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-   -   Major draft from outside detected in basement - how to fix? (http://www.diychatroom.com/f19/major-draft-outside-detected-basement-how-fix-6325/)

mwehnes 02-05-2007 06:14 PM

Major draft from outside detected in basement - how to fix?
 
When standing in my basement by an exterior wall I can feel a draft and see cob webs blowing around. When I pull the insulation out it feel like a fan on low speed blowing feezing outside air on me.. Typically I would just stuff more insulation in but...

My foundation is poured concrete and the house is actually is larger than the foundation. My exterior wall on the 1st floor hangs 2' further out than the foundation. Hope that makes sense, I've never seen this before. The basement rafters sit on top of the foundation and there is insulation stuffed in the 2' area. Cold air is just blowing right in from outside through the seems between the plywood and rafters.

Should I use a product like icynene Spray foam or just cram more insulation in.. I think my problem is the draft which more insulation wouldn't fix... Anyone know what I'm talking about and how to fix it?


Thanks,
Matt

Brik 02-06-2007 08:49 AM

Yep

Your first floor is cantilevered over your basement wall by two feet.

I suspect the floor above in this area is also cold. Confirm.

You will have a two pronged approach.
From the inside-
Yes, just stuff in insulation. The key to insulation is not packing it tight but in making sure it completely fills the void.
From the outside-
You mention plywood. Do you see plywood from the under side of the cantilever on the outside? Any seams? If so, caulk them. If you have vinyl soffit material it can easily be removed to see what you have under. If under any vinyl on the outside you have a air barrier like tyvek you should ensure any seams are taped. They make a special tape for this. Packing tape would work in a pinch.

I suspect you only have the plywood. If that's the case do the following-
caulk seams if you have any.
Add Tyvek or similar
Cover Tyvek with vinyl soffit to protect it.

You may also want to use Great Stuff expanding foam sealer if you have small cracks that are letting air in. Under the sill (the board that sits on top of the basement wall), around pipe or electrical penetrations, etc.

mwehnes 02-06-2007 10:31 AM

Yes, the floor above is very very cold.

I haven't gone outside to inspect the overhang (it's around 15 degrees here), but from inside the basemnet I have found areas I can stick my fingers through to the outside. Looks like when the plywood was installed they didn't get it up against the foundation all the way.

Thanks for the assistance. I'm going to use great stuff to fill in all the gaps and install insulation. This spring/summer I'll revisit installing soffit on the overhang.

Thank you!

sheeter 02-06-2007 07:11 PM

It sounds like, since you have a poured concrete foundation wall, that they may have used this condition for venting. Normally, poured foundation walls don't contain vents to vent the area below the house. Is this overhang at a bay window condition or the entire house?

tvlfleming 02-06-2007 08:26 PM

I would suggest the expanding foam in holes large enough to fill. Loosely install insulation, not packed right in to the area. The air gap barrier between the insulation and outside wall has to be maintained. Then as an extra seal staple or tape a sheet of plastic across floor joists to make more of a barrier. This isnt going to help the cold floor condition though. Thats a summer project from outside, remove plywood and put up 1 inch insulation panels, tape seems and replace pllywood or use vinyl.

mwehnes 02-08-2007 04:56 PM

sheeter: The overhang is only for the dinning room and kitchen. The rest of house sits even with the foundation walls.

As an update... I used great-stuff to fill the gap and then glued (liquid nails) a 3" peice of PT plywood over the gap. I didn't mention the rodent issue before, but it's a problem. This should stop the inflow of air and stop critters from entering my house. I'm installing R30 insulation between the joists right now.

I'm assuming paper side up (towards the floor) is correct?

sheeter 02-08-2007 08:39 PM

Yes, you always place the vapor barrier / craft face towards the heated space.

Webguy64 05-08-2007 09:07 AM

Drafty basement
 
Quote:

Originally Posted by mwehnes (Post 32461)
When standing in my basement by an exterior wall I can feel a draft and see cob webs blowing around. When I pull the insulation out it feel like a fan on low speed blowing feezing outside air on me.. Typically I would just stuff more insulation in but...

I had a similar problem a couple of years ago. I was also getting lots of ladybugs and boxelders. It turned out to be a gap at the top of the foundation (under the vinyl siding). In my case it wasn't large, so I sealed it with silicon caulk. That seems to have solved the problem. Good luck!



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