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.

MHRV

MHRV

Mechancial Heat Recovery Ventilation

I've installed a system in each of the last 4 houses I've owned.

The need for good ventilation provision in houses is one of those things that in the last 20 years is becoming better understood.
We've all seen pictures of mouldy walls and windows in bathrooms and probabl;y experienced condensation on windows and mouldt grouting in bathrooms and showers. Having too much water vapour in your home can damage furnishings, decoration and even the structure of the house.

With MHRV you'll never get mould issues, condensation on windows, lingering smells from cooking and in toilets. After a shower the cubicle will be dry within an hour and it'll be fine to dry your clothes on radiators within the house. Fresher air with normal levels of moisture in your home will bring noticeable health benefits.

An open window or trickle vents integrated into new windows do give some passive ventilation but in the winter heat will escape and you'll get cold drafts and good air circulation/replacement is not guaranteed.

Why ventilate?
Apart from having fresh healthy air in your house to breath, a noticeable lck of smells from cooking (and from the loo) the main benefit is the removal of water vapour. 

During the day the average person produces 3 litres of fluid in the form of water vapour from breathing and sweating. Add to this all the water that escapes into the air during cooking, washing up, showering (and the drying of the cubicle after) and drying clothes and you have a huge amout of water in the air in your house. If this water doesn't get out of your home it will be find it's way into your furnishings, wallls, roof space etc. and will condense on cooler surfaces. This can lead to mould growth and very unhealty living conditions. 

MHRV basically constantly replaces the air in your house with fresh air from outside. The air is replaced roughly once per hour.

Each room has a vent in the ceiling/wall. In the rooms with the greatest amount of water vapour - bathroom, kitchen - the air is sucked out. Then normally drier rooms like bedrooms, living room have air pumped in. Therefore there is a flow of air from those drier rooms into the wetter rooms. The flow of air is very gradual and you are never aware of drafts. Clearly if a room door is very tight and there is no gap underneath, this will inhibit the circulation of air within your house. Sometimes installers will put vents at the bottom of some doors if they are going to stay shut for a long time.

You may be thinking that surely if you suck out the warm moist air out of the wetter rooms and send it outside then surely the heat is lost and you're going to get cold air coming in to replace it.
No. The air that is sucked out of wetter rooms travels in ducting that all eventually join up and lead to the MHRV unit. Inside here, the warm wet air passes into a heat exchanger where at least 85% of the heat is passed onto the cold air coming in from outside. The two air steams do not mix as they are kept apart by the thin walls of the exchanger - only the heat passes from one to the other.
Yes some heat is lost, but this is far less than having windows partially open or other forms of passive ventilation like trickle vents. 

One of the myths about with ducted heating and ventilation is that it can lead to mould growth inside the ducting which could harbour germs and heath risks like legionella. The ducting never gets damp as it's insulated and the flow of air within ensures no condensation occurs. 

Fitting and costs.
The cost of fitting a system will be easily recovered in the coming years by reducing your heating costs, redecoration bills and avoiding potentially costly structural repairs to your property. Plus, it is likely your health will improve.
If you have a standard house with a ground floor and a 1st floor then the MHRV unit may be best positioned in the loft (roof space). Getting the ducting to 1st floor rooms is easy at it will simply  snake it's way within the roof void to each room. Routing the ducting to ground floor rooms will be more tricky and may require some light building work - boxing in the ducting as it travels through 1st floor rooms on it's way to the ceilings in the ground floor. One way of disguising the 'boxing in' is to simply extend a chimney breast by 250mm with some battening and plasterboaad - this way no one will be aware of any change. Other than that it might be possible to run the ducting down the corner of a room next to the doorway or wthin a built in wardrobe.

If your system is properly fitted few people will even know it's there. The small circular vents in the ceilings in each room are the only visible signs. 

The MHRV unit will produce water as the warm air removed from rooms can be saurated in water vapour. This may condense within the hear exhanger. It's all perfectly normal and every system has a way of collecting this and draining it out. Therefore you need to ensure your MHRV unit is placed in a convenient location for these condesates to be drained to the house drainage system - the bath/basin/shower waste for example in the bathroom.

Cooker hood: some advocate integrating the extractor from your cooker hood into the MHRV system. This can indeed be done as the heat from cooking can be utilised to heat up the incoming air. However, it is very important to have very good filters in the cooking hood (which are regularly cleaned or replaced) as you do not want vaporised oils and fat entering the ventialtion system as it will deposit on the ducting walls and the heat exchanger unit resulting in poor performance and eventually failure of the unit.