Putting a DPM in a solid floor increases the damp in walls?

[Penners]

Yes, there is a certain amount up up-splashing on the gunge. But, as you say, it's difficult to believe that the water is getting through the stuff. Underneath is much more likely, I think.

 

[chuckey]

Years ago I went on a short "designing air conditioning installations" course, I remember that the lecturer said that it is impossible to air-con an installation unless it had a full vapour seal. The reason was the massive amount of heat that would have to be removed from the wet air. So wet air transports more heat then dry air. Also wet air is nearer its dew point then dry air, so the heating in a house with a breathable floor will need its heating turned up higher to stop condensation on windows compared with one with a DPC under the floor.
Black gunk and porous red bricks, if the course above the black gunk gets rain on it and the water soaks in, how will it get out? Not via the black gunk?
Frank

 

[Matt Green]

Just because there is a lack of peer-reviewed research, don't jump to the conclusion it's an urban myth. Independent research requires money and no one really stands to gain from proving that modern building materials are not suitable for period buildings. In fact, quite the opposite is true. The industry making money from the refurbishment of period buildings doesn't want to know what the ffects are. That might mean less sales.

A fundamental difference in building philosophy occured a the end of the 19th century. Before that date water that entered the building fabric was managed and controlled. After that date building methods focussed on the complete exclusion of water from the internal envelope.

Taking the average Victorian terrace house as an example:

-You step up into it
-The walls are solid
-The floors are suspended timber or tiled or stone or brick over earth.
-The internal plaster is lime

Water enters it, evaporates through it and no harm is done.

Contrast with modern houses:

-You walk into them
-They have cavity walls
-The floors have membranes or are suspended and supported over the fixed DPC in the walls
-The internal plaster is impermeable

Water doesn't enter the internal envelope and no harm is done. Mixing the two philosphies will result in the building not functioning as intended.

Ask any BWPDA surveyor who is good at their job where to check for damp in a Victorian terrace and they will walk to the old back wall, now internal, that leads to the solid membraned floor of the galley kitchen. The BWPDA might fund some research, though they might also find their member companies would sell less chemical DPCs. The BRE are the people who should know....best of luck.

The Journal of Surveying might have something. There is a paper in the Architectural Journal that might be useful. I'll trawl Science Direct on Monday if I get the chance. We're crazy busy and i've been in an asylum all week. *gibber*


Matt Green

 

[Nemesis]

My own experience of plastic over flags over earth was that the plastic got very wet indeed, on the underside, and in some places the walls were very damp also. Rising through capillary action via plaster or evaporation causing condensation I do not hazard a guess.

Removal of plastic, dry floors and dry walls. Haven't noticed vast amounts of condensation or increased heating bills.

Glad to hear about the asylum Matt - one to be rescued I hope, not one in which you have been sectioned for a week?

 

[Matt Green]

Glad to hear about the asylum Matt - one to be rescued I hope, not one in which you have been sectioned for a week?

Yes, and not a moment too soon given the state of the gutters. As for me:

"No, no change doctor. He still keeps babbling on about weevils in skirting boards. Shall I increase the dose?"