Straightening Deck Beams
2x blocks and a string line are a perfect guide for getting beams straight.
If you need to straighten a curved or twisted beam, it has to be done before the joists are secured to it. To straighten a beam, first plumb the posts that support it at either end (see photos below). Secure the joists closest to the ends with a screw angled through the joist face into the top of the beam. Attach a 2x block to the beam’s side at both ends and stretch a string line between them so the string is taut and flush to the block faces. Use the distance of the beam to the line as a guide for straightening the beam. When the beam is straight and in position, secure the joists to the beam with 3-in. screws or galvanized nails. If the beam has a serious bow to it, you may have to hold it straight until you can fasten all the joists.
1. Check the posts at either end of the beam for plumb. If necessary, adjust the bracing to return the posts to plumb.
2. Fasten the end joist to the top of the beam to hold each end while straightening the beam.
3. Stretch a string between 2x blocks that are attached under each secured joist. Take care that the string is flush to the block faces.
4. Adjust the beam until it is a consistent distance from the string along the entire length.
5. Secure the beam in position by attaching the joists to the beam’s top.
Trade Secret
Use a block instead of a measuring tape to gauge the distance from the string to the beam. With a block, it is easier to see how much space to make up to get the beam straight.
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