Lean to roof with 4.5m span

[shahgidog]

hi all,

i'm about to rebuild an old lean-to for my mother in brittany. the existing structure is 10mx4.5m.

after reading all i can find on the web, it seems that the maximum span for lean-to with hip (?) is 3.8m (this might explain the sagging roof at the mo!)

would like to retain existing size and was thinking of a pole-barn type thingy and was wondering if the following would be ok?

Untitled

• shahgidog
• 27 Jun 2009
• 1

sorry for the dodgy drawing but i hope you get the idea.

the roof will be some kind of corrugated metal/plastic/...
the posts will be fixed to plates fixed to concretes footings.

thanks for any help & advice on this one.

 

[noseall]

after reading all i can find on the web, it seems that the maximum span for lean-to with hip (?) is 3.8m (this might explain the sagging roof at the mo!)

Comment? Quoi?

Those timbers do look a little bit lean.

 

[shahgidog]

thanks noseall ,

how about 2x8s or 3x10s for joists and collar?
does the design seem ok apart from the leanness?

i'm british by the way, never built anything apart from the odd partition wall, my mum lives out here, but unfortunately i don't speak french so am trying to sort everything i need before attempting to buy anything!

cheers

 

[foxhole]

A friends kitchen has a 4metre span and building control insisted on 11"X 3" timber, strange size I know and was diffficult to source.

 

[HomeInspector]

hi all,

i'm about to rebuild an old lean-to for my mother in brittany. the existing structure is 10mx4.5m.

after reading all i can find on the web, it seems that the maximum span for lean-to with hip (?) is 3.8m (this might explain the sagging roof at the mo!)

would like to retain existing size and was thinking of a pole-barn type thingy and was wondering if the following would be ok?

Untitled

• shahgidog
• 27 Jun 2009
• 1

sorry for the dodgy drawing but i hope you get the idea.

the roof will be some kind of corrugated metal/plastic/...
the posts will be fixed to plates fixed to concretes footings.

thanks for any help & advice on this one.

Look up 'Trussed Rafter Roof Design' and 'Mono Trusses' which is what you have basically designed here. This will give you the type of structure you need.

 

[shahgidog]

Thanks for the comments, i'll investigate those threads and see what i find. maybe 11x3 makes more sense in metric?

have found a structure nearby which is of similar dimensions and built by the local authority so i guess it will be to building regs here, so i'll measure their timbers and go from there.

cheers,
gwil

 

[tedpowell]

the whole thing is grossly undersized. under the building regulations the ceiling joists would have to be 195x47mm, the rafters are off the scale completely.
i think you will have to make up a truss type roof remembering that when joining timbers a nail will not be sufficient more likely a 14mm bolt with a double edged bulldog connector between the timbers through which the bolt will run.
you are taking on a lot so dont be afraid of bolting and using flitch beams which are normally, instead of using a 6x2" section of timber, use two no 6x1" with a flat section of steel between bolted together as described above, i have just installed a purlin of 2no 225x25mm joists with 12mm ply between to stop deflection the whole lot bolted together at 300mm centres as described above, the purlin was a 3.8 metre span and carrying plain clay tiles the resultant deflection was nil.
so improvise be careful or dust off the insurance policies.