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S-F · 08-23-11, 05:34 PM

So that spray foam quote was just for the portion of the roof which is not accessible? Do you have an attic of any kind? Here are my thoughts: First things first. Dig around your perimeter and plant some XPS to insulate the slab, wall and whatever block is above grade. This is a fairly simple DIY but it is labor intensive with all the digging. Don't skimp on the foam. I would put 4" all the way down and more from 2' below grade up to your wall. Always think at least R 40 for walls above grade. And air seal the transition well after placing a termite barrier on top of the XPS. For the space behind the kneewall I'd get some kind of board insulation and cover every surface that meets the outside and air seal it all. If you use foil faced polyiso you can tape everything with foil tape. If you use recycled polysio (much cheaper, better R value) then you would just seal it all up with 1 part foam. This will create a gap for your ventilated roof the depth of your bay. You could cut up pieces of foam board to fit the bays, place them in leaving 2" between them and the roof deck and foam them in place reclaiming some of that bay space for insulation. Alternatively you could put insulmesh in the bays leaving 3" or so between it and the roof deck, screw foam to the inside and then dense pack through the foam. Myself, if I were in your position I'd block off a space for the vent, using sheetrock and 1 part foam to make it air tight and then truss out into the space to create a 12" cavity for cellulose. I personally dislike using or living in a house full of foam. After I had everything done before the cellulose was packed I'd improvise a blowerdoor in the door in the kneewall, pressurize the space and look for air leaks with a smoke pen or incense stick and seal them up with extreme prejudice. As for the portion of the roof behind walls I think I'd probably wait, save my pennies, sweet talk my wife with stories of houses that don't need heat or AC and then call in the high density spray foam people. Sucks. They have their place but I'd rather it wasn't anywhere near me. Unless you can outsulate you really are trapped by the tiny space you have to work with. If you plan to keep this house you have to think about more than just ROI. A well sealed and insulated house is just plain more comfortable when you are separating it from the elements. In the winter if you set the thermostat to 75 the house doesn’t feel like it does with the windows open on a 75 degree day…… unless it’s well insulated and air sealed. Then you need to go out the door to feel the difference. It’s about comfort. Not only financial comfort but also physical comfort on a level that most people have never experienced. Everyone’s idea of outside temperatures is different from their idea of what’s created by the temperature on the thermostat.
I have tried to take the crawl space behind a kneewall out of the thermal boundary several times and it has never worked well, it’s labor intensive and it sucks. You have to drill into the floor right by the wall, stuff a feed bag in there, push it way back behind the wall with the hose and dense pack it hoping it creates an air seal. 0.o Dense packing floors is lame any way since you only get minimal insulation in there. And then you have to pray to the air sealing gods that you can actually seal up the knee wall itself (which you can’t). You have to pull up your carpet next to the wall and caulk the trim by the floor using a bastadrized version of the Airtight Drywall Approach. I look at all attics and attic like space as a fantastic opportunity for insulation storage. Just pile it in. Cellulose is cheap and it doesn’t really cost much to have to blown in if it’s not an exterior retrofit. If it’s a loose blow you can DIY with a machine Home Depot will just let you borrow for free. If you have an attic of any kind you can crawl in there with a hose, block off 2” for ventilation with cardboard and Tyvek tape and absolutely fill it with cellulose. No attic = spray foam, $ and petrochemicals. Not to mention all of the other concerns associated with spray foam vs. cellulose. Here’s a rule of thumb I’ve developed recently: If you’re talking to an auditor or contractor or anyone and they say that a certain amount of insulation or air sealing is “enough” you are talking to the wrong person. Enough for what? Get a 1 part foam gun and ask for a case of foam cans for Father’s Day. Foam everything from outside the thermal boundary, but keep the foam out of the light or it’ll go bad. Once cured the foam deteriorates with light contact. You can tell because it turns yellow.

08-23-11, 05:34 PM	#7
S-F You Ain't Me Join Date: Nov 2009 Location: Northampton MA Posts: 662 Thanks: 6 Thanked 71 Times in 58 Posts	So that spray foam quote was just for the portion of the roof which is not accessible? Do you have an attic of any kind? Here are my thoughts: First things first. Dig around your perimeter and plant some XPS to insulate the slab, wall and whatever block is above grade. This is a fairly simple DIY but it is labor intensive with all the digging. Don't skimp on the foam. I would put 4" all the way down and more from 2' below grade up to your wall. Always think at least R 40 for walls above grade. And air seal the transition well after placing a termite barrier on top of the XPS. For the space behind the kneewall I'd get some kind of board insulation and cover every surface that meets the outside and air seal it all. If you use foil faced polyiso you can tape everything with foil tape. If you use recycled polysio (much cheaper, better R value) then you would just seal it all up with 1 part foam. This will create a gap for your ventilated roof the depth of your bay. You could cut up pieces of foam board to fit the bays, place them in leaving 2" between them and the roof deck and foam them in place reclaiming some of that bay space for insulation. Alternatively you could put insulmesh in the bays leaving 3" or so between it and the roof deck, screw foam to the inside and then dense pack through the foam. Myself, if I were in your position I'd block off a space for the vent, using sheetrock and 1 part foam to make it air tight and then truss out into the space to create a 12" cavity for cellulose. I personally dislike using or living in a house full of foam. After I had everything done before the cellulose was packed I'd improvise a blowerdoor in the door in the kneewall, pressurize the space and look for air leaks with a smoke pen or incense stick and seal them up with extreme prejudice. As for the portion of the roof behind walls I think I'd probably wait, save my pennies, sweet talk my wife with stories of houses that don't need heat or AC and then call in the high density spray foam people. Sucks. They have their place but I'd rather it wasn't anywhere near me. Unless you can outsulate you really are trapped by the tiny space you have to work with. If you plan to keep this house you have to think about more than just ROI. A well sealed and insulated house is just plain more comfortable when you are separating it from the elements. In the winter if you set the thermostat to 75 the house doesn’t feel like it does with the windows open on a 75 degree day…… unless it’s well insulated and air sealed. Then you need to go out the door to feel the difference. It’s about comfort. Not only financial comfort but also physical comfort on a level that most people have never experienced. Everyone’s idea of outside temperatures is different from their idea of what’s created by the temperature on the thermostat. I have tried to take the crawl space behind a kneewall out of the thermal boundary several times and it has never worked well, it’s labor intensive and it sucks. You have to drill into the floor right by the wall, stuff a feed bag in there, push it way back behind the wall with the hose and dense pack it hoping it creates an air seal. 0.o Dense packing floors is lame any way since you only get minimal insulation in there. And then you have to pray to the air sealing gods that you can actually seal up the knee wall itself (which you can’t). You have to pull up your carpet next to the wall and caulk the trim by the floor using a bastadrized version of the Airtight Drywall Approach. I look at all attics and attic like space as a fantastic opportunity for insulation storage. Just pile it in. Cellulose is cheap and it doesn’t really cost much to have to blown in if it’s not an exterior retrofit. If it’s a loose blow you can DIY with a machine Home Depot will just let you borrow for free. If you have an attic of any kind you can crawl in there with a hose, block off 2” for ventilation with cardboard and Tyvek tape and absolutely fill it with cellulose. No attic = spray foam, $ and petrochemicals. Not to mention all of the other concerns associated with spray foam vs. cellulose. Here’s a rule of thumb I’ve developed recently: If you’re talking to an auditor or contractor or anyone and they say that a certain amount of insulation or air sealing is “enough” you are talking to the wrong person. Enough for what? Get a 1 part foam gun and ask for a case of foam cans for Father’s Day. Foam everything from outside the thermal boundary, but keep the foam out of the light or it’ll go bad. Once cured the foam deteriorates with light contact. You can tell because it turns yellow.