How to Join Timber Beams

Co-authored by Mitchell Couch

Last Updated: May 24, 2025 Fact Checked

There are many reasons you might want to join timber beams together, such as when 1 beam isn’t long enough on its own or when 2 beams meet on top of a post. There are plenty of ways you can do this using tried-and-true woodworking techniques. We’ve put together this helpful Q and A article to give you an idea of some of the best, most secure ways to connect beams in different scenarios.

Question 1 of 5:

How do you join two joists together?

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Bolt joists together with a timber connector in between them. Overlap the ends of the joists by about 1 ft (0.30 m) or so where they meet and drill a 12 mm wide hole through both pieces of timber in the middle of the overlapping section.^{[1]
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Mitchell Couch
DIY Expert

Expert Interview} Slide an M12 bolt with a washer on it through the hole in 1 piece of timber and slide a spiked timber connector over the end of the bolt in between the joists. Push the bolt through the hole in the other joist and put a washer and a nut over the end. Tighten the nut all the way with a wrench.^{[2]
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- A timber connector is a ring with sharp spikes around it facing in opposite directions. The spikes bite into both pieces of timber to prevent movement.
- This is a good option for when you need to connect joists underneath a deck or a floor, where they won’t be visible.
- The end product will look like 1 long offset joist, since they are not joined end to end, but rather side by side.

Question 2 of 5:

How do you combine two beams on a post?

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1
Secure the beams in a metal beam bracket. Choose a beam bracket that matches the width of the post and the combined thickness of your 2 pieces of timber. Put it on top of the post and drive wood screws or structural nails through the holes in the sides of the bracket into the post. Set the 2 beams into the top of the bracket, next to each other, and put screws or nails through the sides of the bracket into the beams.
- For example, if you’re connecting 2 2 in (5.1 cm) thick beams to a 5 in (13 cm) by 5 in (13 cm) post, use a beam bracket that is 4 in (10 cm) wide on 1 side and 5 in (13 cm) wide on the other.
- This is a good choice when you just want to use commercial hardware and not do any extra measuring or cutting.
- The end result of this is a post with a metal bracket on top of it holding the beams in place in the center of the top of the post.
2
Bolt the beams into a notch at the top of the post. Cut a notch into the top of the post using a circular saw that matches the height of the beams and that is as deep as the combined thickness of the 2 beams. Set the 2 beams into the notch, next to one another, and drill two 0.5 in (1.3 cm) wide holes, to the left and right of the center of the beams and offset diagonally from one another, through the beams and the post. Slide a 0.5 in (1.3 cm) diameter carriage bolt with a washer on it through each hole and put a washer and a nut on the end of each bolt. Tighten the nuts all the way with a wrench.^{[3]
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- For example, if you’re using 6 in (15 cm) by 6 in (15 cm) beams, make a notch that’s 6 in (15 cm) tall and 3 in (7.6 cm) deep.
- This is a good option when you don’t have any commercial hardware available or you want the beams to be at exactly the same height as the post.
- The end result of this is that the beams sit flush with the side and the top of the post.
- Never just bolt beams to the side of a post without cutting a notch into it because the downward pressure of any weight on top can cause them to shear off.

Question 3 of 5:

What is the strongest timber joint?

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The mortise and tenon joint is one of the strongest in woodworking. To use this joint, cut a cavity that’s 1/3 as thick as the timber 2/3 of the way into 1 of the beams where you want to connect the other beam to it. Carve a peg the same width and depth as the cavity into the end of the other beam, cover it in wood glue, and push it into the cavity. Clamp the beams together while the glue dries.^{[4]
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- There are many ways to cut mortises and tenons with hand tools and/or power tools. For example, you can use a router with an up spiral bit to cut the mortise, or cavity, and a table saw and a jig to cut the tenon, or peg.
- This is a good joint to use when it will be visible because it is very attractive and there is no exposed hardware.
- You can use a mortise and tenon joint to join timber together end to end or at 90 degrees.
- This joint appears as if the pieces of timber are just butted up against each other.

Question 4 of 5:

How do you join timber end to end?

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Connect them using a half lap joint. Cut matching notches that are half as deep as the thickness of the timber and the same length as each other into the ends of your 2 pieces of timber using a table saw or a circular saw. Apply wood glue to the notches, fit the 2 pieces of timber together like a puzzle, and clamp them tightly until the glue dries.^{[5]
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- This is a good option when you have 2 lengths of timber that you want to join into an almost seamless single length of timber, since the joint isn’t very noticeable.
- This joint looks like you just have 1 piece of timber since they are joined flushly.
- It’s up to you how long to make the notches in the ends of the timber. However, the more you overlap the 2 pieces of timber, the stronger the half lap joint is.
- You could also put a bolt through the 2 pieces of timber where they are joined together for added strength, which would be a good idea if you’re making a beam that will support a lot of weight.
- There are other types of joints for joining timber end to end, but they aren’t as strong as lap joints. This means they’re better suited to other woodworking projects and aren’t ideal for beams.

Question 5 of 5:

How do you join timber at 90 degrees?

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Make a miter joint. Cut the ends of the 2 pieces of timber at opposite-facing 45-degree angles using a miter saw. Apply glue to both of the angled cuts and clamp the pieces of timber together. Drive wood screws or structural nails through both pieces of timber, from both sides of the 45-degree mitered joint, so the nails go from each piece into the opposite piece where the joint is.^{[6]
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- Miter joints are better for joining structural timber, such as beams, together than just butting the end of 1 piece flat up against the end of the other, which isn’t a very strong joint.
- This is a good joint to use when you want a neat and strong 90-degree connection that is easier to make than something like a mortise and tenon joint.
- This joint looks like the corners of a wooden picture frame.