I am looking at pitching a shallow 15 degree roof, the roof will be supporting 600x32 toughened sealed units at 2.4mtrs long. I will be using mid range joinery grade timber but am having trouble working out the appropriate depth I am thinking 5x2 for an unsupported span of 2050mm. Do you think 5x2 is deep enough as I am taking into consideration the aesthetic appearance from underneath, thank you.
rafter depth
- Thread starter chirpychippy
- Start date
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You need to be careful here. On a roof of that span, ordinarily 5x2 should be OK, but it depends what maximum deflection you can tolerate before you damage the sealed units. How heavy are they?
I am waiting for that info and will come back with it.
39kg is the weight of the glass?
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Sorry, that's one sealed unit there are ten of them, so 390kg
It's the weight per rafter that matters. Each rafter will then be supporting 39kg, which would indeed be less than the weight of the equivalent area of tiles.
The rafters will still deflect, however, and you need to ensure that the deflection will not be so much as to affect the seals.
There are on-line calculators to help you work out deflection of timber beams for a given load and span.
The rafters will still deflect, however, and you need to ensure that the deflection will not be so much as to affect the seals.
There are on-line calculators to help you work out deflection of timber beams for a given load and span.
Blimey, just had a look at those calculators, I think I will ring building control see if they can tell me, thank you.
[quote="chirpychippy";p="2826781" I think I will ring building control see if they can tell me, thank you.[/quote]
Unfortunately, the Bulding Inspector won't know the deflection.
It might be better checking with the glazing people what the maximum permissible deflection would be.
Failing that, why not play safe and have deeper timbers?
Unfortunately, the Bulding Inspector won't know the deflection.
It might be better checking with the glazing people what the maximum permissible deflection would be.
Failing that, why not play safe and have deeper timbers?
I appreciate what you are saying with deeper timbers, what I am trying to achieve is the aesthetic look from the view internally. Possibly rather than using mid grade joinery grade timber I could use C24 5X2 and paint them white?
Whatever the deflection works out at, it will be about 10% less if using C24 rather than C16.
Is douling them up a possibility? Any deflection then would be halved.
Is douling them up a possibility? Any deflection then would be halved.
Thank you, no doubling up isn't an option, I am trying to use as little as possible whilst being mindful that as little as possible needs to be enough, if you know what I mean! 
You could look at going a grade higher than C24, TR26 ? It may give you that bit extra assurance your after rather than having to double.
However, Tony's advice of asking who ever is supplying the glazing what the max deflection is would make the decision alot easier. ?!?
However, Tony's advice of asking who ever is supplying the glazing what the max deflection is would make the decision alot easier. ?!?
Won't the glazed units actually add to the stiffening of the roof?
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