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My deck has double joists on the east and west edges that seem to be separating. I imagine water is getting into the space between them and prying them apart. This deck is located in Minnesota.

In the images, you can see the joists are screwed together. there also seems to be some glue residue. The cracks have small rocks and debris in them.

How can I fix this?

top view

top corner

top view with scale

bottom view

I have many issues with this deck and will likely have to ask several questions on this site. The scope of this question is simply what to do about the double joists that are separating.

  • I would drill through both boards and install carriage bolts to pull the boards together. In the top picture I would drill through both the joist the 4X4 upright and bolt this also. – d.george Jun 27 '17 at 16:04
  • I agree that the issue is mostly cosmetic. It's not water prying them apart so much as typical warpage--the outer face dries out and shrinks more quickly, cupping the board outward. At this point, forcing it back in may crack it or displace the other board. You might just replace them. – isherwood Jun 27 '17 at 16:18
  • I just put a straight edge on the outer board and found that there is certainly a bow. – Jon Jun 27 '17 at 20:21
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From your pictures I would say the outer one is a perimeter board. These are for looks to dress up the outside of the deck.

The inner board is carrying the end of the deck boards but is not attached to the ledger board with a hanger. Bad technique, in my opinion. Notice, the inner joists are attached to the ledger board with joist hangers. But the outside joist is not.

You should be able to add more screws to the perimeter board to pull it back in to the outside joist.

Good luck!

  • It could be that there's a hanger supporting the rim joist behind the siding. – isherwood Jun 27 '17 at 16:17
  • That is possible. Again I would say bad technique since replacing it would then necessitate removing the siding. 😞 – ArchonOSX Jun 27 '17 at 16:22

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