How does damp travel?

laxeylady

When we moved in to the new house we decided to rip out a built in wardrobe in our bedroom (it smelt very foisty and I refused to hang my clothes in it). Behind the wardrobe was an old lime plastered wall covered in fungus threads but no big growths. The damp spread round to next external wall and when we peeled off the wall paper we discovered polystyrene tiles black with mildew. There were wooden joists above the windows with signs of rot (but still quite solid). We went ahead and chipped off all the plaster on the two external walls and round the windows. The ceiling was papered and underneath that was this awful sticky tinfoil stuff so that came off too and basically we boxed the walls and dry lined them. They dried very quickly. Half of the ceiling did not however and in the recent week during heavy rain it seems to have got damper. So we headed upstairs and started pulling off the panelling in my sons room directly above. Its boxed already but with wooden panels instead of plaster.We chipped off the plaster under his dormer window (well it practically fell off) and the sandstone wall beneath it is soaking wet. The damp goes off to the left as you look at it. My question (eventually!!) is could the water that has gotten in through the leaky window travelled along the wall and down into ours? Why is it not going straight down? (the ceiling directly below the window is bone dry and the walls directly above our damp bits seem to be dry - although this plaster is not chipped off yet it still seems quite solid.). We are pulling 3 litres of water out a day with the dehumidifier, and have a new window on the way. What else can we do? We have no cavity, its solid sandstone rendered on three sides but bare on the back. The roof and chimney have all been worked on in last couple of years and external render seems in good condition. If damp has gotten through roof or walls in the past, what effect will the boxed in areas have had on letting it get dried out?

justjohn

Damp just soaks into porous material taking the easiest route up down left right in circles it does not matter. eg the damp/moisture may have a massive stone lintel to pass, and the majority of moisture would go left/right in theory

It can take as long as 1 year to totally dry. the boxed in areas will dry eventually but will take longer. Thats if you have found the source.

Timber damage is a problem sometimes.

David_Aldred

Mechanisms for leaks are gravity, air currents, wind pumping, kinetic energy, hydrostatic pressure, capillary action, surface tension, pressure difference and thermal pumping with contributory factors of location and exposure, in this case thickness of solid walls, type of roof and condition of roof, absorbence of render / walls and state of repair.

The defective window may be a primary point of leakage or simply contributory to a more widespread problem to walls suffering leakage, surface condensation and condensation within the wall itself. Other than resolving the defective window and monitoring for drying down you may want to consider:

Ask yourself how might the building have changed since it was originally constructed and although such changes may have been done with the best of intentions have they actually reduced the way the building was designed to be a breathable structure? Examples of this may be the external rendering of walls with hard dense cement renders compared to original breathable stone and lime mortar, whilst internally blocking up fireplaces and replacing draughty windows / doors with sealed modern alternatives. Insulating roofs without compensating for such by increasing roof ventilation etc.

If the quantity of moisture entering the building fabric goes up (from leakage / alterations / lifestyle) without providing a corresponding means by which it can escape, then a moisture resevoir will accumulate that will sustain unwanted dampness even during more favourable weather. Kindest regards, David Aldred Independent damp and timber surveyor

laxeylady

Thanks for the feedback guys. We do feel that previous inhabitants over the years have trapped moisture in a bid to insulate. In our son's room the sloping ceiling (which is a joist width away from the roof) has been tiled with cork and then papered over. Our room had the polystyrene tiles and foil backed paper. The whole house is double glazed and the guy we bought off admitted they never opened the windows as his wife had thrombosis. We were planning on using some kind of insulation in our sons room, as we are having to pull out the lat and daub ceiling. Thought we could insulate before replastering. Is this a bad idea then?

David_Aldred

Hi laxeylady,
There is nothing wrong with insulating pitched ceiling areas so long as it is done correctly. The Building Regulations recommed 50mm air circulation gap between cold side of insulation and underside of roof covering so you would only be able to put in 25mm of rigid insulation between the inner face of rafters leaving the 50mm air circulation gap above.

Over the inside face of the rafters you can then add further insulation and there various combinations you can use such as Kingspan Kooltherm or similar which is a plasterboard bonded to insulation bonded to a vapour barrier and you can incorporate one of the multi foil insulations such as Triiso Super 10 or similar.

What you must ensure is that the air space on the cold side of the insulation is cross ventilated to remove moisture laden air before it condenses out and causes damp / decay / mould and this can be achieved with eaves vents / under slate vents / ridge vent combinations, in addition to ensuring the vapour barrier is effective to prevent warm moist air from rooms entering the cold side of the insulation and condensing out.

A web search on the Kingspan, Multi foil insulation, eaves and under slate vent / ridge systems will all help with background info and options to vary things. Hope this helps, kindest regards Dave Aldred Independent damp and timber surveyor

laxeylady

David you are a superstar! thanks muchly for all the fab advice. Can I take the liberty of asking a couple more stupid questions please? If damp has entered the house through roof or chimney and these have since been repaired would there be damp trapped? Its just that while the stone itself looks dry, some of the plaster on top of it feels damp (though not soaking). Also, would this damp take longer to dry out of wood? We are finding dampness under the floor between the bedrooms but cant see where its come from. Could the tin foil ceiling paper have trapped it some how and now we have enabled it to escape? I know these are stupid questions but we are scratching our heads here. Should have gone for the new build me thinks. :think:

David_Aldred

Hi laxeylady,
Thanks for the kind words but there is no such thing as a stupid question anyone on here is just trying to help each other out with a pool of ideas. Certainly the tin foil lining paper will tend to reduce evaporation from a damp wall into the room. If the wall itself is dry and the plaster appears damp the plaster could be contaminated with such things as salts that will draw moisture from the air to the plaster irrespective of any other moisture sources in the same way leaving salt out within a kitchen will become damp. Other reasons are surface condensation to external walls (it is unlikely you will get condensation between one room and another) though we are at the wrong time of year for condensation / mould to be in full swing.

In the area of chimney breasts (or where chimney breasts have been removed) sometimes the contaminates of the soot lined brick flues will migrate into the plaster over time and sulphates from soot can play havoc with some plasters causing unsightly brown stains and degradation of plaster. Once this occurs the plaster will not recover even when a moisture source is resolved and you come back to options of re-plastering to a specification that will hold such contaminates back within the wall or a dry lining system that will do the same.

In the area of hearth also be mindful that once a coal fire is no longer in use the hearth / fire-back and all that loose infill behind the fire-back will tend to become damp as there is often no damp proof membrane under the hearth itself because it would be assumed the heat from the coal fire would always keep this area nice and dry. In such circumstances if you are not going to use the fireplace for its intended purpose then taking the fire-back out along with concrete hearth / loose infill and casting a new concrete hearth on damp proof membrane sealed into the wall damp proof course is sometimes necessary to address this moisture resevoir.

The rate of drying from wood compared to walls will depend upon several factors but if the wood remains in contact with the damp wall it will tend to stay damp for as long as the wall is damp since everything wants to be in equilibrium. Hope all of this makes sense - all the best - Dave

sunshinett

Hello are you in the IOM? I live here too

We have a solid walled house 1930's and find that it gets black mould easily

the back part of the house was built in 1985 and that is ok, except you have to watch out that there is enough air flow behind wardrobes etc

i do not have trickle vents in my pvc windows, and dont know whether to put them in. dont know if you have these, new windows are generally fitted with them.

but each morning there is moisture on the windows and the worst parts of teh house for this are the 1930's, but some on the 85 windows, but not so that the windows are totally covered.

the thing is i dont feel like sleeping with window open letting cold air in, and then when the heating is timed to come on in the morning 6am for 1.5 hrs, so that hse is not freezing to get up to, to let all this heating out through the window.

how do you feel about all of this? what build is your house?
I guess in Laxey? we are in Port Erin

I do run 2 dehumidifers each day for a while but not all day as do not know how much electric they would be,but this will zap some of the moisture

I notice you have a fireplace. We have a multi purpose stove, not in use this year for the first time, as it needs new firebricks. we have a cowl on our roof this stops the rain coming down the chimney, but the sort of cowl that you can still light a fire. do you still have your fireplace? with a cowl on it?

bye for now

richardw

First Class if it can afford it, otherwise coach.

27col

Nice to see you back David. You don't post much, but when you do, it always makes sense.