Dave Eastwood (Gadgetman) - Club Chairman Posted June 18, 2021 Share Posted June 18, 2021 32 minutes ago, Mark (smokey mow) said: That guide is fine for a traditional hand cut roof but not for a trussed roof. @Mark (smokey mow) What would be the accepted definition of the truss, so that anyone reading this can tell the difference? Quote Link to comment Share on other sites More sharing options...
Jim RS Posted June 18, 2021 Share Posted June 18, 2021 Basic advice as always is, if not absolutely sure about the loadings/modifications you want, get a structural engineer to do inspection and get building regulation approval. Simply prefabricated roof trusses are quite slender in timber profile, especially against depth, joints are butted against each other, joints are usually plated, frame includes rafters/purlins/internal struts. The whole of the frame is triangulated so that every component has a job to do making the structure strong, light and easy to transport. Bespoke roof structures are usually heavier with timbers quite wide in ratio to depth, joints are normally overlapped for ease of fitting, ridge beam will normally be quite substantial, loft purlins may be to carry load and not connect directly to rafters. Each component is usually independent of each other and such will be heavy especially when compared to the truss design. This is not comprehensive by any means but may give a hint of what's involved. 1 Quote Link to comment Share on other sites More sharing options...
Mark (smokey mow) Posted June 18, 2021 Share Posted June 18, 2021 4 hours ago, Dave Eastwood (Gadgetman) - Club Secretary said: @Mark (smokey mow) What would be the accepted definition of the truss, so that anyone reading this can tell the difference? A truss would be prefabricated and factory made with nailing plates at the connections. The timber size would typically be 3x1-1/2” and the contain a lot of triangulation internally. a tradional cut roof which is assembled on site from individual lengths of timber uses much larger structural timbers. These will have a ridge board which a trussed roof wouldn’t and traditionally would also incorporate purlins at mid span on the rafter sections. 1 Quote Link to comment Share on other sites More sharing options...
wizzer Posted June 18, 2021 Share Posted June 18, 2021 Sounds like you've got a trussed roof ,normally 600mm centers, and a loft hatch fits between the trusses . Not that easy to fit a loft ladder if the trusses are going the wrong way or the spacing isn't right. This is a trussed roof https://3dwarehouse.sketchup.com/model/f708a7030e10fa26ae63b4392562dc5/Roof-Trusses-wStrapping?hl=en This is a traditional roof truss https://en.wikipedia.org/wiki/Timber_roof_truss Don't be cutting the bottom cord on eather. Quote Link to comment Share on other sites More sharing options...
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