Rising Damp or Bridged DPC?

Rising Damp or Bridged DPC?

So you’ve noticed peeling paint and staining to the plaster work of your internal walls
– Don’t immediately assume that this is rising damp.

Take a moment to look outside your house – are there any clues as to what might be
causing the moisture?

Sometimes a leaking gutter or downpipe can be easy to spot but look at the low level
brick work of your house.

Can you see the damp proof course? Hint: You are looking for a plastic or bitumen
membrane or slate sandwiched in between one of the lower brick courses.

Spot the DPC!

Once you have found the DPC, consider its location in relation to the external ground
levels. Good building practice is to have external ground levels maintained no less
than 150mm (two brick courses) below the damp proof course. This is to avoid
‘bridging’ and also to deter the effects of rainwater splash-back through the base of
the walls.

Given the ongoing fashion for homeowners to install patios and timber decking, we
now find that a bridged damp proof course is one of the most common causes of
damp in houses across London.

This raised patio is bridging the DPC and obstructing the sub floor ventilation

The good news is that bridging does not require a DPC injection to resolve the issue.

A more effective and long term solution is to
relieve the existing damp proof course by lowering the external ground levels.

A complete redesign of the external landscape is rarely necessary as the desired
effect can be achieved by installing what is known as a ‘French drain’.
Simply put: a shallow gravel filled trench at the base of the wall. Introducing this will
help disperse damp that would otherwise collect and soak into and up the wall.

Where grounds are seriously waterlogged, consideration can be given to
incorporating a perforated pipe within the trench ensuring that the pipe leads to a
suitable discharge point such as a surface drain.

Now your damp proof course once again perform as it was originally designed.

Any spoiled internal plaster work may require replacing as groundwater contains
‘hygroscopic salts’ and these are likely to be present in a wall that has experienced
bridging. These salts must be removed as they will continue to draw moisture from
the air even though the moisture source (in this case a bridged damp proof course)
has been fixed.

Did you know that the most common causes of damp in houses can usually be fixed
without the need for a new damp proof course?

To find out more, give us a call on 0808 196 0401 – with nearly 20 years of
experience in the industry and an outstanding record of customer reviews – we’re here to help!