Basement conversion: What about rot in joist ends?

[climber]

When a basement/cellar is converted into a habitable room, isn't there a risk of subsequent rot to the joist ends?

Before the conversion, there are normally airbricks, giving a good airflow in the cellar to try and reduce moisture in the walls/joists.

After the conversion, typically, the joists ends are left in the wall (they are not put onto hangers), there will be a membrane going up the wall to directly under the joists, with insulation between the joists, and on top of the membrane, and then the walls and ceiling will be covered with plasterboard. So, it appears that the ventilation of the joists ends and walls will be severely restricted.

Doesn't this mean that it will likely cause rot in the joists ends?

 

[Blagard]

As long as your joist ends are above DPC and the ends are not in contact with wet/damp brickwork it is not a problem.

Where end joist rot has been a problem in the past, the new joists should be wrapped at the ends with a DPC material to form a pocket in the damp wall

 

[climber]

But if there is no problem, why is generally recommended that there should be airbricks into basements?

In a normal basement (that hasn't been converted) there would be some ventilation, even if there were no airbricks, but it seems to be highly recommended that you do have airbricks. But on all the websites describing membrane tanking, I've never seen anything that mentions how the joist ends are ventilated.

Is the assumption that, after the basement is tanked, the airbricks will still allow a very small amount of ventilation to some parts of the joist ends?

I can't work out why airbricks seem to be an important requirement in ordinary basements, but seemingly ventilation to the joist ends is not a requirement after a basement has been tanked with membrane!

 

[tony1851]

More often than not, houses with basements usually have the ground floor joists around two feet or so above ground level (note how many larger Victorian houses have steps up to the front door).

The ground floor joist-ends are then a good distance above the ground itself. Any damp rising up the wall has a good chance of drying off due to air movement outside.

But if doing a cellar conversion, any dampness naturally occuring in the below-ground wall could be driven upwards by any tanking. It will still air-off above ground level, but it is important also to take particular care of joist-ends. As above, wrap in a dpc material, stapled on.