Crawl space wall insulation
I am trying to get my new build R2000 certified. One of the things the R2000 consultant would like to see is more insulation in the crawlspace wall.
The crawlspace is to be heated and is completely below grade. the crawlspace wall is 4′ high, 6″ thick, and the footing projection is 4.5″. the exterior side has brushed on damproofing and 5″ of eps (2″+3″). the consultant would like to see another r8 of insulation added. obviously i’m not going to excavate to add more exterior eps so what do you guys suggest? i don’t mind labour-intensive solutions but would like to keep the material costs down. also, do not want to use foam panels and spray foams are not available. is my best bet a short stud wall filled with roxul? is it not cool to use pressure treated lumber for the sill plate as it is located within the conditioned (i.e., living) space? i appreciate any tips. (outside design temp is -32 celsius)
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Replies
Erik,
I don't know why you don't want to use rigid foam or spray foam, but those are the only two types of insulation that I would recommend for use on the interior side of a crawl space wall -- unless you are willing to consider using Foamglas, an expensive and hard-to-obtain building material.
For more information on Foamglas, see On the Jobsite with Foamglas
To read about why you don't want to use Roxul (mineral wool) or fiberglass, see these two articles:
Building an Unvented Crawl Space
How to Insulate a Basement Wall
hi martin, i didn't want to use foam due to its expense and its need to have fire-rated protection. spray foam is not an option locally.
Erik,
Many building inspectors will accept the installation of Thermax polyiso without further fire protection because Thermax has been tested and received a rating for ignition resistance. You might want to consider installing Thermax.
martin, unfortunately, thermax is not available in canada.
Erik:
Has your R-2000 evaluator given you other options? As you likely already know, the R-2000 standard is performance based and not prescriptive. Is the problem that you are not meeting your energy target? If so, you might have other options at your disposal (depending on what stage your project is at) including mechanical equipment and improved airtightness. What province are you located in?
Gio
hi gio, the project is ready for drywall and is located in bc, 9 hours north of vancouver. the house, as such, does not meet the energy target but the evaluator has been very helpful in offering solutions.
he performed his calculations based on this criteria:
hi gio, the project is in a small town in the rocky mountains of bc. yes, the issue is the house does not meet the energy target and yes the consultant offered different solutions. he has been very helpful and i am grateful for his help. the house is ready for drywall. he performed his calculations based on this criteria:
Ceiling R-64
exterior walls: 2x4 R-14 plus 8" larsen truss r 28 with roxul
foundation: R-21 exterior
slab: R-12
airtightness: 1.5 air changes (assumed)
electric baseboard heating
electric domestic hot water (DHW)
triple glazed, double low-e, fiberglass windows
HRV [assumed Lifebreath 155 with ECM motor]
most lighting CFL
given these specifications, the house does not meet the target. options he has considered are:
added R-8 to interior of foundation wall.
electric DHW tank - added R-10 insulation to tank.
heating: air source heat pump - a ductless mini-split air source heat pump
drain-water heat recovery: 30" unit
With these options, the house just meets the R-2000 energy target.
sorry i butchered the last post. its tricky cutting and pasting emails with an old iphone..
Hello Erik: I'm an R-2000 evaluator in Manitoba, and would have suggested/considered most of these options as well....the current foundation insulation does seem to be on the low side especially considering the rest of the envelope. Do you have to satisfy all 4 listed options to reach the target or just one of them?
Cheers,
Gio
gio, the evaluator has been very helpful. he has also suggested the geospring DHW heater. the house is only 650 sq' so meeting the airtightness is especially difficult. i know nothing but find it hard to believe installing a 30" drain water heat recovery unit would amount to much in a house designed for a single occupant. do you have any suggestions?
i sincerely regret not adding more exterior foundation foam...
Hello Erik:
It sounds like you've got a good R-2000 plan evaluator, and they know your project and region, so I would rely on their guidance and expertise in meeting your energy target.
With an envelope like the one you are building, the portion of DHW energy use compared to other loads will be significant, so the DWHR is an excellent option, especially considering you are using resistance DHW and also considering it is simple, requires no maintenance, lasts virtually a lifetime, and has a relatively short payback period/ amortization (depending on your shower use, cost of hot water, etc). When serving one shower, we are allowed to apply a credit of around 600 kWh (exact amount varies depending on model installed) to your energy model for a 30" DWHR..
Good luck in your project!
Gio
prairieHOUSE Performance Inc.