I have a shallow pitch roof design that involves 225mm timber purlins supporting 50mm counter-battens, then battens and interlocking concrete tiles. Span of purlins is 4 metres. (Insulation between purlins based in knauf insulation examples). Then purlins were to be hung from masonry using joist hangers. What could I replace the timber with in order to make the roof thinner ? I have no experience with composite beams etc. Cheers, Simon.
composite/metal purlins instead of timber ?
Nov 07, 2005
6 Replies
Steel
Do you mean purins or rafters ?
Steel must be boxed in. You need to go back to the engineer and ask him to recaculate. The extra weight may effect him, and he can advise what size you need. Or simply go back and ask if the roof can be done thinner.
Rick
I mean purlins. The counter-battens run up the slope at right angle to the purlins, but are only 50mm.
The ceiling construction will box them in. What engineer ? This is a DIY group ! I'm doing full plans of course.
I have looked at the multi-beam purlins from kingspan. They are light for their strength. The load tables take some figuring out though.
Simon.
Can we have a little more detail please. I guess you have 225 x 75 purlins, but I can't figure out the jack rafters. What size are the battens and what is the weight of the tiles/sq M?
Regards Capitol
If you know the loadings, then get the demo copy of superbeam from the sda web site and fiddle with some alternatives in that. A flitch beam is one way of reducing the size a bit while still maintaining most of the ease of working with wood.
Approx roof span - 4m ridge/eves x 5m. Pitch around 13 degrees.
225 x 75 Purlins at spacing < 1m, 50x50mm counter battens (or call them rafters) at 400mm spacing bearing directly onto the purlins. 25 x38mm battens carrying interlocking concrete tiles (redland regent). Tile + fixings load 0.59 kN/m2 (from
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Timber sizes taken from 1992 part A tables for dead load 0.75, imposed load 0.75. Simon.
That's interesting. I had a loft conversion designed by an architect and well supervised by the BCO. None of the three steels are boxed in.
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