Insulating Concrete Basement

[John]

I live in Canada, where it gets pretty cold in the winters. I'm re- insulating my basement, and have done a lot of research, but surprisingly I still have lots of questions which I can't find answers to.

My plan is this: Use 1 1/2" rigid insulation glued to the concrete walls (apparently the type I'm using is considered vapor barrier). In front of that, I'll build a 2x4 frame, which will be butted against the rigid foam. Inside the 2x4 frame there will be fiberglass vatting. On the front of that there will be a vapor barrier (plastic) caulked on, and then drywall on top of that -- sounds pretty straight forward, right?

What I don't know is how to finish the floors/ceilings. For one, should the rigid foam be glued to the floor to create an air-tight seal or not? Should a small gap be left (I'm worried about moisture getting between the foam and the concrete wall, etc). I read at one place that the panels should be attached with a giant s-shaped glue going from top to bottom -- I can only assume this is related to water moving up/down between the concrete and styrofoam...

Next, the 2x4 frame -- again, how should that be in contact with the floor? I'm told the 2x4s should rest on a piece of plastic, so they're not in direct contact with the cement... Should that plastic be sealed to the vapor barrier in front, or should a gap be left again? How do you attach a 2x4 to a cement floor?

Then comes the ceiling, where the cement meets the joists/joist holes. I'm told that you have to drywall in front of the foam board to ensure that if there is a fire, you have 20 minutes before the toxic fumes fill the house. BUT, if I do what I described, the foam will still be exposed on the top, as I don't plan on drywalling into the joists. I was planning on filling these areas with vatting, and vapor barrier it, but that's it... Should I be doing anything else?

I would greatly appreciate any sage advice on these matters

John

[hrhofmann]

Perhaps you should speak with whatever buildiing code officials control where you llive.

[clare]

I'm in Casnada too - i Ontario. Recommend you use Roxul rockwool bat with no vapour barrier over the taped rigid foam - and use drifloor underlay or just the waffle plastic with standard subfloor or heavy laminate or engineered hardwood flooring over it for the floor. That's what we did on my daughter's place after a lot of research.

We put the 2X4 on sections of dri-floor cut in strips t fit under the sills, and located the walls with tapcons ito the concrete.

We filled the between-the-joist spaces at the header with 2" of rigid foam, then stuffed full with Roxul. Roxul is fire-proof. Drywalled a few inches higher than the suspended ceiling grid.

[Paul Franklin]

You do not want a vapor barrier on the front of the stud wall. That would give you in effect two vapor barriers (the foam and the one on the wall). You never want two vapor barriers; moisture will inevitablly collect and condense in between over time. No vapor barrier is perfect; having only one allows small amounts of moisture to slowly dry out. Use unfaced insulation in the stud cavities.

Don't know about up north, but here in Ohio you have to have a fire stop anywhere a wall meets a horizontal space (like joist bays). This is so a fire in the wall can't spread quickly to the ceiling. Kind of hard to describe, but the easiest way to meet this requirement is to put the ceiling drywall up before you build the walls and use firecode drywall. Run the drywall all the way to the sill plate of the first story. Then build your wall with the top plate up against the drywall. This way there is no path from the wall area to the ceiling area.

Another option is to use a wide top plate for the stud wall that reaches all the way to the sill plate.

HTH,

Paul F.

[Paul Franklin]

A few more points. Tape the seams of the foam with air barrier tape like that used for house wrap. This will keep air from moving through the cracks and condensing water vapor on the cold concrete wall behind the foam.

The wall bottom plates should not rest directly on the concrete floor. You can use sill seal (thin foam made to go between sills and sill plates, but as another poster suggested, Dricore panels are even better. You put it down first and then build the walls on top, fastening the bottom plates to the floor through the dricore. To fasten bottom plates to concrete floor you can use a ramset gun or tapcon screws.

For the belt and suspenders approach, use pressure treated stock for the bottom plates. Required by code here, probably there too, although you may get away without using PT if you use the dricore. Best to ask the local AHJ. If you use PT, make sure fasteners you use (ramsets or tapcons) are rated for use with PT.

If you go with the drywall ceiling first approach, you don't have to do the whole ceiling first, just around the edges. This allows to you to the build the walls, then run wiring and plumbing while most of the ceiling is open. You can even start with narrow strips of drywall that just reach from sill to the inside of the stud wall top plates, and then when all rough-in is done, finish drywalling the ceiling as usual. Anywhere you penetrate the drywall acting as fire stop (like with wires or pipes, you have to seal the opening with fire rated (red or orange) foam or caulk.

Paul Franklin