insulatiing a basement

[Jules]

Hi,

We currently have a basement with poured concrete walls and floors, and I'm tempted to make it a little more habitable - I was thinking of putting some 2x4 framework for the floors and walls, insulating with the glass fiber stuff, then 3/8" particle board over the top of that (for the walls, anyway - 1/2" stuff or thicker for the floor, I suppose). It gets a little chilly down there in Winter.

Questions:

1) Is there any benefit in having an air gap under the floor? I don't intend to run cables / pipes under there, and the existing floor's solid concrete anyway, but maybe some airflow under there's still a Good Thing (and I've got lots of spare bricks that I could put every 12" or so and raise things up by a couple of inches).

2) What's the conventional method of fastening framework to the concrete walls? I'm used to using concrete anchor expansion bolts for heavy-duty stuff, but perhaps that's overkill here, or there's something better I could be using. At the top I can secure it to the beams supporting the floor above (at least on the sides at right-angles to the beams, the 'other sides' might be trickier due to access)

cheers

Jules

[Tony Hwang]

Hi, Wall should be floating(don't make the frame tight fit). R12 insulation is plenty for basement. And vapor barrier. Not particle board. Sheet rock. My basement is always dry so we put down good quality pad and carpet. Also we have air duct supplying heating/cooling down there. Very comfy even in cold winter days. Having a floor means less head room.

[ShadowTek]

Mold can grow on sheetrock paper. Wouldn't it be safer to use some sort of fiberglass board?

I've never done it before, I'm just asking.

[Jules]

Yep, the insulation I've got is R13 (I originally bought it to insulate the ductwork in the basement, but never quite got the tuits together to finish that - and if I end up insulating the whole basement, it's somewhat redundant anyway.

Is the vapor barrier a must? The only apparent dampness down there is on the plumbing from the well pump - the walls themselves seem to stay dry. Maybe it's asking for trouble years down the line not to do it, though.

Purely because it's easier to cover / paint? Or are there other advantages? (I suppose sheet rock's more fire resistant?)

[I'm from the UK originally - which might explain any 'odd' spellings you may spot - so I'm used to working with brick buildings, not timber framing / siding / sheetrock. The learning experience is fun, though]

I suspect I won't carpet it in anything 'good' (it'll always be more of a utility space) - maybe carpet tiles, or ceramic tiles, or lino. Cheap / functional / better than bare concrete, but it'll still be "just a basement".

The clothes drier's going down there (still some investigation to do as to whether I'll need a moisture trap / pump on the vent or not) and ultimately I'd like to get the washer down there too (the waste water / sump work needed there makes that a longer-term project). There's some gym equipment I can throw down there, as well.

Yeah, our system is "interesting". Very random in the planning, it seems :-) One day I'll pull it all out and just start again with a better design, I think.

Sure. We have around 7'8 of clearance now, so I am mindful of space (hence the query about under-floor air gap) - I'll lose about 4" in the floor, plus a little for ceiling down there if I decide to finish that off too. It'll be pushing it a bit, although I suppose I don't mind so long as it doesn't drop under 7'.

cheers

Jules

[Rudy]

In newer homes, they put a vapor barrier below the concrete to keep moisture from wicking up thru the concrete. In older homes, concrete floors without the vapor barrier could transmit moisture (usually unseen) thru the slab. Try this: get a piece of clear vapor barrier(plastic sheet) and place it on your basement floor. Put a brick or two on the sheet and leave it for a few days then lift the bricks and have a look at the plastic. If there' s moisture evident on the bottom of the plastic, (you should see a "dark spot on the concrete too). then you do have moisture travelling thru the slab.

If theres no moisture, you could just put carpet pad down and carpet the bsmt or perhaps try something like this:

if it makes you feel better.

[Jules]

Hmm, well our place was built 1948/49, so probably not if it wasn't common practice back then.

Done (well, apart from leaving it for a few days :-) - I'll see what happens. The junk sheet I have is prety thick stuff, so I assume it'll work as well for testing as something actually sold as moisture barrier.

Well, I think it needs *some* insulating, hence the plan of putting some

2x4s down along with some insulation on the floor then covering. I'm not sure where the frost line's at here (northern MN) though, and maybe most of the cold entering the basement in Winter is actually coming through the walls above the frost line rather than up through the floor.

Interesting. I suppose if I *need* a barrier, it'll be under the wood (even though they show it on top of wood in the photo on that site) - and that implies using something a bit less springy. (it's not something I've ever looked into, but if they sell plastic sheet as a barrier then that'll do as well as anything, I suppose - I'll have a wander around the local Home Depot this weekend)

cheers

Jules

[Paul Franklin]

Since it sounds like you are in an area with cold winters, you have to be careful with basement insulation. If warm air can reach the cold walls, you will get condensation, which can dampen the insulation and framing and lead to mold.

I suggest reading this explanation:

Lot of good info.

I think one of the best methods for basement walls is 1 or 2" XPS foam board adhered to the wall with foam adhesive, and with all joints taped. Then a 2x4 wall in front of the foam with additional unfaced fiberglass insulation in the wall to get the total R value up. Finish with paperless sheet rock (uses fiberglass instead of paper facing..doesn't support mold). Not a cheap system, but works very well and can tolerate the normal moisture levels commonly found in basements. Nothing will work if you have actual water coming through walls or floor, but this system will tolerate normal diffused moisture.

The foam serves as a vapor barrier to keep warm humid inside air from contacting the cold walls and condensing and keeps moisture that diffuses through the wall from getting to the fiberglass. If you just use fiberglass and a warm side vapor barrier, any moisture coming from the outside will dampen the insulation and lead to mold because the vapor barrier traps it.

For the floor, look at:

Provides a slight air space and a vapor barrier. You can insulate with foam on top if you can spare the head room.

Again, not cheap. But you only want to do this once.

HTH,

Paul F.

[Tony Hwang]

Hi, Sheet rock is fire resistanct.

[clare]

Just went through this on my daughter's houe. In my opinion only a few ways to do it. Spray foam, or the way I did it. I put 2 inch Styrofoam SM against the walls, then a 2X4 wall against the foam. The 2X4 wall is set on strips of "dri-core" so I did not need to use PT wood. The

2X4 wall is filled with rock-wool (Ruxul safe and sound) batts - for a total R value of 24. This id covered with paperless wallboard (Georgia Pacific DensArmour plus). I used 5/8" because my local dealer did not have 1/2" in stock. It is HEAVY at 86 lbs per 4X8 sheet.

Don't use regular drywall or fiberglass insulation because it is prone to growing mold if it gets damp (and falloing apart too) And do NOT use partical board in a basement!!!. For the floor, you could use dri-core - but I went with the equivalent of Delta FL with an engineered hardwood (Bamboo in my case) click floor. Forget laminate - I used it in my basement, but never again. Engineered hardwood is so superior - and much easier/nicer to work with (1/2 inch engineered vs 14,, laminate) - and I would never use less than 12mm or half inch in a basement (or anywhere else)

[clare]

Latest wisdom is no vapour barrier in the basement, and R23. Nail the "floating" stud wall to joists and TapCon into the floor. The end walls get nailed to the side walls and support themselves.

[clare]

DriCore is about an inch and gives you the air-space.

[clare]

Count on 4 feet minimum frost, and do yourself a favour and go to R23. Stuff the joist cavities to R28 or better. Dricore on the floor ( or DeltaFL and plywood/engineered hardwood) Putting 2X4s on the concrete if there is any moisture they will rot/mold unless you use the toxic Pressure Treated wood - which I do not want in MY house. My own basement has 2X2 framing on the floor with 3/4" plywood. My location is extremely dry, being built in sand on the high point of the street. No sump pump needed. It was that way when I bought the place but I would not do it that way if I was re-doing it. Our last place (my wife's before we married) also had the 2X4 strapped floor and we had to tear it all out. What a rotten crappy mess it was!!!!!!

[clare]

Absolutely. The cost of materials is a small part of the total cost of the job, and the difference between "almost good enough" and "right" is less than half,

"Why is their ALWAYS enough time and money to do something over, and NEVER enough to do it right???"

[Doug Brown]

Yeah, it does seem to be a quality product but horrendously expensive!

[Jules]

Just to report back on that, no sign of any moisture altogether. I'm wondering if I'm worth repeating that test in a few months during the middle of Winter, though - presumably the "problem" (if there is one) will be worse then than now.

cheers

Jules

[stan]

However; get some advice about how to build on the warm side of that plastic, if laid on the concrete.

The plastic will be cool, real cool and at ground temperature of around 50 - 55 degrees F.

Watching one of those TV shows; you know "Rip it all out Holmes etc." it was said that the cool surface below; in that case I think it was prefinished wood flooring, could accumulate moisture from warm inside air condensing on it! And that moisture could affect the wood flooring above it? causing to darken and warp and grow mould!

Don't know what the answer/proper procedure is; but might be best to get advice before proceeding to build a floor

Just suggestion anyway. Have seen several cool (but damp) basements.

In our mainly unfinished b.ment we run a dehumidifier all the time during these seasons anyway.

[clare]

Which is why I just used DeltaFX under the flooring I installed in my daughter's basement. About $0.50 a square foot for the DeltsFX, plus the flooring on top.

[paulaner]

What's DeltaFX? Simailr to Ditra? Ditra is like $1.50 / sq ft...

[clare]

Similar, but not made for tile/thinset. round "knobbies" instead of square, and wider spaced. Cheaper too.