# Insulating Basement Wall - Sill Plate / Rim Joist



## maurzy01 (Mar 4, 2015)

Hello,

I am currently renovating a laundry area and have a few questions in regards to insulating an interior wall. Previously, only pink insulation was stuffed against the rim joist.

1 - I plan on cutting pieces of XPS foam board, adhering them to the rim joist and spray foaming perimiter gaps. From what I have read this seems to be the next best option aside from hiring a spray foam contractor.

2 - I'm not sure what to do with the open cavities in the block wall. As you can see from the pictures below, there is no sill gasket, nor is the sill plate covering any cavity in its entirety. Should I spray foam these gaps closed? Or should I run another piece of XPS foam board horizontally from the rim joist towards the front lip of the block wall?

3 - Lastly, for the actual front of the wall itself, should I run XPS foam board directly to the underside of the floor joists? Or should I stop at the top of the block wall?

Thanks in advance for your suggestions.


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## Windows on Wash (Aug 30, 2011)

1. Sounds good.

2. I like the idea of covering the hole with XPS and sealing it.

3. No reason you can run the XPS all the way up to the joists but most folks stop short because they come in 4x8 sections.


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## Gary in WA (Mar 11, 2009)

Keep in mind the foam is not a fire-stop from the wall frame cavity to the joist cavities. Showing moisture on the plate in the picture... where are you located and what thickness for wall XPS?

Gary
PS. Welcome to the forums.


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## maurzy01 (Mar 4, 2015)

Gary in WA said:


> Keep in mind the foam is not a fire-stop from the wall frame cavity to the joist cavities. Showing moisture on the plate in the picture... where are you located and what thickness for wall XPS?
> 
> Gary
> PS. Welcome to the forums.



Gary, what do you recommend as a fire stop? What about Roxul in the wall cavities? I am located in Thunder Bay, Ontario, Canada. 2" XPS is what I have. 


Sent from my iPhone using Tapatalk


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## Windows on Wash (Aug 30, 2011)

http://www.firestop.com/education/nbc.pdf

http://www.firestop.com/education/nbc.pdf


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## Gary in WA (Mar 11, 2009)

There ya go.... lol.

How much above grade block wall is there, my concern is forcing the moisture to that non-waterproof/non-sill sealed/non-vapor barrier wood to rot from direct capillarity; http://www.greenbuildingadvisor.com...essure-treated-sill-plates-and-building-code? 

Gary


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## maurzy01 (Mar 4, 2015)

Windows on Wash - Thank you!

Gary - I didn't measure exactly but I would guess in this particular location the blocks extend 2.5'-3' above grade. I don't believe the sill plate has ever been replaced, although it shows signs of moisture, the house was build in 1954. If I sealed the top cavities of the blocks, I am assuming that wouldn't change any wicking issues as wood would still be in direct contact with the conrete.


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## Windows on Wash (Aug 30, 2011)

maurzy01 said:


> If I sealed the top cavities of the blocks, I am assuming that wouldn't change any wicking issues as wood would still be in direct contact with the conrete.


Shouldn't really change it.

My thinking is that the additional insulation on the block and sealing if from the inside air could lessen its ability to dry to the interior in the AC months, however, if the grading and flashing details are good on the exterior, the potential is reduced.

Most of the moisture issues on basement walls in your climate are going to be a result of the winter time conditions and too much moisture (condensation) on the walls via poor insulation materials and application.


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## Gary in WA (Mar 11, 2009)

I've found there are a lot of Gary's on this forum.... send me a PM if you need a one-on-one.

IMHO, use some EPS rather than XPS because it is way more vapor open at least on the bottom 1/2 of wall (and temps are milder there) to let as much moisture as possible through to dry at interior. Otherwise with the lower permanence XPS, more moisture will be forced upward to dry toward exterior and much closer to the wood plate for rot (esp. as you are showing moisture there now- without the vapor retarding foam board). Fill the cavities with a poured insulation, then canned foam the top 3", then top with rigid foam board or required draft-stop, FB under the wall bottom plate for a thermal, air, capillary break to keep the studs dry from wicking through slab; http://www.greenbuildingadvisor.com...ressure-treated-sill-plates-and-building-code

Air seal (caulk) at FB/bottom and top plate, behind the wall FB in 1' square grid pattern to limit indoor air movement; http://joneakes.com/jons-fixit-database/743

*Fig. #3*; http://www.buildingscience.com/documents/information-sheets/basement-insulation

Gary


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## Windows on Wash (Aug 30, 2011)

There is only one Gary that I know of. Who else were you thinking of? 

Information on the sill plate is great but a bit after the fact for this poster unless he/she is going to jack up the house.


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## Gary in WA (Mar 11, 2009)

Let's just say public forums are a lot different than real life...

In my experience, any older basement with CMU as the wall usually has a 2x4 sill plate because that was the norm ages ago- rarely; no sill. They were usually 8" wide leaving sufficient space to pour cavity insulation in to from between the floor joists above. Every so often, the cells are filled with mortar/threaded rod/"J" bolt for sill anchorage- or not. The block under the joists (inboard of the sill plate) is probably just sitting there, at most; toe-nailed on the ends to the sill, easily removed. If there is some pressure on the block, a flat bar/steel-wood wedge/2x4 stud springer to the slab will give room to remove same, adding cavity fill poly beads with very good results; http://www.masonrymagazine.com/1-03/pourpump.html

Gary


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## AllanJ (Nov 24, 2007)

Filling the cinder block cavities with pour in insulation has limited benefit because the cinder blocks themselves including the concrete web structure inside are excellent heat conductors (losing interior heat to the earth outside).

Instead, provide continuous insulation on the inside such as within a stud wall against the foundation wall.

Use pressure treated lumber for any wood touching concrete, such as the sole plate of the stud wall. (The sill plate will have to stay the way it is.) Good practice has a one inch gap between batt insulation in the stud wall and the surface of the concrete foundation wall to avoid moisture wicking and mold.

If there is a black waterproofing on the outside of the foundation wall then omit the vapor barrier on the inside. Cut out a pattern of holes in the Kraft paper representing a quarter or more of the total surface area if you use that style of batt insulation in the stud wall.


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## Windows on Wash (Aug 30, 2011)

Allan,

How do you address room side moisture diffusing through a punctured fiberglass batt and possibly condensing on the cold cinderblock wall?


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## Gary in WA (Mar 11, 2009)

AllanJ said:


> Filling the cinder block cavities with pour in insulation has limited benefit because the cinder blocks themselves including the concrete web structure inside are excellent heat conductors (losing interior heat to the earth outside).-------------------* but filling the cells with insulating beads will stop any convective loops from forming there, regardless of the materials thermal bridging; which I did say to use foam board inside.
> *
> Instead, provide continuous insulation on the inside such as within a stud wall against the foundation wall.
> 
> ...


-------------------------------- *actually, you could use paper faced batts though UNfaced are better for moisture management/drying ability. *

Far as WOW's concern, the vapor drive below grade is interior, and above grade to the exterior only in the summer; yet a frame wall with latex paint is still safe from a moisture standpoint due to the quick drying time. 

*See pages;* 5 for Wall #4
pp. 10 for summertime moisture
pp. 19
pp. 22 and 23 for concluding comments. XPS is the *safest* wall but dry basements can use framed wood walls with no poly/facer. Notice about perforated rolled batt walls, others are acceptable, just need the drywall air-tight and no existing moisture problems to defeat them.

Gary


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