Damp patch when it rains

Sandra67 · 26 Nov 2015

Whenever there is a prolonged period of rain a patch of damp appears at the bottom of an internal wall. It's not huge, maybe 6 inches tall but it used to be half the size it is now (I'm going back a year or so). On the other side of the wall is our conservatory and on this side there are no signs of damp; we've also lifted the carpet and it appears dry underneath but can't get under the conservatory floor as it's tiled. The skirting board appears dry and undamaged.

The house is 1940s.

There is an air brick outside and I'm wondering if that's likely to contribute (see image)? I forgot to draw it but in the bottom left corner is our electricity meter cupboard so it's difficult to see the back of the outside wall if that makes sense, but from what we can see its dry. In summer there is no sign of the damp and during light rain showers it also doesn't appear.

Any ideas?

CambridgeBrummie · 26 Nov 2015

If it only appears during a prolonged period of rain, this could mean it is coming in from above the conservatory roof, but more likely it is from ground water. If the house is 1940's, do you know if it has a Damp Proof Course? There are various chemical injection systems on the market to install a new DPC.

ree · 26 Nov 2015

It could be that no cavity tray was installed over the doorway(?) entrance lintel?

The cavity might be bridged with rubble? The conservatory floor might be bridging your DPC at the doorway(?) threshold?

Most 20thC houses had DPC's of some kind.

Chemical DPC's of any sort are worthless in my opinion.

Its doubtful that the air brick is the source of your problem - is the air brick set above ground level?

Sandra67 · 26 Nov 2015

Thanks for the replies. Our home buyers survey says external walls are provided with an original bitumen based damp proof course membrane. Ground levels rise within close proximity to the dpc line. Allowance should be made for the reduction of the hard standing appropriately below the dpc and the introduction of additional surface water collection- not sure what that means tbh???!!

Here's a picture of the airbrick

ree · 26 Nov 2015

Thanks for the pic.

The air brick is useless: have the little openings cleaned out but later have it replaced with a 9" x 6" plastic air brick.

The ground levels in front of the air brick have been built up too high. I suspect that the DPC might be in the mortar bed below the air brick - dig a little mortar out and see.

All your air bricks should be in 9" x 6" plastic - do you think that you have enough air bricks for thro ventilation under the suspended floors?

If you provided pics of that external wall, and of the damp patch it would help.

theprinceofdarkness · 27 Nov 2015

Ree, that air brick, the cavities have been filled with a blown in fibre, and the little pegs around the edge holes of the air brick stops the fibres blocking the central area of the air brick.
Frank

Sandra67 · 27 Nov 2015

More pics

Sandra67 · 27 Nov 2015

ree · 27 Nov 2015

theprinceofdarkness,

Thank you for well spotting the blown insulation detail. The later pics, of course, confirm what you earlier noticed.

ree · 27 Nov 2015

Sandra67,

Thank you for the new pics unfortunately there's no context so for me, at least, i dont know whats what in the last three pics. eg. where exactly is the damp area that you indicated on the earlier sketch - and which door is shown in pic 3?

As noted above: there's blown insulation. This insulation could be somehow bridging the cavities and or pulling up moisture from any cavity debris.

You appear to have enough air bricks at the front of the house - what about the left hand side and the rear?

FWIW: there's quite a bit of moss and green splash marks at the bottom course of bricks in the bay - it would be a good idea for someone to crawl the house and examine the joists in the bay and any woodwork near the original damp position.

Sandra67 · 27 Nov 2015

Sorry the door to the left of the photos leads to the conservatory and to the right is the electricity metre cupboard

Sandra67 · 27 Nov 2015

We have 6 more airbricks at the back of the house/conservatory. Maybe worth getting a builder in to take a look?

ree · 27 Nov 2015

So the conservatory floor is higher than the house floor?
Is the conservatory floor solid or suspended?
And the house floor under the carpet is a suspended floor?

I still cant see the damp on the wall?

The "hard standing" that the report refers to is the bricks and flags in front of the house - the report is suggesting that you lower the whole area or perhaps cut a drainage channel (eg. a French drain) at the base of the front wall.

You seem to have plenty of air bricks - make sure that the "little openings" in the bricks are cleaned out.

Sandra67 · 28 Nov 2015

Thanks I will clean out the air bricks. The conservatory floor is slightly higher than the house. Not sure if the conservatory floor is suspended but the house one is. It's hard to see the damp as the paint is so dark but it's a darker spot, maybe this picture shows it

ree · 28 Nov 2015

Thanks for the new pic - i can now see the damp on the reveal.

Does the conservatory have air bricks? Modern conservatories typically have solid floors.

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