Wooden beam sizing not joists or rafters

[jamesBen80]

Good evening all, I've been trawling the internet for ages trying to solve this problem so i thought i'd try on here for some advise.
I need to size a beam for a garage/ barn roof. I'm just trying to work out if what i'm proposing is possible before going down the line of expensive planning applications ans structural engineers calculations but i can't find any info on wooden beam loads other than floor joists and rafters!

Basically i need to support a tiled roof (clay tiles 80kg/m2) which will be 8m long on a timber beam which will be supported at each end by a 9" brick wall and 1 post in the centre. My question is what size does the beam need to be in soft wood c16/c24or oak? The beam will support the conventional roof structure joists and rafter, tile batten felt and tiles.

I'm limited by overall height as we are in a conservation area, and i need a minimum height under the beam to get vehicles in and out. I'd prefer not to use steel as the rest of the structure is timber and it will be visible.

I remember doing some beam deflection calcs at uni but i can't remember much about them

 

[John D v2.0]

Don't quote me on this but I think deflection is generally taken care of by having a certain depth of beam, but for beams that support high loads you have to worry about strength a lot more. Trimmer joists are usually doubled to handle the extra load, but beams supporting many joists/rafts would have to be very hefty.
In our roof we have a couple of 3m brand holding the top end of half the tiled roof each, plus a bit of flat roof, and one ended up being about 2no 10x3 bolted together and the other was about 2no 9x2.5 bolted.

Have you considered filth beams, basically two timbers with a steel plate in the middle where you can't really see it? We'd have needed that for any longer span.

 

[Newboy]

Have you considered filth beams

Maybe a Fitch beam?

 

[tony1851]

Maybe a Fitch beam?

"flitched"

 

[tony1851]

It depends on the area of roof it is supporting; also the roof pitch, and the span of the beam itself.
For timber beams and trimmers, deflection rather than bending stress is usually the governing factor, though if it is a shed-type structure, you can
probably tolerate a greater deflection than for a beam with a plastered ceiling, for example.

 

[^woody^]

I'd consider a structural engineer rather than any old filthy beam

 

[Newboy]

filth beams

Fitch beam?

Two wrong typos don't make a right!

"flitched"

At last!

 

[John D v2.0]

Oops, auto correct strikes again, I prefer filth anyway!

 

[jamesBen80]

I hadn't thought of a composite beam "Flitch Beam" I've found this from a Newzeland website https://www.mii.com/artefact/download.asp?aid=61449
It recons a lintel comprising of two 2" x 12" timbers with an 8mm steel plate in the middle would support a heavy roof 5.5m wide with a clear span of the lintel 4m between supports. This sound reasonable as I have about 300mm to play with, so it is possible by the sounds of it?

 

[tony1851]

I would support a heavy roof

It depends what "heavy" means.

 

[jamesBen80]

I assume heavy means a heavy tiled roof but "assumptions are the mother of all muck ups" I'm going to try and work it out using my uni notes but I will get is checked by a structural engineer before I go ahead with the works.

 

[^woody^]

I will get is checked by a structural engineer before I go ahead with the works

Then you might as well just get him to design the thing in the first place. He is going to risk his PI more in checking your work.

 

[jamesBen80]

I was just looking for a sense check on here really. I didn't want to pay a structural engineer to work it all out and he sizes a massive beam that is impractical, or impossible to install in my situation. I hopped someone might have some rules of thumb or sums to be able to work it out but it looks like it's back to the drawing board.

 

[^woody^]

There are no rules of thumb.

And if this beam is at the eves of the roof, it will also need to be restained or designed to resist lateral movement, which wont be the case if it is placed elsewhere. So it's not just the case of "how deep is it", and you might not of done that calculation at uni, unless it was a structural engineering degree.