How to insulate under home extension

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Posted by: from Montreal
9/26/2019 at 7:54:07 AM

I have a small extension on my house the floor joists in the basement extend past the foundation walls about 2 feet, when insulating this space my neighbor told me I have to leave 4 inches from under the floor to let air pass. Is this true or can I seal in the entire area from the space on top of my basement wall to the end of the extension?

How to insulate under home extension
How to insulate under home extension
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Date/Time9/26/2019 at 9:08:14 AM

Don't listen to your neighbor.

Make sure you pack in the insulation tightly and do not allow any air flow to pass..

You want your house to be air tight from underneath... No air or dampness should have any room to by pass into your home.

Any spaces in between your insulation and wood can lead to mold and other hazards.

Thank you for your time.

Have a nice day.

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Date/Time9/28/2019 at 11:28:32 AM

Hi Daniel,

This is an ideal scenario for spray foam insulation!! Best way to create a 100% thermal break.

Some companies have a minimum but this is the route I would pursue...

Derek Birch


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Chris in Burlington
Date/Time10/16/2019 at 10:35:24 AM

I had the same (my extension is 12' x 6') and I just had spray foam insulation installed. Now that I've done that, do I need to cover the spray foam insulation with plywood or some other board?

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