beam size for carport

[JohnD]

I am making a lean-to carport, with a ledger against the house wall, and posts supporting a beam on the other side.

It will be 2400 wide, topped with 10mm twin-wall polyacarb, with rafters in 70mmx32mm at 600mm centres. I will probably use galvanised joist hangers as I am not good at joinery.

It is going to be 6metres long, and I have had difficulty finding timbers that length at modest price.

My local cheap timber yard has decking long enough, the timbers are 145x35 finished, and I am thinking of using one of them, or if necessary two, for the beam on the posts, as well as for the ledger. They are pressure-treated which I think is useful.

To allow room for car doors to open, I would like to have a span of 3metres (or preferably more) in the middle of the shelter, with two posts at each end 1200 intervals or therabouts.

Would this beam be adequate for a 3m unsupported span? I could if necessary put "gallows" braces from the posts to the beam at about 1m from the posts.

 

[foxhole]

You don't need a 6m timber if the widest gap is 3m?
You could make up a beam using a timber top and bottom of a deck board on edge in this style,
http://explodingcoder.com/images/house/DSCF1058.JPG
which gives good strength.

 

[JohnD]

the total length of the carport is 6m

the biggest gap between posts will be 3m

using a 1-piece beam will I am sure be stronger and more rigid than using shorter pieces together to make the 6m

Do you think the timber size I have found will be enough as it is? Bigger sizes will cost quite a bit more, and I would prefer not to construct an I-beam if it can be avoided.

 

[foxhole]

I would build a shallow box frame if using shorter timber, stronger than a single timber span and stop any yawing on the frame.

 

[JohnD]

do you think the timber I have found will do the job?

 

[foxhole]

You didn't mention frame timber details, only roof support and posts?
Treated 3X2 would be ideal.

 

[JohnD]

I think I will use the decking boards for the perimeter, as they will look better, and 2400 rafters in 70mmx32mm at 600mm centres.

The roofing sheets are very light, and will be 2400 long

 

[foxhole]

If you roof sheet is 2400 then bay will be less taking into account the angle.?

 

[JohnD]

what's the bay?

the rafters will be directly under the roofing sheet, with the joining strips screwed to it. The sheet will rest on them. They will be almost flat, except for the fall to shed rain towards the gutter.

The roof will be this sort of thing http://www.nick-gray.co.uk/Carport-Canopy/Timber-Supported-Carport/2-5m-Projection with the supporting wooden posts and frame made-up to suit the gap

 

[foxhole]

I see so 2.5m sheets that should be ok, but the sheet needs to overhang the timber in order to get a gutter on so will be a very shallow run off.
[Was referring to the car Bay/port.]

 

[JohnD]

I was thinking of a two-inch overhang of the sheets over the gutter, with the gutter brackets fixed to the timber. That sound OK?

How much fall is usual? I calculate the sheet size would give me 700mm subject to finished trim sizes, but I was thinking of only 150mm fall and trim the sheets to fit.

2400 is the finished size of the roof to avoid overhanging my neighbour's wall, so the timbers will be inside that and a bit smaller.

 

[foxhole]

That's sound OK, I thought you were trying to achieve a 2.4 m width for the vehicle.