Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: CBC 2304.11.2.2 - 8-inch Clearance from exposed earth to wood framing mem...

[Subject Prev][Subject Next][Thread Prev][Thread Next]
This Section Reads:
2304.11.2.2 Wood supported by exterior foundation
walls. Wood framing members, including wood sheathing,
that rest on exterior foundation walls and are less
than 8 inches (203 mm) from exposed earth shall be of
naturally durable or preservative-treated wood.
This doesn't mean the top of slab or foundation wall has to be 8". With a 2" treated plate and sheathing that is treated, the top of slab or footing stem can still be 6" above ground line. Of course most sole plates are 1.1/2" and we don't normally use treated plywood sheathing.
Stephen Macie, P.E.
In a message dated 2/6/2008 6:53:18 P.M. Pacific Standard Time, dennis.wish(--nospam--at) writes:

For some reason I seem to get bounced off the list a few times a year and for the last several months have not had time to subscribe once again to start receiving e-mail.


The California Building Code section 2304.11.2.2 requires that the top of the finished slab on grade and / or the top of the foundation wall where a mudsill is connected is to be a minimum of 8-inches above finished grade. Historically, this was changed from 6-inch clearance to 8-inches. I’ve not real problem with the code on this as in our area termite damage is the primary rationale behind this section of the code. However, I had a small remodel come in today that only required an engineer to design the non-compliant portion which in this case was the roof beams that cannot be done by conventional or prescriptive codes. I agreed to help him by addressing only the non-compliant section requiring engineering as the rest conforms with prescriptive methods.


One of his other corrections had to do with the height of the foundation wall of a new garage he is adding. It must be two inches higher than the adjacent 6-inch clearance for top of slab/foundation wall and finished grade. The code goes on to say that “Alternately, wood shall be of naturally durable or preservative-treated wood.”


Even if he chooses to use a 3x mudsill, the additional clearance will barely be adequate to provide nailing clearance for the sheathing at the boundary of the panel against the sole plate. One alternative is re-grade the property which is a major project for this client. The second choice since this is a floating sloped slab in the garage is that only the ends of the foundation walls bearing the stud wall framing will need to be raised the additional 2-inches.


Does anyone know if we can rip a 4x pressure treated piece of lumber to secure against the exposed existing wood framing to create a separation between the extended new 2-inches of concrete from coming in contact with the non-pressure treated lumber and then lay the new garage wall PT mudsill over the ripped block to start the garage wall framing?


The second option is to use Timberstrand or PSL lumber to frame the walls and a structural sheathing rated to be “durable” (whatever this means) or preservative treated? Does anyone know if Trus-Joist Timberstrand or PSL lumber used for wall framing will satisfy this requirement as durable or preservative-treated wood? If it does, will OSB satisfy the same requirement for structural sheathing or is there a recommendation of an APA rated panels that will comply as “durable and/or preservative-treated” lumber?


New construction is not an issue, but satisfying an addition to an existing structure poses some new challenges that I have not considered before.