Are you planning on a vapor barrier in the construction of the slab?

You may can use SPF with sill seal foam under it.

 

Yes to vapor barrier, but city marked up original plan that had SPF shown and specifically called out treated lumber.

 

I don't think PT will shrink too much for your use. Even if it does, it will be, hopefully, equal across the floor.

 

Only place where that might matter is the transition and only if you're weaving the flooring without the transition strip. If all new flooring, wait a few months. If must now, plan a good looking transition. I would leave straight edge on the flooring and plan for wide wood strip that can be beveled.

 

Sounds good!
I will continue with the plan to have slab to be 7” lower to allow for typical 5.5” height of 2x6 + subfloor + hardwood.

Had planned on weaving in the addition hardwood into the existing stuff without a transition strip. Will have to give this a second thought.

In all likelihood, the material will get a few months to dry by the time the other rough framing gets done, electrical, ductwork, inspections, etc. In other words, should be able to give it ample time to dry/shrink enough so that it doesn’t cause problems at the transition area.

 

If you believe that the concrete will be perfectly level and flat at the correct height, then I would plan for 5 1/2" and install the 2x6 and difference would be at the transition line. The floor is one of the last things done so as soon as you have the roof on it will start drying.
Any question about the prefect level and flat then I would go deeper and plan on shimming to height.

 

This floor system is going to be awful to implement. These aren't sleepers, they're joists.

You'd have to have zero irregularities in the slab and zero in the 2x6 joists. Otherwise, you'll be scribing the joists into the slab and ripping and planing the underside crowns.

Consider actual 2x4 PT sleepers -on the flat- at 24" or 48" centers and KD joists. This'll help you deal with irregularities in the slab and the joists, give you better anchoring, and reduce shrinkage.

 

He is trying to match the existing floor, I would agree with you if it was all new floor.

 

I think trying to exactly or perfectly match new construction into any existing structure is going to end in disappointment. Construction grade lumber shrinks, concrete shrinks and settles, even if minutely.

 

One important thing that has not been mentioned is the moisture in the PT and the problems that it will cause with the solid 3/4" wood floor. Don't install anything on top of the PT joists until the moisture reading is within two percent of the original wood floor. I would suggest buying a good moisture meter and keeping track of the moisture in the concrete, PT and plywood before you start on the floor. I would also suggest running a dehumidifier after you have the room closed in. A good moisture meter may cost you $400, but it may save you thousands in the future. Here is a link to a good moisture meter that can be used for concrete and wood. There are other good brands, I happened to use this one in the past. If I remember correctly, the concrete should cure for at least 30 days before starting your wood floor, depending on your location. Please read as much as you can about moisture and a solid wood floor.

Ligno-VersaTec - Lignomat | VersaTec Meter (lignomatusa.com)

 

Lots of good suggestions, thanks - will have to think about all of the options a bit more.

Just finished spreading/compacting the 7 yards of crushed stone for the slab base.
After doing so, the height is right around 1.5" too short.
Was going to have a couple more yards brought in, but could also just have them pour the slab at this low height and then use PT 2x4s on the flat + 2x6 KD joists and height would work out.
Would prefer to have top of slab be above exterior grade for any future water intrusion though and the 1.5" would put it just below.

But if I bring in more stone and have them pour with a 7" height difference, that would leave the option to either:
1) go with 2x6 PT, let them dry, lots of planing/shimming to get flat and match existing floor
2) do PT 2x4s on the flats, then rip 2x6 KD lumber to whatever height needed (~ 4") to match existing floor.

 

If you are content that the top of slab will be above the water table, no need for more stone. Build a taller floor system.

Again, option 1 is something a professional builder wouldn’t do. Just not an option.

 

I'm not sure that's 100% true - the idea came from a professional builder.

Reached out to a professional builder during initial planning to get rough idea of scope and associated cost if we wanted to just hire it out.
When discussing the floor system and the need to run HVAC through them, their options were either, A) do a crawl space, or B) just do 2x6 or 2x8 on a slab to match existing floor height.

The reason they even brought up option B is because our existing house elevation is a lot lower than normal.
The top of the foundation wall is 2" below grade (ie. bottom 2" of house rim joist is below grade).
In other words, a slab basically at grade would only require a 2x6 floor system to match and allow for ducting.

I do agree that there will be a large amount of shimming/planing, but realistically as long as the transition is spot on and the rest is relatively flat, what are the other issues?

 

You can bring a horse to water…

I’ve dealt with all of these irregularities far too many times to think that a slab will be flat and agreeable. PT is all over the place. I also won’t build on a slab.

My hardest lessons have also been my best.

 

I do like your method with the PT 2x4 on the flats and then 2x6 KD joists ripped to needed width (~4" here).
This would be easier cutting/planing the KD joists, as well as containing any shrinkage to the PT 2x4 flats along it's width, which doesn't effect floor height.

What I'm failing to see is how it would be less work because you'd still have to shim at all slab irregularities for the sleepers and rip the joists to proper height anyway.


I am leaning towards this way though for the shrinkage advantages, with a few questions:

1. What's the fastening schedule look like?
   • Assuming the 2x4 PT get tapconned or ramset into the slab
   • Do the KD joists get fastened to the sleepers? Or do they just float on top?
     • If fastened, I'd think toenailing would be recipe to loosen over time and cause squeaks?
     • Would you just use a long screw through the top of the KD joist down into the sleepers?
       
2. What's the spacing/code requirements of the sleepers if the joists on top need to be 4" tall (ie. follow same as 2x4 schedule)?
   • These would essentially be floor joists and I'd assume they would have to follow the floor joist span tables.
   • However, all of the building code floor joist span tables only go down to 2x6.
   • Despite 24" oc for the sleepers and 16" oc for the joists being physically robust enough, does this mean there will be problems getting this approved at inspection since it doesn't appear in the tables?

 

I do like your method with the PT 2x4 on the flats and then 2x6 KD joists ripped to needed width (~4" here).
This would be easier cutting/planing the KD joists, as well as containing any shrinkage to the PT 2x4 flats along it's width, which doesn't effect floor height.

What I'm failing to see is how it would be less work because you'd still have to shim at all slab irregularities for the sleepers and rip the joists to proper height anyway.


I am leaning towards this way though for the shrinkage advantages, with a few questions:

1. What's the fastening schedule look like?
   • Assuming the 2x4 PT get tapconned or ramset into the slab
   • Do the KD joists get fastened to the sleepers? Or do they just float on top?
     • If fastened, I'd think toenailing would be recipe to loosen over time and cause squeaks?
     • Would you just use a long screw through the top of the KD joist down into the sleepers?
2. What's the spacing/code requirements of the sleepers if the joists on top need to be 4" tall (ie. follow same as 2x4 schedule)?
   • These would essentially be floor joists and I'd assume they would have to follow the floor joist span tables.
   • However, all of the building code floor joist span tables only go down to 2x6.
   • Despite 24" oc for the sleepers and 16" oc for the joists being physically robust enough, does this mean there will be problems getting this approved at inspection since it doesn't appear in the tables?

Rod beat me to it- only at the points where a joist crosses a sleeper versus the entire length of a joist. Easy to bring up with a shim or down with a notch in the sleeper. That could be a quick cross-grain pass with a power plane. Also, given the smaller surface area of the intersections, slab irregularities will be less pronounced. That’ll help too.

 

Doing it like rodeo suggested the kd 2x6s will not shrink like the pt would. gives you better control on the finished product

 

If it were me, I'd lay PT 2x4 sleepers flat at about 30" spacing, run the straightest 2x4 KD joists you can find perpendicular to the sleepers, and then shim between the sleepers and joists as needed with pairs of tapered wood shims.

 

With a basement house the outside of the concrete is water proofed and there is a perimeter drain below the level of the floor if you have no other choice.
View attachment 811438
You might have special boots made for the heat ducts, you might talk to a sheet metal shop and get some input.

That drain is definitely an option, but keeping this as a last resort!
I agree, there's definitely room for the straight ductwork, but might be tight for the transition fitting.
I don't see any reason a few custom boots couldn't be made though to overcome this problem if nothing in production fits.

With the lattes system you can leave a space for the duct by leaving a gap in the lower 2x4s
View attachment 811439
You could drill and screw the 2x4s down with Tapcon screws or much cheaper is pinning with nails.
Drill a 3/16" hole put in a couple pieces of tie wire or nylon trimmer string and a 3" HDG common nail.

Yes, sorry - was doing a quick model and didn't put that detail in, but keeping the sleepers out of the cavity gives 5.5" of height.

Got it on fastening the 2x4 sleepers down into the concrete!
What about the connection of the 2x4 joist down to the 2x4 PT sleeper & shim?

Subfloor adhesive and toe nail?
Or is there a better option?

 

I have always bought PT lumber and laid it out to dry over a couple of months. I buy extra so if a couple warp too much I have others to choose from. In full sun and racked so air circulates around the boards, they will dry in a matter of weeks.

 

I clamp mine in the drying rack for that couple of weeks, out of the sun, so they all stay fairly straight.