Penetrating Damp

                                                             Penetrating Damp

In the UK we see a massive 25,000 gallons of rainwater a year, so it is no surprise that one of the most common problems in our homes is penetrating damp. Damp is usually fairly easy to fix, but can sometimes be an indication of a more serious problem.

Penetrating damp is by far the most common type of damp problem in UK homes, particularly in older houses with solid walls. As the name suggests, penetrating damp is the result of water somehow permeating the fabric of the house from outside. It is almost always as a result of rain and will often almost disappear after a few dry days. Signs of penetrating damp include isolated stained patches on walls and ceilings as well as areas of mould. The cause of penetrating damp is often easy to fix and, if caught early, should not pose long-term problems

Dealing with Penetrating Damp

The main causes, and symptoms  of penetrating damp.

Bridged Damp-Proof Course

The damp-proof course installed in a wall controls water from moving up the wall, but this is obviously useless if water can by-pass around it. When this happens this is referred to as bridging. The most common form of bridging is when the ground level outside a solid wall is higher than the installed damp-proof course. Other forms of bridging include internal plastering and external wall renders extending down over the damp-proof course line Symptoms - Large areas of damp at the level of the skirting (moisture will spread inside the cavity and effect a large area).


 Cracked or Blown Render

Cracked or blown render allows water to seep behind and soak the brickwork underneath. The water will be trapped and absorbed into the wall. If left, the damage may spread as water effects the surrounding good render.
Symptoms – Isolated damp patches or areas of mould on the inner face of exterior walls.


Bridged Drip Groove

The underside of window sills should have a shallow groove running along the full length. This drip groove stop water running back along the underside of the sill and soaking the wall. If the drip groove is bridged with layers of paint, moss or debris, rainwater will quickly soak the wall beneath the window.
Symptoms – Outside: mould or mildew growing directly beneath the window sill. Inside: Damp patches or mould directly below the window. Rotten timber sills.


Porous Bricks

Bricks in good condition are basically waterproof, but once the face has been damaged, the brick can become porous and act a bit like a sponge, eventually effecting the surrounding bricks as well. Very old bricks can also be porous even when the face seems in good condition.
Symptoms – Large areas of damp on the inner face of exterior walls, increased mould growth on exterior walls.


Loose, missing or broken roof tiles

Broken or missing roof tiles will allow water to leak down into the roof space and then down into the room below.
Symptoms – Damp patches or stains on top floor ceilings.



Cracked Mortar Seals around Windows or Doors

Over time, timber window and door frames can shrink and warp, cracking or shifting the mortar seals between the timber and the wall. Water can then penetrate the gaps and effect both the wood and the wall.
Symptoms – Damp patches around window and door frames. Rotting frames, both inside and out.


Loose or Missing Pointing

Over time, mortar between bricks can dry and fall out. This can allow water to penetrate and spread through the surrounding mortar and into the house.
Symptoms – Small areas of damp on the inner face of exterior walls. Small patches of mould growth.


Damaged or missing Coping Stone

If the coping stone on the top of a roof parapet wallis damaged or missing, water will be allow to soak down through the bricks underneath and then into the fabric of the house.
Symptoms – Damp patches around the outside edge of the room, initially concentrated at the top of the walls.


    Broken or Blocked Downpipe

A crack or hole in the rear of a downpipe (facing the wall) will quickly soak the wall in one spot.
Symptoms – Outside: Mould and Mildew growing in one place behind the pipe. Inside: Isolated damp patches or stains, often halfway up a wall.



Broken or Blocked Gutter

A blocked gutter will cause water to soak the wall in one area, as will a crack or ill-fitting joint.
Symptoms – Outside: Mould or Mildew growing in an isolated place behind the gutter. Inside: Isolated damp patches or mould growth at the top of the wall.  
French Drains
A French drain, drain tile, perimeter drain or land drain is a trench covered with gravel or rock that redirects surface and groundwater away from an area.
French drains are common drainage systems, primarily used to prevent ground surface water from penetrating or damaging building foundations.
Alternatively, the French drain technique may be used to distribute water, such as that which flows from the outlet typical septic tank sewage treatment system.
French drains are also used behind retaining walls to relieve ground water pressure

Other Causes of Damp


Damp might not always be coming from outside your house. Condensation is another classic cause of damp problems, especially in rooms without adequate ventilation. Condensation is caused when warm air meets a cold surface.