Damp proofing for old houses

Damp proofing experts

How can I tell if my old house have a damp problem?

If you’re considering whether to buy an older property, it can be beneficial to commission a structural survey to find out if there are damp issues.

Some common signs you can look out for are:

– Water coming in through walls

– Condensation on walls and floor

– Blistering on walls

– Groundwater on the floor

– Rotting columns, headers and joints

– Damp, humid air

Damp can cause a myriad of problems if left untreated including health issues, furniture damage and, on a surface level, a cold and unwelcoming feeling.

Causes of damp

So what causes damp?

Issues tend to have a catalyst, but luckily it’s not too difficult to find out they are.

Here are potential sources:


Older properties tend to have colder walls.

Why is this important?

When warm air touches a cold surface, it causes condensation – kind of like when you take a cold drink from the refrigerator outside in summer.

Condensation is common in older houses that aren’t well-insulated and that don’t have sufficient ventilation – for example, in period properties such as those from the Victorian or Edwardian eras that have blocked fireplaces.

You can recognise a condensation problem when there is mould on the wall, but it can also occur underneath the floor.

Interstitial condensation

As a rule, condensation occurs when moisture meets with cold surfaces such as windows and outside walls and causes black mould.

It is not the only kind though.

Sometimes, condensation happens when warm, moist air from inside attempts to move somewhere with lower vapour pressure.

If it becomes trapped, it can cause additional issues.

External walls should be airtight, allowing moisture to escape outside.

Usually this form of condensation occurs inside walls and under floors, causing a raft of additional problems.

The main way to combat them is to make sure the wall’s insulation has a temperature gradient.

Substandard ventilation

You need to make sure moisture in a wall has room to move. If it struggles to leave a property, it can be a potential cause of a damp problem.

Penetrating damp

Any structural issues, such as cracks and honeycombing concrete, or misplaced guttering can cause water and moisture to seep into a property.

Chimneys and rooves can also sustain damage, allowing water to enter the home and cause damp.

Breathability and walls

If you’ve purchased an older property, it’s to be expected some moisture will find its way inside.

The movement of air and moisture is more liberated because of the materials used, and the structure makes them less airtight.

This comes with its own issues.

When there is extreme weather, or if you need a warm and dry environment inside, it can become difficult to deal with dampness.

Traditional physical damp-proofing methods, such as a waterproof paint, will most likely cause issues with the vapour permeability of an affected wall.

That means you’ll have dry environment for a short while, but the moisture already in the property is going to have a hard time escaping.

That risks causing timber decay and damage in the long term.


Damp-proof courses, alternative systems and remedial measures

A damp proof course, or DPC for short, is a water-blocking layer built into the wall.

It is applied above ground level, and prevents rising damp that moves up a wall by capillary action.

You can get a professional to do a chemical injection DPC if you need.

However, it’s vital to check they knows what they’re doing because an incorrectly installed DPC can cause big problems for your property.

There are other options you could consider.

Firstly, reduce the external ground levels of the property.

It’s possible that a garden or driveway has raised over time, in turn breaching a PDC.

To tackle condensation, you should also consider a careful balance between insulation and ventilation.

Because older properties were built to allow walls to breath naturally, you must ensure they are able to continue doing so.

If they can’t, you’ll need to keep the affected rooms well-ventilated.

Opening a window or a door, will allow cross ventilation between rooms.

Insulation is another factor to be wary of.

As individuals, we’re keen to reduce higher bills caused by rising fuel expenses and turn to insulation to keep rooms warm.

One issue associated with doing so is it hampers ventilation, trapping moisture inside and consequently causing condensation.

Consider installing an extractor fan a kitchen or bathroom, and occasionally a bedroom too, because these spaces tend to have higher temperatures.

You could also consider a dehumidifier that reduces the moisture in the air.

Installing addition air bricks can assist with ventilation too.

Something to avoid is relying on an inexperienced worker that isn’t familiar with damp proofing installation.

Not only is it a financial risk, but an incorrectly installed DPC or waterproof render can exacerbate a problem rather than solve one.

Be careful too with materials that stop moisture from seeping in because they also prevent existing moisture inside from leaving too.

Cement-based pointing and renders are prime examples of this, and can even add to damp problems that already exist.

Most period properties use lime mortar which is permeable and allows water in.

If, after decaying, it is replaced with cement mortar then it can stop a building from breathing adequately.

Finally, you should also avoid injecting damp proof courses into non-absorbent bricks or any old engineering ones.



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