Dry rot identfication and treatment

19 Sep 2022
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United Kingdom
We are having the upstairs bathroom redone in our Victorian terrace. During the stripping back, a large chunk of plaster fell from one of the outside walls. It revealed what we initially thought were plant roots that had been growing in a cavity where the plaster had come away. We're now having second thoughts. It looked to originate from the point where a ventilation fan had been poorly installed, with the air being directed towards an air brick in the outer brick layer. Whatever it is, it appeared to be contained to the area shown in the pictures. Does this look like dry rot or something less concerning?

There are also two beams running along the length of the top of the wall, holding the roof joists in place. Exactly above the bath, the innermost beam is fairly soft and crumbly to the touch, although completely solid just to the right and everywhere else we have looked.

The builder has removed the potential dry rot material, and is suggesting just applying a dry rot treatment, rendering, then plastering over. Is this advisable?


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Yes looks like it. Don't rely on your builder for advice on treatment unless he's experienced. He can potentially do the work but not specify it.

Rotten timber plus 600mm should be cut out, and proper sterilisation done to all areas. The actual cause also needs to be determined and dealt with. Get proper advice or do proper research, as you don't want to be posting back here a few weeks after the bathroom's all done
You have dry rot.
With dry rot its worth paying an Independent Damp & Timber surveyor to do a detailed survey, & schedule of works, of the bathroom area & to be thorough, the rest of the Victorian house.
Thanks for confirming. Will definitely look into this further with someone who knows what they're talking about.

This is particularly annoying as we just had the entire rear roof redone :/
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