Single Family Roof Deck 1

[mijowe]

I have a couple of town houses and duplexes that because of their size fall under IBC. They have roof decks/terraces and I would like to design these for a Live Load of 40psf. I am going to hang my hat on the on IBC Table 1607.1, Residential, One and Two Family Dwellings, All other areas = 40psf. Recognizing that the same table lists roof loads used for assembly purposes = 100psf.

Chapter 16 does not appear to define what "assembly purposes" means. Assembly is defined in Use/Occupancy and limits are established, less than 50 people being one exception. However, in that exception, they list the occupancy to be Group B which does not apply.

Is there a clear defensible position to use 40psf for roof decks in a single family home?

 

[jdgengineer]

We used to use 40 PSF (although more common was 60) for some residential decks using IBC Table 1907.1(5) - Balconies & Decks - "Same as occupancy served". Note that ASCE 7-10 contradicts this and requires 1.5 x occupancy not to exceed 100 PSF. However, IBC governs over ASCE 7. We only occasionally used the 40 PSF and preferred to use the more stringent requirement when there was a conflict.

However, at least in California, you are required to use 1.5 x occupancy served now due to an emergency regulation put into effect. This regulation was a reaction to the Berkeley Balcony collapse.

https://www.documents.dgs.ca.gov/bsc/Info-Bulletins/BSC_Bulletin_17-01_FINAL.pdf

 

[mijowe]

Interesting, ASCE 7-10 calls out 1.5XLL for Decks and Balconies, but under Roofs used for assembly purposes, it indicates Same as Occupancy served.

 

[JoelTXCive]

Deck collapses have been a hot spot of trouble for engineers and builders.

Aside from the long term weathering of the supports, the loading is often not uniform. People congregate at the perimeter of the deck (or rooftop).

I would go with 60-75psi and sleep easy at night.

 

[JoelTXCive]

Here is a FAQ screen clip on the American Wood Council's website.

I think that it can be inferred that the AWC position is that ASCE7 requires 100psf.

Our office designs large public decks for 100psf.

We design all other decks for 65-75psf.

 

[EdStainless]

40 years ago I worked for a structural engineer, he hated decks.
He designed them at 75 PSF, if the client complained he would suggest designing one that only projected 30".
He was also a stickler for building attachment details.

Joel, reality is even worse, it is everyone running to outside edge of the deck to see what is happening.....

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P.E. Metallurgy, Plymouth Tube

 

[racookpe1978]

"Decks' = NO snow or ice load, or at least, snow + ice live loads + wind loads << Nominal residential people deck loading?

 

[dik]

It's all in the details... it is very unlikely that failure of decks and balconies is related to overloading the members. It's very likely caused by bad connections.

Dik

 

[mijowe]

I agree that when there are deck collapse problems, it most likely has to do with detailing or poor construction, not because of a 40psf live load.

My condition is not hanging off the side of the building, it's on the roof in a single family home. I should be no more worried with the design live load if the party is on the roof deck or in the living room.