Damp

Damp Prevention in your home

Damp patches 1 metre and above floor level 

Damp patches on the 1st floor ceilings are likely to be associated with leaks in the roof or leaks from water tanks/plumbing in the roof void. Most roofs leak at joins - either from one section of the roof to the other (valleys) or around chimneys. 

Damp occuring on walls in kitchens, bedrooms or bathrooms could be due to leaking guttering, leaking plumbing or damaged cavity trays on the top of windows...  but are more likely going to be caused by poor ventilation in your home. Everyday living in homes produces huge amounts of water vapour. If it can't escape it will condense on cooler surfaces and eventually look like water running down the walls. This ultimately leads to mould growth. 

If you currently dry your washing on radiators or an 'airer' then this will contributre to damp inside your home - the water that was once in your clothing becomes water vapour and unless it can escape outside will condense back into water on cool surfaces within your homes - walls/windows etc.

In years gone by adequate house ventilation was not properly understood. The developement of seals on windows and doors and draft excluders all remove accidental and passive ventilation. Modern building regulations ensure that houses built now will have ways to properly ventilate homes. Houses built before 2000 may have little or no provision for ventilation.

Bathrooms and kitchens should have a fan fitted to remove water vapour in the air. Cooking produces a lot of water vapour and a properly fitted cooker hood vented to outside will drastically reduce damp problems in your house. A fan in the bathroom (activated by the light switch) will remove steam/water vapour from bathing and showering and also help to reduce condensation.
If your home has both a cooker hood vented to outside, a bathroom fan, you do not dry clothing inside... and you still get damp/condensation problems, then it's going to be a good idea to fit futher ventilation systems. Opening windows isn't always going to solve the problem and in the winter will lead to much higher energy bills. A whole house MHRV (mechancial heat recovery ventilation) system will solve all condensation and upper wall/ceiling damp issues (not relatd to leaking roofs/plumbing). See previous blog post for more information on this.

Damp near the floor - risng Damp
If  you own a fairly modern house it is unlikely rising damp will be an issue. For quite some time, houses have been built with a DPC - damp proof course. Ths is a non-permeable barrier built into your walls roughly 150mm from the ground. Damp (water) will naturally permeate through stone/bricks from the ground up through walls to height of about one metre above the ground by capillary attraction. The DPC stops this flow and  keeps your walls dry - inside and out.
If you have an older property then rising damp can be a problem as the stones for the walls were often just laid directly on the ground, often with little or no foundations. Also, ground levels may have changed over the years and can end up be above the ground level inside your home.

If your walls are damp near the gound, you get mould growth or the surface gets pitted and flakes off then you will probably have rising damp problems. This will contribute to the water vapour in your house and this can lead to condenasation issues elsewhere and health problems for dwellers.

Remedies
There are many ways to rectify rising damp.
Some advocate injecting a damp proof barrier in the wall with silcone. Ths can work in some cases but it all depends on the construction of the wall. It may not work well for a traditional rubble filled stone wall as the injection process may not proof all areas of the wall, leaving a gap or bridge where the damp can travel past.
Many try to cover up damp walls using a waterproof plaster or cement based covering. In my experience this is rarely a permanent cure as the damp will just permeate to other places or eventually find a way through.
In my opinion, the best way to deal with rising damp in older properties is to fit a barrier preventing the damp from coming inside. The moisture is alloweed to travel into the wall naturally, but you just stop it from spoiling the inside. Basically, you 'tank' out your floors and walls with a plastic membrane to a height of 2m above ground level. It is though, a lengthy process and if you can't do it yourself will incur high labour costs. However, it is the belt and braces 'proper job'.

 

The black plastic on the walls here is Oldroyd and has the benefit of being very strong, easily folded and  having a ribbed surface to aid water transporation downwards.

This membrane can fit over existing plaster (or you can remove it if it is particularly damaged). Fitting the adjoining membrane on the floor will mostly entail breaking up and removing the floor - but this depends on both the headroom of the rooms in the house and the floor construction.
Since there may be condensation behind the membrane on the wals you need to provide a way for water to escape - this can be done in two ways: provide a way for water to pass directly into the ground via a layer of gravel; or create a drain system that collects any condensate and diverts it to outside. This drainage is of course all below the floor membrane so no moisture can make it's way into the room.

In this picture you can see the drainage pipes laid under the floor. These are at a gradient of greater than 1:50. The top of the pipers are perforated to allow the condensates to enter. They all join ip and exit the rooms through the wall below the ground level inside the house.

 

This photo shows the drain system built into the edge of the walls. Over these dranage channels and the concrete floor shown, goes the floor plastic membrane (DPM), insulation and the 75mm of screed (in this case with underfloor heating pipes within). For all this to be fitted the previous floor had to be dug up and excavated to a depth of 300mm.

There are various options to cover the wall membrane to produce the standard smooth plaster finish. Some membrane sytems allow you to plaster directly on them. Or you can add wood battens to the wall using the existing plugs used to hold the membrane to the wall (they are specially designed to allow screws to be fixed into them). 

You can see that in this photo, insulation was sandwiched between the battens and the membrane.This not only keeps the room warm but cuts down on any condesation produced between the wall and the membrane as the membrane will not become so warm. Plasterborad is nailed directly into the battens shown, and a finishing skim of plaster is applied.