Verandah beam cantilever to support rafters

[Captain Dan]

Hi all,

I'm working on building a verandah attached to the front of the house as in the plan below. I think I'm OK with everything except the cantilever length (in blue) and beam size allowances where the beams meet at right angles where the steps are. I think the cantilever length needs to be about 1900-2000mm. There is no post here to support the rafters so I realise the beam has to be capable of supporting the weight. Rafters at this stage are 120x50 at 450mm centres following one on the back of the house - this verandah had a 120x50mm cypress beam as well on 90x90 cypress posts but there was no cantilever issues to worry about. Posts will be 115x115mm or thereabouts and spaced roughly 1800-1900mm.

Pitching beams used for load bearing walls at the rear of the house (like a sunroom area) was much bigger at 240x65 GL8 laminated/primed pine on 90x90mm posts. Should I look at something this size?

Cheers,
Dan

89385

[stevoh741]

I dont think the timber span tables will allow a 2m cantillever. Check span tables in the library section of this site

[Captain Dan]

I don't know why I put that size as the cantilever. It's only about 1000-1200 at most. I'll check through the span tables as suggested - didn't see what i was looking for last time but maybe I just missed it.

Cheers,
Dan

[r3nov8or]

Depending on the member being spec'd, the AS uses percentages of allowable span and/or actual backspan of the member to define the maximum cantilever.

In any case a 2m cantilever will require a pretty massive beam; possibly one so big that it is not available in the timber classifications covered in AS1684. I think you need to consider something engineered, either in steel or in some engineered timber may have better/longer cantilever capabilities for this situation.

[r3nov8or]

I don't know why I put that size as the cantilever. It's only about 1000-1200 at most. I'll check through the span tables as suggested - didn't see what i was looking for last time but maybe I just missed it.

Cheers,
Dan

1.2m is still a fair way. You need to look in the Notes section under the respective table. e.g. "Overhangs shall not exceed 25% of the actual backspan" or "Maximum allowable cantilever is 25% of the allowable span but not more than 33% of the actual backspan." Again, depends on the member being spec'd

[baileyboy]

wouldn't it be cheaper and easier to put a post at that corner?

[shauck]

Would there be any problem with running one of the beams (big enough for the greater span) through to the house wall, and attaching the perpindicular beam to it where they intersect? See pic.


89413

[Bloss]

:wts:

[intertd6]

the common way to solve this problem is to have a gable roof over the steps & verandah with valleys either side & scotch valleys on the main roof.
regards inter

[cherub65]

if that's the way you want to go maybe a 230 x 65mm beam 17c would do the trick . Run it by a structural engineer.