Small damp patch

It's as simple as this - you MUST find out the cause and rectify it.

You MUST. Musty musty MUST.

If you could post some photos showing the affected area, and also some taken from the outside, we may be able to help.

 

Could be broken/cracked pipe to gully.

All vents needs to be cleared to allow good air flow under suspended floor, otherwise you'll get damp & rot appearing.

Need photo's as DA already mentioned.

 

And which exact parts felt damp?

Ok, I can't tell what's going on, but there are a few generalisations I think I can mke:

1) For the sub-soil to feel damp isn't necessarily 'wrong' - after all, it is often chust that - the ground under the house. If you have a high water-table, then it can feel damp. Some fold will even have puddles form under their floors at times. I don't think a DPM was a standard fitting once upon a time, and may not even be so now.

2) However, if only one area of the sub-floor feels damp whilst the rest is bone dry, that would suggest there's a 'cause' such as a leaking drain or similar.

3) Even if the ground under the floor is damp, your timbers should NOT be. Two things should protect them - one is the presence of a DPC along the supporting end and dwarf walls where the joists sit, so that NO moisture at all should be able to pass from these lower walls on to the joists. The lower walls very likely WILL be damp to some extent as they are sitting in soil and do act as 'wicks'. But, the DPC should BLOCK that moisture and keep it from the timber parts. And the other protection (as you know) is the presence of good ventilation provided by enough vent bricks/grills.

So, damp ground isn't necessarily a problem (tho' not desirable) but damp joists ARE! The fact you have damp joists suggest that the DPC is not working, although it could also be down to inadequate ventilation (ie - two ways that your joists could become damp - one is from the moisture coming up the wall bricks and being absorbed by the joists (faulty DPC), and the other is due to the build up of air-borne moisture under there (possibly due to a drain leak) which then condenses out on the joists and floor. This should NOT happen because there should be a good through-flow of ventilating air via these air bricks.

So, so, even IF there is a broken drain, really these joists shouldn't be getting that damp. So, as well as there possibly being a 'cause' for the wetness under there (eg broken drain), I would suggest that the timber's standard protection against damp (a DPC & ventilation) is possibly inadequate.

I think you need an experienced builder to come in and have a look. I do not see this as an expensive job, but if the culprit is due to a broken drain outside, there will obviously have to be some mess created out there in what looks like a tidy finish .

The vent on the outside looks slightly strangely positioned too - I would have expected that the pebble-dashed wall to stop with a bell-strip right on the DPC level, but the vent is actually spanning both the Pebb-dash and the smooth-rendered strip below. It looks as tho' that pebb-dash has been taken down over the DPC layer - a possible breach?

All guesswork - it's time for an experienced builder to come out and report; this should be a simple ask for them.

And, find out the name of the builder who did this work (pebble-dashing, drains etc) on the house because they may well be liable in which case they will have to put it right.

 

Yes, I'm sure a camera will help - I wasn;t suggesting it would need digging up to discover the cause, only to effect a repair - if that was the cause.

It's a good sign if it has dried out when exposed - that would suggest that proper ventilation down there would keep such issues at bay (as it should have...).

An experienced builder should be able to give you a thought out opinion after a short investigation, I think.

Ie - is the damp ground patch unusual?

Is it restricted to that small area?

What has allowed the joists to become damp - is it 'rising' along with a break in the DPC, or is it condensation which hasn't been cleared by proper ventilation?