while we have short winters in Texas, is there a time or temperature to turn off the attic fan so I am not circulating out air that is good for my heating costs?

48. GBA Editor
| | #48

Response to James Howard
James,
First of all, it's not clear from your question whether you have been monitoring the production of your PV array, or just noticing whether your electricity bills went down.

Needless to say, electricity bills go up and down for all kinds of reasons, including the weather and the way that appliances are used.

If your PV system is producing more electricity than expected, the most likely explanation is that the weather in your location has been sunnier in recent months than the long-term average. Of course, several other explanations are possible.

Attic fans (powered attic ventilators) are not recommended. They can increase your home's cooling load by sucking indoor conditioned air through ceiling cracks. In most cases, the best approach is to disable or remove the attic fan. For more information on powered attic ventilators, see Fans in the Attic: Do They Help or Do They Hurt?

49. | | #49

Response to Martin
Martin,
I appreciate your answer. Had not heard that about active airflow. I will monitor. Yes I have been monitoring my production. I average about 1200kwh/month. However my usage has decreased by about 1700kwh. Used to have power bills for 2500-3000kwh/month now get charged for about 800-900kwh. That is where I realize the `800kwh delta between production and net use which I attrtibuted to the solar panels blocking the rays on my southern roof. Again, thanks for any insight.

50. | | #50

Rvalue simplified
R5 - 80%; r10 - 90%; r20 -95% and r100 - 99% effecient. Being air tight and whole wall values.

R20 being very easily attainable and good for zones 5 through 7

PS

Based off of Uvalue. Rvalue is based off of Uvalue as well.

51. Expert Member
| | #51

Ted Kidd
I'm beginning to wonder how much real life experience you have of the construction industry. Maybe things are different where you practice, but around here people who wander onto building sites dispensing insults, the way you seem to, spend a fair amount of their time looking for their teeth.

52. | | #52

Graphs
If I had see these graphs before I placed my window order, I might have thought more about triple glazing than additional foam insulation. Since windows start with a lower r-value, at least from a comfort point of view if not cost, it looks like there is a quicker return there if you already have a reasonable amount of insulation in the wall structure .

53. | | #53

This makes sense - except when it doesn't.
My company lives in a world of closed cell polyurethane foam, and I have long heard stories of diminishing returns, and no one can argue with the math, right? Except when the math meets real world conditions. We all know that insulation performance varies with temperature, and yet this analysis does not consider it. As someone with a degree in the sciences (applied physics) I decided to do some of our own testing with small structures made with stick-frame with insulation with appropriate framing factors, as well as out of different thicknesses of our panels. Forget about how we compared against stick (because no contest) - what was equally as interesting is how our different thicknesses of panels compared against each other in different season scenarios. In the "winter" scenario our 6.5" thick wall panel (with a 5.6" core) performed roughly twice as well as our 4.5" thick panel (with a 3.6" core), and it was not until we were at a 7" core panel that we started to see significant diminishing returns. Our foam has an R value of approx. 7/in at 52degF, and this testing does not correlate at all with your theoretical analysis. Conversely, in warmer weather, we saw diminishing returns kick in sooner than we saw in cold weather - not a lot of difference in the performance between the 4.5" and the 6.5" thick panels (or the 8+" thick panels for that matter). This of course implies that for different types of insulation there is a slope to where diminishing returns kicks in as temperature varies.

Your math simulations anticipate the performance of insulation at 75 degrees Fahrenheit. Do you know who needs insulation at 75 degrees Fahrenheit? Almost no one (a knowledgeable friend told me once that one particular industry suggested to the FCC that they measure insulation performance at that temp back in the 1960s - and it has worked out well for them).

We do this experimentation because we do not see other people doing this experimentation - or we can't afford to join the groups that are. And we constantly question both ourselves, industry convention and the experts. We'll stay at it....

54. GBA Editor
| | #54

Response to Charles Leahy
Charles, you're absolutely right that it's at best an incomplete picture to talk about R-value without discussing temperature dependence. But we have to have some way of characterizing a material for purposes of comparison and this one actually does work pretty well.

It's the same when we talk about heating and cooling loads. We put in design conditions and come up with a single number for the heating load and a single number for the cooling load. The actual loads, however, vary continuously, depending on what's happening outdoors and what's happening indoors. And the temperature dependent R-value plays a role, too.

Finally, let's talk about the test conditions for R-value testing. You wrote:

Your math simulations anticipate the performance of insulation at 75 degrees Fahrenheit. Do you know who needs insulation at 75 degrees Fahrenheit? Almost no one (a knowledgeable friend told me once that one particular industry suggested to the FCC that they measure insulation performance at that temp back in the 1960s - and it has worked out well for them).

That's a common misconception, but you can't test for R-value at a single temperature. You always have to have a temperature difference (ΔT). The test conditions require a ΔT of 50° F with a mean temperature of 75° F. It doesn't mean the outdoor temperature is 75° F.

Kudos to you and your company for testing your panels. That's great.

55. | | #55

Great article and I
Great article and I understand the point it makes.

I live in climate zone 7a (Alberta) and planning to insulate my garage, with the intent of using it as a woodworking shop, even in the winter. Apart from my comfort, it's important that any stored lumber be kept within a somewhat reasonably consistent RH & temp environment. If the garage levels fluctuate too much I'll store more in the house but that would be a hassle.

It has a reasonably-sized natural gas furnace inside (never fired up yet). I'm aware the greatest loss of heat would be thru the garage door, which I believe is insulated but I still plan to add 1-2" of rigid foam on the interior side of the door. Ideally I'd like to limit the use of the furnace, particularly overnight and when I'm not actually inside working.

The garage has no external insulation and it's constructed with 2x4 wood studs 16" oc so I'm planning to install Roxul R14.

My question is, would you recommend that I also install 1" of rigid foam (foil-faced GPS @ R5) on the interior side under the drywall? This can also pass code here as a vapor barrier when sealed. I know it can be done, I'm just wondering if I'll notice the benefit of the added insulation and if it's worth doing?

Fyi, I do also plan to install 1" or maybe more rigid foam on floor plus a plywood subfloor to not just help insulate and control vapor transfer thru slab, but also help protect tools and materials should they fall on ground.

Cheers
Todd

• Five Types of R-Value

There’s a lot more to insulation than the number on the package

• The Fundamentals of Series and Parallel Heat Flow

The R-value of a building assembly depends on how heat can flow through it

• Insulation for Cold Climates

Although extruded polystyrene (XPS) is rated at R-5 per inch, it performs better than R-6 polyiso in cold temperatures

• Air Leakage Degrades the Thermal Performance of Walls

No surprises here — but testing by the Building Science Corporation begins to quantify the problem

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