What's the difference between rising damp and penetrative damp? How to tell which one is affecting your home

Knowing the difference between rising damp and penetrative damp is key to tackling the problem, and will give you the best chance of getting rid of damp in the home.

Rising damp and penetrating damp differ in their causes and where they occur. The former is caused by moisture from the ground being absorbed into the walls of your home, whereas the latter occurs when water enters your home from outside, usually as a result of external moisture.

There are some telltale signs that will allow you to distinguish one type of damp from the other, which in turn will give you the best chance of reducing the problem. We spoke to the experts and asked them about the difference between rising damp and penetrative damp, plus any other need-to-know info.

What's the difference between rising damp and penetrative damp?

'Rising damp and penetrative damp can look very similar and both can cause damage to the walls in your home, however, both have different root causes and require different solutions,' Ryan Calvert, product expert at Hiatt Hardware says.

To explain the difference between rising damp and penetrative damp, the experts break it down as the following:

• Rising damp occurs when moisture from the ground is drawn up into a building's walls through capillary action, which happens when there isn't any DPC (damp proof course). DPC is a barrier that stops water from moving up a wall in the first place, therefore preventing rising damp.

• Penetrative damp occurs when water infiltrates a building from the outside in, usually through walls/roofing. It's caused by external issues like cracks and gaps in brickwork/plaster, leaky gutters, broken roof tiles, poor window seals, poor door seals.

The water that travels up the walls in rising damp may also contain salts, and it can be absorbed by other building materials such as timber, plastering and floorboards. Water from penetrative damp doesn't contain anything else.

'You can tell the difference between the two because rising damp is restricted to the lower parts of walls (up to 1m), while penetrative damp can be anywhere on either walls or ceilings,' Gary Jarman, building expert at Building Shop explains.

When do they occur?

Signs of rising damp are rarer than penetrative damp, and usually only occur in older buildings. In these cases, DPC may never have been installed in the first place, or it might have been worn down due to excessive long-term use. Newer buildings can also suffer from rising damp if the DPC isn't installed properly.

'Sometimes, the DPC can exceed its lifespan,' says Jess Thomas, director of Drainage Central. 'External ground levels such as driveways or pavements that have risen over the years can gradually rise above the installed damp-proof course, thus rendering it ineffective.'

Penetrative damp on the other hand can be caused by several things, including:

• Damaged roof coverings, such as cracked or missing tiles and loose or defective flashing around chimneys and roof joints.
• Blocked or damaged guttering.
• Damaged or blocked windowsill grooves can lead to a build-up of dirt or moss growth if not cleaned regularly.
• Over time, bricks and mortar can start to become porous and provide an entry point for water to get into a property.
• Cracked rendering can also allow water through into a building.

How to tell the difference

Because of their different causes, there are different telltale signs which will help you distinguish one type from the other.

As Jess summarises, 'rising damp can often be mistaken for condensation, but it will usually only occur at ground level in a building, usually no more than a metre and a half up a wall. In comparison, penetrating damp can occur at any level in a building and is usually caused by external issues like faulty drainage or porous building materials.'

What to do about them

Knowing what kind of damp you have is the first step to tackling the problem. To treat rising damp, a damp proof course will need to be installed by a professional. We recommend researching local services to get an idea of how much this will cost, before making any commitments. It's also important to improve drainage outside of the home, to avoid any future issues.

'After a damp-proof course is installed, the affected wall should begin to dry out and any salt-contaminated walls will need to be replastered with a compatible plaster,' Jess says.

To fix penetrative damp, any damaged brickwork, flashing, roof tiles, or gutters will need to be repaired. 'Any windows and doors should be resealed, as should external cracks,' Gary from Building Shop says. 'It's also important to ensure effective ventilation to help affected areas dry out.'

Use one of the best dehumidifiers to lower the humidity levels in your home, and prevent condensation levels from rising. This will make a big difference in reducing any penetrative damp in the property.

Our current favourite dehumidifiers

FAQs

Can you sell a house with penetrating damp?

Yes, you can sell a house with penetrating damp, but the issue must be disclosed to any potential buyers. Be aware that problems with damp can decrease your property's value.

'Although you can sell a house with penetrating damp, leaving it untreated may turn away potential buyers and could reduce your home’s value by approximately 10%,' Ryan from Hiatt Hardware says.

'Before you put a house on the market, it is worth considering whether the cost of fixing the damp is more or less cost effective than losing 10% of the property’s value.'