(Another) basement insulation question

17 years ago

Hi All,

I've read most of the posts here regarding the various suggestions on basement insulation, but have an additional question...

First, my basic basement insulation plan...

1. Dry-loc the walls for moisture (done)

2. Fasten foam board sheets directly to the walls

3. Build a steel-studded wall (with CCA 2x4 beneath the lower track) against the foam-board.

4. Use standard, paper backed bats between the steel studs

5. Sheet rock over the studs, leaving the sheetrock an inch or two above floor level (to be covered with baseboard).

(No additional vapor barrier).

I know there are different schools of thought regarding the proper way to insulate a basement, and I know that at least a few people will tell me to avoid the fiberglass all together, but I haven't found any other way to "affordably" do this...

So, the first question. Does the above sound adequate for a general plan? Finally, the reason for the post...

Two of the concrete walls in my basement are the below-ground walls which are at the "front" and "side" of my garage (which is up one level from the basement). So, these walls aren't really "exterior" walls, as the earth behind them is beneath the garage floor. Is it necessary to insulate these walls to the extent of the true exterior walls? If not, what is the best way to handle these?

Thanks for any advice.

Jeff

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Comments (6)

jgodfrey
Original Author
17 years ago
Two additional things I should mention...

1. I'm near Kansas City, MO (I assume my climate may be an important part of the equation).
2. I'm outside city limits, in a county with no building codes. So, while I'm not really forced to do anything a particular way, I'd like to do this as right as possible...

Thanks,

Jeff
jgodfrey
Original Author
17 years ago
Does anyone have any input on this?

Thanks,

Jeff
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@koszta: that stinks. Not a good feeling to have that happen. @worthy: Thanks for the link in post. I saw something about the zones somewhere on the net and couldn't find it again. That answers a few questions I had running through my mind. I am curious about something though...can I just put this foam right in between the 2x2's and butt them right to the wall like the studs are? Just not sure if this will cause problems for me in the future. I have not looked in detail at the link you gave. Maybe that will be answered there. In any case thanks again for the info. Appreciate it. Edit: Just had an idea.... (which I may or may not find an answer to in future readings) was thinking I can trim foam board to fit in between studs, put a layer of roll insulation, then the drywall? Also...is drywall gonna be too heavy for the 2x2's? Oh well... gonna go read some before I spam forum with more questions! This post was edited by PFlies on Sun, Nov 23, 14 at 17:17
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Okay, please bear with me. We jumped into the building process, and yes, have already made "many of the common mistakes found in home construction." Your help is greatly appreciated, but you just need to keep in mind that the exterior is up and was unfortunately not taken into account as part of the building envelope. Truly, I had never heard of the building envelope concept until just yesterday. So I have to attempt to do what I can with what I have. Roof - Um, it's just a roof. We covered it with tarpaper and put shingles on it. It is vented. HVAC - geothermal Moisture/Air Control - not sure what you mean. Windows - low-e something or another Site Orientation - The front of our house faces South. Exposure/Shade - We are surrounded by trees with the north-facing front facing a pond. Does that help at all? I really appreciate you taking the time to work with me.
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"First, unless your local authority requires it, I know of no code requiring insulation for basement ceiling joists (or 1st floor joists). I live in an area of winter lows between -20 & -30 and there was no such requirement at a 2008 completion date; and NY bases their code on the IRC. " Chapter 11 of the IRC from the 2000 through 2009 versions all have required basements to be insulated....even in New York state for 2008 builds. See the link below. The International Energy Conservation Code (adopted in most US states) also requires it. ------------ Basements is nearly all US locations are required to be insulated either in the ceiling or foundation walls. How much insulation is determined by where you live, what type insulation you will use, where the insulation will be located, whether or not your basement walls are considered below grade or above grade, and from what materials the basement walls will be constructed. For most locations, newly constructed basements either need to be insulated in the ceiling of the basement using a minimum of R-30 or on walls using R-13 cavity insulation (batt) or R-10 of continuous (rigid foam). As mentioned, the best insulation is rigid foam located on the outside of the foundation. But rigid foam cannot be used in regions of high termite infestation and must be parged with mortar when installed on the outside above grade. Rigid foam used on the interior of the basement walls can also work, but as mentioned, it must be thermally isolated from the habitable space to prevent ignition in a fire. This can be done by framing walls in front of foam applied to the masonry foundation...then installing wallboard to themally isolate it...or by installing faom insulation like Thermax which has a foil coating which can be considered a thermal barrier. Bottom line is that insulation for Virginia and most places in the US is mandatory in new home construction. The only question is where the insulation and how much is required to be installed. Here is a link that might be useful: New York State Building Code
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I'm unclear on the flooring myself - I guess there are beams going the opposite direction of the joists. Ok - I can picture it. What about your r-19 grouped with some foam? I am imaging 1 inch of foam on the plaster/drywall sprayed in to seal it. It also adds some R-value and thickness. Then if you wanted some more r-value, you could do 1 inch rigid foam (or 2 inches) on top of the joists. This would help with thermal coupling of the joists. Getting to a magical R-value is not the only concern. Sealing properly is worth a lot. That being said, you would be at r-27. Spray foam is about a dollar per sq foot at an inch thickness. So you are looking at $1500 - but you might use less because of the joists. The rigid foam is about 1/3 of that so you would need $500 for that. Not cheap but 30% tax credit would count. I think you would be fine from a vapor barrier standpoint. 1 inch of rigid foam does not count as a barrier but 3 inches would. I would want some independent confirmation on the vapor barrier question.
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woodinvirginia
17 years ago
First off I live in the Mixed Humidity portion of Virginia and I am building an underground basement as we speak. Since Virginia is roughly on the same Latitude as Kansas I will answer. Don't know how long your basement walls had time to DRY out before you painted them, but I would have thought at least a years time since you built/acquire the house. (Builder friends of mine recommend that concrete (poured or block) be allowed to sit for 1 year before painting it; concrete takes a long time to cure; especially underground and with moisture present block walls attract it like a magnet; even if they are grouted!)
2nd,How was house waterproofed outside? How thick is the coating ? Did you do it or a builder? Does it have Insulation on Exterior wall? How thick is it? Or is it just a slab with no vapor barrier or Insulation on EXTERIOR wall ?
3rd I would recommend Green Board to be installed in the basement if you don't know the answer to the 2 questions above.... That way if you walls sweat ; even a little bit you will have moisture resistant Gypsum Board already in place.

Good Luck.
jgodfrey
Original Author
17 years ago
Thanks for the reply. Regarding your questions...

1. The basement walls are poured concrete, and were left bare for about 5 years. I put a cement-based water-proofing substance on them about 4 years ago (the house is about 9 years old).

2. The house is waterproofed via exterior drain lines around the footing, and a waterproofing "tar" like substance on the exterior of all below-grade walls. There is no exterior wall insulation that I know of. Also, I have a standard poured concrete slab, with no vapor barrier (AFAIK).

3. Green board - yes, I already have it purchased and stored in my garage until I'm ready for it.

Thanks again.

Jeff
homebound
17 years ago
Don't forget to insulate & seal the rim joist area. On the inside, I installed 2" solid extruded foamboard, cut with a serrated bread knife). The I filled any remaining gaps & edges with canned foam insulation. (I'd avoid "Great Stuff" since the plattic nozzles break too easily - try to find an alternate.) BTW, you can use a long drywall screw w/ a cardboard "washer" to hold some of the pieces in place.

I read that it's not a good idea to stuff fiberglass insulation up there, since it will retain moisture and can cause damage over time.

I'm framing out our basement now, and have noticed a tremendous improvement. It's in the 30's outside, yet 60 in the basement today just from the furnace, boiler & water radiator line that supplies the floors above.
homebound
17 years ago
You could nix the greenboard and go get some Dens Armor Plus. No paper in that to worry about. You might want to search this website for more info on it. Some of the home depot's have it. That's what I'm planning on using for ours, qat least for the walls, since greenboard still has a paper facing to provide a mold food source.

(Another) basement insulation question

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(Another) basement insulation question

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