Cement slab insulating ideas feedback
Hello All,
We have a barely below grade room that we want to finish out. Please take a gander at the pic. The room has a cement slab floor right now where the top of the slab is ~1′ below exterior grade. The foundation walls extend about 2′ above the slab with 6′ stud walls making up the remainder of the wall. The foundation has drains at the footing level, the foundation walls have a layer of bitchuthan <sp?> on the exterior and the slab has the thick plastic sheeting underneath it. The slab-walls are about a year old and there is no obvious signs of water intrusion. Even cardboard boxes left on the slab for long lengths of time don’t really get damp.
Plan for the floor is to use the Delta-FL stuff on the floor then lay on top of that a network of 2by4 stringers set 2′ oc. I will attach the stringers to the slab with tapcons dipped in sealant to prevent moisture from migrating up through their penetrations. Inbetween the stringers I will use rigid foam the same thickness as the stringers and glue it in place with beads of spray foam. I then glue-screw 1 1/8″ T&G plywood to the stringers to finish the subfloor. I will leave a gap around the edges to vent the Delta-Fl as described in their literature. I think doing it this way I will have a sturdy-dry-moisture free subfloor. What think you all?
I do not have a good plan for the walls yet. For the studbays I will probably use encapsulated bat insulation underneath the earthquake sheathing. I think that I should use rigid insulation on the 2′ cement walls but I am not sure how much and then how to tie into the upper stud walls. What think you all?
I have read the articles on damp-proofing basements and I think that I am following the spirit of the articles if not the exact letter.
Any help would be greatly appreciated.
Daniel Neuman
Oakland CA
Crazy Home Owner
Replies
You're doing a few things that I would probably not do; I use powder actuated nailers for putting down the sleepers, for one thing....IMO, the sealant with the tapcons is probably unnecessary.....but nothing wrong with all that.
I usually put 2 X 2 ( 1 1/2" X 1 1/2" with 1 1/2" rigid foam) sleepers on 16" centers and use T & G 3/4" subfloor....the 1 1/8" seems a little overkill....
I do like doing a basement floor this way. The rigid foam has a bit of give and, compared to the concrete, it has a nice feel walking on the subfloor.
What is your finished floor going to be?
Hello Notchman,
The tapcons with the sealant is per the instructions from the Delta-Fl underlayment company.
I agree that the thicker subfloor is over kill but I am trying to match grades with the existing stair landing into this room and the level of the bathroom in this room.
Finished floor will be some sort of higher quality industrial carpet. This room is going to have a treadmill and a free standing heavybag on wheels so the floor will take some abuse.
Daniel Neuman
Oakland CA
Crazy Home Owner
What is the frost depth where you live? My guess is that you are going through a lot of trouble if you just want insualtion (based on your thread title), but on the other hand if you want a more comfortable to walk on floor than concrete, I think you are on the right track. Personally I think I would use a powder actuated tool to shoot the striingers down to the concrete and go on 16" centers. If you feel you must screw them down, get a rotary hammer; if you use a hammer drill, you wil be screwing down stringers of a week...
Hello Dirishinme,
The frost depth here in Oakland CA ~2 miles from the SF bay could not possibly be more than three inches.
Yes I want an insulated more comfortable floor to walk on. The drill bits that come with the tapcons are not spec'd for rotary hammer work and the couple that I have driven with a hammer drill haven't been too bad. I am not putting the tapcons in more than every 2' I think. Luckily I am just a HO so if it takes extra time well then it does.
With the 1 1/8" subfloor I think 2' oc is under spec why would I go to 16"oc? Just seems like extra money-work for me? I am planning on putting down the stringers around the periphery first then under where the partition walls are going, then fill in the open spaces 2' oc.
Daniel Neuman
Oakland CA
Crazy Home Owner
Does anybody have any thoughts on how thin I can go with the foam board insulation on the foundation walls?
thanks,
Daniel Neuman
Oakland CA
Crazy Home Owner
One thought is that once you are below the frost line (if there even is one) the need for insulation is somewhat minimal. Another thought is that when setting up a building envelope (talking your sidewalls here) it is as important if not more to stop air and moisture infiltration as it is to acutally provide R-x amount of insulation. For example here in centeral NC, (I think our temperatures are somewhat similar if not a bit colder) we are only required to provide ~R-6 of underslab insulation and this only for 2' around the perimeter. I think the idea is that this enough to give a thermal break from the backfil below. A rule of thumb for foam insulation is R-5 per inch. Re the walls, if you use rigid foam, you need to devise a stratigy to get a tight fit - be it my using foam in a can to make the panels fit thight or whatever. Considering the mild temperatures you are dealing with you might want to match your side wall foam thickness up with your interior framing thinkness - say 1.5". Personally, I wouldn't go less than an inch though. Also, I think rigid foam is pretty much sold in thickness iincriments of 1/2".
I missed the part about the 1+" thick subfloor and in that case I agree that 24" OC will be fine.Matt