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I had a recent energy rating and recommended that I beef up my insulation of my crawlspace. Specifically:
"Your foundation wall has only R11 batts in the 2x6 cavities. The current standard is a minimum of R19. You can achieve this, and provide a air seal, by installing 2" thick fire retardant foam sheets over the framing. Seal the joints with an appropriate tape or apply acoustical sealant to the framing before attaching the foam."
Two questions for y'all:
1) Tape or acoustical sealant, what are the pros/cons of each
2) I have 6 mil plastic sheeting on the floor and running up the walls. What should I do with that, reinstall it over the foam sheets?
"Your foundation wall has only R11 batts in the 2x6 cavities. The current standard is a minimum of R19. You can achieve this, and provide a air seal, by installing 2" thick fire retardant foam sheets over the framing. Seal the joints with an appropriate tape or apply acoustical sealant to the framing before attaching the foam."
Two questions for y'all:
1) Tape or acoustical sealant, what are the pros/cons of each
2) I have 6 mil plastic sheeting on the floor and running up the walls. What should I do with that, reinstall it over the foam sheets?
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Anchorage
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Re: insulating a vented crawlspace
Sat, August 2, 2008 - 2:24 AMJust curious why are they specifying acoustical sealant... easier to stop air flow than noise, I actually had to go look it up and found ABSOLUTELY NO INFORMATION on R factor increases. Put the sheets up with Liquid Nails waterborne formula. It is the gold and light blue tube and is designed to stick foam up. In a crawlspace in a minute I will chose a tube borne sealant... Why? Tape sucks ass... Dust on your back and what have you.
JSin
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Re: insulating a vented crawlspace
Sat, August 2, 2008 - 7:52 AMI can only guess the acoustic sealant is recommended because they didn't know how to spell Cyanoacrylate or Polyurethane to tell you to get a water resistant foaming sealant.
I'm guessing they didn't want to recommend a trade name. Great Stuff by Dow Chem is great stuff indeed.
It'll seal insulate and resist water. Maybe the type of acoustical sealant they've used skins over (like a urethane) in a nice thick skin which would prevent insects from burrowing.
Insects, in my experience, will burrow where ever they please excepting for concrete glass and steel.
Any way any adhesive foam will do the trick. But then so would any caulk. The only reason not to go with a good caulk is the idea of optimizing the R factor. It reality it prolly won't make a tinker's damn worth of a difference so long as you stop air migration.
So the world-of-shit-that-seals is your oyster. Any damn thing that you use will prolly be just fine. -
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Re: insulating a vented crawlspace
Sat, August 2, 2008 - 11:44 AMawesome, thanks for the clarification!
Another thing that I have stumbled upon is that some rigid foam require a fire barrier (gypsum board) per code/insurance. Have you heard anything about this? I am working on a crawlspace and rather not "finish" it with drywall if I don't have to.
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Re: insulating a vented crawlspace
Sat, November 8, 2008 - 12:15 PMsigh... after much research to find this mysterious "fire retardant foam sheets" (see above- I am so not drywalling my crawl space), I realized that the entry hole to the crawl space (the largest opening to it) is about 2ft on the diagonal and 4 feet deep. GETTING the rigid foam boards down there will consist into chopping them into small pieces.
Soooo, I am thinking of ditching the rigid foam idea, and using fiberglass batts. Question is: Can I add another batt under my R11 (which is paper backed) or do I need to get/should get all new insulation? -
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Re: insulating a vented crawlspace
Sat, November 22, 2008 - 7:49 PMThe drywall code only applies to living space not the crawlspace so forget that lame info. Rigid was suggested likely because the floor supports of 2x6 which are very shallow would not allow more fiberglass batts to fit in between them without over compressing them and loosing their insulation capacity. The rigid foam if you could get it inside the entrance way would sit proud [that is below toward the ground on the outside of those boards and thus require the seems to be taped or sealed another way to block airflow.
If you do find a way to use the pink soft fiberglass it should be purchased without a vapor barrier as you should not have two on one surface as it traps in moisture. Theo ONE you have should be on the surface closed to the heated interior surface also. There should be no reason to take out the existing insulation that is there unless it is totally trashed.
If no one has told you the floor is the least important area of your home normally to insulate given the the expensive heat in your home rises.
Not sure if in Alaska you can seal the vent openings (on the lower side walls of your structure) in the cold season like I see done where I live in Oregon but that reduces the cold air from going into the crawlspace enough to give you more insulation capacity.
That 4mil black plastic covering the earth is suppose to stay on the ground for a moisture barrier by the way. Hope some of that information helped if you are still working on this project. -
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Re: insulating a vented crawlspace
Wed, November 26, 2008 - 1:45 PMI used R13 paper backed fiberglass batts over the R11 nonbacked batts. Even with only 1/2 the crawlspace completed, I could feel a huge difference in temperature in the first floor, especially on the floor. I don't have to wear heavy slippers anymore!
The vents are sealed with a few layers of rigid foam board glued together (kinda like a foam block) so that they are easy to remove in the summer.
Len, thanks for all the advice. I had already taken care of the attic (R38 in there), and the floor on the 1st level was always so cold. That's what made me choose to beef up the insulation in the crawl space next. -
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Unsu...
Re: insulating a vented crawlspace
Wed, November 26, 2008 - 3:02 PMWow! You got instant results from your work! Your heating bill will probably go down too, as a result of your newly installed additional insulation.
I bet you'll notice a difference in summer too!
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Re: insulating a vented crawlspace
Wed, March 11, 2009 - 12:37 PMLen,
Could you please help me? The floor over our crawlspace is ice cold.
We are not sure how to properly insulate the ceiling of the crawlspace
because it occasionally gets wet down there. There is presently
batt insulation between the rafters, and I believe some of it may have
mold on it. Would rigid insulation work? Maybe we wouldn't have to
worry about that getting wet. Also, I have heard different opinions about
whether a crawlspace should be vented or not. I guess we are in the
middle, because we have small holes in the door to the crawlspace,
and no other venting. The floor of the crawlspace is cement.
Thanks for any thoughts you might have.
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Re: insulating a vented crawlspace
Thu, March 12, 2009 - 11:39 PM
funny this should come back up...
i was just thinking the other day about my options for insulating my crawlspace and started to get pretty curious about the aluminum bubble wrap stuff. I forget the specifics, but the manufacturer claims a fairly high R-value for this application. I'm guessing that if it's installed properly it will cut down on the air leakage and by design it should be effective against radiant loss ...am I correct in these assumptions? ...could that thin layer actually do a good job as well as be relatively easy to install? (just staples n' tape ...no tyvek suits or masks!)
experience?
opinions?
