Roof rafter spacing

[vixerfixer]

Evening folks.would 600mm centres be ok for a garage roof,4m span with 8x2 rafters.

 

[noseall]

Evening folks.would 600mm centres be ok for a garage roof,4m span with 8x2 rafters.

No. I think you are just under (C24) at that span. At 450mm c/c (C24) you may just nick it.

 

[Dereekoo]

All depends on your loading but C16 timbers with a snow load of 0.75kn/m2 and dead load of 0.75 kn/m2 gives a deflection of 11mm against an allowable of 12mm and a bending moment of 1.9knm against an allowable of 2 knm

Not sure if you are flat or sloping roof but these tables will help

Free UK Span Table for Flat Roof Joists to BS 5268-7.2 (C16, 0.75 kN/m² load) - Timber Beam Calculator

www.timberbeamcalculator.co.uk

Free UK Span Table for Rafters to BS 5268-7.5 (C16, 0.75 kN/m² load, slope 15° or more but less than 22.5°) - Timber Beam Calculator

www.timberbeamcalculator.co.uk

 

[vixerfixer]

It’s a flat roof with a slope.c24 joists.

 

[robinbanks]

Not sure if you are flat or sloping roof but these tables will help

Neither of the tables you linked to permit 4m with 8x2 C16 and 0.75/0.75 loadings?

No. I think you are just under (C24) at that span. At 450mm c/c (C24) you may just nick it.

Depends on the loadings, lighter weight constructions of not-regularly-walked-on will be acceptable

 

[noseall]

Depends on the loadings, lighter weight constructions of not-regularly-walked-on will be acceptable

So two overweight blokes, a few rolls of felt and a full bottle of gas, is a no-no.

 

[Dereekoo]

Neither of the tables you linked to permit 4m with 8x2 C16 and 0.75/0.75 loadings?

Never said they did, just some reference tables that don't flag up 200 x 50 joists either just to give him a feel for things but thanks for the heads up

 

[^woody^]

Even with two fat blokes and a pallet of bacon sandwiches the roof will stay up. The main concern is that the joists will deflect over time leading to ponding.

 

[Dereekoo]

Depends on the loadings, lighter weight constructions of not-regularly-walked-on will be acceptable

Plastic roof with no footpaths then?

 

[vixerfixer]

Thanks peeps for your input.just gonna go 400mm spacing I think with 18mm osb.only a garage at the end of the day‍

 

[Dereekoo]

Thanks peeps for your input.just gonna go 400mm spacing I think with 18mm osb.only a garage at the end of the day‍

In that case have as many footpaths as you want

 

[robinbanks]

Never said they did, just some reference tables that don't flag up 200 x 50 joists either just to give him a feel for things but thanks for the heads up

Ah, I thought your first paragraph was giving the deflection etc you'd calculated from the OP's spec, plus some assumptions, and declaring the proposed joists to be just on the right side of acceptable..

 

[vixerfixer]

In that case have as many footpaths as you want

 

[Dereekoo]

Ah, I thought your first paragraph was giving the deflection etc you'd calculated from the OP's spec, plus some assumptions, and declaring the proposed joists to be just on the right side of acceptable..

I was but not from the OP spec as he only gave a joist size, but from my loading assumptions which showed with the loadings assumed the joist size to comply with acceptable parameters

 

[robinbanks]

I was but not from the OP spec as he only gave a joist size, but from my loading assumptions which showed with the loadings assumed the joist size to comply with acceptable parameters

Are you running your calcs on a 200x50 size?