It is currently 28 Mar 2024, 21:12
Mike G wrote:
Given the loadings on a ridge beam are almost entirely vertical, (if the walls were forced apart by the un-tied rafters the ridge beam would be dragged directly downwards) one has to resist that vertical force. Now, this is most easily done with a post. However, if we are relying on the rafters at the gable (as we would be at the gable above the lintel over the big door opening) to hold the ridge beam up, we need a suitable junction between the rafters and the ridge such that an elephant sitting on the ridge board at that end wouldn't push the ridge down out of connection with the rafter ends. There are lots of ways to achieve this. One of them is to have an upside-down birdsmouth, so that the ridge beam physically sits on part of the rafter. Unfortunately, given your timber sizes, this wont work.
What I suggest is this:
Bolt a piece of 195x45 hard up underneath the ridge beam at the gable rafter location.
Further, as you don't want to be throwing load onto the lintel below, the end rafters should be doubled up, and nailed together (alternately top and bottom edge, max 500 C's). This is going to complicate your OSB lining somewhat.
The other end can be dealt with as per mine, with a post under the ridge beam. This should be directly above a stud in the wall (in other words, when you set your wall out, you need to put a stud exactly in the centre). The rafter only need be a single pair, not doubled.
Mike G wrote:"Is this adequate?"
Yes. More than......
9fingers wrote:Looks like that slab won't be going anywhere!
A great start!
Bob
Mike G wrote:Remind me what's going on your roof? This will make all the difference to your rafter spacing.
Mike G wrote:Double studs?..........Sort of. One is a full height stud, and then inside that is the cripple stud which supports the lintel. So yes, there are two bits of wood side-by-side, but technically only one of them is a stud. If you have big heavy doors consider adding extra noggins either side of the opening to help stiffen everything up.
spearos wrote:However it didn't cross my mind to think about how the rafter spacings fit with the Onduline roof sheets I plan to use.
9fingers wrote:OK but maybe careful rafter spacing will make insulation easier too
Worth thinking through the steps now rather than later?
Bob
Malc2098 wrote:Mark,
I found that I couldn't visualise my thoughts. So I learned to use Sketchup. You are drawing your some of your ideas, and other guys use different CAD apps.
The stages you've just gone through, the rafters, the Onduline, the purlins, the wall frames and the vertical studs, would freak me out, if I didn't have a way of recording the idea.
So I drew my ideas in Sketchup, and if they didn't fit, I'd find a way to make them fit by drawing/modelling them.
I would advise you to draw your ideas to find out what doesn't work. that way, you'll find out what does work. It doesn't really matter what app you use, whatever works for you.
Mike G wrote:Firstly, you don't have a choice if you only have a single plate: your rafters must sit above your studs. However, if you double the top plate, your rafters can go anywhere. The usual practice is to space them according to set centres (400, 600, or occasionally 450), and have a narrower gap at one end of the roof. This is because there is usually some sheet material involved. In your case, you'll be lining the underside of the rafters with something. Generally, boards are 1200 x 2400, so you space the rafters to suit that. Sometimes you find that the board is imperial (1220 x 2440), and so you might space them out accordingly.
Mike G wrote:No, you'll either need a couple of ties to help it out, or make use of a principle truss at the midpoint, halving the span.
spearos wrote:Mike G wrote:No, you'll either need a couple of ties to help it out, or make use of a principle truss at the midpoint, halving the span.
Would collar ties suffice? Fixed hard up against the underside of the ridge (as per your earlier drawing)?
Correct me if I'm wrong but a principle truss would severely restrict head room for raising a vehicle?
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