Rotten deck joist query

[Manupatree]

Hello. I have merbau decking supported by pine joists, which is surely an annoyingly cheap way to go about it. One of the pine joists is partly rotten so that a single merbau plank now gives way when trodden on. My question is, can I fix this without having to strip the whole deck? The merbau is all in good condition but I don't know about all the joists as the deck is too low to get under. Thanks.

[aldav]

It's very difficult to give advice on something like this without seeing it. It seems odd that it is only one board that is affected by the rotten joist unless the rot is very localised. It doesn't help that you are unable to do a visual inspection. If it is only one short section of one joist that is causing the problem you could run a new joist alongside it to take the load, but you would need to access the underside of the deck to do the job. If the existing joists span two bearers or more and your replacement will be a single span you would need to increase the size of the replacement joist.

[Manupatree]

It's very difficult to give advice on something like this without seeing it. It seems odd that it is only one board that is affected by the rotten joist unless the rot is very localised. It doesn't help that you are unable to do a visual inspection. If it is only one short section of one joist that is causing the problem you could run a new joist alongside it to take the load, but you would need to access the underside of the deck to do the job. If the existing joists span two bearers or more and your replacement will be a single span you would need to increase the size of the replacement joist.

Thanks, aldav. The rot is indeed very localised. The part of the joist the loose board screws into has rotted about a third of the way through while the joist is still good where it supports the two boards on either side. It's a narrow deck so the joists are only supported at their two ends.

[rwbuild]

From your description there is no membrane between the decking boards and the joists https://www.bunnings.com.au/our-range/brands/p/protectadeck , it also seems from your description that the localised rotting is under a join between 2 boards end to end.
If the boards are screwed, remove boards, replace joist, if nailed use a multi tool to cut nails or cheasts way as aldav said just place a new joist beside the old one

[Manupatree]

You're correct on both points -- no membrane and the part-rotten joist being under a join between two boards. Rather than taking up all the boards and replacing the joist I'm wondering whether I can take a short-cut and just replace the rotten part of the joist with suitable support for the boards.

[rwbuild]

The joist being supported at each end only eliminates any localised replacement where is rotted only. The affected joist is now none compliant in respect to its load carrying capacity and the whole joist needs to be replaced. There is no method what so ever that will repair the joist where it is rotted only.
The bad news is if there are more locations on other joists where the boards join they will be rotting as well. From a long term fix point of view I strongly advise you to pull the boards up, replace defective joists, install Protectadeck and SCREW your boards down. I know its not the answer you wanted but in the long term financially you will be in front and have no liability if someone were injured if the joists gave way. Insurance companies today have made it an art form to find a reason not to pay out and the classic one is "you failed to maintain the structure in good repair and condition fit for purpose".

[Manupatree]

The joist being supported at each end only eliminates any localised replacement where is rotted only. The affected joist is now none compliant in respect to its load carrying capacity and the whole joist needs to be replaced. There is no method what so ever that will repair the joist where it is rotted only.
The bad news is if there are more locations on other joists where the boards join they will be rotting as well. From a long term fix point of view I strongly advise you to pull the boards up, replace defective joists, install Protectadeck and SCREW your boards down. I know its not the answer you wanted but in the long term financially you will be in front and have no liability if someone were injured if the joists gave way. Insurance companies today have made it an art form to find a reason not to pay out and the classic one is "you failed to maintain the structure in good repair and condition fit for purpose".

You're right, of course. Seems unlikely that just one of many cheap pine joists would have become rotten. Seems like a massive and joyless task though -- maybe I'll send a small child down there to check for rot. :rolleyes:

[rwbuild]

Tape your mobile phone to a stick, start video recording, poke under deck, view results.
DON'T send small child under there, you don't know what nasties or discarded sharp objects (tin, glass, needles spiders) is under there. I know you wouldn't but there are some Neanderthals who would

[Manupatree]

Tape your mobile phone to a stick, start video recording, poke under deck, view results.

I like it! Thank you.

[rwbuild]

Your welcome, good luck. Let us know how it all goes.