Sill plate insulation question

Users who are viewing this thread

Jotun

New Member
Messages
11
Reaction score
0
Points
1
Location
Hampstead, MD
I am finally getting underway on my basement remodel, and I'm not sure how to go about dealing with the exposed top of the concrete exterior walls in some areas. I have 2.5" EPS foam for insulating the rim joists, and am 1" and 1.5" EPS to do two layers for a total of 2.5" on the walls as well.

In a lot of areas, the previous homeowner tacked electrical wiring along the concrete near the sill plate. How should I handle the area in my attached picture? Is it ok to put fiberglass or mineral wool in the gap, then seal a block of EPS over everything? I wouldn't want to use expanding foam like in this picture with the wiring there...

Thanks!
 

Attachments

  • RimjoistSillplate.jpg
    RimjoistSillplate.jpg
    62.9 KB · Views: 176
  • BasementRimJoistDiagram.jpg
    80.3 KB · Views: 1,105

Dana

In the trades
Messages
7,889
Reaction score
502
Points
113
Location
01609
Both the top of the sill plate and the ledge need to be insulated to avoid a significant thermal bridge at that point.

Is there a sill gasket or sheet plastic/metal/other under the sill plate? If there is a capillary break material between the foundation and foundation sill the moisture (safely) stays in the masonry/concrete, and the wood is unaffected. If not, moisture from the concrete or masonry will wick into the wood, and the wood needs to dry toward the interior. A couple inches of unfaced EPS is over the top of the sill plate is sufficiently high-permeance to water vapor to not present a problem unless the foundation is chronically wet from poor surface drainage or roof edge splash-back.

Insulating with fiber insulation overlayed with foam board would keep the moisture in the fiber insulation layer, and the wiring staples would be at risk of rusting over time. But when encapsulated in closed cell foam the staples are protected. Can foam is typically 1.5-2lbs per cubic foot density, waterproof, and fairly vapor retardent- even at a half-inch thickness it approaches the vapor retardency of 2" of EPS.

Is "...in the gap..." , referring the hollow cores of a block wall, as in your diagram?

index.php


Fiberglass is a lousy choice as core-filler, since it wicks moisture freely from the masonry to the sill plate, and would increase the moisture content of the sill plate. Rock wool is only marginally less wicking, and still not great. It's better to stuff chunks of EPS board in there as filler then squirt expanding foam between the EPS rubble and sill as a sealer, since both EPS and can foam are reasonably good capillary breaks even in thin layers.

Using 1.5" EPS under the joists to insulate the foundation ledge, filling in the gap over the wiring gap with can foam works. When the foam has set, trimming it flush with the top of the EPS & foundation sill would allow you to add another 1.5-2.5 " of EPS of the top of the foundation sill to make the insulation layer continuous. If the insulation isn't continuous the heat leaks is pretty signficant- the t op of the foundation looks like it's on fire during cold weather in an infra-red image, and wintertime moisture adsorption into the sill from the indoor air remains an issue.
 

Jotun

New Member
Messages
11
Reaction score
0
Points
1
Location
Hampstead, MD
Both the top of the sill plate and the ledge need to be insulated to avoid a significant thermal bridge at that point.

Is there a sill gasket or sheet plastic/metal/other under the sill plate?

Yes, there is a sill gasket under the sill plate (at least in the areas I have been able to access so far, so hopefully everywhere)

Is "...in the gap..." , referring the hollow cores of a block wall, as in your diagram?

Sorry, I should have been more specific. I was referring to my picture, with the gap being the top of the foundation and front of the sill plate, where the wire is stapled (it would be a gap if I just put a solid piece of EPS over top, from the rigid foam at the bottom of my picture to the rigid foam at the back)


Using 1.5" EPS under the joists to insulate the foundation ledge, filling in the gap over the wiring gap with can foam works. When the foam has set, trimming it flush with the top of the EPS & foundation sill would allow you to add another 1.5-2.5 " of EPS of the top of the foundation sill to make the insulation layer continuous. If the insulation isn't continuous the heat leaks is pretty signficant- the t op of the foundation looks like it's on . fire during cold weather in an infra-red image, and wintertime moisture adsorption into the sill from the indoor air remains an issue.

I think I can go this route then, I guess I was thinking I shouldn't conceal the wiring within the spray foam but I guess it's no different than it being concealed elsewhere. I have plenty of chunks of EPS so I can just fill in and spray foam as I go. Thanks so much for your help!
 
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks