Span tables

[geraldthehamster]

Hello

OK, flat roof, with joists supporting internal PB, OSB (one, possibly two layers), Celotex and EPDM. Does anyone know roughly where I need to be looking in the most recent freely available span tables in:

http://www.planningportal.gov.uk/uploads/br/BR_PDF_AD_A_1992.pdf

that is, which column in which of Tables A17 - A22?

I've no idea what the loads are likely to be for such a roof, though I imagine at the lighter end of the spectrum. I appreciate that SE calculations would give me a precise answer. I'm just hoping for a rough idea.

Cheers
Richard

 

[pinenot]

What span are you going for?

 

[geraldthehamster]

What span are you going for?

Thanks - the span will be about 3350. But whatever the span, I just want to know what table to be in, and how far to the left ...

Looking at all the tables I could be looking at anything from 38 x 170 (at the lightly loaded end of A17) to 47 x 195 (at the heavy end of A22).

Reverting briefly to inches, I'm hoping to be able to use 6 x 3 or 7 x 2.

Cheers
Richard

 

[RonnyRaygun]

Does anyone know roughly where I need to be looking in the most recent freely available span tables in:

Cheers
Richard

If you assume you are between 0.75 and 1.00kN/m2 and SC3 (C16) timber then you are on the right hand side of table A17.

Base your joist size on that and you won't go far wrong.

 

[geraldthehamster]

Does anyone know roughly where I need to be looking in the most recent freely available span tables in:

Cheers
Richard

If you assume you are between 0.75 and 1.00kN/m2 and SC3 (C16) timber then you are on the right hand side of table A17.

Base your joist size on that and you won't go far wrong.

Thanks for that. Out of curiosity I wonder what kind of roof would fall under the left hand column? Felt rather than EPDM?

Cheers
Richard

 

[RonnyRaygun]

Thanks for that. Out of curiosity I wonder what kind of roof would fall under the left hand column? Felt rather than EPDM?

Cheers
Richard

Possibly a felt roof with exposed joists, or a simple corrugated roof, or something similar.

Even with a felt roof you might go over 0.5 if there is PB and ply etc.

 

[maltaron]

In old money: Span in feet divided by 2 plus 2 = depth of joist in inches.

 

[geraldthehamster]

In old money: Span in feet divided by 2 plus 2 = depth of joist in inches.

Thanks. I assume the width of the joist is taken to be 2 inches?

Cheers
Richard

 

[maltaron]

Yes 2"