insulating under wooden floors

[Mark]

Ok so if rising damp exists how far does it rise ? I'd also be interested in your ideas as to how you would stop it rising.

[IMM]

Prey tell?

[IMM]

Put a snake down there, Andy will advise.

[IMM]

What is the difference?

[IMM]

He sees me in his sleep.

[fred]

In article , John Rouse writes

What's that got to do with sealing the gap between the skirting and the floorboards?

[fred]

In article , IMM writes

More words reqd . . . .

[Peter Taylor]

John Rouse wrote

That's possibly true but it's the rate of evaporation that's important, and this depends upon the relative humidity. A saturated brick of any size or porosity will evaporate nothing in 100% RH. If you are trying to say that rising dampness can't exist because of evaporation, please explain how a timber plate on the top of a simple unrendered sleeper wall without a damp proof course can become damp and rotten.

That does happen frequently with soft facing bricks, especially in warm dry weather or when they're straight from the kiln. It's quite normal to have to dunk bricks in water before they're laid in order to kill the suction and prevent the cement from becoming dehydrated.

Peter

[IMM]

What is the difference before and after?

[Peter Taylor]

Mark wrote

There is no definitive answer - it depends upon various factors, such as the rate of evaporation, the porosity of the brickworrk, the amount of moisture. It's generally accepted that in most "normal" situations (external wall, plaster inside/brick outside and no dpc), rising dampness will not extend above about 1 to 1.2m above the source of the moisture, and often as little as 300mm. However I once saw a party wall between two basements where the dampness had risen the whole storey height and was affecting rooms at ground floor level. There was a good reason for this - both owners had had their basements tanked with waterproof rendering at different times, but each had objected to the other inserting a dpc in the wall, which would have prevented the dampness rising. Instead, the rendering on both faces of the wall prevented any evaporation and the dampness just kept on rising until it reached a point where it could evaporate. You sometimes see this when people have put aluminium foil under the wallpaper and the dampness appears at the top of this

Also remember that ground water contains dissolved nitrates, chlorides and sulphates which it can only pick up in the soil. It is a definitive test for dampness coming from the ground whether these salts are present when the moisture in a damp wall is analysed. Penetrating water, say from a defective rainwater pipe, will not contain them. The salts are hygroscipic (they attract vapour from the air) and often they can make the wall appear and feel damp long after the true source of the dampness has been cured. The salts are also partially conductive, and can give a false reading on an electronic moisture meter, even though the wall is actually bone dry. It's a sad fact that many surveyors and so-called damp specialists are unaware of this, and many properties have been treated for dampness unnecessarily and often ineffectively.

I could write a book! I would be very happy to help with your particular case if you like, but you will need to give me more information on the house and the problems you've encountered, ideally with some photographs. I would suggest you take a look at

which has masses of sound advice on dampness and timber problems, written by an independent consultant, Graham Coleman.

HTH Peter

[fred]

In article , IMM writes

Before and after which, the u/f insulation or the gap sealing?

Ok, answer to a): it was warmer, answer to b): it was less draughty.

Floor is noticeably more pleasant to sit on or walk over in winter, difficult give an objective measure of improvement, but was surprised to walk over a cold spot and then realised it was where an area over an access hatch was uninsulated. Old, light coloured carpet bore the signs of 'dirty draughts', replacement carpets are clean & I can choose where & when I want to open ventilation.

How's that?

[IMM]

Sounds fab to me.

[M. Damerell]

[snip]

You have a MAJOR problem. I know this is UK.DIY but I think you need expert advice urgently.

To original poster: It is a very bad idea to do anything that might compromise underfloor ventilation or damp-proofing. You run the risk of getting dry rot. If you are raising boards, take a good look underneath. Check for damp, bad smells, beetle, rot, mice, etc. Remove rubbish (in case it bridges the DPC). Clear all airbricks.

[Duncan Lees]

The weevils should be in bug heaven now, along with the woodworm. If they were still active that is. Wrong time of year to be sure. The main thing was to get the treatment guarantee for when I sell the house, as any survey that actually looks under the carpets would spot the worm damage. Unlike mine.

Thankfully the few affected joists are still sound. Just the wood on top of the sleepers and floorboard are shot. The guy who came round to look at the house (Rent-a-kill Home Care, good service) suggested replacing the wood supporting the joists with simple plastic roof tiles. Anything like that as long as it's plastic and solid.

Yeah, I removed quite a bit of rotten wood and dirt that was sitting on the substrate. Looks like the previous "treatment" for the rot was to replace some of the rotten floorboard and drop the old wood under the floor. You've got to love some peoples idea of a job well done...

-Duncan

[Duncan Lees]

The walls are fine. I just need to stop the moisture from the ground finding it's way into the timbers under the floor. It doesn't matter if it remains damp underneath the polythene.

It's not that bad. I'm on a gentle hill, so the problem is likely due to rain finding it's way down hill. I think it would be a different matter if I was at the bottom of a hill and the water didn't have anywhere to go.

That's the main thing the house has lacked. The ventilation is okay, but could be better. I'll put in a couple of extra ventilation bricks while I'm doind the floor.

-Duncan

[John Rouse]

In article , Peter Taylor writes

Like your house is under water?

Lack of ventilation.

J.

[John Rouse]

In article , Peter Taylor writes

Never! You may get a few mm of moisture up a brick set directly in a pool of water but a metre! You've been talking to too many "damp course" salesmen.

That isn't rising damp, its an Artesian Well!

First sensible bit you've written.

Just open your wallet and say after me......

J.

[John Rouse]

In article , M. Damerell writes

No he doesn't. Wet rot is only a problem if the structural integrity of the timbers is affected. Get rid of the water and the rot won't grow.

J.

[Peter Taylor]

John Rouse wrote

John, I am a Chartered Building Surveyor. I qualified in 1975 and was elected FRICS in 1989. I have been in practice as a Consultant for 20 years and often act as an expert witness in claims against damp-proofing contractors.

Your statements about dampness in brickwork are blatantly misinformed and I don't really understand where you can have picked up such silly ideas. If you are not prepared to accept advice then I don't see the point of wasting my time any further.

Peter

[PoP]

Numpty question time.....and really one relating to options for my kids after they leave school. Not that they've expressed interest in this career option but just so's I have a general idea of what's involved. I'm trying to keep them from deciding that a career in IT is worthwhile!

I wondered how one goes about become a surveyor (chartered or otherwise)? Does this involve degree education etc?

PoP

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