Adding new attic insulation

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Posted by: from Raleigh
5/10/2012 at 8:19:48 AM

I would like to add insulation to an attic with fiberglass batts, but do not wish ti use fiberglass. We wanted to remove the fiberglass and use sprayed foam, but removal appears to be difficult and might spread the fiberglass throughout our home.

Moreover, we live in a remote area. No spray foam insulation folk work in our area.

I have used rigid foam sheets in many areas in the house. Is it acceptable to use rigid foam panels over the top of the fiberglass?

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Robert from Electrilight Ltd. in Oakville
Date/Time5/10/2012 at 12:59:03 PM

Rigid foam is not recommended in attics (you'll never seal it properly), nor spray foam (very costly). These do not keep the temperature and air from transferring from one source to the adjacent. Batt s and blown are by far the biggest insulator and the most cost effective. You get 16" of blown in and you'll never beat it.

Why do you want to get rid of the fibreglass?

Electrilight Ltd

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Date/Time5/10/2012 at 12:59:56 PM

Hi Charles, In general, you never want to create a situation where you are trapping moisture. Your ceiling should be a vapour / air barrier between the living space and the attic. Any humidity that gets into the attic from your house goes through the existing insulation and is vented out the top of your attic by the ventilation that should be in place. If you put more than 1 1/2" of rigid foam over the fiberglass, you are creating another barrier that will trap moisture in the fiberglass. This will eventually condense onto your ceiling and potentially cause mould.

Your best bet would be to "top up" your existing insulation with blown in fiberglass or cellulose. Both can be added over the fiberglass. The current recommended level is R50. You would need to install baffles up from the soffit vents to above the height you will build the insulation up to so you maintain the air flow through your attic.

Good Luck with it!

Jim Kuzma

Kettleby Handyman Services

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Bruce from Interior Craftsman in Vernon
Date/Time1/29/2013 at 1:15:04 PM

Hi Charles,

I agree with Jim, just wanted to add a reassurance to you, I'm familiar worth working with asbestos, and unlike asbestos, fibreglas does not have the same properties to create a situation that could harm you, especially if you leave it undisturbed and top it up as suggested.

Should you be concerned that it may enter your living space, then you can drop your light boxes, fans, etc and seal around all the boxes as well as any openings (such as wire grommets, not ducting) with a good quality sealant such as Silicone II., This will also help with heat loss and humidity migration.

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