Timber outbuilding framing

[angelboy]

I'm building a glorified shed/outbuilding and wondered if the timber posts are OK to be 2 x 4s - doubled up at the corners and round the door frame.

It's single skinned brick dwarf wall up to 825mm then about 1200mm uprights in timber to the roof plate. The roof will be clay rosemarys so I wanted to know if 2 x 4's were sufficient.


Would you go for 4 x 4 timber posts on the corners instead?

 

[angelboy]

Anyone?

I'd seen another post where the architect had specified 120mm x 50mm for a residential timber framed extension. Do I need that extra inch or is 100 cls c16 framing timber ok?

 

[big-all]

it doesn't help that you don't mention centers or spans and wall or roof construction

i personally dont know the answer but others might with enough information

 

[angelboy]

Aren't the centers somewhat dependent to the timber sizes anyway? Like joists, the span is relevant to the width and depth of the joist to which the centers can be determined (under normal loading) or vice versa, so a timber upright - I would have assumed - would work under similar principles.

I assumed that someone might say that 4 x 2 posts would take the roof (general weights for a rosemary tiled roof - not from facts from experience) based on 450 centers - as I'd already given the length of the individual timber.

Where does the span come into it? I know what size roofplate and headers I need but why is the span important.

I do have some calcs on how to work out timber upright sizes but I'm totally lost with them - they might as well be in Chinese!!!

If someone knows how to decipher them then I can post them if it helps.

 

[big-all]

we need to know how wide the roof is to work out the weight

but i would personally aim for 400 or 600 centers for the walls to fit in with sheet material

and dependent on the span[width]off the building and roof construction will decide the loading on any individual timber

 

[angelboy]

Oh, OK.

The building is roughly 4m x 3m.

30 degree roof pitch.

Roof design 32mm ridge board, 100 x 50 rafters in pairs at 400c on a 100 x 50 roofplate. As it's below 3600mm in span there's no need for any collars (so Roy Chudley says).

Chudley talks about dead shoring formulas for struts, slenderness ratios, effective length under compression with both end fixed etc. etc. etc......?!?!?

 

[catlad]

Rough calculations the roof comes in at a metric ton. I think if you are going to use 4x2 then you need to build it well. I would be using 6x2.

 

[angelboy]

Ok.

So I'd build them off the sole plate which would then be 150 x 50. Does it matter with an overhang on the 100mm wall below?

 

[angelboy]

Bit more complicated but I suppose I could do a brick corbel to take the extra 50mm