Damp Extension Base

[Gary0]

Probably a daft question but ...

I presently have the floor up in the extension so that I can modify the routing of cables and pipes etc.. And I have noticed that the concrete base can be noticeably damp on one side, under where an air brick is located. At first I assumed water was getting through the holes in the air brick, but on further investigation I am no longer convinced. The brick is well above the ground level, outside. And being a couple of foot max from the fence, I can't believe it blows in. In any case, to a *much* smaller extent, the base can get damp near the exterior door also.

Is this normal for houses ? Or something to be concerned about ? As far as I can tell the damp-proof course appears to be a few brick layers above the base level (although it doesn't stick out sufficiently to be obvious, I can just about see a black line in places) and damp isn't seen anywhere near the floor level. I just wasn't expecting the base to become wet each time it rained.

Cheers.

 

[Gary0]

Seriously, no one knows ?

I thought those with building experience would know instantly, or is everyone thinking it's too obvious ?

 

[TexMex]

Does water pool against the bottom of this wall. If so, it can penetrate through the brickwork to the inside. Once it's inside, it will dry out slower than the pool, from whence it came. If this is your problem you can probably solve it by means of a french drain installed against the wall, leading the water away to a soakaway.

 

[Gary0]

Thanks for the reply.

Neither outside nor inside on the extension base does it get bad enough to pool. The concern is more to do with the fact that a clear damp patch occurs inside. I wasn't expecting that, but have no building experience so don't know if it's normal and should be ignored, or something I need to address while the floor is up, before it causes a problem.

Next time it rains (tomorrow probably if the weather stays as it is) I'll check the outside to be sure, but as I recall it just becomes normal wet concrete. No obvious reason why it should be taking in water.

 

[TexMex]

It's most likely just rising dampl Since you have a suspended floor, this is quite normal. As long as a DPC exists under any structural timber for the floor, there is no requirement to have a DPM in the oversite. Unless there is excessive dampness, it's nothing to worry about.

 

[Mr Winston]

what is the use of the extension

if a utility/kitchen or similar have you had any flood or leak or spillage in the not so distant past

id assume youd have mentioned it if you had - but its possible

 

[Gary0]

Thanks both. I'll assume it's ok to leave it then.

It was a kitchen before I ripped all the units out and started refurbishing it. Will be again hopefully before too long. But this is definitely weather related. Comes and goes with the rain.

 

[diyjon]

my parents have a similar problem. they have a tiled concrete floor with a dpm underneath it. When it rains part of the kitchen floor gets damp. I am repointing the external wall and going to redo the dpc but its very puzzling. does seem to be weather related because it doesnt appear when its dry. anyone else hazard a guess? could it be condensation? it only happens at the end of the kitchen next to an exposed wall.

 

[TexMex]

my parents have a similar problem. they have a tiled concrete floor with a dpm underneath it.

Not that similar then. My guess is rubbish in the cavity to a level above the DPC.

Remove a couple of bricks outside just above the DPC (CAREFULLY, DON'T DAMAGE IT). Have a peek in between the two walls. You should see the cavity extend below the DPC. Anything breaching here will lead to dampness carried across into the inner skin, and thence into the concrete ABOVE the DPM.