A friend of min (REALLY TRUE in this case) has a ’70s vintage house. He has replaced the windows, and added vinyl siding with the extra 1-inch blue foam underneath. He still complains about his heating/cooling costs. (I wonder why).
I am sure that in this Chicagoland house that there is 2×4 walls with batts for insulation. If he REALLY wanted to improve the insulation of the house, the only solution I can think of would be to remove all the sheetrock from the exterior walls, remove the old insulation, and put in cellulose or even foam.
My question–about how much would this cost? (Don’t add in the cost of the divorce from his wife caused by the mess).
Replies
I wonder if this would be a good application for Air-Krete, a cementious foam. Advantages: foamed in place, even within existing walls, apparently even with FG already in the wall cavity (squishing it aside as it expands), so no need to remove sheetrock inside - a cost savings. Decent R value: 3.9/inch, and sealing against air infiltration.
Disadvantages: like open cell foams, is porous to water vapor. If there is a vapor retarder in the wall under the SR, that would be ok. If no VR, latex paint can be used to provide the VR. However, if the wall construction is such that drying the cavity from moisture intrusion is accomplished by its present leakiness, then eliminating the air infiltration could make things worse.
If he goes the SR removal route, he may as well use a closed cell foam to get maximum R in the existing space. He ought to see a real 17-18, allowing for thermal bridging of the studs in the space between rigid foam outside and SR inside. If loss of space inside is not an issue, I imagine Mike Smith would advocate Mooney wall application, using the less expensive cellulose. Either the closed cell foam in 3.5" cavity or the cellulose in a Mooney Wall would get about a real R20-21, same basis. Studs 16" oc assumed.
Edited 6/12/2007 4:50 pm ET by DickRussell
Insulating walls will be about the least productive avenue. The two main sources of heat loss are air infiltration and inadequate ceiling insulation.
Have him deal with that first. Seal and/or weatherstrip all door and window openings, seal where the walls meet the rim joist, and make sure the attic is well insulated.
I imagine that only if the walls are actually cold does it matter much what goes on in the walls.
he should do a blower door test and find out where the air leaks are
if it's a " 70's " house, then it is probably sheet rock
you can blow stud bays from the inside and patch the sheetrock
i'd blow cells depending on what the energy survey tell him