Identifying cavity wall insulation problems

Problems associated with cavity wall insulation could be widespread. One newspaper reports: “1.5 million homes are blighted by damp after cowboy builders cash in on a Government insulation drive”. Another asked: “Could the cavity-wall insulation scandal rival PPI?”.

Many post war properties (and quite a few pre-war properties) were constructed with external cavity walls. These comprise an outer leaf (usually of brickwork), a gap and an inner leaf (usually of brickwork or concrete blockwork).

The construction reduces the risk of water penetration through the outer walls and enhances a wall’s thermal performance. Each leaf of the wall is connected to the other by a series of cavity wall ties, made of either stainless steel or mild steel or iron, depending on the age of the house. Older steel or iron ties are susceptible to rusting and failure so a programme of cavity wall tie replacement is often required, but that is a matter for another posting.

Recent building regulations require that modern cavity walls are insulated, typically with a rigid insulating ‘batt’ within the void. Older walls, typically over 30 years old, often have no insulation at all and the void is open.

For some years, additional cavity insulation has been recommended as a means of improving a building’s thermal efficiency. The process seems simple, drill into the outer wall, inject a fibre or bead insulation into the cavity, make good the holes, sit back and enjoy reduced energy bills. A system of government grants over the years has encouraged householders and contractors to carry out work across the country. The problem is that this fills the cavity with a material that can act as a sponge.

But not all cavity walls are suitable for insulation. When done properly to a building in the right location there is no question that a building’s performance is enhanced. However, done badly or applied to an unsuitable property, a building’s performance can be significantly compromised. Problems of water penetration, condensation, dampness and cavity wall tie deterioration can occur.

Witnessing cavity wall insulation problems first hand

Over the past 12 months we have inspected several properties where expensive cavity wall insulation has led to expensive remedial work. These are buildings where cavity wall insulation should never have been installed in the first place.

Typical problems include the bizarre to the downright dangerous:

  • Attempts to cavity insulate a solid brick wall – yes really!
  • Poorly filled cavities resulting in cold spots and internal condensation (the image below shows with infra-red where the insulation in the wall is missing ).
  • Blocked bathroom and bedroom ventilation bricks causing condensation.
  • Blocked air bricks forming part of a gas heating ventilation system – just simply, dangerous!
  • Internal dampness caused by the cavity being bridged by insulation and allowing moisture to penetrate from outside through the wall to the inside
  • Insulation of obviously and excessively exposed walls – cliff top, seaward facing property – something many of my Hythe readers should be aware of!

Suitability for cavity wall insulation

The installation of retro fit cavity wall insulation is covered by the Building Regulations and must be carried out and designed by a person in a competent installer scheme. The regulations are based on a withdrawn British Standard BS 8208 “Assessment of suitability of external cavity walls for filling with thermal insulants”. This suggests a series of checks that an installer must follow to establish whether a wall is suitable for insulation. This must be done before work starts. They are common sense logical checks. If they have not been carried out, or not carried out properly (a tick box form is not sufficient as it is necessary to actually calculate the exposure a building has) then, in our humble opinion, an installer has been negligent in progressing their work. Although the BS is withdrawn its methodology is sound and would need to be followed to meet building regulations.

In every survey we have carried out as part of a dispute over problems caused by cavity wall insulation, those checks were not undertaken.

There are many factors to consider when establishing suitability for cavity wall insulation. This includes the construction and site conditions which includes the calculation of exposure to wind driven rain in accordance with BS5618. Unless a property is fully protected you simply cannot guess the degree of exposure. Other aspects to be assessed include presence of cavity bridges, the width of a cavity, the condition of the brickwork and the presence of services and ventilation. Walls not suitable for insulation include:

  • Walls exposed to driving rain
  • Walls with a cavity of less than 40mm
  • Timber frame walls – these often have a brick outer leaf and look like cavity walls
  • Walls with lots of cavity bridges
  • Walls in a poor structural condition
  • Walls with a parapet that does not have a cavity tray
  • Walls more than 12m high

This is not an exhaustive list and you should always seek advice if you are unsure.

How can we fix it?

As far as remedial actions are concerned, none are especially straightforward. In some cases, the best course of action is the removal of the insulation. This may require sections of the outer leaf to be removed and subsequently rebuilt to facilitate access. In one case we dealt with, the whole outer leaf was taken down and rebuilt . Alternatively, and depending upon other factors, some form of external sealant or cladding may be appropriate. Each case needs to be reviewed on its merits. There may also be internal decorative and remedial work to undertake.

So, who pays? Well, possibly you. Many installations are covered by a CIGA guarantee – often sold as being government backed. It isn’t. CIGA is an independent provider of guarantees for work undertaken by its registered installers only.

If you have internal dampness you think is due to cavity wall insulation or if you need to make a claim you may want or need an independent survey and inspection. Collier Stevens can inspect cavity wall insulations and verify their compliance or otherwise with the relevant British Standards and Codes of Practice. This includes the all-important calculation of exposure to wind-driven rain. This is the bit that installers very often trip up on! If you think we can help you with a dispute, or you would like some advice, please give us a call.

(Originally published by Steven Way, 9 March 2017)