Quote:
Originally Posted by Drake
Haven't caught on to the attraction of the PassivHaus standard myself. The standard I want my home to meet is the most sustainable energy required to keep me the most comfortable at the most affordable cost with the least amount of my personal leisure time needed to maintain it. All the passive house homes I have toured, though impressive, have all been far outside "affordable" housing prices. When they include a realistic "cost factor" in the standard it might have some worldwide value IMO.
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The Passivhaus standard for primary heating load is based on trying to make things passive and cost effective for Germany. ..and it is. It's also far more expensive to build the common heating system in Germany, hydronic heating, versus the typical cheaper to install forced air heating in the US so that is a factor to consider, they skip the hydronics and save a bunch and oddly enough the heat that is needed in the Passivhaus and other low energy buildings I've seen in this area have all been forced air in some fashion or another except for the Habitat for Huamanity house that has multiple wall mount 1kw plate-type resistance heaters. The odd thing is that mini-split heat pumps generally always seem to be added later for air conditioning needs due to not realizing the consequences of overglazing. I spoke with the owner and told him to use the mini-splits unless they really can't produce the heat needed.
The fun thing about Passivhaus is there is a recommendation on peak heat load but isn't one for cooling loads, that just gets lumped into the primary energy usage. ..why not just let the builder decide the heat load needed to get to the primary energy usage target. There's also the part about the 0.6ach50 requirement was set for dealing with condensation more than energy. It's later been determined by others that 2ach50 is plenty good for reducing condensation risk.
The cost effectiveness of following Passivhaus to the letter to get certified in Minnesota might not be worth doing, especially for people holding a 30 year mortgage to do it. I think the R60 roof versus an R120 roof, R40 above grade walls instead of R60-80 walls, R10 sub-slab instead of R30+(seriously?), R5(u.2) windows is plenty fine for our climate.
My personal goals for my retrofit are about R80 roof via 1000 pounds of cellulose added to the current R25. Walls add 4" of XPS to the existing R13 batts and 3/4" polyiso wrap. I'm finished with my work on air sealing although a B-vent stack going out the roof might take awhile to go away depending on how long the water heater lasts and I'm having issues with considering the expensive of replacing a working gas furnace with a condensing one considering my methane bill for January was 39 therms, $41. Windows are expensive and will come last. This will be expensive to do on a 2100sq ft house but I think those figures for target R values make sense.