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Brock
Registered Users
Posts:128
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| 05/09/2008 10:35 AM |
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| I was always told fiberglass had the insulation value of its thickness. So if you take fiberglass meant for 2x8 depth and stuck it in a 2x4 space you would have the same insulating value as straight 2x4 glass, maybe a bit less actually since there was less trapped air. |
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Green Bay, WI. - geothermal heated indoor pool with a small solar setup |
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PanelCrafters
Registered Users
Posts:1279
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| 05/09/2008 12:01 PM |
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| You guys are correct, however, I think that Mark has 2x6 framing, in which case 2" of foam and and 3.5" batt fit perfectly. And, if you are aggressive, they do make 3.5" 'High Density' Batts that are R-15. |
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....jc
If you're not building with OSB SIPS(or ICF's), why are you building? |
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Mark Fleming
Registered Users
Posts:185
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| 05/09/2008 12:47 PM |
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I think most codes now require 2x6 framing, because it's impossible to get the required R value in 2x4. Usually, 2x6 has R19 glass, period. You can put up tyvek or tar paper in an attempt to keep the wind from blowing through the seams on your wall sheathing (and your glass insulation), but I don't think it's even required by code. I put it on because I hadn't decide to foam at that stage.
With just glass in a code compliant wall, you have R19 where there 1) isn't a stud 2) a sill or header, 3) an electrical box, 4) wiring), 5) plumbing, or 6) an air leak in your sheathing/wall wrap. By leak, I mean that if the structure was turned upside down and used as a boat, would it leak? Basically, you have R19 nowhere in your wall despite the printing on the insulation. How much less depends on how complex your wall and how much your "hull" leaks.
A properly foamed structure doesn't leak. I have approx. 2" of foam (R14), leaving a stud bay about 3.5 inched deep. That's followed by 3.5" of glass (R13), still the cheapest bang for the buck in glass insulation even though 2x4 exterior wall construction should be on the way out. I loaded up when glass insulation went on sale at Home Depot.
The stud sides have some foam on them to a depth of about 3 inches (a little overspray), so I've even reduced the heat loss through the studs a little bit. I may actually have a little better than an R19 whole wall value. On a windy cold night, that would be several times the effective R value of a code compliant glass insulated wall. Put it this way, if given a chance to patch your "leaking boat" of a structure, which would you chose, foam or glass. No fair using resin with that glass, but it's understandable that boat builders need to use resin.
There was a web site where one of the posters was a professional foamer in Idaho. He did both residential and commercial (mostly potato sheds and frozen food storage). He stopped doing residential because the code required such a ridiculous amount of form to compete against the phoney R value of glass. But the potato farmers knew that a relatively thin even layer of foam over the entire storage shed worked better than stuffing pieces of 12 inch thick insulation haphazardly around the structure and taping it all together. Plus, no condensation issues.
Mark
Wall with sheathing, Tyvek and windows going up. |
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Brock
Registered Users
Posts:128
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| 05/09/2008 3:59 PM |
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| Well said. We were truly amazed with foam on our first home. They foamed it in late November on a warm day. Two days later it was windy as all get out, with our north facing house, you could stand anywhere and not hear or feel any air movement. They put a 20,000 btu heater in the basement and the house warmed up to 70F in a matter of hours (20F outside). I swear by it now. In our current construction they tried to talk us out of foam, but we wouldn’t budge. We actually ended up with 2x6 walls, 2+ inches of spray foam, R13 bats, then 1 inch of pink foam (the electricians hated that, they had to space out their boxes on the exterior walls), but it gave us the thermal break on the studs. We also used a tyvac and a vinyl siding that is supposed to be R4. Basically just 1 inch white bead foam behind the vinyl, supposed more for looks and stability, but I like the extra R4. So we should be set. Our new house is south facing, with a south walkout, 20 windows on the south side and 3 on the north. |
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Green Bay, WI. - geothermal heated indoor pool with a small solar setup |
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PanelCrafters
Registered Users
Posts:1279
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| 05/09/2008 5:57 PM |
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Posted By Brock on 05/09/2008 3:59 PM
We actually ended up with 2x6 walls, 2+ inches of spray foam, R13 bats, then 1 inch of pink foam (the electricians hated that, they had to space out their boxes on the exterior walls), but it gave us the thermal break on the studs.
No worries about moisture getting in between the spray foam and the foam board(and into the fiberglass)? I've always wondered about that, especially in a cold climate. I hear that it gets somewhat cool in Green Bay %^). |
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....jc
If you're not building with OSB SIPS(or ICF's), why are you building? |
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Brock
Registered Users
Posts:128
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| 05/09/2008 11:13 PM |
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| That came up but they said they have never had any issues. I do have a temp/humidity sensor in 4 different walls. They started out pretty high but have been dropping since it was closed up. |
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Green Bay, WI. - geothermal heated indoor pool with a small solar setup |
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Jelly
Registered Users
Posts:216
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| 05/21/2008 2:51 PM |
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Mark, could you give us a rough idea of what the Tiger Foam ultimately cost, and did it cover as much as it should have, and as thick as it should have? Or anybody else with DIY spray foam experience?
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BrianA
Registered Users
Posts:1
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| 05/21/2008 11:33 PM |
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| To help you save costs and create a home that is energy efficient go with a good .5lb open cell foam and expierenced contractor. In the basement frame walls with 2x4 held an inch from the concrete wall, then spray from floor to ceiling including rim joist to create a continuse layer of foam. Upstairs fill all stud cavities, making sure their are no voids or places where the sheeting is visible. all stud junctures top and bottom plate need to be caulked a must. In the attic, spray six inches on top of sheetrock creating an unvented attic is usually cost prohibitive due tothe large rooflines. Use low expanding foam around all windows and doors, this will create a home that will amaze you at how little energy it will use to heat and cool. then install a properly sized high efficiency heating cooling system and a hrv a must with a house this tight. Also the water heater needs to be a power vent type. A house insulated like this will easily save you 50 to 100 dollars in the heating cooling months. Be cautious about spraying 1 inch lifts of foam then covering with fiberglass especially in colder climates. The dew point always needs to be inside the foam or you end up with condensation on the foam in a sealed cavity and all that does is grow mold and cause problems. feel free to contact me if you have questions and enjoy your home. |
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Mark Fleming
Registered Users
Posts:185
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| 05/22/2008 12:41 PM |
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Jelly,
It's the shipping cost on the foam that's the killer. I ordered a pallet, which was more than I needed. I think that was 5 kits (each consisting of two "propane tank" containers). I don't remember the amount of board feet, but it was just under $3,000. With this, I did walls and roof in the living space above a garage (plus the rim boards around the basement). The foot print is only 600 square feet, and the roof is 12:12. Much more expensive than had I used glass, but I wanted a DIY foam project before using it on my house.
When I got the foam, I saw that it has an expiration date, so I decided to use it all. I would guess that I spent twice as much as I would have trying to do the same job with just glass. I would also guess that I could reduce the cost 15-20% next time by more accurate spraying. I would also certainly get a professional bid next time.
Mark |
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