Posted By Skeptix on 27 Sep 2012 11:18 PM
I used 91F and 12F for the outside design temps. I like it warm in the winter, that is why I used 75F in the winter. And cooler in the summer so I used 70F. The crawl space is poured concrete and insulated with 2" polystyrene sheet. The crawl space is only exposed to the outside on 2 walls and I want to use it for storage, so I want it to be conditioned. The basement has the same insulation as the crawl space at this point 2" polystyrene.
There is no insulation anywhere in the house yet, which is going to change here shortly. I used standard R-19 and R-49 fiberglass in my load calculation. I was planning on having the attic blown in. My original quote was for fiberglass. The house should be fairly tight, I have sealed every joint and seam on the exterior before the Tyvek went on.
The windows in house are Andersen 400 series vinyl clad wood with Low-E glass.
Colby
I strongly recommend making the attic insulation blown cellulose (specify borate-only, sulfate free fire retardents), and meticulously air-sealing the attic floor/upper-floor ceiling prior to insulating, since fixing it after the fact is a serious pain. Sealing the stop of the "stack effect" stack is critical- far more important than sealing the wall sheathing.
The walls would be tighter if either open cell foam, blown high density fiberglass (1.8lbs density min.) or cellulose (any density if wet-sprayed, 3lbs min if dense-packed.) R19 batts are junk (as are R23s). If going with batts only "cathedral ceiling" high density batts cut it. In 2x6 cavities R19s perform at R18 , and R23s only perform at R19 within the ASTM test range, and worse at higher delta-Ts than 30F (due to higher convection currents within the low density fiber layer.) For the labeling they're tested at full manufactured loft, which is deeper than 5.5". High density R21s perform as-labeled, even with higher delta-Ts than tested, but only if installed perfectly, with no compressions or gaps.
Sprayed or blown insulation have inherently fewer voids, and if installed at sufficient density, will usually meet or exceed their labeled performance.
Conditioning an unfinished basement or crawlspace in winter to fully 75F for storage is just silly.
If the siding isn't up there's still time to add foam to the exterior. With exterior foam at R7.5 or higher it keeps the sheathing sufficiently above the dew point of the interior air that no interior vapor retarder is required, which gives the assembly MUCH better drying capacity. Going with 1.5" of XPS gets you there, and still has ~ 1 perm of drying capacity toward the interior. Using 1.5" of foil-faced iso gets you there too with a somewhat higher R, but puts a vapor retarder on the exterior, making it more important that you not use low-perm finishes or vapor retarders on the interior (standard latex/acrylic is fine.
Going with 1.5" XPS cuts the heat loss through walls by about 1/3, going with iso cuts it nearly in half: Without the exterior foam, with the thermal bridging of the framing factored in the "whole wall" R of 2x6 framing with any of the cavity insulation mentioned is only R13-R14. With 1.5" of XPS that rises to ~R20-21. With 1.5" of iso that becomes R22-23. At your +12F heating design condition iso & XPS in a 1-2" thick sheathing application perform about the same, but at your average winter temps iso will outperform XPS at any equal thickness.
The biggest untreated air leak on most new construction is at the foundation sill and band joist, adding up to several times the air leakage of all window & doors. A sill gasket helps, but not very much. Sealing an insulating the band joist & foundation sill with 1" of closed cell foam (right up to the top edge of your 2" rigid foam) is good, 2"of foam in this critical area is better. By stopping air leakage into the basement/crawl, it lowers the flow of stack-effect induced infiltration losses. If you then also air-seal the top floor ceiling and any plumbing/electrical penetrations/chases into the attic it takes it down even further. At
ANY ACH/50 number on a blower door test, sealing the basement & attic fixes more infiltration volume than even much bigger wall leakage under pressure in the intervening floors.
The Andersen 400 series comes with a number of different low-E options, and the U-factors can be as low as U0.24 or as high as U0.30, which is a big enough difference in performance to affect the load numbers, so it's good to check the label/models and put the right numbers into your heat load calculation tool. The orientation, shading, and SGHC numbers will also affect the cooling load numbers.