Thread: Pressure treated sill plates

Since about the late 1980's I have been under the assumption that sill plates should be pressure treated wood (or decay resistant). Virtually everything I have seen constructed since that time has been. I was looking at a recently constructed addition the other day. The sill plates were not pressure treated. One part of the foundation is more than 18 inches above grade level. In looking at the IRC, it appears that this sill would not need to be pressure treated. Am I missing something in the code, or have I just assumed this all these years?

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Originally Posted by Mark Reinmiller

Am I missing something in the code, ...

Yes.

(bold and underlining are mine)
From the 2012 IRC (but it has been this way for a very long time)
- R317.1 Location required.

- - Protection of wood and wood based products from decay shall be provided in the following locations by the use of naturally durable wood or wood that is preservative-treated in accordance with AWPA U1 for the species, product, preservative and end use. Preservatives shall be listed in Section 4 of AWPA U1.
- - - 1. Wood joists or the bottom of a wood structural floor when closer than 18 inches (457 mm) or wood girders when closer than 12 inches (305 mm) to the exposed ground in crawl spaces or unexcavated area located within the periphery of the building foundation.
- - - 2. All wood framing members that rest on concrete or masonry exterior foundation walls and are less than 8 inches (203 mm) from the exposed ground.
- - - 3. Sills and sleepers on a concrete or masonry slab that is in direct contact with the ground unless separated from such slab by an impervious moisture barrier.
- - - 4. The ends of wood girders entering exterior masonry or concrete walls having clearances of less than 1/2 inch (12.7 mm) on tops, sides and ends.
- - - 5. Wood siding, sheathing and wall framing on the exterior of a building having a clearance of less than 6 inches (152 mm) from the ground or less than 2 inches (51 mm) measured vertically from concrete steps, porch slabs, patio slabs, and similar horizontal surfaces exposed to the weather.
- - - 6. Wood structural members supporting moisture-permeable floors or roofs that are exposed to the weather, such as concrete or masonry slabs, unless separated from such floors or roofs by an impervious moisture barrier.
- - - 7. Wood furring strips or other wood framing members attached directly to the interior of exterior masonry walls or concrete walls below grade except where an approved vapor retarder is applied between the wall and the furring strips or framing members.

Item 3 does not have a height associated with it.

Jerry, Thanks, I saw that, but I am in the land of basements (and some crawl spaces). So the sills are sitting on top of foundation walls. As I read this if the sill is more than 8" above grade (or 18" in a crawl space with a dirt floor), then it seems that PT wood is not required.

Every once in awhile when I go back and reread a code citation it is not worded the way I think it is. I must be getting old.

Originally Posted by Mark Reinmiller

Jerry, Thanks, I saw that, but I am in the land of basements (and some crawl spaces). So the sills are sitting on top of foundation walls. As I read this if the sill is more than 8" above grade (or 18" in a crawl space with a dirt floor), then it seems that PT wood is not required.

Mark,

I am missing where you are getting that for with regard to sills.

Every once in awhile when I go back and reread a code citation it is not worded the way I think it is. I must be getting old.

Good ... glad to know that I'm not the only one that happens to!

This one,

2. All wood framing members that rest on concrete or masonry exterior foundation walls and are less than 8 inches (203 mm) from the exposed ground.

Not this one,

3. Sills and sleepers on a concrete or masonry slab that is in direct contact with the ground unless separated from such slab by an impervious moisture barrier.

Jeff, I was aware of that one, but I forgot that it only applied when the sill plates are less than 8" from the ground. I guess because around here all builders switched to PT sills in about the late 1980's regardless of the distance above grade. It has become so standard I did not think non-PT sills were ever permitted.

Originally Posted by Mark Reinmiller

Jeff, I was aware of that one, but I forgot that it only applied when the sill plates are less than 8" from the ground. I guess because around here all builders switched to PT sills in about the late 1980's regardless of the distance above grade. It has become so standard I did not think non-PT sills were ever permitted.

We started using them in the 80's as you stated. Do not remember exactly when. Before that I used Douglas Fir sill plates on a layer of insulation, (sill sealer). Most of ours in Nebraska and Minnesota were well above the 8" requirement. In Colorado back then anything goes, as only Denver had a code.

#2 is the one that applies. Good practice is to use a sill sealer and or felt paper. In termite country a metal shield should be installed.

Originally Posted by JeffGHooper

This one,

2. All wood framing members that rest on concrete or masonry exterior foundation walls and are less than 8 inches (203 mm) from the exposed ground.

Not this one,

3. Sills and sleepers on a concrete or masonry slab that is in direct contact with the ground unless separated from such slab by an impervious moisture barrier.

Yep ... I just got through eating and realized that the key word in 3 was "slab", only to come back here to correct myself and find that I have already been corrected.