External wall issues

Damp-proof courses were starting to become compulsory around the 1870s in England through local housing orders, but individual builders are known to have been introducing them in some form or other around the same time. Therefore, no definitive date can be usefully given for when DPCs were introduced in the UK. The main materials used were slate, asphalt, tar, lead or zinc, and, later in the period, engineering bricks, all of which work extremely well if correctly installed.

There are many reasons why a wall can show signs of being damp, and a thorough investigation must be undertaken before reaching a diagnosis and prognosis. The general assumption that a chemical damp course specialist is required because moisture meter readings are high is not a useful mindset. Surveyors must be aware of how to correctly interpret modern moisture meter readings and consider all the other causes of damp penetration. Incorrect recommendation and installation of a chemical damp proof course is a common mistake causing unnecessary cost and disruption to clients.

The Victorians generally had a healthy understanding of the need to ventilate enclosed spaces, and often it is the blocking of vents that causes most problems to floors, and raised ground levels that cause solid walls to saturate. Attending to these points resolves the majority of minor defects.

There is a school of thought that asserts that DPCs don't fail, but are compromised. As yet, there has been little effective argument to suggest otherwise.

Chimney stacks can act as a large wick and can also absorb sulphates from open fires. This results in symptoms that can give mixed signals as to what may be happening to the walls. Even if a form of DPC is visible in the walls, it may not extend from the walls into the chimney stack as it passes through to ground level. Due to the difficulty of access and the localised nature of the defect, chemical damp-proofing can provide a useful remedy to redress the balance in the wall, if applied in a limited area, but only as a last resort once all other sources are ruled out.

Basements were tanked using asphalts and bitumen, if the room was intended to be habitable. This is unlikely in the smaller industrial terraced developments. Tanking methods can fail if water tables rise, increasing the hydrostatic pressure, and remedial action other than replacement is limited.

For more information on diagnosing and remedying damp see the section on damp.