Home>Discussions>INSULATION & HVAC>Adding foam insulation to wall cavities that already contain fiberglass insulation
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Sherry
Adding foam insulation to wall cavities that already contain fiberglass insulation

I was at a home remodeling show recently and I saw a foam insulation that is designed to go into the stud cavities of existing, finished walls. The contractor takes off some siding and drills holes in the exterior sheathing. Then they put the foam (low expanding foam) line in each stud cavity and fill it with foam. The existing fiberglass insulation is squished toward the back of the drywall and the foam goes towards the exterior sheathing.

I saw TOH put low expanding foam into the walls in the East Boston house where they left the plaster in place but I think those walls had no insulation in them to begin with.

Has anyone heard of this before or does anyone have it? What do you think of it?

canuk
Re: Adding foam insulation to wall cavities that already contain fiberglass insulatio

The one negative that I see .....

The existing fibergalass will take up volume in the wall cavity. When the fiberglass becomes compressed by the foam it may create areas within the foam that wouldn't be a uniform thickness and possible voids.
This would also affect the advantage of the foam to seal gaps that it could if there wasn't anything in place to impede it.
When the fiberglass becomes compressed it's insulating performance is greatly reduced.... having little advantage other than taking up space in the wall cavity.
I'd be curious to see with an infrared scan if there would be hot/cold spots within the wall cavity using this method.

Just my guess.:)

foammaster
Re: Adding foam insulation to wall cavities that already contain fiberglass insulatio

he is right, fiberglass has a R 2.8 per inch and tripolymer injection foam has a r-value of 5.1 per inch. Are you going to worry about a small gap? That is the down side with glass in the wall but what are you going to do? take down all the drywall? cellulose will most likly not fill properly,and settle, and if you have all ready seen how this works it should be a no brainer. just make sure if it isn't Tripolymer, it isn't an "Amino-plast" aka Urea-formaldehyde foam (Polymaster)
www.injectionfoam.com
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KKelly
Re: Adding foam insulation to wall cavities that already contain fiberglass insulatio

I've heard of it and it's a quick fix, which doesn't effectively change the R-value by an appreciable amount. Under normal installation it binds up in the wall interior and under optimal installation it's far more expensive than normal insulation and finishing. If you're restricted by historical or structural limitations then it's the best and often, only option. Otherwise, beyond the nominal effect, I believe, it's a waste of time and expense. And few proponents will ever boast any proven effect beyond nominal.

If you cannot remove the interior lathe or drywall then it's really the only option. But, for any living habitation, not intended for resale, removing the interior wall covering and installing proper insulation is the only practical choice.

foammaster
Re: Adding foam insulation to wall cavities that already contain fiberglass insulatio

injection foam is just that. it is injected under pressure allowing it to push the fiberglass that has a low R-Value any way, out of the way and replacing it with an R-5.1 per inch. far exceding cellulose, batt, loose fill, or pour in that might deminish or settle over time any way, i don't know to much about "pour in" low expanding foam. Tripolymer compairs in price with blown in and most of the time faster. it flows like shaving cream to reach evey where, even all around plugs and switches. will also last the life of the home, new or old.

sprayseal
Re: Adding foam insulation to wall cavities that already contain fiberglass insulatio

its definately not the typical way to insulate a wall but the technique does have some merits. I think like most things in construction its best to plan things properly first and then implement a suitable system. I would say that spray foam is best for insulating roofs as you have to use layers if you want to use it with walls. Some good examples of work from us here http://www.sprayseal.co.uk/industrial-insulation/

Sherry
Re: Adding foam insulation to wall cavities that already contain fiberglass insulatio

Thank you all for your comments. I currently have “regular” fiberglass bat insulation but I really like the idea of beefing up the insulation and sealing the many little air leaks by using foam. I also hope it would help prevent bugs from getting in. (I get a bunch of Asian lady beetles and Box elder bugs in the fall.)

I remember something from a TOH magazine article where Tom Silva suggested cutting a small horizontal strip (I think about 2”) in the drywall midway up the wall and pulling out the existing bat insulation. Then you’d patch the strip (and tape, sand, prime, and paint). Then you could inject foam into the wall cavity. I think I like this idea better. It still would allow me to get foam into the walls, I wouldn’t have to take my siding off, and it’s not as invasive. I think what I’d do is also cut a small strip at the top to allow access for putting in the foam hose. Then I’d have another strip to repair instead of a bunch of holes.

If I pursue this option I’ll let you know.

Sherry

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