Need Details on Deck Load Capacity

by DJ
(Canada)

I have read several articles regarding how to design a deck to support a particular load. For example, a deck to support 50 psf, 10 dead and 40 live.

But I don't know how to convert this idea of live load to actual people or things.

For example, if I have a deck that should support 40 psf of live load, how many people can safely stand on the deck? How many 50 lb planters?

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Jun 07, 2008
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Deck Load Capacity Resources
by: Editor - Rich Bergman

This is one of the best questions - what is deck load capacity and how to figure it out. I have written a very detailed article on how to actually calculate the weight being imposed on any given footing on your deck and you should definitely read it first before following up on some other helpful links I am going to refer to you further on in this article.

This is a complex engineering question which has many variables so it is almost impossible to answer your question without a lot of other questions first.

But I have done a fair amount of research on loads for floors, decks and balconies and I can refer you to some great research tables, articles and online tools.

The American Wood Council has some great tutorials you must read. Start here:

Span Tables.

Now, back your first question. I would recommend you build for 60 psf which is for a balcony. It should be more than enough load capacity for the extras you are thinking about.

If you read the article I mentioned above, it will show you how to divide your deck up into tributary zones over each respective footing. From there you can add in extra weight you are expecting from your live load over a given tributary area. Then divide that weight by the square foot area of the footing.

You would do this for each tributary area to get an idea of what kind of loads are going to be imposed on each footing. And probably the best thing to do after that if you are finding the ultimate imposed loads are getting close to the soil's bearing capacity is to increase the area of a given footing or add more footings to spread out the weight of the structure. In effect what you are doing is bearing less weight on each footing.

But these links should also really help you.

I would also get the tables from the Canadian Wood Council.

So there you go - a great series of fairly authoritative sources on the finer engineering aspects of load capacity for wood structures and decks.

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