Damp in basement flat

[Nibus]

hello all,

I live in a basement flat (about 3/5 of the walls below ground level) which is suffering from damp. When we got the mortgage for the place the surveyor recommended we get the damp sorted (although not as a condition of the mortgage). The mortgage broker recommended this firm:

The floor is concrete and according to the surveyor has no damp -or very little. The trouble we have is with the base of the walls where we frequently get mildew/black mould forming. The plasterboard wall behind the sink in the kitchen is practically soggy. The adjoining building next door is empty and has been for years, so I don't know how much that contributes to the problem.

Now, reading through this newsgroup's posts about damp, I'm a bit confused where to go next - we have uPVC windows throughout, which apparently contribute to damp/condensation, and the heating is poor (electric heaters bolted to the walls). The heating in the bathroom is just an electric fan heater stuck to the top of the wall.

Because our heating is so bad, we don't keep the windows open very much

- the only other ventilation is slot vents on the windows and air bricks in the walls just above ground level. We have patches of mildew forming where the air bricks open behind the plasterboard.

We have about =A33k spare to fix the problem, but I don't want to get a quote from a damp remedial company who has an interest in selling me a remedy I don't need. I'm wondering whether central heating + improved ventilation will have more effect than damp-proofing I may not need. Also, I don't want to go ahead and do the central heating first in case damp-proofing *is* what I need.

Any advice what to do next?

[Stuart Noble]

I'd go for the central heating first. You really can't make any assessment about damp without a reasonable temperature and ventilation, especially in a basement. That said, I'd block the air bricks because

*that* much airflow from outside in winter would be counter productive. IME heat from cooking tends to find its way to the coldest spot in the house and will be more obvious lower down the wall. Try testing this next time you cook some greens. Often the strongest smell is not in the kitchen at all. The soggy plasterboard behind the sink sounds more like a plumbing or waste leak. Is it tiled? Is the seal between worktop and tiles okay? If it's an inset sink, the area behind the taps needs frequent mopping IME.

[Tim Mitchell]

As the mildew/mould is forming on the coldest places on the walls, it just sounds like a condensation / ventilation problem rather than a real damp problem. My house, which is entirely above ground, has exactly the same problem if we don't open the windows often enough.

[Harry Bloomfield]

on 04/08/2005, Nibus supposed :

I would suggest there are several problems.

1. A cold or cool atmosphere - you need some adequate heating to be installed.

1. Poorly planned ventilation. All the moisture from your breathing, cooking and washing remaining in the atmosphere. Add a cooker hood extracting to outside. Bathroom fan, plus ensure there is some through natural ventilation for other rooms.

2. You might also consider adding a dehumidifier, to draw water out of the air.

Once the above is done, you may well find the damp problem disappears.

[Pete C]

Hi,

Do you know how much insulation there is in the walls, floor and ceiling?

cheers, Pete.

[Nibus]

hi Pete,

The floor is flat concrete with underlay and then carpet, the walls (as far as I can tell) have no insulation - plasterboard on studs holding it away from the brickwork, and I'm pretty sure there's no insulation in the ceiling - the upstairs neighbour had the floorboards up for a water leak and I didn't see any insulation.

Thanks everybody for your replies. Central heating will get installed eventually - we don't have mains gas so that will have to be installed too :/

[Pete C]

First of all it would be worth running a dehumidifier along with some heating to dry the place out a bit, and check on how much moisture it's removing and whether this decreases or remains at a high level. Also get a hygrometer to keep an eye on relative humidity.

It could be well worth adding insulation between the studs in the form of foil backed Kingspan/Celotex (google this group for more info) as doing so after the CH rads are in will be quite a hassle.

The gap between insulation where the studs are is then taped over with foil tape to maintain a vapour barrier.

If there's a lot of damp coming through the basement walls the insulation should spaced away from the wall using battens which could be stapled to the studs, and this cavity vented to the outside with airbricks.

Usually there is tanking to stop this happening, if there isn't any or it's failed then your damp problems could be a lot worse.

Is it the plasterboard that is mildewed and is the bottom in contact with the concrete floor? If so it would be worth spacing it away from the floor with a wooden batten or leaving a gap to stop any cold bridging that would encourage condensation.

If there isn't a decent extractor in the bathroom then that makes a big difference to humidity. Also a cooker hood and maybe dishwasher will help keep humidity levels down.

If insulating the ceiling rockwool batts and plasterboard without foil backing could be best, they will keep the heat in but allow some humidity to escape upstairs :)

cheers, Pete.