Rotten floor joists - help!

[Elementary]

Hi! We’re fixing up a Victorian terraced house and could really do with some advice.

There is an air brick in the downstairs front room wall which was installed at street level. Since then, whenever it has rained or snowed, water has made its way directly into the surrounding brickwork and into the wooden beam/girder directly in front of it. We are planning to replace that air brick with a regular brick, and install a periscope air brick above street level.

The beam is quite rotten (at least half of it has disintegrated), and so have the ends of at least two floor joists. We’ve included some photos here.

Here’s our thinking at the moment—please tell us if this would work and/or what you would do differently. We’re planning to support the two affected joists from below, using temporary timber supports. We would then cut the rotten ends off both joists, and then extend/sister them with fresh timber (c24, treated). Before extending them, however, we would take the opportunity to cut out the rotten segment of the beam and replace it with fresh timber as well, so that when the joists are extended again, they’ll come to rest on fresh timber.

Thanks in advance!

Leon and Kat

 

[Munroast]

just looks like a bit of wet rot in the ends, that dies once the source of dampness is gone - so hopefully nothing to worry about


that bit of wood they are sitting on needs fully exposed to make sure there is no dry rot going on. could that bit of wood be replaced with a course of bricks (bit of DPC between brick and joist)

May be the flooring joists could just sit on bricks and may not need to go back into the wall? just make sure no wood is in contact with damp walls

whats going on with the air vent - it looks like its been taped up - get that unblocked so there is plenty of air movement

 

[^woody^]

Any timber built in to the wall will need protection from damp. Treated timber is not enough.

Deal with any excess water entering the air brick. Divert any runs of water that directly affect the area, and fit a liner at the back within the wall so that water does not soak into the surrounding masonry.

 

[ree]

OP,
You have a very shallow space below the suspended floor. See "Similar threads" below: 18 August 2024.

Could you post pics of the front and rear elevations at ground level - could you also point out the front and rear DPC's?
Ventilation under your suspended floor(s) is meant to flow from the front elevation to the rear elevation.
Air bricks spaced at 1500mm centres provide the ventilation.

After supporting the floor & cutting off rotten joist tails remove the rotten "beam". Collect all wood debris scraps and clean out wall pockets. Spray the brickwork with fungicide.
Replace the beam with a similar beam wrapped in DPC material.

All timber joists & plates should be shielded from masonry by DPC material.
Chimney breast alcoves are always suspect for joist tail rot & lack of ventilation.