Insulating extension

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Apr 2, 2023
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New York
So two sides of my second floor extends out. I am middle of a bathroom renovation and when I removed the mortar bed, there was basically nothing else left. You can literally see the siding (siding contractor put soffit under the extension part) — as you can see in the pictures. There’s about 6” of space between the soffit and top of the joists. I was wondering what’s the best way to seal/close/insulate this area.


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Were it mine, I'd incorporate radiant barrier with the mass insulation- whether it be foam or batts.

Radiant barrier made a world of difference in our home- both in winter and summer. We did extensive testing at work before committing. We also researched NASA, D.O.E and several university studies for more study.

An extra place we used it at work was for our trades' workshop. The shop cantilevered out; therefore 3 concrete walls, the concrete floor and concrete roof were exposed 150 feet above ground. Simply pasting the walls & ceiling with radiant barrier let us take 250,000 BTU/hr of heaters offline permanently.

Be sure to purchase pure un-coated. Bubble stuff and many foam boards are coated. If it's under or over mass insulation, use perforated. And, very important is that there is a 19mm or larger gap on one side or both. (Either side is OK)

There are lots of places selling fake stuff, so shop carefully. The only reputable supplier I know that is still around is AtticFoil Com. They will be more than happy to guide you to the correct product and installation method.