rafter depth

[tony1851]

Won't the glazed units actually add to the stiffening of the roof?

That would be making the units structural, in which case he would have to make some rigid connection between the units and the rafters. How? Nails!?


@ Woody; yes, the rafters will deflect less with the glazing than they would if the roof was tiled. But that still does not mean that the (reduced) deflection would be permissible for the units.
Obviously these things will take a bit of bend, the question is - how much?

 

[noseall]

Won't the glazed units actually add to the stiffening of the roof?

That would be making the units structural, in which case he would have to make some rigid connection between the units and the rafters. How? Nails!?

Not nails but silicone mebbe.

Anyone who has tried to remove a silicone bedded unit will know what I'm on about, particularly one that has ben locked in with a good glazing bead.

 

[tony1851]

(scraping the barrel!?)

 

[catlad]

Does this job need to be timber there are alloy profiles that will look a lot slimmer.

 

[^woody^]

Won't the glazed units actually add to the stiffening of the roof?

Yes they will

If these rafters deflect more than a few mm, then either the units will shatter or the whole lot will leak

The units are inflexible and so will put an evenly distributed load on the rafters, which in turn wont deflect a great deal as the loadings are well within their capabilities

 

[tony1851]

@Woody;
I've just checked up on a structural glass site, and for glazing used horizontally, the maximum recommended deflection is span/360. That is for single-sheet glass. If sealed units are used, the permissible deflection will be less, say span/400? or a maximum permissible deflection of 5mm on a 2m span.

So, maximum glass load per rafter is 39 x 9.8 = 0.38 kn.
Add live load (snow) of 0.75kn, total load per rafter = 1.28kn,
say 1.4 kn with rafter self-weight and fixings etc.

Using the standard equation for deflection, on a 5x2 C16 timber, on a 2m span, it comes out at 3.5mm, ie span/570.

You may well be right - it might just work - but at least I've worked it out and not just guessed