Or put it another way, how much is enough?

The question:

Has anyone got any bright ideas about controlling the level of under
floor void airflow, and also setting the appropriate levels?

The background:

When we moved in here, there were some damp areas near the bottom of
walls, and a rather musty smell in a long deep (unheated with little
airflow) cupboard under the stairs. Investigation in the cupboard found
that condensation was forming on the cold outside wall and running down
it into the skirting and floor. This was rotten and rather wet. Looking
under the floor found a rotten joist against the wall, and more
worryingly the undersides of the floor boards were literally wet, and
not just close to the source of the water.

So I replaced the joists, and insulated that end wall in the cupboard to
fix the condensation.

To address the general dampness under the floor I concluded that the
main problem was lack of airflow in the substantial underfloor void (4'
deep or so in places with lots of dwarf walls holding up the downstairs
floor joists), and investigations showed that there were only air-bricks
on one side of the house, and not many off them. So I stuck in an
additional few where there were conspicuous by their absence.

The result after several years, is that the under floor space is now
bone dry, and also as a bonus the walls that were previously a little
damp at the bottoms[1] have also dried out nicely.

So far so good. However the downside of this solution is that we are in
a windy location, and that extra ventilation under the floor wastes more
energy. Even though the floors are carpeted, and have underlay, on a
cold windy day you can feel the difference. One fix would be to throttle
the air flow a bit - we probably need less to keep it dry than that
required to actually dry it out, but how much?


[1] probably down to condensation again, since they are 9" solid walls
with render on the outside - so less able to breathe than they might
otherwise be


--
Cheers,

John.

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