When building structures or adding on to a structure, sometimes you must connect wood beams together to increase height. Connecting them together incorrectly could cause instability or a weak beam that cannot withstand any extra weight, and may result in an unsafe structure. There are two fairly easy ways to connect the beams and maintain their strength as if they were actually one solid piece of wood. One is for light construction and the other for more substantial construction.
Lay the beams down end to end.
Set down a joining plate so that it is located with one-half of its length on each beam. The plate has rows of holes all over it.
Drill wood screws into the holes in the plate. The length of the screws will depend on the size of the beams.
Flip the beams over once the holes are all filled. Place the plate side down.
Put another plate on this side of the beam and line it up as you did in Step 2. Next, push the plate a little off from the other plate so that the holes on it do not line up exactly with the ones on the other side.
Drill screws into all the holes in the second plate as well. The beams are now connected.
Locate the middle point of the end of the beam.
Draw a line down the length of the beam at the midpoint. Draw the line for 20 cm (8 inches), and then draw it out to the left edge of the beam. Repeat the process with the second beam.
Use a handsaw to cut out the drawn section of the beams. When you are done, the end of the wood will have a notch cut out of it.
Place the two beams together so that the notches fit together like a puzzle piece. One of them will have to be flipped over for them to fit together.
Drill wood screws into the sections of beams that are now together so that the screws go through one notch and into the other. The size of the screws depends on the width of the beams, but they must be long enough to go almost all the way through both notches so that they secure them tightly together. If the beams aren't going to be exposed, consider using bolts instead. After inserting screws in one side, flip the beams over and repeat the process on the other side.
For beams that need to be joined at a right angle, you can use a right-angled metal joining plate in the same way as a flat one.
Using joining plates to connect beams together is for light construction only, such as adding height to a fence. It is not for building structures or decking, unless it is approved by a building inspector.