Can I use plywood for a "sill plate"!?

Paul Kirkland · 09-19-2009, 07:02 AM

I'm a first-time homeowner with lofty goals and I'm adding on 200 sq ft to my kitchen.

Foundation is poured (8" stem wall) and mudsill is on (2x10 PT ripped to 8"). Due to my grade I'm having to install floor joists inside the foundation with HU210TF joist hangers on one side and a ledger board on the other.

I borrowed a laser level and my foundation appears to be 1" too short to match up the height of the floor inside and, when installed, out... I can't just add another 2x sill on top of the PT mudsill because then I'd be 1/2" too high for the T&G subfloor.

Here's my question! Can I rip some thick plywood and nail to the top of the mudsill, then nail my top flange joist hangers into the plywood? Will that pass inspection?

Thanks so much for any quick replies!!

(Picture is from before I installed the mudsill)

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**Scott Patterson** · 09-19-2009, 08:09 AM

Originally Posted by Paul Kirkland

I'm a first-time homeowner with lofty goals and I'm adding on 200 sq ft to my kitchen.

Foundation is poured (8" stem wall) and mudsill is on (2x10 PT ripped to 8"). Due to my grade I'm having to install floor joists inside the foundation with HU210TF joist hangers on one side and a ledger board on the other.

I borrowed a laser level and my foundation appears to be 1" too short to match up the height of the floor inside and, when installed, out... I can't just add another 2x sill on top of the PT mudsill because then I'd be 1/2" too high for the T&G subfloor.

Here's my question! Can I rip some thick plywood and nail to the top of the mudsill, then nail my top flange joist hangers into the plywood? Will that pass inspection?

Thanks so much for any quick replies!!

(Picture is from before I installed the mudsill)

I have never seen it done. Most of the time metal shims are used to level the joist, but that won't work with the hangers. The hangers will be only as strong as to what they are attached.

Paul Kirkland · 09-19-2009, 08:16 AM

True. The only other things I can think of would be:

1. Try to get a 2x through my table saw to make it an inch thick.
2. Add an inch of plywood on top of my subfloor after it's installed (much more expensive).

Which would you pick? Any other suggestions? Thanks!

**Scott Patterson** · 09-19-2009, 08:29 AM

Originally Posted by Paul Kirkland

True. The only other things I can think of would be:

1. Try to get a 2x through my table saw to make it an inch thick.
2. Add an inch of plywood on top of my subfloor after it's installed (much more expensive).

Which would you pick? Any other suggestions? Thanks!

I would go with the additional subfloor. This will provide you with a stiffer floor that you can then work off. Looking at the size of the addition it looks like 4-6 sheets of plywood or OSB would be all that is needed. Don't think less expensive think about quality.

**Gunnar Alquist** · 09-19-2009, 08:52 AM

I can't see why a layer of plywood would be a problem. The exterior walls of 2 story houses will bear on plywood.

I only see 2 vent openings in the foundation stemwall. Seems a bit light to me.

**Jerry Peck** · 09-19-2009, 09:33 AM

I would install the floor joists on a ledge board all the way around, that way you can set the tops of the floor joists EXACTLY to the height you want, without even being concerned about the height of the stem wall.

Then, when building the frame wall, simply build the frame wall with two bottom plates if needed.

Not only is that the easiest and cheapest way to do what you need, it is also a very good way to do it.

Or you could use something like the Simpson HU/HUC/HSUR/L hangers.

Paul Kirkland · 09-19-2009, 10:02 AM

Scott, Gunmar, and Jerry thanks so much for the advice! I'll get out there and consider my options. Will let you know what comes out of it.

So much appreciated!

Gunmar, plans call for 2 vents so hopefully I'll be good there.

**Jerry Peck** · 09-19-2009, 10:09 AM

Originally Posted by Paul Kirkland

Gunmar, plans call for 2 vents so hopefully I'll be good there.

Paul,

I don't see an access into that crawlspace from the outside, is there one from the main structure?

Believe me, you will (someday) want an access into the crawl space.

Here is something else to consider: If the inside of the foundation area is not going to be filled with soil to at least the level of the exterior grade, you WILL be having moisture problems in that crawlspace at some point in time. And, if that is to be filled to the exterior grade, then your floor joists do not look like they will be high enough above grade.

Just some things I notice which should be considered carefully.

Paul Kirkland · 09-19-2009, 10:19 AM

New picture uploaded. I did cut into the foundation after that previous picture. I just put in the header but haven't tied it in yet. I won't be filling in up to grade. Were you saying I'd have moisture problems because I didn't have the cutout yet or is there another reason?

**Jerry Peck** · 09-19-2009, 11:31 AM

Originally Posted by Paul Kirkland

I won't be filling in up to grade. Were you saying I'd have moisture problems because I didn't have the cutout yet or is there another reason?

Because, unless you are in a very dry area with very good run off and very good percolation, water runs downhill, and downhill is into that crawl space.

However, I was thinking your existing crawlspace was a basement, instead it is a crawlspace with a floor which is also below grade, so whatever problems you have, or have not, been having will (should anyway) continue.

Looks like a metal duct there with insulation falling off it? And blocking that access from the old crawlspace to the new crawlspace.

Paul Kirkland · 09-19-2009, 12:01 PM

I don't currently have any moisture problems in the crawlspace so hopefully that continues! The ducting will be moved with the project. One of these days...

**John Kogel** · 09-20-2009, 05:30 PM

I would suggest you install a tightly sealed 6 mil or heavier vapor barrier on the crawlspace floor before you lay the joists up. Hopefully we'll get some dry weather for that, because you want to close it in dry if possible. For a deluxe crawl, add a 2" skim coat of concrete.

I imagine you have installed drain pipe around the footings. That is probably mandatory. Tied in to the existing perimeter drain, that will carry moisture away.

We don't use plywood for what you suggested, fasteners into the edge, because the fasteners will separate the plys and not hold properly. Also, plywood needs to be kept dry, so it's nfg anywhere near ground level.

A.D. Miller · 09-21-2009, 04:21 AM

You may be using a direct-drive 15-amp DIY "table saw"? If so, it is understandable why you might not feel comfortable ripping 2X material in your saw. There is nothing wrong with using 3/4" CDX pressure-treated plywood. I might also suggest the use of either pressure-treated joists and ledgers. Failing that, consider spraying everthing before you install it with a borate solution such as Timbor or Boracare. This includes all cut ends.

Put the 6-mil polyethylene down like has been suggested, regardless if you have moisture issues in your existing crawl space. It's cheap, effective, and now is the time to do it.