I’m new here, so be gentle . . .
I’m in the process of planning the finishing of our basement. I’ve read all the (very good) material at the Building Science Corp site, as well as the articles in FHB (esp Andy’s Feb 205 piece:
http://www.taunton.com/finehomebuilding/pdf/protected/021169078.pdf) I want t get this right, and would appreciate any input form those with experience.
The house was built in 1959 in southern Ohio. Basement walls are concrete block. The house has no sump/sump pump. I don’t know if there is gravel under the basement slab. The walls have parging and a faint sign of some tar/damp-proofing applied, but it is probably not very effective anymore. We have lived here 4 years, and have had a little water coming down the walls in a few places and also some small leaks at the wall/floor joint after heavy rains. This is minor–maybe two gallons total, it dries up on its own. Last fall I dug curtain drains around the two uphill sides of the house (approx 18″ deep, placed in sand, drained to daylight) and dug another semi-footer drain along the same two sides (24″ away from the wall on the outside, but 12″ lower than the footer. This lower drain slopes to a sump pit outside our foundation). My intent with the upper drain is to prevent surface water from ponding or saturating the soil near the house, the lower drain is intended to prevent a rising local water table from flooding my basement. When the weather warms up I’ll get back out there and finish up by sloping everything away from the house for ten feet. My hope is that all this will significantly reduce the chance of external water from flooding the basement.
Radon: It is slightly elevated (6 pC/l) and I need to do something about it.
My present plan:
Walls: Platon dimpled membrane sealed at the top (to provide a way for any water to drain down, and to provide a barrier to radon), 2″ of EPS (with borate in it), furring strips, drywall (the kind without paper)
Floor: Platon (to stop water vapor infiltration and radon infiltration), 3/4″ of XPS, solid floating flooring (see below).
Issues/questions:
1) I know the air under and behind the Platon will be at/near 100% RH year round–the only place it can dry is outward through the wall at the top of the basement. I’d prefer a different solution, but what I’ve outlined seems consistent with the “Slab top vapor control” approach recommended by Building Science Corp. Still–I worry that I’m building a mold colony.
2) Flooring: We don’t want carpet in the basement. The three options I’ve considered:
a) Laminate directly on the XPS. This would be inexpensive, but has two potential problems: the palstic laminate forms a second vapor barrier above the Platon, and if the floor gets wet (busted pipe, external water, etc) I have to tear it out.
b) Plywood on the XPS with solid cork flooring above: Pricey, but would look good. No double vapor barrier, but if the plywood gets wet I’ll be tearing it all out.
c) PVC solid flooring on the XPS: I ran across something called “Foresta”, a flooring that looks like laminate, but is made of solid PVC. It can get wet without any damage. It costs about $5/sf, so it’s not cheap, but it seems worth a look for this application. I’m hopeful that the seams between panels will allow any water vapor down there to get out.
Comments are welcome/solicited on this approach. Any opinions on this “Foresta” flooring? Does anyone have a recommendation for a good source for cork I could glue down directly to plywood? Should I actively vent behind the Platon to get the water vapor/radon out of my house? (I would think the fan would only have to be very small–but where should the makeup air come from–outside?) Any other suggestions for a solid-surface flooring material that “breathes”?
Sorry for the long first post. Thanks for any assistance.
Edited 2/16/2009 9:19 pm ET by vigilant1
Replies
Call in a "basement systems" company and have them install "interior" perimeter drains. This will handle anymore water that is coming in and direct it to a sump pit that will pump it out when it gets filled. My own recommendation for a basement floor would be ceramic tile.
Ceramic tile would leave the floor feeling cold, but we could reduce the problem with some strategically-placed throw rugs. It would last a long time and wouldn't be susceptible to water damage, which is very nice. I'd still like to reduce radon infiltration through the floor--I wonder if a special thinset would block it. Sealing the slab would require me to grind off every bit of the left-over mastic from the previous asbestos tiles, and even then I'm not sure the thinset would bond to the sealed concrete slab. Thanks. I do like ceramic.
You should have heated tile floors. Once you have them you wonder how we ever got along without them!
We just finished our basement with similar issues.
Radon...I don't think your barrier will actually be a barrier. It's going to vent into the inside somewhere and hence you'll get it inside. No matter the barrier, the inside of your basement will be lower pressure and it'll get in via any crack.
You likely want to go with real forced-vent-based remediation. We had it done in one day for about a grand and we went from 4 to 2.
As for finishing, we went with 3" EPS, steel studs, Densarmor rock. No flooring. We just stained the concrete. We were worried about it being really cold (as it was pre-finishing) but it's surprisingly comfy once we get the gas fireplace going.
Questions:
1) ...I'd prefer a different solution, but what I've outlined seems consistent with the "Slab top vapor control" approach recommended by Building Science Corp. Still--I worry that I'm building a mold colony.
I followed BS's suggestion with the EPS and no vapor barrier. Concept is that it's breathable, so ultimately can dry either way if need be.
2) Flooring:
As stated, we stained. Few reasons: 1) cheap! 2) we were going for the industrial look 3) same fears as you with having carpet in a basement.
One bonus of the vented radon remidation is that it supposedly sucks a lot of humidity out of the floor during the summer, leading to a dryer slab.
We may eventually put down some rugs, ideally synthetic.