Insulation Question

Started by n74tg, November 09, 2013, 11:07:17 AM

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n74tg

Hello guys, I've been away from the forum for awhile.

Our local post office is being re-roofed.  They are pulling off 2" exterior grade foam (4x8 sheets) which is heavy duty foil covered on both sides and taking it to the dump.  They have offered me all I want, they will even bring it to my site. 

I'm thinking of using it in my exterior walls (probably double layer), with maybe an expanding Foam seal around the edges to stop air movement.  That should give me an R-24 wall which in central Arkansas isn't bad.  I'm also thinking of putting it between floor joists in crawl space, probably 2" thick and also on the inside of my crawl space concrete block walls, probably 2".

I think it's closed cell foam, I know the air bubbles in it are tiny tiny.  So, I'm thinking it doesn't absorb water.

The way it was installed on post office roof is foam first, then rubber mat, then mopped with tar.

Anybody got any serious reservations about reusing this stuff.

thanks
Tony
My house building blog:

http://n74tg.blogspot.com/

n74tg

As an alternative I'm toying with the idea of putting it down directly on top of 3/4" OSB subfloor as my "mat" underneath my laminate flooring (like Pergo).  I would do that instead of having to cut it to size to go between floor joists from below.

thanks
My house building blog:

http://n74tg.blogspot.com/


flyingvan

As long as you can provide some way for moisture to escape from everywhere, you're good.  Home interiors produce lots and lots of water---just breathe on a mirror and see what you're losing...Add to that boiling pots, water vapor any time you burn gas, showers, ground transpiration....Not just the interior spave but every joist and stud bay needs to have an escape for water.  Closed cell foam doesn't breathe
Find what you love and let it kill you.

MountainDon

n74tg, you CAN add foam to the exterior walls or use only foam on the exterior walls. There are some factors to be considered. Go to buildingscience.com and search their articles. Or use Google there are other sources with great info on this; greenbuildingadvisor is one other.

When adding foam on the exterior the colder the climate more foam R-value must be used. Yes, well installed foam creates a vapor barrier and IF you already have a vapor barrier on the interior this can be a problem. This is very much a climate related issue. In hot 'n' humid climates it is now recommended to have the VB on the exterior... don't know if your area of AR qualifies as hot 'n' humid.

Climate zone info here...
http://www.greenzone.com/general.php?section_url=12

http://en.openei.org/wiki/ASHRAE_Climate_Zones
Just because something has been done and has not failed, doesn't mean it is good design.

Erin

You're talking about basically creating your own SIPs without the "S". 

What you've described is exactly what we're doing for our exterior walls. 
Recycled and everything... (We didn't get it free, though.  Congrats!)
The wise woman builds her own house... Proverbs 14:1


DaveOrr

I'm getting 3" thick Styrofoam SM off cuts from the local builder here that has a couple of large commercial jobs on the go right now.
I'm going to use it as my flooring insulation.

I see no reason why you can't use reclaimed insulation from the PO.
As for putting it on the exterior, they do it all the time up here in the North when they redo the siding on older homes to increase the R value. I don't think they would do it if it didn't work.  :)
Dave's Arctic Cabin: www.anglersparadise.ca

MountainDon

Quotethey do it all the time up here in the North when they redo the siding on older homes to increase the R value. I don't think they would do it if it didn't work

The key to adding on the outside is to add a sufficient amount (R-value) to make the interior face of the exterior sheathing stay warm enough to prevent in the wall condensation. Keeping the temperature above the dew point is necessary.
Just because something has been done and has not failed, doesn't mean it is good design.

n74tg

Guys I'm not adding foam insulation outside the structure, it will be installed in the same place that the fiberglass insulation would have gone if I was using it. 

Since i sprayed the inside of my metal roof with foam a couple of years ago it has performed very well.  this is just effectively the same as if I had spray foamed the stud bays.

Yes, i will make sure the sheetrock is not a vapor barrier on the inside.  I've been reading a lot on buildingscience.com for many years.  It seems to me what I'm proposing is basically how they describe to do it. 

I know doing this will create a pretty sealed house, one not likely to breath easily.  I will be having forced ventilation for air exchanges and I plan to use dehumidifiers in crawl space, main living area and even in attic if necessary, trying to maintain roughly 55% relative humidity.

thanks
My house building blog:

http://n74tg.blogspot.com/