How to build a mono-pitch roof. Skillion/flat roof framing and erecting

Mono-slope roof
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How to scribe mono-pitch roof rafters

In this video I just want to quickly show you how you can mark out the position of your birdsmouth on a skillion or flat or what else they call a mono-slope mono-pitch roof.

Here’s my top plate as you can see. This is the low end we’ve extended this end up, however as I said in our previous video this is not the best practice.

Best practice would be to construct this wall at full height to start with.

But anyway, that’s what I’ve got so the next step is to throw up your piece of timber making sure it’s a little bit longer than what you actually need.

Then all you need to do is to scribe up where the timber meets the plates. In this case, I’ve used a ruler but there’s no reason why you couldn’t use anything with a straight edge. A straight piece of timber or a spirit level would be preferable because you’ll be able to make sure that it’s plumb.

If I zoom in you can see I’ve just come up straight off the plate straight up, and that will give me my what we call the plumb bevel and I can just draw a line up there as far as I need depending on what height I want my Birdsmouth to be. That’s it as I said a spirit level would be good because you can check that it’s actually plumb and presuming this wall is plumb then I can just simply set my ruler on my plate.

We don’t want this to much more than 20mm thick and that will give us the depth of our birdsmouth. Once again you can use a piece of timber that’s the depth of the bird’s mouth that you want and that will give them a level bevel of my common rafter.

And remember we’re repeating these steps down at the bottom end as well, and we get our check out for our birdsmouth cut out.

Then all you need to do is measure from the back of birdsmouth whatever your overhang distance is going to be, mark it and cut it and repeat the same at the front end.

We measure from the back of our birdsmouth allowing for our the width of our plate and then whatever the overhang is going to be at that end.

Then we have ourselves a pattern rafter for this skillion roof.

That’s a very quick and easy method of doing it. You can do a traditional pattern rafter as you would for a gable roof and that method is covered in another video.

However, that’s a very quick and easy way of doing it for a skillion roof.

How to raise mono-pitch roof

So in this video, we’re going to have a look at the erection procedure for a skillion or a flat roof.

I’m going to start with a equal height top plate although as you’ll see in the video no reason why you can’t vary heights as you go, you’ll see that as we proceed.

So once again if you’re going to have a flat ceiling underneath the skillion you need to consider that as you go and you need to mark that out in conjunction with your skillion roof.

And, as usual, I’ll get rid of that just to save some confusion, and then we’ll get into it.

Building a jack wall

So the first thing you need to do is to create your skillion or mono-pitch/single-pitch roof is obviously one side needs to be higher than the other. You can do this by building a little jack wall on top of your existing wall or possibly if you’ve the situation this wall could have been constructed at a higher height to start with.

That’s normally preferable because the break in the studs here may cause some bracing issues. It’s normally preferable to bring your studs through full height and – the next job – rafters go on. Rafters on a skillion roof generally will have a very shallow birdsmouth both ends.

A small birdsmouth or no birdsmouth?

However, if the roof is flat enough, then sometimes that’s not even worth putting a birdsmouth in it.

Okay, but generally we’ll have a small birdsmouth at both ends, and I have another video I’m showing you how to work out where they go once you get your rafters in position.

You can transfer this height across on your wall and at the other end you transfer this point of the study birdsmouth across and cut in a verge plate.

And obviously, to support the verge plate, we’re going to need some gable studs and once again, I have another video that shows how you can easily calculate the length of these studs with very little calculation.

So once that’s done at both ends, we can then put our trimmers in for our overhang and our verge rafter which is exactly the same as our common rafters except there’s no birdsmouth cut out ceiling frame.

We bring back into play you can see how it all ties in depending on how flat the roof is you may actually have to move this hanger across a little bit more because if the roof is too flat, the hanger may hit on the rafters, so it might have to go across it a little bit more.

And that’s it. That’s the procedure for erecting a skillion or a mono-pitched roof.

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