Joist/bearer sizes when using hangers rather then joists on bearers

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Fordtimbers span tables aren't any good as tehy are ... for in-house, not deck.

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Why would the timber sizes be any different for a deck? When planning a timber framed deck, I would use the "bearers not supporting roof loads" and "floor joists not supporting roof loads" tables from the framing manual. A deck is just a floor with no walls, isn't it?

True, the stress grades listed in the Ford Timbers tables are higher than you would typically use on a deck but I don't see any reason that span tables for a non-load bearing floor in a house would be any different to those for a deck.

Hi Silent and All,

These days deck timbers are calculated on a live load of 300 kpa or 300 kgs per mtr sq - interior domestic floors are calculated at 150 kpa or 150 kgs per sq mtr.

I'm not exactly sure of the reasoning behind it.

Doog

The std for decking is usually the 3.0 live load for balconys isnt it - so the timber sizes are sometimes a bit bigger. the reason is to do with the the loads experienced on decking - eg 20 people on a 6 sq metre balcony, the drop if they fall (3 m hurts - even when drunk), plus the lack of load spread of decking timbers (flooring is either sheet or tongue and grooved so acts as one large sheet, whereas decking only has strength as singular lengths of timber)

Every summer it seems a bunch of people are standing on a deck that colapses with ensuing carnage - the AS1684 seems to be trying to fix it.

OK that's something I wasn't aware of. I just work off the NSW Framing Manual - granted it's a bit long in the tooth. It doesn't have a section for balconies.

The other problem with the Fordtimbers tables is the F rating F14 and F17 refer to hardwood. You can't get F14 treated AFAIK. (Even though an F rating in treated and hardwood have the same strength.)

The timber sizes are also hardwood sizes, not treated sizes. i.e 38 + 50 thick as apposed to 35 + 45.

Unfortunatley you can't "predict" the equivlanet F5 / F7 sizing. You can go the other way though, i.e. using a lower F span table and timber of a higher F rating.

I am assuming of course that Treated pine will be used, as in my experience hardwood is useless for decking framing. Both houses I have owned were built in the 80's with cantilevered hardwood decks, which were deathtraps. They now have treated pine decks.

A span table for treated joists is here. Unfortunately they don't publish bearer tables.

http://www.timber.net.au/documents/d...of_F7_Pine.pdf

Hey guys AS 1170.1 loading code... specifies for residential flooring and decks under 1m be designed for 1.5 kPa load. Decks over 1m are designed for 2.0 kPa.

so the maths:

1 kPa = 1000 Pa
= 1000 N/m2
= 100 kg/m2 (assuming g = 10)

AS 1684 has tables for decks over 1m high for F and MGP grading. These are in the supplements.

Cheers
Pulse