supporting purlins on an angle - 1992 part A table A23

On 20 Oct 2005 02:46:02 -0700, a particular chimpanzee named sm snipped-for-privacy@hotmail.com randomly hit the keyboard and produced:

They're built it into the walls, both sides. You may be able to use restraint-type joist hangers, as, IIRC, the spans require end restraint.

You're intent on pursuing this idea of using purlins, aren't you?

If I understand your query correctly, then the "high" end of the purlins should be notched underneath, so that there is a flat area which would be parallel to the top surface of any brick on which it would rest.

Haha ! I'm learning a lot fast, thus the profusions of questions to the group. Only using the purlins idea because I saw it in the regs diagram, and it results in shorter spans. I would need purlins anyway, so why not just purlins ...? Cheers, Simon.

Have you any more info on this. Is the restraint to hold it against the slope, or to hold the walls in ? Simon.

On 20 Oct 2005 14:06:53 -0700, a particular chimpanzee named sm snipped-for-privacy@hotmail.com randomly hit the keyboard and produced:

Neither. I'm sure Tony Bryer can explain this better than me, but the beam will be better able to resist bending if the ends are not free to rotate (held in place). Try it with a ruler; hold it in place by its ends and press down in the middle. Now try it without holding the ends.

On 20 Oct 2005 13:43:14 -0700, a particular chimpanzee named sm snipped-for-privacy@hotmail.com randomly hit the keyboard and produced:

OK, let's examine your plans.

As I understand it, you're building a lean-to extension, with the clear span along the slope of 5m, and counter of 4m. You've gone with a low pitch; now correct me if I'm wrong, but this would imply to me that you've got to get the roof to fit under a window or some other obstruction at first floor, or you want to keep the height below a certain height to keep within Permitted Development rules. I'm presuming that you intend doing as much of the work yourself as you can, or employing individual trades rather than a main contractor.

1. "Conventional" cut roof: You would need a purlin at the mid span of the rafters, and as in a previous post, it would be best if it was a steel beam. Without calculating it, you would possibly need a

1. "Purlined" roof: You're planning 75x200 C24 purlins at 900mm centres. Assuming 590kg/m³ for softwood, this is a weight of 37kg each. For 5m, you're going to need 6no. These will have to be built into the wall as they're installed, so a bit of juggling to get them in the right place while someone else cuts some blocks and mortars around them is needed. Do you want to trust that to your mates? Once that's all done, then it's down to the plywood sheathing, then the counterbattens & felt, and then the battens. This will give you a roof with an overall thickness of 244mm +battens & tiles over