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Old 05-31-11, 01:25 AM   #54
MN Renovator
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Insulating an attic ceiling with R60 over R25 is about $400 for 1000 sq ft of attic space, less if you get it directly from a distributer rather than your local megastore. I'm actually looking at getting nearly R75 in my attic after finishing air sealing(top plates, drop soffits, gasketing the access) and its about the only place in my retrofit that I can add additional insulation without tearing out walls. If I had new construction, I'd go with R60 in the attic at the minimum since Energy Star recommends R49-60 where I live and in the mid-80's when my house was built they put in R25. Over time the amount that is recommended will increase and I see no reason why anyone shouldn't be ahead of the curve with air sealing and insulation.

I spoke with a housing builder at the Living Green expo at the Minnesota State Fair earlier this month, they air seal and insulate and I think his numbers were R30 floor, R4x wall, and R60 attic. He said depending on what the owner wants they will add more but he said that they blower door test and the houses get a HERS rating. He said a recent house was less than .5 air changes per hour at 50 pascals. I've read about challenges getting a passive house below .6 and when I told him that he said that it really isn't that difficult with new construction. He showed me a picture of a house and the homeowner wanted a geothermal setup and the homeowner decided to have a different company install it but there was snow on the ground by the time they were going to trench the ground so the homeowner managed to keep the house warm enough using two 1500 watt space heaters to where the occupied rooms were warm and the rest of the house was warm enough to keep the pipes from freezing, we had -22 degrees F this winter. Impressive in my opinion for a house of a little over 3000 sq ft. I think with that kind of insulation that the installation and equipment cost of geothermal would never pay itself off financially with such a low heat load but I don't see that as a reason to not insulate and air seal to lower the heat load. If someone lives in a house for 30 years the additional cost would very easily be covered by the cost of insulation, especially considering inflation, $5/bag of cellulose at a home improvement store will probably seem leagues cheaper than will be in another 20 or 30 years. In 1975 a new house could be bought for $40 grand, the house would be bought used today for around $150 grand. If we had the same insulation and spray foams that we use today available then and that home was owned by the same person today, they would have been stupid not to do what they can with the knowledge and materials available then to take care in building a good envelope as in todays standards the cost would be minuscule by comparison.

If I ever move from my current house to a different one its most likely going to be new construction just so that way I can get the insulation levels I want, air sealing to my satisfaction and tested with a blower door while there are no walls up to fix any issues, HVAC done right, and if I don't buy a new place for some reason, I would be picking one sited properly for solar heat gain, roof pitch and space appropriate for PV solar, have enough space in all rooms to be comfortable with tearing the walls down to insulate the walls, proper access to the attic with no funky knee walls, cathedral ceilings, drop soffits, etc. so the retrofit is easier. In the end it would be cheaper to buy new then to rip walls down. The contractor I spoke too told me that before they started doing retrofits and after they started the pricing increase is so minimal and not much more effort to do that there is no reason why houses shouldn't be built this way and due to the advantages their company provides its helped them tremendously through the housing bust with maintaining business because it was when the whole 'go green' attitude really started to gather momentum.
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