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E4 – Main Walls

January 7, 2011

Badly spalled red bricks to bay

In the RICS Homebuyer Survey, E4 – Mains Walls refers to the external walls only. There are many types of wall defects, however I’d like to show you some common ones.

NB The walls I inspect will typically be 240mm thick and solid brick.


My inspection of the main walls is initially focused on cracks. However, in pre-1920 houses the odd crack around windows and bays is very common.

A well camouflaged crack over a brick arch

 I start my inspection by scanning the wall for anything either asymetrical or out of plumb as cracks are often found in these location. However, a proper look requires a degree of focus and concentration as some of the defects are quite well camouflaged. I’ve often found myself looking at a wall only to find passes-by starting to looking at what I’m looking out!

I’m looking for uncommon cracks which are usually diagonal in direction and wider at one end compared with the other. I’ve found that one single crack doesn’t usually send alarm bells ringing, however several cracks in certain adjacent locations will certainly make me suspicious. A crack passing through a main wall is certainly a concern.

Poor brick bonding to front porch

I also have a good look around extensions and porches as often the new brickwork is not bonded into the existing and a vertical crack will open up. Butt jointing an extension onto your house is going to open-up. The photo to the right is very common.

I also split the building into its north and south sides. Cracking on the south sides (SE-S-SW) may well be due to thermal stress as the surfaces on these exposed elevations expand and contract greatly throughout the year. When visiting a house it’s a good ideal to take a compass to check the orientation. You’ll get more cracks on the south side than the north.

In older properties, large window openings cause stress “bottle-necks” because the structural loads are forced to pass around the opening (loads can’t pass through a void). This often means slender sections of brickwork are overloaded which results in distortion or cracking of the bricks. Overloading cracks can be mistaken for subsidence as the crack pattern is similar.


During my external inspection I’m assessing the condition of the main walls and adjacent elements for the risk of internal dampness. Damp seems to be a very common complaint amongst homebuyers. The main problem with dampness is that it’s very seasonal. A survey carried out in summer is unlikley to find serious damp issues compared to the same survey carried out in winter.

The adjacent elements are what I refer to as my 3Gs (Gutters, Gulleys and Ground levels). See post with the same name.

Slate DPC just above ground level

To this end a good start is to find the damp proof course (DPC) at the base of the wall and then to check that there’s at least 150mm of exposed wall, from the DPC down to the external ground level. The shorter the distance between the two, the greater the risk of internal dampness. The photo to the right shows the slate DPC almost at ground level and adjacent a blocked rain water gulley. This will result in sever internal dampness.

See my post: Raised ground levels will cause internal dampness to show what happens when the ground level is higher than the internal floor!

A very blocked gulley will always cause internal dampness

Blocked Gulleys (drain points for waste and rain water pipes) are a perennial favourite when it comes to internal dampness. See photo to the left. I think if everyone cleaned out their drainage gulleys the incidents of internal dampness would be halved!

The blocked gulley allows water to flood the ground against the wall. The bricks will quickly absorb the standing water allowing moisture to pass through the wall.

Ferns growing out of the wall - No coping stones

Plant growth is a very good sign that moisture is present and when plants are able to grow on a brick wall you know something’s a miss! The photo to the right indicates that the wall is regularly wet and the lack of coping stones to protect the top course of bricks is probably the reason.


This air grille turned out to be the front door for a family of rodents.

Air bricks or grilles are vents found at the base of a wall, that allow air to flow below the suspended timber floor. For affective cross flow, these air bricks and grilles need to be installed both on the front and back walls of the house.

Their purpose is to allow water vapour and condensation to escape while allowing drier air to enter. The drier air helps keep timber floor joists below the critical 20% moisture content level. The 20% threshold being the point at which timber becomes vulnerable to decay.

 How many do you need? The more the merrier!

A poorly maintained air vent (see above right) is an open invitation to rodents as I found at this property.

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