Framing Basement Walls


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Old 04-23-15, 12:54 PM
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Framing Basement Walls

I'm in the very early stages of planning to finish my basement, and have some basic questions when it comes to building/framings the walls, insulation etc.

I live in Buffalo, NY so we do get cold winters, and our home was built in 1989 and has poured concrete basement walls. And building code at that time did require the builder (no idea who that was) to install full insulation on all outside basement walls of the home. I will check the R rating tonight, but believe it is either R13 or R15. And we have a pretty dry basement so i'm not to concerned about moisture.

And I currently have exposed ceiling/rafters in the basement.

Now, my initial plan is to build the walls in place vs on the floor. And in thinking about it, I was wondering if I really do need a top plate for the walls?

The current ceiling rafters are all 16" on center. can I get away with installing a bottom plate (pressure treated) and then place each stud next to a ceiling rafter?

Main reason I ask is that my ceiling height is ~ 7FT, and it will be much quicker/easier if I do not need cut down 8' studs by being to able go slighter higher into the 'ceiling'.

I was planning to tear down the existing insulation as it is already falling down anyway. Then beam the wall with studs 1/4" off the basement walls, and then install batt insulation between the studs. I could probably install a 1/4" foam board barrier against the concrete, but not sure it is a necessary step or precaution needed.

Ironically, I called my town and the women on phone said there was no code requirements and I could do what I want in all aspects. But I will call them back again next week to try and confirm, as I do not want to have any issues long term if every decide to move one day.
 
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Old 04-23-15, 01:14 PM
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IMO, I would use 1" of rigid foam against the concrete then studs against that. Use the batt insulation of choice, although I do like Roxul. Then no vapor barrier to allow whatever moisture that sneaks through to pass to the inside as opposed to accumulating against the VB.

Pressure treated at the bottom, but be sure all fasteners that attach to the pt are rated for that purpose. Others dissolve in 3 or 4 years.

As for a top plate, the mice say don't bother. I prefer a top plate and where the wall extends above the foundation, if the top plate doesn't block that then add something to avoid unwanted tenants.
BSD-103: Understanding Basements — Building Science Information

Bud
 
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Old 04-23-15, 03:44 PM
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Yes, you need a top plate... not only does it keep the top of the drywall straighter but it also serves as fireblocking. You also need to block the top plate solidly back to the concrete and seal any gap where the two meet with fire rated spray foam.
 
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Old 04-24-15, 10:37 AM
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Thanks for the help and suggestions and seems 2 different points of view on using a top plate.

I can see how a adding top plate would keep your sheet rock straighter being able to screw in between the studs at the top.

But.... why would you be pushing the top plate flush against the concrete wall? Wouldn't your top plate then be subject to seeping moisture from the concrete?

Also, wouldn't the top plate then not being matching up flush with your studs that are set 1/2 to 1" off the concrete walls for that same reason?
 
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Old 04-24-15, 12:25 PM
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There are 2 schools of thought on having a gap between the new wall and the concrete. Old school and I believe the most valid is to prevent contact with the concrete and to allow your new wall to be vertical and straight. But that gap then provides a circulation path where moisture from below can be circulated up to condense and freeze on the colder exposed portion of the concrete. If your exterior foam covers the above grade portion and is sufficiently thick (2") then condensation would not be a problem. If it is less than 2" thick then some searching would be necessary to determine how much inside foam is needed to prevent that condensation.

That is where the new thinking comes in, adding inside rigid foam prevents warm inside air from reaching a cold surface. It also acts as a spacer to keep the framing away from the concrete.

As for closing the gap behind the top plate, mice are a real concern, but codes rarely address those little pests. Having a continuous fire stop as X stated is more important.

Regardless of what codes were in place when the house was built, the renovations you make now need to follow current codes. Again, I would have to do some searching, but in your extremely cold climate that might be more than 2 inches of foam from footings to the house above.

Your code office would have the final say.

Bud
 
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Old 04-24-15, 12:30 PM
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Walls ALWAYS need a top plate.
 
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Old 04-24-15, 03:44 PM
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But.... why would you be pushing the top plate flush against the concrete wall? Wouldn't your top plate then be subject to seeping moisture from the concrete?
You don't push the top plate against the concrete. You add 14 1/2" long pieces of blocking (drywall or red fire resistant plywood or whatever the inspector in your area requires) to the bottom side of the top plate. That blocking comes "close" to the wall... close enough that you can spray foam the gap between it and the wall and in the 1 1/2" gap between those individual pieces of blocking and the concrete wall (behind the studs).
 
 

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