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Older house energy audit recommendations – conservative?

vap0rtranz | Posted in Energy Efficiency and Durability on

Hi GBA folks,

We received our report from a home energy auditor and my question is: are these target goals conservative? or limits of an older house?   Hoping folks can chime in with experience and if we can be more aggressive on the outcome, like a lower heat load.

Data are below:

House:
1940s built house (originally had knob-and-tube electric, “Otocpus” central heat, root cellar, cistern, etc.)
1300 sq ft, 8′ 2×4 walls, unfinished basement (adds ~500 sq ft)
Cape cod style w/ multiple roof pitches, knee walls upstairs &  3 attics
~1990s upgrade done, possibly via a weatherization program (fiber batt added to attics, doors & attic hatches sealed, windows & doors replaced, etc.)

Data:
1720.83 sq ft modelled (so includes unfinished basement)
2896 cfm50, 16.04 ACH50
162.05 sq in leakage
Wall insulation: R3 (cavity) @ 1720 sq ft
Attic 1 & Vaulted Ceiling insulation: R5 @ 260 sq ft
Attic 2 insulation: R7 @ 217 sq ft
Vault 2 insulation: R8 @ 422 sq ft
Basement insulation: none
Windows: double pane, not Energy Star
Doors: not Energy Star
Energy Star: Zone 6
Heat load: 65,450 BTU @ -5F outdoor & 70F indoor

Recommendations & Target Goals:
Air seal: 1740 cfm50, 9.64 ACH50
Insulate Attic 1 & 2: R49, blow in cellulose & foam where needed
Insulate knee walls: R13, blow in cellulous & foam where needed
Insulate Vault 2 (sloped ceilings): R13 cavity, R3 continuous
Insulate walls: R13 cavity (no continuous), dense pack blow in cellulose from exterior
Insulate basement (rim / sill): R18, rigid foam
Heat load: 42,202 BTU
Energy savings: 33%
Payback: 11yrs

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Replies

  1. Expert Member
    Dana Dorsett | | #1

    >"Energy Star: Zone 6"
    ----
    >"Insulate Vault 2 (sloped ceilings): R13 cavity, R3 continuous"

    In DOE climate zone 6 on an unvented roof at least half the total R has to be outside the first condensing surface. Or is this 2x6 raftered roof fully vented, with the plan for R13 batts in the cavities and R3 polyiso behind the ceiling gypsum?

    >"Insulate knee walls: R13, blow in cellulous & foam where needed"

    R13 batts need a full air barrier on all sides to perform to spec. R15 batts are dense enough to perform well enough without an explicit air barrier. R13-R15 with 1.5" -2" of polyiso detailed as an air barrier on the attic side of the kneewall would be appropriate and would have sufficient dew point control for walls. (Reclaimed roofing polyiso is dirt-cheap and appropriate for the application.)

    The load numbers (both before and after) seem suspiciously high. Has that been verified by the fuel use numbers?

    Is the R18 basement insulation is from the slab all the way to the subfloor?

  2. vap0rtranz | | #2

    Hi Dana,

    Here's what I know about your replies:

    >Or is this 2x6 raftered roof fully vented,

    Yes, there were 6 roof vents installed in the various attics by the previous owner when new shingles were done a few years ago.

    Though this is still a concern that I told the auditor. We got 2 big ice dams this past winter.

    >R13 batts need a full air barrier on all sides to perform to spec.

    Ah thx for this reminder. So I should push for cellulose or foam instead of batts? especially in hard to reach / work areas of the attics.

    I recall the auditor cautioning us about some insulating materials being installed almost blind in these hard to reach areas of our attics ... he mentioned something about one material that installers get at with wands or tubes and mixes at the end of that wand/tube and the installer can't actually see if the mix was successful or directed in the right location. Sound normal? so some installation material (maybe it's some types of foam) can be installed improperly with our kind of attics?

    >Has that been verified by the fuel use numbers?

    No, I will run those #s.

    >Is the R18 basement insulation is from the slab all the way to the subfloor?

    No, we are battling a wet basement so I've read that insulating the basement walls from slab to subfloor with introduce more moisture problems in our case. So just the wood sill and rim joist sealing & insulating is being recommended, I believe.

    But I find it odd that the subfloor of the basement, so underneath our 1st floor, isn't being insulated in the recommendations. I mentioned cold floors to the auditor when he was onsite but the report and recommendations don't include getting our 1st floor insulated from the basement. Right now there is just floor joints and subfloor separating our basement from 1st floor -- no insulation at all. Is insulating the underside of the 1st floor considered bad? or useless?

    Justin

  3. Expert Member
    Peter Yost | | #3

    Don't forget that your energy audit and its recommendations for improving energy performance need to be considered/completed AFTER you address any water management issues. You need to figure out why your basement is wet in order to determine how to manage it.

    If you are configuring your enclosure so that your basement is considered conditioned space, then perimeter insulation and air sealing and no insulation or air sealing at the first floor is the right approach.

    Quite often, basements are really "semi-conditioned" space since space conditioning equipment and delivery systems keep the basement reasonably conditioned indirectly until you finish y0ur basement and then condition it more fully and intentionally. In terms of heating and cooling and ventilating basement, the codes are generally quite inexact.

    Peter

  4. vap0rtranz | | #4

    >AFTER you address any water management issues

    Flooding in the Midwest was not something we planned with Mother Nature to coincide with scheduling the energy auditor's onsite visit. :) It's been a problem here in Wisconsin for weeks (state-wide flooding emergency).

    >If you are configuring your enclosure so that your basement is considered conditioned space ... until you finish y0ur basement.

    We are not going to condition the basement. The auditor told us the models (air leakage) include the basement regardless. He did suggest air sealing at the joists. That is all.

    I still find it odd that the only information I've found on renovating unconditioned basements, which is what we want, and when our only ask is for the floor on the 1st floor to be warmer, which is related to the basement, is to basically force the basement to be conditioned. That option makes no sense -- we will have to do huge effort to dry out the basement, all sorts of work to the foundation, insulating walls down there, etc. $$$. We understand the basement needs to be dry, and we are working on that separately, but dry doesn't equal conditioned from what I've read everywhere.

    Why would we condition 500+ sq ft + walls when all we want is the basement to have less affect on the temp of the 1st and 2nd floors? I'm not the expert but it seems like separating the basement from our living space is the way to do it. I've looked around and downstairs/attached garages can be done this way -- to keep the temp and the fumes away from the living space. I'd think the way downstairs/attached garages are done is similar to how we want our basement.

    I don't understand why the basement shouldn't be separated off from the conditioned space and made even cooler. We _want_ it to be cooler so it can be root cellar. And yes we have to consider what colder temps mean, like insulating plumbing, etc. if we do that.

    It seems the recommendations are always to condition the basement ... maybe that is all the rage in American homebuilding, so Americans can enlarge the square footage of their home by finishing the basement; but again, we do NOT want to do that to our basement.

    Do folks recommend conditioning attached garages?! At least not when they're used to park cars. :)

    Justin

  5. Expert Member
    Dana Dorsett | | #5

    >"Is insulating the underside of the 1st floor considered bad? or useless?"

    -----

    >" I don't understand why the basement shouldn't be separated off from the conditioned space and made even cooler."

    If the furnace and ducts are in the basement insulating between the uninsulated basement and first floor guarantees that most of the distribution and jacket losses are truly lost. That can be up to 25% of the total heat loss of the house, even if the basement isn't actively heated and drops to 50F or colder during cold weather. Insulating the basement walls to code min cuts the basement losses (which is heat you ARE paying for) by something like 90%. Most houses of that description would see at least a 15% reduction in the heating bill by insulating the foundation walls.

    >"...we are battling a wet basement so I've read that insulating the basement walls from slab to subfloor with introduce more moisture problems in our case. "

    Insulating the basement from slab to subfloor doe NOT introduce moisture problems as long as the insulation is resilient to moisture (read "not mold food"). With CMU or poured concrete foundations this can be a fairly straightforward DIY project. Insulating the foundation keeps the interior surfaces warmer in summer, requiring less mechanical dehumidification to keep "musty basement smell" at bay.

    You don't need to actively heat the basement, but it will stay warmer and drier year round if the walls are insulated.

    >"Do folks recommend conditioning garages?!"

    Yes.

    (Providing it is adequately ventilated, and there is conditioned space above it.)

    Don't conflate "conditioning" with "heating and cooling". Bringing the garage inside the thermal boundary of the house is a good thing- reduces mold and moisture problems in the garage, and lowers the heat loss from the house.

    Your uninsulated basement is ALREADY conditioned space, which is why it is included in the modelin, even if not actively heated. It's just extremely LOSSY conditioned space. To take it out of conditioned space would require both insulating and seriously air sealing between the basement and first floor (difficult to do well with myriad plumbing, flue, electrical and duct penetrations), which would increase the mold risk in the basement, and would increase the risk of plumbing freeze-up during cold snaps in your climate zone.

  6. vap0rtranz | | #6

    Hi Dana,

    I have some heat #s but cannot find how to revisit the BTU load calculation, mostly because I don't run these #s like smart folks and also because our heat fuel is LP via a tank, so there's no utility bill from them to reference. But I do have some #s below.

    Our furnance used 631 gal from 1st of Nov to 1st of April. Our electric utility provider says that time period is 5737 heating degree days. (Their bill also says that time period is 152 days, which is a bit off but +/- 2-3 days hopefully is not huge factor.) Our furnance is 90% efficient, and we have a set temp of 68F. Is there a way I can take these #s and redo the BTU load calculation? I noticed Martin Holliday's book says one can assume upto 93,000 BTUs per gallon LP, which gets me to total BTU used in the time period, but I cannot find where to get at BTUs per sq ft of conditioned space. Or maybe I am missing some #s?

    >That can be up to 25% of the total heat loss of the house,

    Understood. But our goal is to remove all fossil fuels, so the plan is to retire the LP furnance and ducts (though I realize some folks like ducted minisplits, but no need to digress), so there would be nothing heating the basement anymore. Wouldn't the loss shift to leakage between the 1st floor and basement, not losses from indirectly heating the basement?

    >Insulating the basement from slab to subfloor doe NOT introduce moisture problems as long as the insulation is resilient to moisture (read "not mold food").

    OK since I wrote this we went from moisture to flood (1" standing water) so I still don't think putting up insulation in our basement is a good idea right now. The priority is to get it dry (sump pumps, landscaping, gutter rework, etc.), which we are working on, but I don't want to invest all this money in conditioning the basement only to have insulation, studs, foam, etc. ruined by the next 10/20 year flood. I've lived through the cycle of 10/20 year flooded & moist conditioned basements from hurricanes in a previous life and it's just a real pain.

    >To take it out of conditioned space would require both insulating and seriously air sealing between the basement and first floor (difficult to do well with myriad plumbing, flue, electrical and duct penetrations), which would increase the mold risk in the basement, and would increase the risk of plumbing freeze-up during cold snaps in your climate zone.

    Understood. I'm weighing pros & cons of doing that.

    Justin

  7. Expert Member
    Dana Dorsett | | #7

    >"used 631 gal from 1st of Nov to 1st of April"

    The heat content of LP is 91,600 BTU/gallon, not 93K.

    At 91,600 BTU/gallon x 90% efficiency is 82,440 BTU/gallon delivered to the heating system, x 661 gallons= 54,492,840 BTU

    I doubt the power company is measuring the HDD from the first of each month from a weather station less than 5 miles from your house. Got a ZIP code? With better locational information we can look up the weather data. We would also need that to verify the 99% outside design temperature for calculation the heat load.

    Assuming the 5737 HDD numbers were correct (not a great assumption but it won't be wildly off) that would be 54,492,840 BTU / 5737 HDD= 9498.5 BTU per degree-day, which is (/24= ) 396 BTU per degree-hour.

    With an indoor temp of 68F it's fine to use the 65F degree day base as the presumptive heating/cooling balance point. So if your 99% outside design temperature is +10F you would have 65F - 10F = 55 F heating degrees, and a presumptive heat load of 55F x 396 BTU per degree-hour = 21,780 BTU/hr

    If the 99% design temp is indeed -5F that would be 65F - -5F = 70F heating degrees for a heat load of 396 x 70F = 27,770 BTU/hr

    That's a HELUVA lot less than 65,450 BTU/hr-less than half! It's also a third less than 42,202 BTU, which makes me suspect gross errors in the load calculation methods used by the auditor. Even in a high wind it's unlikely to hit the 42K load number AFTER you've tightened the place up a bit, or maybe even before upgrades.

    If the basement will no longer heated by distribution losses from ducts it become even more imperative to insulate the foundation or actively heat it to some minimum temperature to avoid freeze up potential during cold snaps.

  8. Expert Member
    Dana Dorsett | | #8

    >"OK since I wrote this we went from moisture to flood (1" standing water) so I still don't think putting up insulation in our basement is a good idea right now. The priority is to get it dry (sump pumps, landscaping, gutter rework, etc.), which we are working on, but I don't want to invest all this money in conditioning the basement only to have insulation, studs, foam, etc. ruined by the next 10/20 year flood. "

    You don't have to install studs to insulate with rigid foam board, and EPS foam doesn't need to be replaced if it gets wet- it dries just fine when the tide goes out. Insulated concrete forms are made with EPS, and tolerate flood and soil contact just fine.

    If using polyiso it's good to stop well above the high-tide mark, since it can wick moisture if submerged, taking forever to dry. I have 3" of polyiso in my basement that has a history of flooding to 3-8" in some parts of the house, but the bottom edge of the polyiso was purposely installed above that mark by a few inches.

    When an ice storm took out the power for 10 days several years ago the sump pumps quit (we have four of them) and at least half the basement had water above the slab, nothing had to be replaced. The foam is covered with gypsum board (unpainted in most of the basement), and the kick boards at the bottom are water tolerant PVC trim boards (which was OKed by the inspector.) I'm not worried about having to repair/replace any of it due to future flooding, which surely WILL happen.

    Yes, the priority this week should be correcting the bulk moisture management measures as best you can, but unless you are on a flood plane and can expect complete innundation of the basement every decade or two it's still fine to insulate the interior.

    Even if it WERE on a flood plane, if you're digging in exterior perimeter drains, insulating with 3" of EPS down to 4' below grade and finishing the above-grade portion of the EPS with a cementicious protective material such as Quikrete Foam Coating (or even a half inch of stucco scratch coat reinforced with chicken wire) will keep the basement from freezing. Even insulating the exterior down to 2' below grade makes a big difference, but in zone 6 it's "worth it" to go deeper. (Slab edge insulation for slab on grade houses would need R10 down to 4' below grade to meet current IRC code for zone 6.)

    At the top you would need to slip Z-flashing in behind the drain plane on the framed wall to direct water out to the exterior side of EPS. That's usually not a big deal, and despite the thermal bridging of the metal it's still a huge improvement over an uninsulated foundation.

    3-4" of EPS can be pretty cheap if using reclaimed roofing EPS/XPS or factory-seconds goods. (Used roofing foam is usually less than 1/3 the cost of virgin stock goods, cheaper per R than box-store pricing on batts even.) Just don't use reclaimed (or new) polyiso on the exterior- if wedged between the foundation wall and wet soil it becomes saturated over time, reducing it's effectiveness.

  9. vap0rtranz | | #9

    Dana,

    Wow! Yes that is MUCH less! ty!

    I had to read your replies multiple times. Lots to digest here.

    I forwarded snippets of your #s to the auditor to get at lower/actual heat load. I'm assuming the best and that he used national averages / rule-of-thumb loads.

    On the wet basement: details on what has been working for your basement are invaluable. And the options that are available (like the polysio stopping above the flood level) for occasional flooding isn't something I'd thought of until you shared that tidbit. Luckily we have not had anywhere near 8". I'll look at these options again.

    Ty!

    Jp

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