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IBC exterior deck

  • Thread starter Thread starter Sifu
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Sifu

Sifu

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2018 IBC. I have a design using the IBC for a residential deck. It is woefully short on details. Some are pretty easy to call using the IBC, others not so much. Why they chose to do this is a bit of a mystery, but it is their choice. One thing I don't see is any specific requirement for lateral load support specific to exterior decks. IBC 1604.9 says the lateral force resisting system must meet the code and ASCE-7. The engineer has not specified any specific lateral load resistance like we might see for an IRC deck. My assumption is that the engineer does not see the need for it. Is this a fair assumption?
 
There are a lot of points made in the IRC that are not in the IBC, I assume because the IRC is oriented to a non-engineered deck, where the IBC is less so. The plan I have is missing a lot of information. Lateral resistance is often overlooked even in the IRC which requires SOMETHING per 507.9.2. It is a somewhat controversial requirement IMO as it is seems to be performance based, but then calls attention to "options" which most seem to assume is a requirement. I usually accept anything reasonable when using an IRC prescriptive design, but if engineered and there is no method in the design I assume the engineer sees no need for it. Without any specific requirement I think the same approach must work for the IBC as well.
 
Sifu said:
There are a lot of points made in the IRC that are not in the IBC, I assume because the IRC is oriented to a non-engineered deck, where the IBC is less so. The plan I have is missing a lot of information. Lateral resistance is often overlooked even in the IRC which requires SOMETHING per 507.9.2. It is a somewhat controversial requirement IMO as it is seems to be performance based, but then calls attention to "options" which most seem to assume is a requirement. I usually accept anything reasonable when using an IRC prescriptive design, but if engineered and there is no method in the design I assume the engineer sees no need for it. Without any specific requirement I think the same approach must work for the IBC as well.
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I'm with you....The picture shown in the IRC is not required.....Whatever I will accept is what is required....
 
ASCE-7 will require that any structure be designed to resist both wind and seismic lateral loads. I have never liked that fact that the IBC now defers so much to ASCE-7, because most building departments don't have a copy of ASCE-7 and, even if they do, it's not written as a code, it's a design manual.

A deck designed under the IBC and ASCE-7 should allow for wind (which will be minimal on a deck for lateral, but could be considerable for uplift) and seismic. Just ask for the engineer's calculations.
 
Not often, but I used to live in a coastal community. The New England states don't see real hurricanes very often but, when we do, things get interesting.

Typically, in New England the rule-of-thumb for stick-framed residential is that wind load is greater than seismic, so if it's designed for the wind lods it will be good for seismic.

Decks can be the opposite, because they have a very low vertical exposure to wind, but enough mass that seismic may override wind for lateral loading. And we also want the lateral (sway) bracing in case a party all starts doing the Macarena and stomping around the deck in sync ...
 
Yankee Chronicler said:
ASCE-7 will require that any structure be designed to resist both wind and seismic lateral loads. I have never liked that fact that the IBC now defers so much to ASCE-7, because most building departments don't have a copy of ASCE-7 and, even if they do, it's not written as a code, it's a design manual.

A deck designed under the IBC and ASCE-7 should allow for wind (which will be minimal on a deck for lateral, but could be considerable for uplift) and seismic. Just ask for the engineer's calculations.
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You can't function as a building department in south Florida without having access to the ASCE-7.
 
steveray said:
How often is it considerable?.....Just because I have never seen one fail up....And for once I am not actually trying to be a SA, but maybe it just comes naturally....I don't think too much of uplift on decks
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Wouldn't that be noticeable if your deck failed due to uplift? We're talking about hurricanes and tornadoes which would likely be the only wind event strong enough to do anything.
 
Penguin87 said:
Wouldn't that be noticeable if your deck failed due to uplift? We're talking about hurricanes and tornadoes which would likely be the only wind event strong enough to do anything.
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IMHO all bets are off with tornadoes. We've had a few of those, but this isn't tornado alley. It's also not Florida, but we typically get at least one hurricane about every three years or so.
 
Yankee Chronicler said:
IMHO all bets are off with tornadoes. We've had a few of those, but this isn't tornado alley. It's also not Florida, but we typically get at least one hurricane about every three years or so.
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Decks are not occupiable space. Therefore, like most of residential construction being unpermitted, does it matter?

If a tree falls in a forest...
 
steveray said:
Hunh?
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I've read that it is estimated that well over half of all residential construction in the US essentially unpermitted. Either stuff built out in the sticks in a county that doesn't require one, to lots of minor improvements that go unpermitted.

Hell, I live in a major city and the building inspectors I talk to mentioned off the record that they have done unpermitted work on their own houses.
 
Yankee Chronicler said:
Then why do we assign occupant loads to them and require means of egress from them?
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Sorry, you're right - I meant habitable space, not occupiable. That obviously doesn't make sense! I just meant that people don't sleep/live on a deck.
You should most definitely design a deck to support the expected occupant load of the deck.
 
Penguin87 said:
I've read that it is estimated that well over half of all residential construction in the US essentially unpermitted. Either stuff built out in the sticks in a county that doesn't require one, to lots of minor improvements that go unpermitted.
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I always winder about the large industrial sites that have not had a permit for many years with a large Maintenace staff. Hard to believe they never needed one.
 
Mr. Inspector said:
I always winder about the large industrial sites that have not had a permit for many years with a large Maintenace staff. Hard to believe they never needed one.
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Those are fun when an inspector finally ends up on site and finds 3,000 unpermitted modifications to the building. We do a lot of those types of jobs.

"What do you mean I can't store 534 barrels of pure acetone in front of the only egress door on the back of the building? Next to 50 containers of compressed oxygen.
 
Penguin87 said:
Those are fun when an inspector finally ends up on site and finds 3,000 unpermitted modifications to the building. We do a lot of those types of jobs.

"What do you mean I can't store 534 barrels of pure acetone in front of the only egress door on the back of the building? Next to 50 containers of compressed oxygen.
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This sounds more like a fire code inspection. our state did not adopt the IFC so once they get a C. O. we have no right to go back.
Before I was an inspector I worked at a resort where I and others did work a few times a day that would have required a permit, but the owner did not want to get any. Now when i see construction, HVAC and electrical trucks going in and out of a large, gated complex where no one ever got a permit it makes me wonder.
 
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