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I am replacing a poorly constructed deck, extended from what was originally a smaller cantilevered deck. The original dates back to the construction of the house about 35 years ago. Some parts of the joists are rotten and I don't feel comfortable integrating them into the new deck. I'm particularly worried about rot eventually reaching the part inside the house. And in any case, I want the replacement wider than the area with cantilevered joists so it seems like it would be a lot more work to reuse them.

So I'm looking at removing the original joists, at least enough to get them out of the way. I am thinking about cutting them as far back as I easily can, which might mean about an inch or two behind the face of the bricks. Then treating the wood and covering the holes with mortar. Is this a good idea? Am I missing something, or going about this completely wrong?

the partially removed deck

The red pieces are just sistered outside the house and had support further away. And in case anyone wonders: no, I do not intend to anchor a new ledger board to the bricks.

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I don't like the idea of extending framing through your envelope for deck support either.

I'd probably start by chopping them flush to the brick and then oscillate cut them back to give them an angle that slopes away from the side of the house to shed any water that may come into contact with them. At that point I'd paint them with pressure treated paint. Mortar / Concrete tend to wick water so embedding the end of your interior joists in the mortar isn't a fantastic idea. You could create a sheet metal cap for each of them and then embed them in the mortar but that is a fair amount of work.

The last deck I did I anchored posts with 3/4" threaded rod epoxied into concrete. The posts didn't touch the ground. I then put a beam on top of the posts that was 1-2" away from the edge of the house so there are very few connection points between the house and the deck (only the posts anchored to the concrete wall). I did this instead of a ledger board as I didn't want to open up inside for seismic anchoring within the joist bays where ledgers typically attach. I also didn't want to penetrate the envelope.

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  • Good point about mortar and water. Metal cap is indeed too much work but a layer of silicone sealant perhaps? I don't think that would hurt anything.
    – Olivier
    Apr 29, 2023 at 13:07
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    I'd probably take either some blueskin or some joist tape and use that to cover the ends Apr 30, 2023 at 21:48

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