Structural glazing?

[Pickup]

Hi,

We're wanting to replace a lean-to porch with one which has a pitched roof.

We'd like the gable wall to be brick up to about 700mm above floor level then to be fully glazed (two windows following the roof line ) is it possible to specify some sort of "structural" window frame so that the ridge of the roof is supported through / by the window frame or would we have to support the ridge with a timber post between the two windows?

Thanks

 

[stevethejoiner]

A diagram would help but if I understand you correctly you will have a wall plate on each side and rafter going up each side to a ridge with glass gables.

If that is right the ridge loading depends on the pitch, the span and if there are any collars or ceiling joists from wall plate to wall plate.

If the rafters go up to a ridge and down the other side without tying in with collars or ceiling joists then you will require a good strong ridge well supported at the gables as it will be taking a lot of roof loading.

If the design has triangulation built in. Rafters tied with collars or ceiling joists the ridge will be not taking a roof loading so theoretically you could have open gables or triangular glass ends with NO centre timber post .

So your answer all depend on roof design, thus a drawing or scketch would by useful.

 

[Pickup]

Thanks Steve,

Had done a (very) rough sketch but couldn't upload it from my wife's computer (iPad thing) so here's an even rougher one I did tonight.

View media item 49448
No triangulation ie interior ceiling follows roof line (hence the shape of the gable windows.)

Thanks again

F

 

[freddiemercurystwin]

What are the side walls doing? Pretty much anything is possible if you throw enough money at it. Presumably you have something in the walls and if needs be at least you could get some columns in the corners.

You could just have a very slender tie behind the glazing maybe even just a tensioned cable tie. Like this:

http://www.s3i.co.uk/image/s3i/Tie-Bar.jpg

You may able to do it without the vertical.

Structural glazing (the proper structural glazing) is proper expensive like ££££/m2.

Trouble is any timber rafters won't offer much resistance to wanting to sink without a tie and will consequently always want push outwards at the eaves. This is why you need the ties.

I'd say if you did a steel rafter each side that had a good connection at the ridge, if it were designed properly that would be able to resist spreading and eliminate the need for a tie. Its only a porch after all so pretty small. You'd probably need a structural engineer to knock up some quick sizes and a good connection.

 

[freddiemercurystwin]

If you're after a contemporary look what about a flat roof instead?

eg

http://www.cdparchitects.com/img/projects/36/fs/porch1.jpg

Many homes won't take such a strong feature but just a thought.

 

[stevethejoiner]

Hi again.

Yes with what you have drawn you will have to support the ridge or the downward force will push the side walls/window frames out.

So if your not going to tie in the side walls do something like freddymercurystwin has suggested with a slim collar and use a centre post at the gable to support the ridge.
The connection with the ridge and gable centre post is important. If you used a 45 x 225 ridge you could slot it into a 95x95 centre post and bolt the two together. The other end of the ridge can be supported by a joist hanger or keyed into the brick face of the house.
If using glass at the side I would use a 95x 95 plate over the window frames. Building inspectors today prefer truss clips fitted on the plates to locate the rafters rather than birdsmouth joints. I would use 45 x 195 rafters and then the competed timber structure will support a tiled roof.

You dont indicate a pitch angle. A steep pitch say 45% will have less outward force on the sides than a shallower pitch. So keep the pitch nice and steep.