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Forum / Residential Code Discussions /Deck Footings
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Aaron Yuma
(7/22/2008 5:07:51 PM)
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Deck Footings

We all know footings are to extend below the frost line. However, we haven't been requiring decks which are low to the ground and not supporting a roof to do so. We have allowed the precast piers to be placed into native material but not excavated below frost line. Curious what other jurisdiction have been doing. Thanks. Aaron
Dale Bohannan
(7/22/2008 6:10:01 PM)
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RE: Deck Footings

Aaron,
Up until the adoption of the new 2008 Oregon Residential Specialty Code, we did just as you indicated. However, it appears that Section 403.1.5.1, exception #3 of the new code, exempts decks that are not supported by a dwelling from the frost depth requirement. Let me know what you think! Dale B.
Robert Rice
(moderator)
(7/23/2008 8:04:40 AM)
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RE: Deck Footings

We have run across this before. We hear all the time that, "We've been doing it like that for years".

R403.1.5 is the charging statement regarding depth. It states that, "All exterior footings shall be placed at least 12 inches below the finished grade on undisturbed ground surface." (Period)

Then the second statement says, "Where applicable, the depth of footings shall also conform to R403.1.5.1 and R403.1.5.2

R403.1.5.1 covers frost protection and gives four options the first of which is to be below the frost depth in Table R301.2(1). There are also some exceptions listed.

However, here's the key point to remember. This section is talking about "Frost depth". R403.1.5 already established that, regardless of frost depth, all exterior footings shall be a min. of 12" below grade.

This can be confusing in our region where the frost depth may be 12". Picture an area like Michigan where the frost depth may be 48" or more. In that case, the exceptions in R403.1.5.1 for freestanding structures say that you only have to go the 12" per R403.1.5.

Bottome line: All exterior footings have to be at least 12" regardless of frost depth.

Robert
Dale Bohannan
(7/23/2008 8:39:47 PM)
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RE: Deck Footings

Robert, when you're right, you're right. The frost depth not withstanding, footing depth is 12" below grade. HOWEVER, would you apply this to a deck that is less than 30" that is exempt from permits?