Damp problem - advice needed!

[Graham]

Hi,

I have a bungalow built in 1950s with a suspended floor and a pitched roof extension. The extension measures 12ft x 15ft and is heated by a 2ft x

2.5ft single radiator (inadequate, I know). Since moving in 9 months ago, I have noticed mould growing on curtains / carpet etc particularly in the extension. The extension is noticably colder than the rest of the bungalow even though it's directly off the lounge. I pulled the carpet up today and found that there was white mould (smells mushroom-like) underneath the underlay on the chipboard flooring - it feels damp. I removed a piece of the flooring and got a good draught so the air bricks must be Ok. It's just chipboard flooring - no insulation of any kind. The original part of the lounge has floorboards and does not feel damp.

What do you reckon - is it a ventilation problem? Should I take up the chipboard and lay floorboards and hope that improves things? Or does the floor need insulating - how would I go about doing this? Could condensation have built up in the chipboard due to inadequate heating?

Any advice greatly appreciated!

Graham.

[Set Square]

Are the joists wet? What is supporting them? Is it possible that there's a sleeper wall under the joists which doesn't have a proper DPC?

[Graham]

You are spot on! The joists are wet and they do appear to be supported on a sleeper wall. How should I damp proof this? Can I lay a damp proof membrane directly under the joists?

Thanks,

Graham.

[Set Square]

Yes, there should be a strip of DPC material on top of the sleeper and under the joists to stop rising damp from being transmitted to them.

This is pretty fundamental. If the builder got *that* wrong, I wonder what other nasties are lurking there!

[xaftor]

It is unlikely that your mouldy curtains, or indeed the majority of symtoms you are suffering in the room are the result of anything other than condensation.

Which elevation is the extension on - North, North East? or is it in a particularly windy environment?

Also, being built in the fifties, It will have dreadful u values in the walls and floor which aren't going to help.

Heat it better, ventilate it better (does it have PVCu double glazing?), generally follow all good guidelines to combat condensation and your mould will disappear.

If you do indeed have wet joists this could be caused by a lack of damp proofing on the sleeper wall, as SS suggests. Howver, if this is so, it's an error on the builder's part and, to be honest, if you've had wet joists sincer 1950, you're very lucky you haven't got any kind of rot. You should check on top of the sleeper walls for a black substance between the brickwork and the timber, probably plastic but maybe bituminous which is acting as a dpc. If you can't see it, the sleeper walls may be built directly off the oversite and they've put a dpm beneath that.

If you really haven't got any form of dpc then you're going to have to slightly jack up east joist (quarter of an inch or so) in the vicinity of the sleeper wall and slip a piece of dpc between the wall and the joist - no big deal. To be honest, this is unlikely, it's more likely to be sub-floor condensation.

If you can hire (beg, borrow,steal) an electronic damp meter, your joists should have a mosture content of less than 22%. Ideally it should be less than 20% but sub floors are never ideal places and they're usually on the high side. Don't use it on the walls, you'll frighten yourself with the levels of condensation you obviously have :)

If you want any more info on condensation, email me directly and I'll give you the url of my website.

HTH

Xav

Have alook and post back

[Graham]

It's on the South.

Yes, it has PVCu dg, but it doesn't help that it has three outside walls and a double patio door.

It's only on the extension that we really have a damp problem and it was built in the 1970s. The neighbours say it was built by the then owner who was "a builder".

The joists feel very damp. I have lifted more of the floor and I have 3 layers of bricks, then a *possible* dpc, then a piece of 4x2 on it's side and then the 4x2 joist on top of that. The dpc seems very poor - it's more like a heavy gauge polythene - like the blue damp proof membrane that B&Q sell. It's been mortared over in places. Does that matter?

Thanks for your help,

Graham.

[Graham]

On closer inspection there is some form of dpc, but it's not very good (see my other reply) - it's like a heavy gauge polythene. There was even some plant life underneath - some ivy had managed to find it's way in. The joists feel very damp.

A few months back we had a new fireplace fitted and the guys found that a piece of roofing felt had been used as the damp course for the hearth. Is this dodgy?

Graham.

[xaftor]

The joists feel very damp. I have lifted more of the floor and I have

3 layers of bricks, then a *possible* dpc, then a piece of 4x2 on it's side and then the 4x2 joist on top of that. The dpc seems very poor - it's more like a heavy gauge polythene - like the blue damp proof membrane that B&Q sell. It's been mortared over in places. Does that matter?

That's probably Visqueen and it's fine, as long as it stops damp striking through, just make sure the mortar doesn't bridge it anywhere and touch the joists.

You've put your finger on the cause. Three external walls, 1970's construction (no cavity wall insulation) and PVC windows that probably haven't got trickle vents and are kept shut all the time!

Go to

and have a little read

HTH

Xav

[Graham]

I think in places the mortar does bridge it.

Thanks for the link - very interesting indeed. We do have black mould in places (above the floor), but under the carpet/underlay it's white speckly mould and smells mushroomy - almost like brie rind in texture. Also, if it is condensation, how would the moisture get from the room down through the carpet/chipboard flooring in order to make the joists damp? Below floor level there are three air bricks and there seems to be good air flow. The damp proof course for the outside walls appears to be exactly at floor level - is that how it should be?

Thanks,

Graham.

[xaftor]

Your joists should be sitting on your dpc and the air bricks should be between the joists so that air circulates around them.

As for the mush, it may be a reaction from the adhesive in the chipboard or carpet underlay. Try folding the carpet back, airing the room and look again in a day or so.

A logical approach to this might help you. Moisture can either rise from the ground or penetrate via a structure such as a wall which has moisture on the other side of it. From what you say, your's could possibly be rising but the chances are it isn't and that the dpc (such as it is) is working. The only other kind of moisture available other than plumbing leaks or rainwater is that which soaks into materials from the atmosphere, - hygroscopic.

Rule them out one by one and you'll be left with your cause. From what you say it's the latter kind, i.e. condensation. This is evidenced by the mould in the room itself and the conditions you describe.

What is the sub floor base made out of (beneath the floor), is it just earth or is there a concrete screed over it? Also, does the ventilation cover the whole floor or is it windy just in one place?. Also to check, is it just ventilated when the wind is in a certain direction or is it constant?

I can't see it being anything other than condensation but that's not to say you shouldn't be concerned. Condensation is the number one cause of dampness I see and it can be very destructive.

However, you need to check the moisture content of your joists before I can advise you further because what might seem wet to you could be dry as far as fungal activity is concerned. If that's the case, all we have to cure are the problems in the room itself.

Sorry if this is disjointed, bit late in the day, been up since four o'clock. If you're still worried tomorrow, give me a ring and I'll go through it with you on the phone.

xav