Why is My Basement Damp?

Last Updated 28 August 2018

Basement damp

In London, it can be difficult to find the room or get permission to extend your property. This means that more and more people are turning to their basements for extra space.

But no one wants to spend time in a basement if it’s covered in damp and mould. Here are the most common causes of damp in the basement, and what you can do about it.

What are the causes of basement damp?

1: Ground water

Your biggest enemy if you have a basement is groundwater.

As you can probably guess, groundwater is water hidden beneath the surface of the earth, stored by soil and porous rock.

If this water seeps through cracks or is soaked up through porous building materials, the wall can become damp or even start dripping.

The water level (the level at which ground becomes saturated with water) changes from area to area, even from house to house.

If your home is built on ground with a high water level, you’re more at risk of damp and flooding in the basement.

2: Poor ventilation

For basements to be a comfortable space to live in, they need ventilation to cycle out stale, damp air and bring fresh air in.

This is especially important if you have bathrooms, pools, spas, kitchens or washing machines in the basement, otherwise all the moisture released into the air will have nowhere to go.

If moisture can’t escape, it will eventually settle onto the walls and floors as the air cools, causing damp and creating the conditions for mould to grow.

3: Cold surfaces

Even with adequate ventilation, you can still end up with damp issues if the walls or floors if they’re too cold – which is a common issue it poorly heated basements.

Cold surfaces cause moisture in the air to cool on contact, collecting on the surface as condensation. Too much condensation, and you end up with damp.

4: Faulty gutters and drains

Gutters and drains are supposed to transport rain and wastewater away from the property, but if they’re faulty they may simply be dumping it in the ground.

This water can then seep down the sides of foundations or collect beneath the basement until it seeps into the walls or floors.

How can I fix basement damp?

If the cause of your damp is poor ventilation or a faulty gutter, then fixing the problem will be relatively quick and inexpensive as all you need to do is install ventilation or fix your gutters.

Drains can be more difficult depending on the source of the fault as it may require excavating beneath the basement, while a cold basement would require the installation of a new heating system.

Groundwater seeping in from outside the basement is the most worrying cause, as it means that the tanking system has failed, or is nonexistent.

The exact cost of installing a tanking system depends on the condition of the basement walls and the surrounding water level.

A simple tanking system involves applying a waterproof coating over basement walls to block water from reaching the interior.

This is appropriate for minor damp issues where water blocked by the waterproof coating is able to drain back out of the wall into the surrounding soil.

If the soil is too saturated with groundwater, water trapped in the walls won’t be able to drain out. Pressure will build until the water forces its way through the wall.

When a simple tanking system isn’t enough to hold back the water, you should install a cavity drain membrane, where there’s a small gap between the wall and the waterproof coating for water to drain away.

This water can then be pumped out by a sump pump into the drainage system where it’s flushed away into the sewer.

Call us now if you’re worried about basement damp

Our team at Environ Property Services are experts at making basements dry, comfortable spaces, perfect for your new spa, kitchen or cinema room.

If you have any concerns about basement damp, give us a call now or request your call back.

Need Help or Advice? Then request Your Callback

Holly from environ calling a customer
  • London Based
  • Free Advice
  • All Works Guaranteed
  • Friendly Service Team

Here are some helpful related articles

Damp Proof Paint is Bad For Your Home

Waterproof paint on exterior brick walls doesn’t fix damp in period properties. In fact, it can make it much, much worse. Find out why, and what to do instead.

Damp Proof Paint is Bad For Your Home

Should I Paint Over My Damp Walls?

Damp proof paint has its uses, but by itself it can’t fix most damp problems. Learn about three types of damp proof paint, what they treat and what they won’t.

Should I Paint Over My Damp Walls?

What Causes Lateral Damp?

Lateral damp is caused by groundwater which has saturated your walls or floors. It’s most common in basements and more severe in areas with a high water level.

What Causes Lateral Damp?

What is Lateral Damp?

Lateral damp is common in basements, where groundwater seeps through the walls. If untreated, moisture-attracting salts from soil accelerate the spread of damp.

What is Lateral Damp?

What is penetrating damp?

Penetrating damp is damp which comes from exterior defects or leaking plumbing. If left untreated it can lead to mould, rot or even dangerous structural issues.

What is penetrating damp?

What Causes Penetrating Damp?

Penetrating damp has many causes, from plumbing and drains to tiles and cracks. Some can be fixed with a bit of DIY, others require a help from a professional.

What Causes Penetrating Damp?

How to treat penetrating damp

How To Treat Penetrating Damp

Penetrating damp needs to be treated ASAP to prevent property damage and mould. Read our blog to find out how we identify, treat and repair penetrating damp.

How To Treat Penetrating Damp

Damp advice

How To Avoid Damp Scams

During many of our damp works, we discover properties that have fallen victim to damp scams

How To Avoid Damp Scams

Rising damp causes

What Causes Rising Damp?

Rising damp worrying you? Learn how to identify rising damp and what causes it in this blog by damp expert and Environ Property Services founder, Terry Clark.

What Causes Rising Damp?

How To Treat Lateral Damp

What is lateral damp, how can you spot it and what’s the best way to treat it? Answer all these questions and more with our guide from damp expert Terry Clark.

How To Treat Lateral Damp

How to treat rising damp

How To Treat Rising Damp

Find out how to spot rising damp, what causes it and the best way to treat it with this handy guide from Terry Clark, damp expert at Environ Property Services.

How To Treat Rising Damp

Pointing causing damp

Is My Pointing Causing Damp?

Decayed or poor quality pointing damages bricks and leads to penetrating damp. Read our blog to learn how to spot problem pointing and how it harms your walls.

Is My Pointing Causing Damp?

Damp from chimney

Is Damp Coming from My Chimney?

Damp from your chimney can lead to rotten roof timbers and expensive repairs. Discover the causes of a leaky chimney with this blog by damp expert Terry Clark.

Is Damp Coming from My Chimney?


4.75 Average

131 Reviews

Rachel harmes

I Couldn’t recommend Environ property services enough! I requested at call back at 7am for a pest control issue at my home. By 8.45am I had a slot …


Highly recommend this company! After we travelled back through Asia we picked up some nasty little critters, however Environ came out and with no …

Esther W

Over moon pest free! Highly recommend this company to anyone who has a pest problem, we travelled back from Manialla and picked up some very pesky …

Holly is available to take your call

Call Holly