Damp crawl space – Fixing damp under the floorboards

When you living in an older house damp is a constant threat to be kept at bay.

We’d already spent a couple of weekends fixing damp problems in the house, and I was really happy with the results.    The house has been drying out nicely, and the constant wet patches in the basement have now disappeared.

However, while checking for leaks in pipes under the lounge (there were none) a few weeks ago I noticed how damp the subsoil under there was.

A damp crawl space (the space under the floorboards) is a really common problem, but not one to ignore.

Moving rubble to avoid breaching the damp course
Moving rubble to avoid breaching the damp course

Woodworm thrives on humidity.  Anything under 70% humidity and woodworm won’t get started.  Dropping the humidity just a little lower, to around 60-65% will stop even existing woodworm from continuing to spread.  This is why modern houses, with central heating, rarely suffer from the woodworm that used to be such a threat to older houses.

First thing to do to sort out a damp crawl space is address the source of the problem.

Damp
Damp

In general damp under the floorboards can only be caused by one of three things:

1.  Poor sub-floor ventilation

2.  Rising damp from the soil

3.  Water entering from above, for example a leaking water pipe or drain.

The first of these I tackled was the easiest.  Ventilation is provided by air bricks.  These are really important, but some people seem to want to cover them up to stop cold air getting in.  Bad idea.

In our case the air bricks at the back of the house were in place, but were so clogged up with dirt, dust and old paint that no air could get in.  I chipped off all the old paint, and the iron underneath was so fragile and rusted that it disintegrated.  I’ll need to replace the brick, but for now at least they let air in.

Eli clearing under floor
Eli clearing under floor

To get air movement you  need air bricks on both sides, so I checked the front.  From outside these ones looked fine.  Clear and clean.  However as soon as I go under the house I saw the bricks were covered by the glass-fibre insulation that had been fastened under the floorboards.  Easy job.  Done.

Freeing up the air bricks alone has made a good difference.  Already the air has lost its musty smell and the ground looks drier.

But to really speed up the drying out the next job was to clear out some of the  old rubble, building waste, soil and general detritus that had been dumped under the house over the last 100 years.

All this old abandoned rubbish attracts and holds water, so needs to go.

So, this weekend, Eli and I armed with trowels, dust masks and buckets, cleared out all the old muck.  Not a pleasant job.  There was very little space to work and lots of sharp old nails and stones to get in the way.   But, very satisfying to complete.

Above are some pictures of the work.  I’m pretty confident that the space will now dry out nicely.  And just to monitor it I’ve installed a remote humidity meter so I can monitor it over time.

Piles of damp soil in the crawl space
Piles of damp soil in the crawl space

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