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Zedder 11-08-2010 06:03 PM

Insulating walkout basement walls
I am considering finishing our walk out basement and wanted to get some advice on insulation. The walls currently are framed above the foundation walls and have fiberglass batt insulation between the studs and a vapour barrier. The foundation walls below the studs, have fiberglass insulation fastened with vapour barrier and strapping. We don't want a half wall, so we will be running new framing from floor to ceiling infront of the existing walls. So, I know I need to take the vapour barrier down and place it on the warm side of the new studs, but how do I handle the insultion? Should I leave what's there; remove it and replace with insulation between the new studs; or, leave the existing insulation AND add new insulation between the new studs? Thanks in advance!

GBR 11-11-2010 08:07 PM

Here is some incite: Info-511: Basement Insulation — Building Science Information

BSD-012: Moisture Control for New Residential Buildings — Building Science Information
Read up and ask away.......


Zedder 11-12-2010 08:42 AM

Thanks for the links Gary...they contain great information! However, it doesn't address my specific question. If I don't want a half wall and decide to put up full height framing in front of the existing half wall (lower half foundation with framing on the upper half), do I leave the existing insulation in the existing framing that is on top of the foundation wall and then put insulation between the studs of the new floor to ceiling framing (therefore having doulbe the insulation on the upper portion of the wall). Or, do I take the existing insulation out of the existing half wall framing (leaving a large air space) and just put new insulation between the studs of the new floor to ceiling framing?

GBR 11-12-2010 11:18 AM

It’s better to be tight to the warm side as in Fig. 2a. You want the insulation to stop the heat at the closest to the source.
In Fig. 2b, notice the 300% loss as stated above the pictures. You would still get convective loops if there are any gaps between foam board/stud walls, as in Fig.1-(f). After installing foam board on top of the concrete lip next to the sill plate on the wall, run another foam board on/over the sill plate to touch the back of the new wall insulation to stop any gap there. I’d use Roxul rather the poorest performing fiberglass batt. Be sure to air seal the drywall (ADA), Info-401: Air Barriers
add a sill sealer under the new bottom plate (capillary/thermal break), seal the top of wall/joist bay against fire/air, and seal the rim joists with rigid foam board. Pressure-Treated Sill Plates and the Building Code |

Insulate Basement Rim Joists | The Family Handyman

And don’t ever side staple batt insulation for a convective loop.
Foam any wire/plumbing holes in either wall- top, sides or anywhere, that lets air travel through. Give me a day and I will post on your vapor barrier……. No time today.


Zedder 11-12-2010 01:32 PM

Thanks Gary...It looks like I have a lot of reading to do!!!

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