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fred54 07-27-2012 01:49 PM

basement insulation
searched but have found many conflicting answers. I would like to partially finish the basement in my 50-year-old zone six house. Currently half of the basement has tiled floors the other half has painted floors. The block walls are painted. I have no sump pit, no french drain, no perimeter drain and not even a hint of moisture anywhere. My house is basically sitting on a giant sandbox. The humidity is 41% right now down here and I don't run a dehumidifier.

It is neither heated nor cooled but is always between 65 and 75 degrees.

There is a working masonry fireplace on the side I want to finish.

I basically want to sheetrock the two outside walls, (the third wall is smoothly finished concrete) but I am at a loss for what the proper method should be.

I don't need the insulation for personal comfort. The only reason I want to frame up the walls in the first place is so that I can hang cabinets on one side for a mini-kitchen and unobtrusively run TV wiring on the other. It also will look nicer and I plan on putting in a drop ceiling to complete the room.

Furring strips with rigid foam in between doesn't give me the space I want for wiring and drainpipe but a 2 X 4 studded wall with an empty cavity seems to be an invitation for critters to move in and get comfy.

Moisture is not an issue now but will it become one if I cover up the block?

Should I just leave it alone and leave my wiring exposed? (It is all in conduit) Maybe put in a 6 foot stud wall for the kitchen?

The more I search the more confused I become.

jklingel 07-29-2012 09:04 PM


Originally Posted by fred54 (Post 975564)
I don't need the insulation for personal comfort.

Then just frame it and go. ???

MLMIB 07-30-2012 05:50 AM

If its critters you want to stop you can fill it with spray foam, that should remove any space available for bugs etc. and since spray foam will move move the dew point into the middle of the foam it won't be a concern.

jklingel 07-30-2012 11:34 AM

bugs will burrow into spray foam in a heart beat, and voles (and likely mice) will chew through it almost as fast. borates will deter them.

Del Ray 07-31-2012 03:27 PM

Barricade Insulated Wall Panels
Another alternative that eliminates framing the perimeter basement walls is insulated wall panels. The 2' x 8' modular panels have ship lap joints and provide R12 XPS insulation bonded to OSB engineered wood. They are attached with tapcons directly to the concrete wall.They provide a nailing surface for sheetrock and a superior substrate to attach shelving, flat screen tvs etc.

Gary in WA 08-03-2012 12:20 AM

Aren't those OSB backed XPS? IRC doesn't require a Class 1 (poly plastic) or 2 (OSB, Plywood) in basements anymore due to mold problems. The 2" of closed cell (0.5 perms) and the OSB (0,67 perms) together could be a problem. The summertime vapor drive could wet the OSB (hygroscopic) unless the indoor humidity was kept in check with a dehumidifier. It couldn't dry to the backside, only to the inside.... I would never put an engineered sheathing in a basement environment that distributes moisture inside it rather than out the face. Is it 2# closed-cell foam? Is the OSB aspen species?


Del Ray 08-03-2012 04:34 PM

Basement wall insulation
The wall panels have 2" of Dow closed cell extruded polystyrene insulation. The panels interlock to prevent bulk water from migrating inside, so moisture will dry to the outside. The OSB still has to be covered with sheetrock. The OSB is aspen species. Humidity levels inside the basement still have to be kept under control in summertime.

Gary in WA 08-05-2012 04:12 PM

Basement Barricade

OSB shouldn’t be used below grade in a basement with foam sheathing because it is a Class 2 vapor retarder; you need a vapor-open assembly (not even wood paneling): http://www.buildingfoundation.umn.ed...jectReview.htm
The thickness of foamboard used may not be enough for colder climates (don’t double-up on Barricade; vapor retarders): http://www.buildingfoundation.umn.ed...timum-main.htm

Your installation directions are flawed because the foamboard has to be glued air-tight to the concrete/block wall to be effective. Remove any plastic sheeting from framing when adding Barricade:
No air gaps behind the f.b. for convective loops to form:

Foamboard directly adhered to OSB is not a good idea (above/below grade), the OSB can only dry in one direction:

Poured concrete wall may require thinner layers (2-1”) of f.b. glued to them due to irregularities of the surface, better for efficient air sealing with off-set laps also; pp.59.
Page.35- the relative humidity (32-98%) on the inside face of the foam board goes through the very permeable drywall (50 perms) to dry to the inside (32-62% RH- Figure 27). But add some OSB (45%RH= -2 perms to 60%RH= 4 perms) and you may have trouble on the north/above grade portions unless the foam thickness is over-kill for the location, pp.53- 4” of foam with a foil facing on the polyiso (moisture tolerant, not wood chips OSB).

Your wiring channels (used or unused) will take an R-reduction hit and let air/fire follow them (hopefully the homeowner is smart enough to fire-stop them at top of the wall and canned foam the electrical outlet box) per minimum Code; fire-stop wall-to-ceiling and every 10 linear feet of wall between the foam boards, check with local AHJ: Might check with your lawyer if you are liable or not, unless I missed it in your installation instructions (as the wiring chase is inherent to your system).

A cheaper/better system for DIY'ers is to install the correct thickness f.b. (per location) and strapping or a frame wall after the f.b. Even Dow understands not to use an interior vapor retarder; though they also missed the foamboard requires gluing for air-tightness to the concrete….. notice their wiring design:

Per your instructions, running the floor Barricade product under the wall; supplies the concrete wall with air from under the sub-floor product, as said before---keep the basement air from the concrete wall to avoid condensation. I usually recommend Delta F.L. or foam sheathing/plywood instead of the box store Dri-core (or similar with OSB) with plastic air-design grid work, both for cost and ease of installation:

Foamboard with plywood layers, Fig.15:

Fig. 1-3:

The wax coating on OSB slows any diffusion trying to dry to the inside:

The aspen species of OSB is faster at growing mold/mildew than other species, pp.8-13:

OSB is hygroscopic, distributing any moisture/water into the product before face drying as plywood does and foamboard/OSB: enough of the OSB (long as it isn’t around water/moisture) slams, I hope I gave you something to think about… my 2 cents.


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