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Discussion Starter · #1 ·
The condition that exist when building with basements in regions having expansive soils dictate special detailing for walls and their openings in basement finish work.

What is done is referred to as floating walls, walls framed so that they hang from the wood-framed main floor structure, and a "contraction gap" is maintained between the sub-bottom plate and the P.T. plate fixed to the floor slab.

If you are familiar with this, you know the drill. A space of about 3" is maintained between the on-slab plate and the wall plate above it, and to fix and align the two, 60d nails are run through a drilled clearance hole in the raised plate, and driven into the on-slab plate, this on 16" to 24" centers.

Enough nail shank is left above the raised plate so the floor can fall a little, and the 3" gap permits the floor to heave up that much.

The walls are sheetrocked to the bottoms of the raised plate, and the on-slab plate gets padded out 1/2". The tall base moldings are nailed ONLY to the on-slab parts.

So here is question. What does one do about the doors? It seems to me they are the weak link in the chain.
 

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The condition that exist when building with basements in regions having expansive soils dictate special detailing for walls and their openings in basement finish work.

What is done is referred to as floating walls, walls framed so that they hang from the wood-framed main floor structure, and a "contraction gap" is maintained between the sub-bottom plate and the P.T. plate fixed to the floor slab.

If you are familiar with this, you know the drill. A space of about 3" is maintained between the on-slab plate and the wall plate above it, and to fix and align the two, 60d nails are run through a drilled clearance hole in the raised plate, and driven into the on-slab plate, this on 16" to 24" centers.

Enough nail shank is left above the raised plate so the floor can fall a little, and the 3" gap permits the floor to heave up that much.

The walls are sheetrocked to the bottoms of the raised plate, and the on-slab plate gets padded out 1/2". The tall base moldings are nailed ONLY to the on-slab parts.

So here is question. What does one do about the doors? It seems to me they are the weak link in the chain.
You leave the larger gap on the sides and the top and you use longer nails... as the trim goes, you nail the casing into the jamb only and not into wall. this way everything can be moved with the floor movement.
 

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Discussion Starter · #3 ·
Thanks.

So if our standard ROW for a 2/6 door is 2/8, leaving a nominal 1/4" clearance for fit, should this be opened up to 1/2" at the sides? Our do you go more?

And at the top, sounds as if we ought to go 2" or more clear. What do you do?
 

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Thanks.

So if our standard ROW for a 2/6 door is 2/8, leaving a nominal 1/4" clearance for fit, should this be opened up to 1/2" at the sides? Our do you go more?

And at the top, sounds as if we ought to go 2" or more clear. What do you do?
2" top and sides, because the movement will definitely exceed 1/2-1"
 

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Discussion Starter · #5 ·
Wow! Do I understand correctly that the opening clearance at sides should be 2" EACH SIDE?

That means I might be using AT LEAST 16d finish nails to fix doorframes to studs, and more likely 20d.

And the shimming between rough and doorframe, what about that? I have always placed shims at the hinge points, and at the latch. Furthermore, I have always used at least one long hinge screw at the top hinge to help fight sag.

This large-clearance long-nail thing with the casings fixed to doorframe only, seems to mean the door is just pinned there rather loosely, and has to swing from its hinges and latch to itself, all by itself, pretty much independent of its wall. All so that in the event of the floor doing a heave, it can move up with the floor, and not move its wall surround with it.

2" each side, right? What are you doing for shimming? 2" rigid foam chunks?
 

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Discussion Starter · #6 ·
OK, researched it some more, and arrived at a detail I will use.

Top margin is 2", sides are 1-1/2" so we can use 16d finish nails. The rigid foam blocking is cut to be a precise fit and provides a little solidity
behind the fastening points.

Moving the side margins up to 2" would require the use of 20d finish nails for the jamb-fixing, and the larger shank size of the 20d versus the 16d would mean nails would bend less readily when floor heave wants to push the door unit up in its opening.
 

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There you go.... :thumbsup:

You can also frame the opening on its own, separated from the wall, i.e king and jack stud with the cripple and a single plate as one section and leave the reveal for movement between the king stud and the wall and between lower and upper plate and install the door the typical way using shims, this method is more likely be preferred by architects.
 

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OK, researched it some more, and arrived at a detail I will use.

Top margin is 2", sides are 1-1/2" so we can use 16d finish nails. The rigid foam blocking is cut to be a precise fit and provides a little solidity
behind the fastening points.

Moving the side margins up to 2" would require the use of 20d finish nails for the jamb-fixing, and the larger shank size of the 20d versus the 16d would mean nails would bend less readily when floor heave wants to push the door unit up in its opening.

I don't see how the nails in the side jambs are going to allow the wall to move up and down.
A slot behind the stop and then common nail with washer would allow up and down movement.
This is sort of like log building except with log it is primarily going one way...down.
 

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After more research, why would anyone bother to finish a basement if the slab is built on expansive soil?
With differential heaving, the floor can move 2-4". Not to mention foundation wall pressures.

IMO, you'd have bigger problems than just framing the walls.
 

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Discussion Starter · #14 ·
In the better houses built along the front range where these soil conditions exist, basements have one of the various types of structural floors, not simple slabs on grade. Thee are above the subsoil, hung on the walls, with any intermediate bearings pier- or caisson-supported, like the walls.

This floating wall stuff is done in the lesser, usually tract-built housing.
 

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Fort Collins Used to require Floating walls for Basement Finishes.
Now they allow the contractor to decide if they want to do floating walls or not. Theory being that if the slab was going to heave, It would have heaved by now. There are some neigborhoods here that are notorious for "hot soils", but for the most part, Fort Collins isn't too bad. If we are finishing a basement in a 40 year old home, and the slab hasn't moved, we might just frame it tight. But in a newer home, we'll float the walls. The real trick is supporting the stairs.

Back in the 90's, there were some national tract builders that came into the Denver area, and learned some hard lessons about expansive soils.
 
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