Sectional Double Garage Lintel

[mikkymo]

I have an 18' x 20' sectional double garage - post and panel type, just like post and panel fencing - which I'm putting a PVC coated steel pitched roof onto. At the minute, the layout with the posts and panels forms a 'U' shape like so:

o---o---o---o
|.................|
o................o
|.................|
o................o
|.................|
o................o

At the front of this my plan is to build two 2' wide brick columns (with rebar and concrete down the middle) which will leave a gap of 14' for a double roller door.

o---o---o---o
|.................|
o................o
|.................|
o................o
|.................|
o................o
[.].............[.]

The door is in the gable end of the building and the only thing above the door will be some OSB and PVC cladding, like so:

Can I get away with a wooden lintel to provide some bracing to the structure? The trusses will all sit on an 'L' shaped wooden wallplate which runs across the tops (4"x2") and down the sides (8"x2") of the posts. Can I just extend this over the top of the door?

 

[theprinceofdarkness]

I am unhappy with the foundations for your new pillars, in that you might be building them off some unknown garage base and each one will weight a half ton or so and balanced on two edges of said concrete and with the added weight of the lintel or beam over the opening and a bit more for the cladding and fixings. I could foresee the front edge of the base cracking and the pillars starting to lean forwards. One problem is that to bind the pillars into the existing structure the pillars must be bolted to the panels or the last corner post ( if left in place).
I would put in a diagonal strut across each new corner, say 4' back along the wall top to a point 4' out along the lintel from the corner.
Frank

 

[mikkymo]

Thanks for the reply!

I'm hoping the foundations for the pillars will be solid enough - the whole base is 6" concrete with A252 8mm fabric/mesh reinforcement sitting on 2" insulation, blinding and 6" well compacted hardcore. There will be a good 6" to the edge of the pad. The plan would be to bolt them to the last post as you say.

What sort of lintel should I be looking at? There's no brickwork up there to support and (unless I'm mistaken) the roof loads are being carried by the side walls of the garage?

If I made a wall plate from 4"x4" steel angle to tie (bolt) all the posts together and ran it across the top of the door, would that do?

 

[theprinceofdarkness]

I am not sure that that would be the best way to use that weight of steel. Its heavy and long, I suspect that it would twist and sag in it's middle. On my concrete garage I seem to remember that the truss carrying the timber planking over the 10' wide door was the same as the roof trusses, made from 1 1/4" X 1/8" steel angle. You need to extend the roof by 2' as well so just (!) make another truss matching your original ones.
Frank

 

[mikkymo]

Was yours a pent roof or a pitched?

Why do I need to extend the roof by 2'?

 

[theprinceofdarkness]

Well as I understand it, your present roof will end inches in front of the existing pillars (0) in your sketches. you are then going to put your 2' square pillars in front of this line ( [ ] in sketch). You must be moving the door forwards else you could just use the existing lintel. If not, what is going to cover the top of the pillars?
Frank

 

[mikkymo]

Ahhhh sorry - I should have pointed out that the sectional garage isn't up yet. The roof is a brand new wooden truss roof which are in my garage waiting to go up. The original garage which I disassembled had a pent roof which had leaked like crazy, so the steelwork which attaches to each wall is gone and the walls have been levelled/cut down to accept the new roof.

Going to go for an L shaped wooden wallplate (as described before) and lintel over the door for 3 reasons:

1. Once it's screwed together and bolted to the inside of the posts it will provide enough rigidity to support the roof and brace the walls.
2. I can screw the trusses directly into the wooden wallplate.
3. If it's good enough to 'pass code' in USA and Canada, then it'll be fine here.

Thanks for the help!