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403.1.4 minimum depth

rktect 1

rktect 1

Gold Member
Joined
Oct 20, 2009
Messages
1,112
Location
Illinois
Well, today we had a person who was caught with a brand new deck built in his backyard. About 15'x20'. No columns, beams or concrete piers. In fact he built a rectangle 15'x20' with 2x8's and infilled the area with 2x8 joists at 16 inches on center. It is floating (is supported entirely) over/by the existing concrete patio. So I got to thinking that I had read about free standing decks somwhere and lo and behold I came across section 403.1.4 which we amended to read 42 inches below the undisturbed ground for foundations. This led me to 403.1.4.1 frost protection and on the very next page to the exceptions #3. "Decks not supported by a dwelling need not be provided with footings that extend below the frost line." And the funny thing about these decks, in this particular townhouse subdivision, is that their association rules specifically state that no deck is allowed to be directly attached to the dwelling which was written back in (guesstimate) 1980. It's funny because the deck serves as his required landing outside his patio door and by todays code, that landing shall be attached to the dwelling per 311.2.1

So can the guy keep his free standing wood deck or have him remove it?
 
Don't get hung up with Section 311.2.1 requiring what you have to be attatched to the dwelling. It is not raised off the ground, supported by the dwelling unit or post or piers or columns. If the deck heaves will it block the patio exit door ( assuming the door swings out) if not let it stay, charge him the permit fees and move on. If the door may be blocked due to frost heave discuss your concerns with the owner. If he has been there any length of time he knows if the patio has heaved in the past. Permit it with a condition that you reserve the right to monitor it thru the winter and if the problem arises he will have to correct it.
 
It would be easier if I were not only the plans examiner but the inspector. As it is I have gone over these sections with the inspectors and we have come to the same conslusions as stated above. We will accept the permit for the deck and inspect it. But I don't really do something I can't get my inspecotrs on board for. If they said no way, it's no way. I have to prove my case basically.
 
* * *

rktect1,

While your scenario may not meet the actual wording and application

of the code, I too agree with the others on here... don't lose a lot of

sleep over this, ...or create a new ulcer or something. Permit it

and move on!

It has been, and continues to be, my experience that If the deck

has been there for any length of time, usually [ not always ], it is

almost impossible to have them remove it.

FWIW, if possible... learn to pick your battles, and not every battle

[ issue ] needs to be fought.

* * *
 
RKTect,

I'm not so sure that this should be ignored. The next time your inspectors drive by that home; there will most likely be a roof above that floor.

Concrete slab-on-ground (3 1/2" thick); R506; is not designed to carry a permenent structural load (like a deck); and does not require a footing.

The flooring of the deck should be supported by footings not less than 12" in depth per R403.1 (regardless of the frost line); and 12" wide per table R403.1.

And if piers are used for the footing; the footings should be spaced to accomodate the load of the deck.

When a homebuilder built a new home with a concrete patio (without footing) ; we made a note on our inspection forms (for the permenant record) to avoid problems of patio covers being built without proper support; and sure enough within a year or two; the owners were buiding wood frame roofs over the patios.

I believe your inspectors are well aware of this; and, are not in favor of allowing the "deck" to be placed on the patio (slab).

R301.1 requires all loads to be safely supported thought the "load-resisting elements to the foundation". The slab-on-ground is not designed to carry structural loads (the deck) in accordance with R301.

Hope this helps,

Uncle Bob
 
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I agree with UB's scenario but there are many times when we are pretty sure what will happen later and want to base our requirements on that experience, but I would caution against that approach, just make a note to the file and also try to speak to homeowners in advance of the construction (haha), and have them choose to plan for a future scenario.
 
Yankee,

I probably shouldn't have added my scenario. A deck is a very heavy dead load; and I believe it must be supported by more than a 3 1/2" slab.

Uncle Bob
 
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Uncle Bob said:
Yankee,I probably shouldn't have added my scenario. A deck is a very heavy dead load; and I believe it must be supported by more than a 3 1/2" slab.

Uncle Bob
Click to expand...
No, I would agree that the slab maybe "should have been" a compliant slab-on-grade with turned down footings depending on the code year it was built. Even given that, the slab is existing and I don't know that I would have required any additional concrete work for the deck joists to be built on the slab.
 
if it breaks the existing slab.. so?

if it's typical patio slab construction, it's not attached to the structure, and neither is the deck.. it sinks into the soil.

IF they build something on it, there may be a problem. I'd ask the question... if you want to invest that much time.
 
This is where common sense enforcement of the code comes in. It's essentially resting on the ground, it's not going to pose a hazard to life safety, is it? A lot of what we should be looking for is life safety, or safety to the building. Does this "structure" pose a danger as it's built? We cannot required things based on what someone "may" do down the road. We can note what we observe, put it in the file and call it a day. If we all want to cover our bases, agree to issue a permit for the structure contingent on the owner submitting an affidavit that no additional structure will be built on top of this deck. When/if they move towards building something else, you'll have an affidavit to hang your hat on when you refuse to issue permits without them providing the proper footings.
 
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