Condensation and damp carpets/underlay

[dickrickulous]

Hello!

I am just buying my first house (which i live in as a tenant at the moment) and wanted some advice on some damp I have found.

I had a survey that pointed out high damp readings downstairs and recommended 2 new air bricks at the rear, double glazing throughout and potentially a new damp proof course if required.

I have been checking the house myself recently and seen damp areas in the carpet near the skirting and concentrated more heavily towards the rear of the downstairs which is colder (and where the new air bricks are needed). There is a damp proof course there but the survey said it was set slightly too high.

Lifting the carpet up shows the underlay to be partially damp at the edges and very damp near the rear. However the wood underneath seems fine and dry. I haven't checked under it yet but will be doing so this weekend.

My question is - can condensation cause this kind of damp to occur or is it likely to be rising damp? Also what is the best way to deal with this? I am intending on laying a new carpet down anyway but perhaps I should get a thorough inspection of the cavity below the boards?

 

[Heathero1]

We have the same problem. The carpet is very damp and the backing of the underlay is wet as well. However the floor underneath is dry. It is in a corner of our bungalow which sticks out south west facing. No smell or mold on the carpet or underlay, so the conclusion is that it is condensation. BUT we are not too sure how to stop it.
The carpet is ruined as is the underlay. At the moment we have it all pulled back hoping to dry it out.
The floor is concrete.

Any help or advice please?

 

[WoodYouLike]

What is your existing floor underneath? Old-fashion praquet or mosaic flooring?

 

[JohnD]

you have checked for water leaks, especially around radiator valves, haven't you?

to find out if the watrer is coming up from the floor or down from the room, tape a piece of clear plastic tightly to the flooring. If water forms on the underside, it is coming up from the floor. If it forms on the top side, it is condensation from the room.

But to get a floor wet from condensation is very unusual.

 

[WoodYouLike]

Not always JohnD. If the original floor is parquet or mosaic flooring which now has been covered with any plastic or dpm kind of underlayment the normal evaporation (old method) through the parquet or mosaic has been blocked = hence "condensation"

 

[JohnD]

damp coming up through the floor is not what I would call condensation.

 

[Heathero1]

The floor is concrete with tiles stuck on, then the rubber underlay and then the carpet. No mold on walls, skirting boards completely dry and solid (not spongy).

The floor underneath is bone dry, no water coming through.

Interstitial condensation is coming to mind. Am I correct or am I on the wrong tack?

Would a dehumidifyer be the answer.

 

[WoodYouLike]

damp coming up through the floor is not what I would call condensation.

What I meant was: normal moist now condensates onto plastic cover. Happens often when no thoughts are given to the old method/old circumstances in houses where wood blocks (parquet or mosaic) are now covered up.

Heathere1, it could be that your tiles are "sweating" and causing damp. In cases where such tiles are not removed prior to new floor covering it is always best to lay a DPM sheet over it first to make sure 'sweat' does not reach up. (Happens with old marley tiles etc)

 

[JohnD]

interstital condensation occurs when there is a temperature gradient through a material (e.g. wall cold on one side, warm on the other), and there is no impermeable membrane on the warm side to prevent warm, moist air diffusing into the wall, and the dew-point occurs within the material.

since I would expect your carpet to be inside a heated house, I would expect the carpet to be warmer than the floor, so not subject to interstital condensation.

Have you checked for the water leaks yet?

 

[Heathero1]

Yes, I did check for leaks from pipes, central heating etc. There are no pipes near that corner at all, the radiator and fire are over to the other side of the room. The tiles I mentioned are like hard plastic (old lino type - deep red) and no sign of warping or lifting in the joints of them. The bungalow was built in 1969, so no membrane under floor. The damp is only in that one corner which is approx 2 mtr square. The underside of the underlay is bone dry, just the top material bit of it and then the carpet on top of that.

 

[JohnD]

The damp is only in that one corner

Interesting to have damp carpet but not damp subfloor.

Have you got a dog?

Try the taped plastic.

 

[Heathero1]

No, we don't have a dog!!!
A couple of more questions, how do we get the carpet and underlay dry (we have them pulled over at the moment to let the air get to them)
Once we have it dry (I think we will need a new carpet) how do we keep it dry, is it a matter of putting down an insulated plastic sheet on top of the original floor and under the underlay (to stop the cold coming up) and buying a dehumidifyer to put into that corner?

 

[JohnD]

if you do the taped plastic test, we can work out where it is coming from and decide how to address it.

If it turns out to be condensation, //www.diynot.com/wiki/building:condensation_in_houses

 

[dickrickulous]

im going to try that plastic/condensation test. There is a radiator in that corner as well as a window and its also where we have been drying clothes up until recently. Could be a leak as well I suppose but can't see anything.

There was a damp proof course put in that corner in 2000 but my surveyor reckons it needs a new one as well as two extra airbricks for ventilation. Had a look under the floorboards and all seems fine down there - no rotten joists or anything.

 

[paulho]

No, we don't have a dog!!!
A couple of more questions, how do we get the carpet and underlay dry (we have them pulled over at the moment to let the air get to them)
Once we have it dry (I think we will need a new carpet) how do we keep it dry, is it a matter of putting down an insulated plastic sheet on top of the original floor and under the underlay (to stop the cold coming up) and buying a dehumidifyer to put into that corner?

Any ideas about a patch of damp underlay in a ground floor bedroom? The wood below is dry but the carpet and underlay are both wet!