Assessing Damp in Cavity Walls.

Original Article
February 10th, 2018


Dampness in an insulated cavity wall is very complex. It is also a controversial area where I suspect many surveyors who find dampness in an insulated cavity wall will assume the wall insulation is the cause of the problem without following a diagnostic approach allowing the precise cause to be identified.

Surveyors will be providing services to clients at a range of levels and must differentiate the advice they provide accordingly. For mortgage valuations/valuations, the level of knowledge and ‘trail following’ is much less than at level 2 (the Home Condition Survey and HomeBuyer Report) and level 3 (building survey) requires an even greater depth of knowledge.

We must also be alert to the issues CIGA has been facing recently. Recently they have come under the spotlight of
consumer publications such as Which? and ‘You and Yours’ (the Radio Four consumer programme). The BRE has published two important Good Building Guides on cavity wall insulation (GBG 44 parts one and two) and Ofgem has published the very important supplementary guidance issued under the ECO banner in 2013. They have a particularly useful form that Chartered Surveyors have to complete when they are assessing a wall for suitability for insulation.
(See the Ofgem website for ECO2 Chartered Surveyor Recommended Measure Report)

One of the main points about cavity wall insulation is because water will regularly run down the inside face of the outside wall (especially during periods of wind driven rain), cavity wall insulation will always get wet, or rather will always be susceptible to getting wet. Hopefully, if it has been properly manufactured (with water proof additive) and properly installed (compacted with no gaps or voids), the water should not get into the material and across the cavity. It is only when something is not right (many of which Chris has identified) that some level of investigation is required.

The problem then comes with the investigation. It is difficult with a borescope and not much better when taking bricks out because the source of a visible leak can be remote from where the leak is appearing on the inside. One promising option is a thermal imaging camera – but the use of those can be variable depending on the time of year and the operative.

This is the basic ‘triage’ framework I use for assessing cavity walls that have been insulated:

Valuation level 1
What are the indicators?
• Is it a cavity wall?
• Has it been insulated?
• Is it covered by a guarantee/warranty scheme with at least 5 years left to run?
• Where insulated, always follow this trail. On the most exposed elevation(s),

  • Is the outside face of the insulated wall in a satisfactory condition?
  • Using a moisture meter, check around all window openings for signs of dampness/mould growth
  • Visually check rest of inside wall surfaces for signs of dampness

What action should I take?
If any adverse signs are noted, call for further investigation by appropriately qualified person

Refer the matter to the legal adviser if there is a warranty issue.

HBR or HCS – Level 2
What are the indicators?
All the above plus:
• Are there weep holes over the openings (is there a cavity tray?);
• Is the outside skin of the wall built in natural stone? (this would make it a hard to treat cavity);
• Has the cavity wall been repaired since the insulation inserted? (this will affect the guarantee and/or the distribution
of the insulation.

What action should I take?
As above but include a (very) brief outline of the issue and likely consequences.

Building Survey – Level 3
What are the indicators?
All of the above.

What action should I take?
As above, but include an outline of the problem, the likely consequences and the scope of the likely repair work.

*See BRE Good Building Guide 44