Advice on Wet Rot and Woodworm

Hello, You will probably be better off replacing the sections of defective joists with pre-treated ( tanalised ) timber or just apply a preservative such as Cuprinol Five Star to untreated timber. Cut back the joists around 300mm past the last sign of any rot. Same applies for the floorboards. If it is dry rot then you may have to remove some of the plaster in the surrounding area and sterilise the walls before putting on a new plaster. The main thing to do is to stop the timbers getting damp as this is what starts the rot so make sure there are no leaks and that there is plenty of sub-floor ventilation (air-bricks) to dry out the under floor area. I hope this helps.