The Brew Cabin

Hello,

The construction of our new extension is close to completion. While removing some of the builder's rubbish I discovered damp on the screed and to a lesser extent spreading along the skirting boards (in an attractive green!!) in one corner of a room (this is also a corner of the property). In this corner is a boxed in internal SVP that is fed from the ensuite located upstairs. The ensuite is not yet in use and the drains are running clear.

I have read many of the posts that might relate to this problem and I think the underlying problem is poor drainage. I have come up with the following idea:

Our garden slopes downwards and generally towards this corner of the property. Before the extension was built there was essentially level ground extending about 4.5m from the original wall. n.b It had an external SVP. It is possibly a 1 in 4 to 1 in 5 gradient and I'm thinking that with the current absence of landscaping or specific drainage anywhere else for the water to run off to it is running down the slope of our garden, reaching the exterior wall and then running along the perimeter to this corner and then collecting in the soil. You can clearly see that the bricks below the DPC are holding a lot of water.

If that idea holds I'm then trying to figure how it enters the property. I'm doubtful that the DPC is breached. Is it feasable that it can enter in the gap between the DPM and the internal SVP. Is this a realistic idea? Most of the damp is on the floor and it is very local to the boxed in SVP. The adjacent room also facing the slope is a cloakroom and it too has an SVP. There is no damp there but if my theory holds it is because this is "upstream" from where the problem area is.

As an experiment I have removed some of the soil that is against that corner but I don't really see how that will help if it is a drainage issue. - It just made me feel a little better.

We owned the house before the extension was built and there wasn't a damp problem then.

So what solutions exist? drainage, improved damp resistance?

The builder hasn't seen the problem yet - but in a telephone conversation with my wife he suggested the screed was still drying out. I don't think he appreciates the problem yet! Also the Building Control Officer is due out early next week to provide a completion certificate - I guess this is a problem he will observe (assuming I'm there and can steer him in the right direction) and the certificate (and my final payment) will be withheld until the problem is rectified.

I would greatly appreciate anyone's thoughts on this. Perhaps we need to raid the piggy bank to landscape the garden already.

Apologies for the length post, Best Regards
Martyn

The web is a wonderful tool for may things, but when it comes to giving advice on a specific problem, there's not a lot it can do unless you fix-up a web cam so we can all see the problem.

I could be summat as simple as the screed being a few millimetres lowers at that point than elsewhere, and so the new bvuilding work all 'drains' towards that one point. I really can't see that the external groundworks will be responsible, given that you have a DPM built-in and that the BCO are involved in standard inspections.

I think you have to give your builder a channce to see it and then give you their interpretation. I've seen hundreds of new builds and extensions that seemed riddled with damp (in some cases, under 50mm or so of standing water) and then, just a couple of weeks later, the work is finished and the room is in full use with no apparent problems.

If you feel your builder is giving you a load of bull, then you have the option to ask the BCO to check the worksmanship and construction, but, to be honest, I can't help feeling that you're worrying unnecessarily.

I find most dampness problems are solved by the application of a little heat, plenty of ventilation and time.

However there is the possibility that you have an "Artesian Well" effect, with the building and DPM providing an impervious capping and the SVP providing the only outlet for the head of water that has built up beneath the extension.

The solution to dampness problems is rarely more damp-proofing, the water will only find another way out. Witness the number of people who have their floors asphalted and then end up with damp walls.