Dampness in ground under suspended floor.

[Mike D]

I have a Victorian end-of terrace house, built with a cavity brick wall and a brick foundation. It does have some rising damp. When I take the ground floor floorboards up, I find a lot of dampness in the ground (i.e. the old rubble) near the walls. Two or three feet in form the walls, however, the ground seems dry. Even after two ro three weeks of no rain, the dampness remains.

Is this normal? Outside the house, there is a tarmac pavement, which I would have thought would prevent much rainwater from soaking into the ground... but perhaps not.

The house is also at the top of a rise, so drainage is good around the outside of the house.

I'm just wondering if there could be a leaking water main near the house that is making the ground damp unter the road and pavement. How can I determine whather this is the case?

Thank you,

Mike D

[meow2222]

Ground is normally damp, thats why the floors are suspended. Really though this is not a good place to ask these kind of questions. Ask:

[Stuart Noble]

Will you stop redirecting everyone to your bloody shop. Suggest it as an alternative by all means, but it's not your place to trash the opinions of people on here.

[bp]

Mike,

There is another thread by someone else that is asking a similar question that has been posted very recently. You may want to look at that as well. Here is my reply to that thread

BTW, when I lifted my floorboards, the ground was very damp as well. espacially near the walls. I found there was loads of rubble towards the edges. I removed a lot of that. I think that in my house the problem was many of the air bricks were blocked, thereby preventing airflow underneath.

Hope this helps

[Steve]

Absolutely and well said.

Though I do read the "periodpropertyshop" forum occasionally, I find that it is, like most web forums, not easy to navigate and awkward to use.

uk.d-i-y has many experts on many subjects and a lot of people with a wealth of experience on just about everything including damp problems.

Steve

[The Natural Philosopher]

Yes.

Or evaporating out, or running into the ground somewhere else.. .. but perhaps not.

I doubt it.

The sort of weather we have been having is hard enough to do two more three things.

1/. Splash off that tarmac pavement into the wall above the damp proof. Or below it, if there is loose rubbled piled up bridging it (assuming it HAS a damp course).

2/. Raise the local water table enough to allow moisture to seep through the foundations and under the house

3/. Drive rain in through the ventilation holes.

If you have the floor boards up, clear out the rubble at the least.

If it hasn't got a DPC you can control the rising damp by injection, and its no bad idea to put a waterproof render outside above the DPC where it may get splashed..but I suspect that isn't the real problem in this case..and may make things worse if it stops the outer leafe breathing.

Finally, underfloor ventilation is there to keep the timberwork dry and prevent rot..it won't clear surplus underfloor water tho, not is it designed to.

Normally you do that by ditching round the property and backfilling with gravel (and often a perf. pipe too), and a drain to the moat so formed, to a soakaway or what have you.

That is the most effective way of lowering the local water table round a property..put in a moat!

[Mike D]

Thanks. Yes, that sounds like what my place could do with. I have loads of under-floor ventilation, as the airbricks are all unblocked. I have already cleared the rubble away from the walls under the floor, to improve the air drying, but even after 2 weeks, the inner skin, below the slate DPC level is still almost as damp as before, as though it is still sucking up moisture from below ground level.

Mike

[Mike D]

Thanks. My air bricks are clear and I have plenty of underfloor ventilation. I think thee is just a lot of moisture in the ground surrounding the house.

Mike

[The Natural Philosopher]

Well if its below DPC, frankly my dear, who gives a damn?

I assumed you had a problem inside the habitable areas..

When I demolished my house, there was a small POND under the living room floor.

The only internal problem was the fireplace sucking it dry..no easy way to damp proof a whole structural chimney stack.

Of course originally that would have had a permanent fire. Sucking wetness up the chimbley

[Jim Alexander]

When my Victorian house had the various damp treatments the one that has really made a lasting difference was the laying of a vapour barrier to the solum - sand, polythene, concrete in my case. The moisture level below the slate DPC is not that important but the moisture level in the wall plate and joist ends in particular is. My wall plates were shot with rot and needed replacment and a new DP membrane under. You will need a meter to test the timber properly.

The airbrick provision in a Victorian house is less than current standards even though there is more moisture present. Not advocating this but damp specialists will advise more if you ask.

Jim A

[Mike D]

I do. The DPC doesn't exist all the way around the house, believe it or not... Also, the cavity has some debris in it, and I can't be faffed to clear it out. :-)

Mike

[bp]

Hi,

Please explain the 'perf. pipe' you talk about. I have done the ditch thing on a wall in my house where the outside ground level was too high, but did not use any pipes.

An explanation would be useful to decide whether I need to consider this

Thanks

Bhupesh

[meow2222]

this is inappropriate for historic brick constructions, which handle damp differently to modern builds. This approach has been used for long enough for people to be quite familiar with the problems & damage it causes.

yes, it may. There are other known problems with this approach too.

no comment.

The site i mentioned is not mine, and the forum is not commercial. Its a place where you can be pointed to some of the research and get it explained by people that know the subject. Its a shame this is a bit of a blindspot with ukdiy, which is an otherwise very good newsgroup.

NT

[The Natural Philosopher]

Oh dear. Here we go again.

If you want to live with coal fires and drughty windows, then fine.

I don't.

[The Natural Philosopher]

Its simply a 'leaky' pipe..you can buy it cheaply. Its a slightly cheaper alternative to traditional unglazed clay drains..the theory being it forms a slow entry fast exit for water if it is laid in a gravel filled trench. Its less suitable for heavy loads though, being thin plastic...