Helpful? 2

Installed R-60 insulation in attic... now using AC more than before

I had R60 blown into my 1000sqft attic where there was previously only about R11. Baffles were installed in almost every roof rafter. Air sealing of attic floor was performed. This is a low pitch asphalt shingled hip roof over the whole house.

As expected, the temperature in the house doesn't fluctuate as much. However, I feel as if I'm using A/C more. Before the R60, the A/C would be on when it's 80+ degrees out. Now I'm using it even when it's low 70s outside because the house refuses to budge in temperature when trying to "air" it out by cracking some windows open. For example, daytime temp can be 85 degrees, and the A/C cools it down to 78 degrees. Overnight the outside temperature might by 70 degrees, and after leaving windows open all night, I wake up to the stat saying it's 79 degrees.

What explains this? I have a hunch maybe I don't have enough attic ventilation so all that hot mass stored in the insulation just releases itself instead of ventilating outside. I have 8 soffit vents and 2 turtle vents at the top of the roof. Do I need more?

Asked by Jeff Watson
Posted Sat, 07/12/2014 - 16:12
Edited Mon, 08/18/2014 - 08:49

Tags:

44 Answers

Select your preferred way to display the comments and click "Save settings" to activate your changes.
1.
Helpful? 0

One would need hard data numbers. The problem with "feeling" is that there is no way to base any scientific results on it. What were your A/C bills prior to the R-60 insulation? Compare the R-11 A/C bill with the R-60 A/C bill and make sure the outside temps were similar as were the inside A/C control temps.

As far as the attic venting goes. From what GBA stated in articles past, attic vents are mostly overrated and the main reason for vents is to DRY any moisture that may be on the wood, it doesn't really do much to "cool" an attic with more vents or fans based on the premise that it will somehow keep the home cooler. It was debunked as hype, especially those selling attic fans.

Maybe your A/C is on the fritz and it is not cooling like it did before and therefore you are running it more often? Maybe the relative humidity is higher this year and you feel hotter, therefore you are running the A/C more often?

Answered by Peter L
Posted Sat, 07/12/2014 - 17:43
Edited Sat, 07/12/2014 - 17:45.

2.
Helpful? 0

Yeah, not enough data to draw a conclusion. You would need to track interior temps, exterior temps, probably some measure of solar loading, A/C runtimes or preferably actual output.

An easy thing to do is check the A/C itself. Refrigerant charge and other specs should be verified.

Answered by David Meiland
Posted Sat, 07/12/2014 - 18:40

3.
Helpful? 0

Thankyou Peter & David. I agree that if my goal was to determine if I'm using the A/C more, I'd need to collect some data & have a pre-R60 baseline to compare that data to.

But my underlying goal is a step before that; along the lines of "why does it take forever to air out the house to drop interior temperature that I have to resort to using A/C," and that's assuming there's at least an 8-10 degree difference between exterior & interior temperature.

I'm not too concerned with tracking my A/C usage; just the situations in which I actually turn it on. I don't consistently use A/C all day...I'm one of those "last resort" guys who turns it on if I(or the lady) just can't take it, and right after the R60 install, I'm hitting that scenario a lot more when outside temp would not necessitate A/C if we had the same temp before the R60.

So I guess my question is less about A/C performance in its current environment, and more on the house environment & its resistance to cooling via natural means.

Answered by Jeff Watson
Posted Sat, 07/12/2014 - 18:59

4.
Helpful? 0

Assuming that your A/C is mechanically sound, the biggest variable might be the air sealing.

Did you do the work yourself, or better yet, was it tested with a blower door? Attics are awful places to work, and there is a strong incentive to cut corners, especially when the work will be buried beneath R60 of insulation.

A second, related thought is whether there are any ducts in the attic that may have been damaged during the work, thereby connecting the super heated attic to your house. Even without the forced air system running, you would have a large pathway for heat to enter the conditioned part of your house. It's very easy for some ducts to become disconnected.

Answered by Graham Fisher
Posted Sat, 07/12/2014 - 19:27
Edited Sat, 07/12/2014 - 19:57.

5.
Helpful? 0

Graham, I hired an insulation company to do the work. I do not have blower door numbers post-insulation, but what prompted the install was a recommendation by an energy audit that I had (that did include a blower door test). According to that test, my house was 1370 CFM @ 50 Pascals. When the insulation guys came & did their test before doing the insulation, it was 2500 CFm @ 50 Pascals, so not sure who to believe. They didn't take an 'after' test.

I don't have any ducts in the attic; all my ducts run under the floors (single story home w/basement).

I just don't understand why the temperature in the house rises overnight when it is colder outside & I've got literally all windows open.

Answered by Jeff Watson
Posted Mon, 07/14/2014 - 09:11

6.
Helpful? 0

Very interesting and timely question! We are in the same boat. Had R49 blown into our attic about 6 weeks ago and got the first bill. Our kwh's used were higher this June vs last year. I'm going to post a similar question, but do you have any areas that aren't well insulated? Also having an energy audit performed in a couple of hours as well.

Answered by HD S
Posted Mon, 07/14/2014 - 09:57

7.
Helpful? 0

Jeff,
A few more points: while heat gain through ceilings can be significant, especially in a house that has very little ceiling insulation, two other sources of heat gain are often more significant: heat gain through windows and internal heat gains from lighting and other appliances (oven, kitchen range, refrigerator, TV, etc.).

If any of these factors has changed in the last year, these will affect your cooling bill. Of course, so will the weather, which may be different this year than last year.

Answered by Martin Holladay, GBA Advisor
Posted Mon, 07/14/2014 - 10:08

8.
Helpful? 0

Is it possible that the extra insulation is now trapping heat that otherwise could have escaped? Martin alluded to this as well...just a thought...

Answered by bob holodinsky
Posted Mon, 07/14/2014 - 12:07

9.
Helpful? 0

Bob,
It's not really possible for the attic insulation to be causing any problems. If the outdoor temperature is in the low 70s, as reported, it's not as if you can cool a house by conduction through the ceiling drywall. The attic isn't going to be cool enough to pull heat from the house under these circumstances.

Answered by Martin Holladay, GBA Advisor
Posted Mon, 07/14/2014 - 12:37

10.
Helpful? 0

AC is not a window fan

Using it the way you are it is impossible to judge how much energy you are using. It is likely you would use less energy leaving it on at a reasonable temp than the way you are using it.

Look at the 3 day forecast, if it is going to be AC worthy turn it on and forget about it.

You are not saving money making the AC pull all the moisture out then lowering the temp only to shut it off again

Answered by Keith Gustafson
Posted Mon, 07/14/2014 - 21:18

11.
Helpful? 1

Not sure if I'm getting my point across, so let's forget all about A/C for a minute. I'm not trying to compare cooling bills or the weather from last year. Just want to understand what is causing the heat flow.

Since I'm talking about the temperature within the house rising overnight, this means all lights & heat-generating things are off, most windows are open, and the sun has already set. If it's 78 inside with windows open, how can the temperature rise overnight within the house if it's 70 or lower outside?

Bob H, I am kind of thinking something along the same lines - that the insulation is somehow releasing the heat within the house instead of outside.

Keith G, I'm not trying to gauge my energy usage, but I see where you're coming from. We only use A/C during the day and just don't see a point to using A/C overnight especially if it's 70 or below. That's when we crack the windows - only overnight. But that is what prompted this post - that now the house doesn't cool off overnight with natural ventilation.

As an aside, we know the air within the house is at least circulating because our carbon dioxide meter might read 2000ppm right before we are about to go to sleep (from leaving the windows closed for A/C) and it'll be about 500ppm in the morning.

Answered by Jeff Watson
Posted Mon, 07/14/2014 - 21:34

12.
Helpful? -1

Jeff.... I understand what you are thinking... If your roof is cooling way down maybe due to night sky radiational cooling then indeed it would have more effect on your living space with less insulation above the ceiling.

Interesting.... I remember a scientist testing out whether he could concentrate night sky radiational cooling with a parabolic dish mirror he had that was about 3' in diameter.

Answered by aj builder, Upstate NY Zone 6a
Posted Mon, 07/14/2014 - 21:36

13.
Helpful? 0

I think Jeff has narrowed his question down to the simplest terms:
How come, prior to the insulation, he could cool his house at night by opening the windows, but now he can't?

The answer is equally simple: There is a lot of heat stored by the thermal mass of the attic insulation, and this heat radiates downward.

When you have a large, well insulated mass exposed to outside air, it will tend to hover within a few degrees of the average daily temperature, which Jeff says is 79F

I've personally lived with this, and that's why for summer cooling I'd much rather have an unvented R60 foam roof than a vented attic full of fluff. Stop the heat at the roof plane, then you don't have to cool down the attic somehow before bedtime. A vented attic with fluff gets heated all day by the attic ventilation air.

Now Jeff must install forced ventilation in the attic, to be used only at night. None of the articles and studies that denigrate forced attic ventilation have addressed this phenomenon. http://www.energyvanguard.com/blog-building-science-HERS-BPI/bid/75600/T...

A whole house fan is worth considering, but they are usually a bad thermal bypass in winter. http://www.greenbuildingadvisor.com/blogs/dept/musings/fans-attic-do-the...

More soffit and turtle vents won't help because they don't move enough air volume, and can't be turned off during the day. Solar powered attic ventilators ditto.

If not a whole house fan, then Jeff would benefit from window fans left on all night.

Answered by Kevin Dickson, MSME
Posted Tue, 07/15/2014 - 01:03
Edited Tue, 07/15/2014 - 01:22.

14.
Helpful? 0

Jeff,
Q. "If it's 78 inside with windows open, how can the temperature rise overnight within the house if it's 70 or lower outside?"

A. Refrigerator. Set-top box. Dishwasher. Small transformers. People. Dogs. Aquarium pumps. Internet routers. Computers.

Answered by Martin Holladay, GBA Advisor
Posted Tue, 07/15/2014 - 05:58

15.
Helpful? 0

I am surprised at the wide range in the Blower Door Results...
And wonder why the Contractor did a "Pre-Improvement" Blower door and didn't bother with an "After".
Was the pre-test done mainly for the "Show" so he could get the "Dough"?
How Airtight is the House Now?
Did the Neutral Pressure Plane Shift After the Improvements?

I agree with Keith Gustafson.
Build Tight, Ventilate RIGHT ....
Get the House and contents in "Good Condition".
Maintain the "Good Condition" ...Coast when you can...
Avoid STOP and GO (City Driving)

Answered by John Brooks
Posted Tue, 07/15/2014 - 09:21

16.
Helpful? 0

Martin,

The temperature didn't rise overnight before the attic insulation upgrade. Now it rises. Internal heat generation sources haven't changed.

Answered by Kevin Dickson, MSME
Posted Tue, 07/15/2014 - 15:08

17.
Helpful? 0

Kevin,
There is a temperature gradient through the insulation on the attic floor. The bottom inch of insulation is at the same temperature as the ceiling drywall. Jeff reports running his air conditioner during the day to maintain the temperature of his indoor air (and his ceiling drywall) at 78 degrees. So when Jeff turns off his air conditioner and opens his windows to go to bed, the ceiling drywall and the bottom inch of attic insulation are at about 78 degrees.

So, when it is beddy-by time for Jeff, is the top inch of attic insulation warmer or cooler than 78 degrees? I'm not sure -- that depends on how hot his attic is. If the weather is hot enough for Jeff to want to run his air conditioner, it's not cold up there. Jeff mentioned two outdoor temperatures: "the low 70s" (that's when he feels like turning on his air conditioner) and "85 degrees" (a typical day when he is running his air conditioner). Using this data, and my knowledge that attics are often hotter that the outdoors during the summer, I'm guessing that his attic air is at 76 degrees to 95 degrees on the days that we are discussing.

So, the bottom inch of his attic insulation is at 78 degrees when he goes to bed. The top inch of insulation is somewhere between 76 degrees and 95 degrees when he goes to bed. My conclusion: the thick blanket of insulation on his attic floor either has no effect on his indoor temperature (when his attic is at 76 degrees) or is helping to keep his house cool (when his attic is 79 degrees or warmer).

Answered by Martin Holladay, GBA Advisor
Posted Tue, 07/15/2014 - 15:23
Edited Tue, 07/15/2014 - 15:27.

18.
Helpful? 0

I think jeff is rightly mentioning some type of phenomena that is directly related to the insulation change.

Time will tell and be on my side.

Do as I do. Eat bacon and eggs and use real butter, and you will attain a life of joy and bliss... Positing ever so to your fellow man.

Answered by aj builder, Upstate NY Zone 6a
Posted Tue, 07/15/2014 - 17:35

19.
Helpful? 0

An R11 attic/roof will radiate quite a bit of heat to the (much colder than 70F radiation temp) sky at night, which will cool the house a bit. An R60 attic not so much, since the insulation slows the heat loss through the roof. The exterior roof temperatures will often reach the outdoor dew point, which can be 10F or more cooler than the overnight air temperatures, so you get a bit of "free" overnight cooling from this lossy roof. The thermal mass of the attic framing wood & roof deck store some of the daytime gains, and the amount of this "free" night time cooling isn't huge, but measurable

But with an R11 attic there is a lot of heat gain from the roof in direct sun that makes it into the conditioned (much higher than the overnight freebie cooling effects), whereas with an R60 attic most of your heat gain inside of conditioned space will be from windows, with very little heat entering or leaving via the roof.

The thermal mass of R60 fiberglass is negligible- about 0.2 BTU/ per degree F per lb., and for R60 you're looking at about 1lb per square foot of ceiling area for about 0.20 BTU/degree-foot^2 of ceiling area. The thermal mass of open-blown R60 cellulose is about 3x as much, but still small ~0.33 BTU/ degree-F-lb at about 2lbs per square foot of ceiling, for about 0.66 BTU/degree-foot^2 .

For perspective, standard density 1/2" gypsum board at 1.7lbs per square foot and a specific heat of 0.26 BTU/degree-F-lb which makes makes it about about 0.44 BTU/degree-foot^2 of ceiling. That's more than half the thermal mass of the entire cellulose layer, and more than the thermal mass of R60 fiberglass.

The mass effects of cellulose insulation are real, but don't get very "interesting" except in higher-R dense-packed (greater than 3 lbs per cubic foot) densities, not so much at open blown density. The mass effects of fiberglass insulation is small, almost "in noise" of measurement error when totaling up all of the thermal masses of different elements of the assembly.

The thermal mass of all the stuff in your house, combined with interior heat sources like dogs & DVRs, refrigerators & girlfriends generally keeps the interior temps about 5F warmer than the outdoor air in an R11 house, but 10F or more warmer than the outdoor temps in very well-insulated houses. When the outdoor temp is lower than the indoor temp you can get some cooling via ventilation, but unless you have a tall house and big windows to take advantage of stack effects to drive the air exchange, simply opening the windows won't necessarily get you there.

Answered by Dana Dorsett
Posted Wed, 07/16/2014 - 12:40

20.
Helpful? 0

Night sky radiational roof cooling. I Bingo-ed first Dana.

Peter Yost, yaa better chime in and agree when this thread gets a blog write up.

Answered by aj builder, Upstate NY Zone 6a
Posted Wed, 07/16/2014 - 23:34

21.
Helpful? 0

"The use of cellulose insulation material does not make HVAC installations superfluous, but it
can decrease the calculated capacity of these installations, and therefore generate a positive
effect upon the environment."

Flexible buildings and cellulose insulation
Stefan Hulsbosch
Edwin J. van Dijk Ir.
Elisa C. Boelman, Dr. Eng. MBA
Christoph M. Ravesloot, M. Sc. A., M. STS

http://www.bk.tudelft.nl/fileadmin/Faculteit/BK/Over_de_faculteit/Afdeli...

These seem pretty low temperatures for air conditioning unless the humidity is uncomfortably high. Instead of wasting AC electricity, box fans in upstairs windows blowing outwards, with down stairs and cross-room windows open, will cool down the house rapidly and for pennies.

Answered by flitch plate
Posted Thu, 07/17/2014 - 00:39

22.
Helpful? 1

You used to have a house that needed 100kwh to cool during the day, and 0 kwh during the night

Now you have a house that needs 50kwh to cool during the day and 10 kwh at night

You need to start running it like the house you have not like the house you used to have

Answered by Keith Gustafson
Posted Thu, 07/17/2014 - 07:57

23.
Helpful? 0

Flitch Plate:

FWIW the referenced T.U. Delft paper states:

"...normal density for cellulose insulation is 60 kg/m3..."

which is about 3.74 lbs per cubic foot, somewhat higher density than most dense-packed wall applications in the US, and ~2.5x as dense as open-blown attic installations.

But at that density it's not surprising that at that density they found:

"When building with a light (flexible) construction, the use of cellulose insulation material
yields an advantage of 10 to 20% over glass wool, under the conditions assumed in the
calculations."

http://www.bk.tudelft.nl/fileadmin/Faculteit/BK/Over_de_faculteit/Afdeli...

Yes, there is a measurable difference due to the mass effect, but it's not going to be a huge factor in most assemblies. In figure 1 on p.3 (PDF pagination) the temperature differences between fiberglass & cellulose are negligible in the overnight hours, but about 2C cooler for the afternoon peaks. And that's with dense-packed cellulose, not open blown. But it's NOTHING like the mass effect temperature moderation you get with concrete (as seen in the paper), which yielded a 10C or greater difference in peak temps from the celluose & glass wool cases.

Answered by Dana Dorsett
Posted Thu, 07/17/2014 - 18:21

24.
Helpful? 0

"You need to start running it like the house you have not like the house you used to have"
Best comment award goes to Keith Gustavson. If you have a well-sealed and well-insulated house with decent air quality, night venting during the A/C season makes absolutely no sense.

Answered by James Morgan
Posted Sat, 07/26/2014 - 14:29

25.
Helpful? 0

Ok, so I guess the gist of what you all are saying is that now that the attic is insulated pretty well, that small heat sources now have a more significant effect on the indoor temperature, and not necessarily the insulation having some huge amount of thermal mass that is slowly released.

The only major heat sources at night: 2 people & a refrigerator. We turn stuff off when not using (e.g., cable box, TV, computers/internet) - only stuff left on would be the microwave/stove/dishwasher which are only powered for running the LED displays/clock & not actually doing anything.

We did go on a 3 day vacation recently and left all windows closed. Upon coming back, the house smelled like cardboard on the inside. I presume we were just smelling the cellulose...but could this indicate air leakage from attic into the living space?

Forgot to mention - this is a single story house; basement & attic. I have a feeling that since it's only a single story, that attic air sealing & insulation in a sense appear to lower the "hot zone" more towards the living space floor since before the sealing/insulation, that hot air could rise into & out of the attic, but now it is more trapped below the drywall & relies more on mechanical means (A/C) to exchange it. Does that make sense?

Answered by Jeff Watson
Posted Sun, 08/17/2014 - 16:59

26.
Helpful? 0

James & Keith, put that way, I can sort of agree; It's just that I've never read about this phenomena before deciding on getting the extra insulation.

When an insulation contractor or energy auditor tells you that you'll use less energy to cool the house, you don't necessarily picture in your mind that you will now have to run A/C overnight. Makes you feel like running A/C more often equates to spending more money. I just don't think these are accurate comparisons of energy bills if scenario 1 is: R11 attic + turn off A/C overnight while scenario 2 is: R60 attic + run A/C overnight.

I thought it was common to turn the furnace down overnight, why isn't it the same for A/C (e.g., turning it off at night)?

Answered by Jeff Watson
Posted Sun, 08/17/2014 - 17:06

27.
Helpful? 0

BAD DESIGN - A misunderstanding of the heat capacity and moisture storage content(an electrically charged material that attracts moisture which causes it to expand at the surface, store and release moisture based on RH) and their ability to breathe. Has less to do with dew point, temp, attic insulation, etc...more to do with dynamic material properties (specific heat, density, thickness) design that most do not understand...to begin to understand that you have to understand the valuation and difference between dynamic mass and steady state r-value.

Synthetic manufactured gypsum is a bad choice, most concretes with high levels of portland cement as the binder is another. Neither have much useful mass, high heat-cool storage capacity, or the ability to expand-store when wet, shrink when dry...you can not force these materials to perform in ways they are not design for by changing the environment they are placed in.....wrong approach!

Hempcrete, limecrete, and especially earthcrete with the right types of clay are much better than OPC_concrete. Better IAQ and for the environment too. You won't find much complaining like this from these homeowners, house stays cool in summer, warm in winter, little heat-cool loads, no humidity control required.....allergy problems solved, no mold and mildew.

Knowing where to place mass is the other challenge, The chemistry is a big challenge. There is more than BTU exchange and guessing or neglecting moisture effects on BTU loads going on here.

Another way to cool mass if you had it is HR, pump water from the hot mass during the day to the metal roof at night to cool by night time radiation, send the cool water back to the mass during the day. Some have a reported a 10 degree load drop at the expense of running a water pump. Leaving your windows, some even doors, open at night makes perfect sense in the right design as proven by builds over all the world, mainly Europe. You have to think beyond r-value as the norm for a "well insulated house" you can have one of those that does not perform as you have found out the hard way.

Answered by Terry Lee
Posted Sun, 08/17/2014 - 17:37
Edited Sun, 08/17/2014 - 18:58.

28.
Helpful? 0

The short version:
After beefing its insulation up to R-60, your ceiling now gains less heat during the day than it did before (good), but it also loses far less heat, so any previous nighttime cooling through the ceiling now no longer works (bad). Since you were successfully practicing nighttime ventilation and benefiting from cooling through the attic, you have noticed the difference. If the roof/attic wasn't a major source of summer heat gain before (maybe it's very cloudy where you live or your roof is largely shaded by big trees), then you may have gotten very little summer benefit from the "upgrade."

The long version:
What you are discovering is IMHO the dirty little secret of the American building science and energy retrofit industries: the pitfall of a better-but-not-perfectly-insulated house with low-mass construction. With little thermal mass to store and release heat to buffer interior temperatures, that heat just stays in the air, rather than being stored in the mass itself, able to be released at a later time or cooled down by your A/C during the daytime. So now you need to run your A/C at night to evacuate that heat. Thermal mass is most useful during the cooling season when its trait of averaging out the diurnal temperature differential results in an average temperature that is very close to the human comfort level in many climates. With the outdoor temperatures you're describing, many people living in mass homes around the world would be laughing at your needing to use A/C when it's 85 degrees out.

Insulation decouples the interior temperature from the exterior temperature such that you are less affected by its extremes (good) but also less able to use ambient temperatures to your advantage, whether deliberately or passively (bad). This takes the form of traditional strategies like nighttime ventilation, night sky cooling, and solar irradiation having less of an effect, since previously there was less insulation for those heat flows to contend with as they moved heat from one side of the building envelope to the other. Whether the gains outweigh the losses will largely depend on the climate, the level of insulation and mass in other building components, your temperature sensitivity, and how many traditional strategies you are currently employing with success. Because when you better insulate your house to stop uncomfortably high or low temperatures from making you sweat or feel chilly, you are also making the house less dependent on the world around it and more dependent on mechanical systems you control and pay for to provide comfort on demand.

Now, if you insulate your house well enough (Pasivehaus level), you can size those mechanical systems to be so small as to be negligible or even remove some of them entirely. But before you hit that point, the benefit of more insulation is very climate-dependent. Anytime the world around your house is currently assisting in the house's interior comfort or temperature balance, insulation will reduce that. You have to weigh that against the upsides of reduced system sizing or runtime, or interior comfort. If the insulation you're thinking about beefing up won't make you able to reduce the size or cost of your mechanical systems, or won't increase your comfort, then it's a waste.

Answered by Nathaniel G
Posted Sun, 08/17/2014 - 23:35

29.
Helpful? 0

ORNL Thermal Mass Calculator shows that two inches on interior concrete mass drops cooling bills significantly compared to stick/r-value homes in most climate zones. Use their calculator to estimate your cost saving's. As I said, changing the environment or band aids based on peoples opinion is not going to change the results of their extensive testing and modeling, you need different materials. The best way to remedy your issue is to add mass in the form of natural plaster that breath to the interior walls, leave the well insulated-air sealed envelope as is. Earth plasters have the best ability to regulate moisture as well as heat-cold....plenty of proven examples on the internet. There are all kinds of books on natural plasters out there, do not use any OPC. You might test it on a room with some solar gain, open the windows at night, or see how the hvac makes a difference. I think you will be pleased at what you can do with plasters, the IAQ and beauty they create. You can create walls that are gorgeous! I agree with Nathaniel a pitfall of the industrial revolution and manufactured products that cost more and do not perform as well. If you DIY you can add the mass dirt cheap ;)...you loose a little floor space but lower your cooling and heating bills, reduce or eliminate VOC, cold-hot spots, moisture issues, etc....

Answered by Terry Lee
Posted Mon, 08/18/2014 - 06:53
Edited Mon, 08/18/2014 - 08:10.

30.
Helpful? 0

Jeff,
Terry's opinion that "the best way to remedy your issue is to add mass" is not universally shared. In most homes, adding thermal mass costs so much money that you are unlikely to see any payback from the investment.

Improved airtightness, high-quality insulation, and proper shading of windows (or the use of low-solar-gain glazing) are proven approaches.

For more information on thermal mass, see All About Thermal Mass.

Answered by Martin Holladay, GBA Advisor
Posted Mon, 08/18/2014 - 08:46

31.
Helpful? 0

Jeff, two questions and one comment:

1. What is your location? I don't recall any specifics about your local climate in this thread, I apologize if it's buried in there somewhere but I don't have time to go back and read every comment right now. Bottom line: if your climate is hot and dry in the summer, night flushing will help. If it's hot and humid, it won't, it'll just load up your house with more humid air for the a/c to deal with next day.

2. Have you addressed other enclosure issues - specifically do you have a vented, unsealed crawl space? As a general rule of thumb we seem to find here in warm humid N. Carolina (a very broad rule, with many exceptions according to the specific condition of the home), attic insulation upgrades improve heating season performance, closing and insulating vented crawl spaces has the greatest impact on summer cooling performance.

Finally, you ask "I thought it was common to turn the furnace down overnight, why isn't it the same for A/C (e.g., turning it off at night)?". Response: do you open all the windows in the house when you set back the furnace? if not, you shouldn't expect to do that when you turn off the a/c either. Here's an easy experiment that can increase your data set: continue to turn off the a/c at night but leave the house closed up. Continue to use ceiling and floor fans if you wish, and if you have them - in inhabited rooms only, of course - to keep a little cooling airflow over your bodies. What does this do for your overall summer a/c use?

Answered by James Morgan
Posted Mon, 08/18/2014 - 08:59
Edited Mon, 08/18/2014 - 09:08.

32.
Helpful? 0

Adding mass is mostly impractical in existing stick built construction unless you're willing to add big water jug pillars or a huge masonry heater or double up your interior drywall or something. But even that last suggestion often doesn't work well since the quest to make drywall lighter and cheaper has come at the expense of its mass, resulting in its largely being an additional layer of weak insulation rather than really having much heat-storing abilities.

The solution to this problem is pretty much going to boil down to simply plowing ahead and continuing with the "conventional" insulation retrofits, addressing the new top source of heat gain or loss for every project.

Jeff, why is your A/C unable to cool your house down below 78 when it's 85 outside? that strongly suggests to me that either your A/C was grossly undersized from the start (unlikely here in the USA) or there is a major unaddressed source of heat gain fighting the A/C all day. Are your windows old and bad and do they receive a lot of direct sunlight? That'll do it. Are your exterior walls dark-colored, have poor insulation, and receive a lot of direct sunlight? Those poorly-insulated walls will soak up and radiate a lot of heat into your house. Is your roof covered in dark shingles? Even with the R-60 attic upgrade, a dark shingle roof plus framing represents an enormous thermal mass receiving heat all day during summer that's located right where you don't want it (outside the insulation) that your attic floor insulation will be fighting long into the night as it cools off. Could there be any internal gains you're unaware of or not considering? A gas water heater that's within the thermal envelope and running for hours and hours a day, for example? Two plasma TVs? A gas oven and a gourmet chef?

Those are some of the things you'll have to address next to stop some of that heat from entering and staying in your house.

Answered by Nathaniel G
Posted Mon, 08/18/2014 - 13:07

33.
Helpful? 0

See Martin's quote below: Inaccurate and lacks comparative data, simple because you can not make a comparison between mass effect and (windows, air sealing, r-value insulation, shading") although dependent on one another, the outcome of the two differ dramatically, it's like comparing apples to oranges.

The mass effect I use and refer to, the pay back is immediate and the cost in most cases less than mainstream and other options, especially if DIY as I said. Adding mass to one wall can be effective depending on location, and it can be take less than a day labor, few hundred dollars, compared to air-sealing, replacing windows, insulation, etc.... with materials cost at close to nothing.

All though there are some poor attempts above, it is very difficult to quantify adding mass and it's dynamic effect benefit in all climate zones, this is what ORNL attempted to do after lots of prototype builds and modeling from their results, 1000's of models, many builds, to establish at DBMS cost comparison value for manufacture products(I manufacture my own products).....so I'd like to see this 'universally' shared" collection of data in "most homes" where the remedies captured all the pay back parameters and did a comprehensive cost of performance analysis based on lower utility bills such as the field study and extensive modeling ORNL did. My guess is that has never been done or captured, submitted to code books, standards, etc....and this 'universally accepted" standard in just a matter of wide based limited US opinion based on mainstream bad construction methods using factory built products and assemble knowledge. There are other natural methods that have been "universally" proven world wide to be a higher cop just not in this country. The great thing for my business is this inability to think outside the mainstream box, and lack of supporting data, leaves the door wide open to remedy situations like this with better performing "alternate materials" per code.

The best suggestion for Jeff is to not listen to any of it, educate yourself more, run some test if possible, look at your situation, then decide what is best. There are faster cheaper ways to add mass than plastering I mentioned. No one out here can make that judgement call for you, we simple do not have all the facts.

Answered by Terry Lee
Posted Tue, 08/19/2014 - 06:37
Edited Tue, 08/19/2014 - 08:46.

34.
Helpful? 0

Terry,
I stand by my statement. While high-mass walls can lower air conditioning costs in some climates, adding mass to existing walls isn't easy or cheap. Most fans of thermal mass overstate the benefits (or underestimate the cost) of building high-mass walls.

Answered by Martin Holladay, GBA Advisor
Posted Tue, 08/19/2014 - 07:12

35.
Helpful? 0

"My guess is that has never been done or captured, submitted to code books, standards, etc."

Mass-effect benefits are enshrined in code, have been for at least the last three iterations of the IRC. Like all IRC codes it's somewhat blocky, not a perfectly tuned energy use model (or even an imperfectly tuned but still protty-good tool like DOE2, that's adequately predictive for these purposes), but it's in there. See the mass-wall allowances in TABLE N1102.1.1 (R402.1.1) in chapter 11 of IRC 2012.

http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_11_sec002.htm

FWIW: ORNL vetted the thermal mass modeling of the DOE2 tool in one experiment by building two identical houses side-by side, one stick-built to (then) code min, the other with a bottom-of-the-line R16 ICF, and operated them for over a year while monitoring.

http://web.ornl.gov/~webworks/cppr/y2002/pres/114086.pdf

Modeling the dynamic effects of fiber or foam insulation layers looking at the insulation's thermal mass isn't that important from a total point of determining peak or average loads of a house, the way it might be for say, controlling the temperature of a superluminescent diode in a fiber-optic gyroscope used for satellite or aircraft navigation, or any other system that needs very tight temperature control even when subjected to temperature swings/energy inputs over a wide range of time scales. The time scale of diurnal temperature swings are just too long for the very small amount of internal thermal mass of the insulation. to be relevant. While it's measurable in fairly thick layers of fiber insulation on those time scales, it's more of a "who cares?" third order effect.

Even in ICFs or AAC wall assemblies the dynamic effects still really only a second-order effect, but significant enough to acknowledge in building codes.

Answered by Dana Dorsett
Posted Tue, 08/19/2014 - 11:38

36.
Helpful? 0

Terry Lee... Interesting posts... Curious as to your background... Engineer... Contractor?

Answered by aj builder, Upstate NY Zone 6a
Posted Tue, 08/19/2014 - 12:18

37.
Helpful? 0

Hi AJ, I have a long history in Engineering, structures & systems design, renovation, restoration, and testing in several industries. I recently quit a test lab to design buildings for our construction company. My son is the licensed contractor that manages our storm restoration and renovation division.

Right now I am testing and developing methods to cast-pour in place, plaster, etc., mass of different types. I am finalizing a new product using a high silica cellulose and a pozzolanic hydraulic cement binder. It has been a challenge determining the percentages and chemical compositions for production homes. This particular mass design would offer moderate level breathability or regulation of heat-coolth-moisture, a high ability to absorb CO2 improving IAQ. It also surpasses burn rates of mainstream, sound proofing, insect and rodent. If is mainly an insulation for the envelope, but if those attributes are important to a client we can add to existing walls, or build new for less than $3.00 ft2 plus labor. So if you DIY, a 2" x 10' X 8' wall would cost less than $300 material. I can cast a 2” 8’ x 10’ foot wall in about 4 hours. Simple plywood forms casted in place to any shape desired fast…..If you had to extend an electrical box or register couple hours more. No need to remove moldings nor add them back or render. What makes Martin’s statement correct is you will not find this at Home Depot. Other counties that have a much better understanding of mass, since it was not abandoned post-industrial revolution, poor people, have a better understand and have developed this technology proven for centuries to be cost effective. I just updated and modified it. What effect, what value, what load drop, is what I stated that Dana and others misunderstand do you place on that. That is where it gets complex, ORNL attempted to quantify it using concrete but, fell far short. They realized that and state they had a lot more work to do. I imagine budget constraints, it does take lots of R&D money.

Mass effect has little to do with R-value or the table that uses concrete Dana made reference to. The mass effect I described is not capture in any code, or if it is it is misrepresented, devalued, especially giving it and steady state “r-value”, not even remotely close. What needs to be listed there at a minimum is ORNLs “DBMS” values for different types and thickness of concrete mass which still falls short neglecting more effective mass, or whole house dynamic mass that may be used in total or partial construction, or alternative materials that perform much better than concrete with high levels of Portland cement, or gypsum wall board, ICFs; with high levels of junk, inert fillers and aggregates to cut manufacturing cost that result in low internal mass performance, plasticizers, VOCs…. etc. ORNL DBMS value falls short of the other benefits and design of mass that surpass heating and cooling loads. There is no design guide, or code, to provide a prescriptive path to the chemical composition, density, specific heat, thickness, for a given building in a certain climate zone. I am just getting started, there are other mass designs that offer a totally different set of “benefits” if you will, I offer clients depending on what they desire or the issues are. If it is cooling loads and moisture, the above design would not be the best choice. I’d use a material that had a high ability to regulate moisture and cold air loaded from night time air or hvac. If it were storm or debri resistance the client wanted we use a different ballistic mass. On MANY occasions home owners have reported a 30-80% reduction in utility bills from mass depending on quality of design, allergy issues solved, odor issues solved, sound issues solved, etc….many have noticed DRASTIC differences in IAQ in addition to hvac load drops, both dependent on the type, location, design of mass. To say it is not that important is absurd! To say that most have under-estimated its cost and performance or misunderstood it is accurate.

Dana: I have written those test reports MANY times, very boring BTW. Let me help you understand the design-build process used by many companies world-wide. The modeling “tool” used, DEO2, WUFI, whatever, is a great tool for initially determining what design path say A vs B to fund, after that it takes a back seat. The models are usually not that accurate in the early stages of design especially if heat-cold-moisture-CO2-wind-hail-snow-seismic-etc is being modeled which is extremely difficult along with interior and exterior environments in many climates zones. Developing the modeling effort in man hours there is A LOT of R&D cost most builders cannot afford. Sometimes a team of engineers need to be present. In conjunction with the product design there is parallel test fixture design and test procedure effort, lots of R&D cost to. Test readiness reviews, collaborations with clients if the lab is a third party, etc…testing commences, the results are back calibrated to the models, results such as thermocouple and pressure gages, accelerometers, strain gages, etc……it can take months or years to go through all the hot box testing, lots of changes an iterations. The design is released for field testing that again back calibrates the models and test fixtures-procedures. 1000’s of test gage results, interpretations, and models later the final models are useful to some extent, hence the birth of ORNL “DBMS” value and “Mass Calculator”, REAL DATA that surpasses opinions.

Got a meeting with a developer Friday to put some of these natural mass designs to use I need to prepare for. Wish me luck!

Answered by Terry Lee
Posted Wed, 08/20/2014 - 08:09
Edited Wed, 08/20/2014 - 09:27.

38.
Helpful? 0

Nathaniel G - I think your post (#28) explained it best to just your average concerned home owner who doesn't have a background in building science or construction. If I understand, you're basically saying that instead of the hot air being able to easily pass through my ceiling (since it has added insulation), that heat stays within the living space & thermal mass now plays a more important role. Mechanical means are now required to remove that heat. When my A/C is on, it has no problem cooling down the space; it is functional & effective when it is turned on - don't know where I mentioned that it couldn't cool the house.

James Morgan - You ask:
1) Location: I am in Chicago, where the summer daytime temps might peak in the upper 80s and overnight get down to the upper 60s or 70s. If it's upper 60s at night & not too humid, I crack open the windows & use fans overnight.

2) I have a single-story brick house, with a basement and attic, and yes the roof is dark shingles. I do believe that I will see a much more obvious benefit during wintertime with the added insulation. Summertime - maybe the effect is not as easily observable, but can only be verified with electric bills. We're pretty energy conscious - we turn things off when not using, the water heater is set pretty low, we hardly cook, we have a single TV/cable box which is only 22" big that probably only gets a couple hours of use in the evening, no pets, we don't have any big furniture or interior decorations so maybe that means we have very little thermal mass. Adding mass just seems pointless if this is not a new construction.

3) Opening windows overnight during heating season - you're correct; I don't crack the windows in the heating season overnight; however we're talking about two different phenomena, because I crack the windows during summer nights because it's hotter inside than outside. On the same thinking, I would be cracking the windows in winter if it was colder inside than outside overnight (an impossible scenario).

This thread has shown me that I am "using my A/C the wrong way." It seems you guys are saying A/C should be left on all the time (all day, all night) with the windows closed. So I tried that for about a week, but then I ran into a different issue - CO2 levels get way too high. This was the second reason for opening windows overnight. Now I feel like I have to constantly run my 80cfm bathroom exhaust fan for ventilation & the levels still don't budge by much. This means more electricity to run the fan. I'm afraid of my upcoming electric bill because I've been running A/C nonstop (yes it cycles on & off) & the bathroom fan pretty much nonstop as well, and still haven't seen my CO2 levels go under 1200ppm when we're home. Now, of course if I was doing this pre-R60-insulation, I'm sure I will see a difference in electric usage; but I wasn't, so in a sense, adding insulation has forced me to use more energy.

No offense to anyone who is an energy auditor, but they made it seem black & white - install this much insulation & you'll save X dollars. Where was it mentioned that I now have to run A/C 24/7, that I have to have my bathroom fan on 24/7, etc...prior to installing the insulation, we've never ran the A/C for more than a couple of hours a day - just enough to cool off & let the overnight temperatures take over. I guess auditors should be assessing the homeowner's usage habits before being able to turn an "improvement" into a dollar amount of savings. If I was told all this beforehand, it's one of those things that's like - hmmm...maybe I should just search for a house which already has a better design than this old house that's just going through upgrades & retrofits.

Answered by Jeff Watson
Posted Sun, 08/24/2014 - 21:03
Edited Sun, 08/24/2014 - 21:22.

39.
Helpful? 0

"This thread has shown me that I am "using my A/C the wrong way." "

Welcome to the rabbit hole… It's insidious, isn't it?!

First, you build a building without regard for energy efficiency in a climate with 1) a heating season, 2) a cooling season, and 3) a humidity load (ugh, Chicago).

Then you add an air conditioner and a heater for comfort. All is well.

Then OPEC turns off the oil! Energy prices go up by a factor of ten overnight! Your jaw hits the floor when you get the bills for running these things!

So you add insulation to your attic and walls, and you replace your windows.

Where you put the insulation in relation to other components (e.g. inside the brick wall or outside) and what type of insulation it is (massive insulation like cellulose vs lightweight insulation like foam) are critical details that must be correctly matched to the context, but nobody tells you this. They may not know themselves.

Likewise with the windows; what kind of glazing, which orientations should receive the different glazings, etc.

The added insulation helps during the winter but seems to make the summer worse.

The new windows help during the summer but are a wash or have a disappointingly small effect in the winter. Your house also has less natural light, so you spend more money on electric lighting.

You do some air sealing. You learn to use your air conditioner correctly. You keep your windows shut.

Suddenly your indoor air quality is terrible and you're practically suffocating! You discover that your gas furnace is now backdrafting and poisoning you with carbon monoxide!

You quickly replace your furnace with a sealed combustion, high-efficiency model (ka-ching!). But your indoor air is still stale and full of carbon dioxide.

So now you have to add a mechanical ventilation system that brings in outside air. You need to add an HRV to avoid undoing all of your hard work by flushing your conditioned air outside and replacing it with unconditioned air that your furnace or air conditioner will have to condition.

If you don't have ductwork that's in use year-round, you need to add dedicated ducting and air handling for the HRV…

You see how this goes? Most buildings simply don't take well to energy retrofitting. They were designed in an earlier time, and they worked well for that time of lower energy prices and lower comfort expectations, but bringing them up to snuff in our modern world is a can of worms the size of the suitcase full of money you're going to have to spend to do it.

I used to be really gung-ho about energy retrofitting. The more I learned, the more I became convinced that especially if your energy pig house is in a climate with both a heating and cooling season, anything short of turning it into a superinsulated, mechanically-ventilated passivehaus is mostly a waste of time and money. The rabbit hole is too deep. Without methodical planning, what you do to help in the heating season will hurt in the cooling season, and vice versa. You'll discover that you need to caulk everything, replace your combustion appliances, add mechanical ventilation doodads, wrap your house in all kinds of petrochemicals that smell bad and worsen the quality your indoor air, you name it. You'll take two steps forward and one step back. And there are a lot of things that are largely outside of your control, such as orientation, slab insulation, roof overhangs, and window sizing and placement.

The costs, payback times, and carbon footprints of all these retrofits can border on the absurd, especially if you hire them out to pros. It might be worth it if you can do most of the work yourself and your current bills are insane because have an oil furnace and an ancient A/C. If not, you'd probably be better off saving the money to eventually build or buy a new, modern house with all of this stuff done right from the start.

Answered by Nathaniel G
Posted Sun, 08/31/2014 - 22:37
Edited Sun, 08/31/2014 - 23:23.

40.
Helpful? 0

Jeff

As to running the AC 24/7

Yes and no

When you want AC during the day, do not shut it off at night. In my own home north of Boston, we tend to run the AC for weeks on end in the summer, but then when a nice dry warm spell comes, shut it off and open the windows. The weatherman is your friend. When walk out the door and say wow, it is gorgeous out check the weather to see what the next 3 days hold and act accordingly.

I have hardly run the AC this year, a week or so in July and right now, but last year it was on almost all summer

When you say high CO2 I respectfully suggest you are overthinking. I have no idea what my CO2 is but if the house gets stuffy [two kids and a big windy dog] yeah, we open the windows.

I will say basically the same thing I said before, learn your house, it will take some time

Consider a rule that the AC needs to run in 48 hour cycles as a thought process. On for 48 hours or off for 48 hours[rather than 12 as in the past] Modify as you deem necessary, it is your house..........

Answered by Keith Gustafson
Posted Mon, 09/01/2014 - 12:22

41.
Helpful? 0

I wish people would stop posting costs for their projects or proposed solutions based on DIY to make them look more appealing. Sure things are cheaper if you don't include labor costs, but if you need to cut that out to make your case then what you are proposing really isn't a viable option.

Answered by Malcolm Taylor
Posted Mon, 09/01/2014 - 12:43

42.
Helpful? 0

Malcolm, our company (as do many) provide three basic levels of construction service.

1. Design-build
2. Design- build (some client DIY involvement)
3. Consultation (100% DIY involvement)

The 3rd pushes E&O liability, put people and the internet do it all the time. We put bids together and do jobs almost daily for clients that want to DIY and cut cost. Most builder's in the midwest leave basements unfinished so clients can DIY to save money. DIY is a very real viable option in today's economy. Where I am heading with my methods are low skill set high performing DIY, that is one of our markets, that is the market of the past when people had to barter labor (family and friends) to avoid going into large dept and large mortgages, that is what I am pushing into this generations mindset, stay out of debt, DIY. Not all have the time, but in labor exchange it can happen. Our attorney does not like it, the liability, but my insurance agent has the workers comp and E&O solution, "endorsements" :)

All besides the point, with the proper low skill set low labor hour designs it is a false myth that adding mass is expensive, it's not once you understand how and where, compared to other solutions.

Answered by Terry Lee
Posted Mon, 09/01/2014 - 20:28
Edited Mon, 09/01/2014 - 20:35.

43.
Helpful? 0

[Nathaniel G]
Nice way to describe it. Saving money on energy is always nice but a lot of this retrofitting stuff I seek out because I just want things that simply work efficiently.

Just like you said, you do one thing, then that leads to another. I think the issue is primarily that homeowners don't have knowledge of all steps that must be taken at the very beginning, and we kind of only learn thing as the issues arise. Of course if we learn everything up front, we might just say forget it altogether...which in turn would hurt industry or guys in the business of say attic insulation.

I am a new homeowner, have never lived in house, but I try to learn as much as possible. The way we used A/C was just to get the temperature down & we would then turn it off; it'd run for a single cycle. I now know that the A/C reduces the temperature of the air so that the living space can then transfer its heat to the cool air. This process needs to continue because the heat can't flow to the exterior as easily as it did with less insulation, hence the need to let the A/C remove that heat (from the inside), even when it's colder outside. I also learned the humidity in my house may be too high as well...it's about 60-65% RH and 65-75% in the basement...learned that I'm supposed to aim for under 50%.

[Keith]
Thanks for the advice as well. I have another thread about my CO2 problem, but after the R60 insulation, seems opening the windows hardly does anything without also running fans (and it still hardly does anything).

[Malcolm]
True, costs are more appealing if there's some (hidden?) DIY work involved. At the same time, I feel DIY encourages seeking additional knowledge vs. if you just paid someone to do something (unless this person is very forthcoming about knowledge transfer...with what I've seen so far with people who've worked on my home, they don't like to share too much about their trade). Can't blame them though; if my job was in the trades, I'd probably do the same...primarily for the reason Terry mentioned - liability. For a thorough individual seeking knowledge, it sucks, but unfortunately that group of people is probably the minority, so it's best just not to say anything!

Answered by Jeff Watson
Posted Sun, 09/07/2014 - 11:13

44.
Helpful? 0

I think one of the issues with blowing attic cellulose insulation is it installers tend to aim high so that the cellulose will fall down gently on the floor of the attic in an even blanket. This means that they're aiming their tube at the upper end of the baffles and the ability of the baffle to carry air means it's a natural thing for the cellulose to go into the baffle and clog it up. My suspicion is that this has dramatically reduced the air flushing potential of the area above the insulation in your attic so that attic is holding on to heat and not cooling the roof above it in the evening. A simple experiment would be to ask a friend to walk around your house with a leaf blower blowing directly into the soffit vents and monitor the air movement in the attic. If the baffles are clear you would see minor plumes of dust shooting out of the tops of them. If clogged you might see major plumes if the blower can get enough pressure to open them up.

Answered by Michael Chandler, GBA Advisor
Posted Sun, 09/07/2014 - 12:28

Other Questions in General questions

Half insulating stone basement

In Energy efficiency and durability | Asked by Geoffrey Cook | Oct 31, 14

Minimum R-values for exterior foam for 2x6 walls

In Energy efficiency and durability | Asked by Craig Steinman | Oct 30, 14

How to seal 4" EPS foam at slab edge (radon concerns)?

In GBA Pro help | Asked by e c | Oct 29, 14

Pipe leak in basement

In General questions | Asked by Andrew Sirianni | Oct 31, 14

Foam insulation question for 100-year-old brick home

In Green building techniques | Asked by Wes Leland | Oct 30, 14
Register for a free account and join the conversation


Get a free account and join the conversation!
Become a GBA PRO!