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How to Create a Birdsmouth Joint
Jul 22, 2022
With the help of Foundations Up, DIY Doctor explains how to create a Birdsmouth Joint, including all the materials and tools needed, an explanation on what a Birdsmouth Joint is and what it's used for, and how to measure the right angles for any Birdsmouth Joint.
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Hi, today we're going to discuss how to cut this bird's mouth joint
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It's traditionally used in roofing, in cutting roofs, but today we're going to use it for a slightly different application
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And let's go ahead and get started. So as I said, this is traditionally used in cutting roofs, but today we're going to use it for something different
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We're making an architectural drawing board so that we can look at all of our drawings for our projects
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So in a roof you would usually have the ridge beam, which this is going to be our ridge beam today
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and you would have the wall plate. This is the edge where the weight sits on
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This is where we're going to cut our bird's mouth joint so that our piece of timber can sit here
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And as it's loaded down, it's pressed down instead of sliding out like this
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this, the load is pushed down into the wall plate and that's what takes the weight
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So if you've read our article online, you'll know the first thing that we need to do is to find
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the angle to cut the end of our rafter, or our support, on the ridge beam
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And the way that we do that is with a little bit of nuts
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First of all, we'll measure out the horizontal distance from ridge beam to wall plate
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and measure that and that is 600 and also measure the vertical distance from wall plate to bridge bean and that is 670
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from those two measurements we can calculate the angle that we need to cut our rafter at let's go outside and cut that
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Okay, so taking our two measurements that we had, we had a horizontal distance of 600
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and a vertical distance of 670. I'll take a square on this piece of scrap timber, and just mark out a square line
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Now taking my tape measure, I can measure. 670 representing my vertical distance 600 representing my horizontal distance If you cutting in a roof of course these distances are much bigger
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you just divide them both by a factor of 10 or something like that
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you'll find much easier to draw. With a straight bit of timber I just connect those two marks that I've made
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and that is an exact representation of of the angle that I'm looking to create
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Here we have the base, the height and this is going to be my timber
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Okay, so this is the angle that I'm looking for to cut my roof truss
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Okay, I'm going to take that angle with my sliding square. This is a simple tool
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It's got a wing nut there to lock this adjustable piece of metal in, the right angle
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Reference the timber against this. edge of the woods, line up the metal and tighten that in place
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Just double check that it's the right angle before I use it. Okay. Okay. Okay
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So as you can see, using that to mark gives me
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the angle cut for my ridge bean. Okay, so we're going to cut this piece off and move on to the bird's mouth
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Okay, and there we have the angle of our for our ridge bean cut
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We're ready to go and mark out the bird's mouth at the other end. So we're going to go ahead and mark out our bird's mouth
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I'm going to cut my bird's mouth halfway through my timber so I found the centre line on both ends
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I'm going to align the centre mark of my timber with the top of my ridge up here
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And that means that as where I mark my timber, once the bird's mouth is cut, it will just drop down halfway through the timber
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and everything will align and sit exactly as it's supposed to. So if I line this up at the top here
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I mark on where my timber should be cut And there we have the position for the start of the bird mouth I going to mark out where my bird mouth will be just to make sure I don make a mistake
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and take it away. So let's go and cut that and then we'll come back and see whether it fits
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So I'm going to use my drawing because I know it's exactly to scale. It's a one-to-one scale
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But what you could usually do is just take it back to your workplace, press your
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cut face against your ridge beam. Okay, so just check that it's nice and flush with it
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And as you then slide your timber down, where it touches the wall plates
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just make a little mark there. And that is the beginning of your bird's mouth cut
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Now of course, when you've cut your bird's mouth, your timbre will slide down further
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where this notch that we're about to make will accept the wall plate into it
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and that will create a seat for your joint. So I just drawn a square line across the start of the bird's mouth joint
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and I put a mark in here to show me where I'm cutting. If you've read our article online you'll know this is the heel cut and this is the seat cut
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The heel cut is going to be at the same angle as the top of the rafter
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So I haven't adjusted my adjustable square, so I'll just use that
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And I'll mark out that heel cut. Okay
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Now as I said, the bird's mouth is going to be cut halfway through the timber
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So if I find the centre of my timber again, I can just draw a line
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same distance in from both sides. I know the center of those two lines is my midpoint of my timber
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And then from my heel cut line, I can just square off at that point
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It's give me the seat. And this is my bird's mouth joint to be removed
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So let's cut this and then we'll go check it. Then we'll go check it in place
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There we have our bird mouth cut There no excess timbering right in the corner of the joint It will hold the joint out away from where you want it Just clean
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that up with the saw. And there we are, we have it cut. One end the bird's mouth, the
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other with the angle for the ridge beam. Let's go back to our workplace and test and see if it fits
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Okay, so I'll offer up the timber to where it's supposed to be
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Lining it up, you should see it. Everything drops down smoothly. The seat hits onto the wall plate and it will now sit there all of its own
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Whereas before it would have just slid off, we now have a flat surface that takes the vertical loads that we're resting on it
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Okay, so I'm happy with that. I'm happy with that. I'm going to cut two more and then I'll go ahead and fix them in place and we'll get our desk all made up
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So there we have it, our three roof rafters or supports for our drawing board this time
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As you can see I've just drilled some holes and counter-sunked them with screws
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Usually you just use a framing nail gun in a roof. But this is now ready for me to take my drawing
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drawing board slide it up and screw in in place
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and we're going to be ready to get on with all our projects
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and there we have it there is our architect's drawing board ready for us to use
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that's the great thing about joints like this the bird's mouth is traditionally used in really
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but with a little bit of ingenuity, you can adapt it to your own personal needs
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All right, thank you very much
#Home Improvement
#Construction & Power Tools
#Roofing