Premier Heritage have over the years undertaken investigation of some fairly horrendous attacks of fungal decay in all types of buildings which occurred as a consequence of unwanted moisture ingress and resulted in extensive damage to the interior fabric of the building, the loss of structural and joinery timbers and more importantly distress and expense to the property owners.

In a lot of cases these attacks could have been avoided with simple routine maintenance, cleaning of guttering drains etc which are one of the major contributors to fungal decay, particularly the dry rot fungus Serpula lacrymans.

When one undertakes a survey for fungal decay the initial objective is to establish the source of moisture responsible for the attack, however our recent investigation of a 1930’s detached bungalow, initially failed to identify the cause of a significant outbreak of decay that affected the two (back to back) bedrooms.

Our client’s first indication of anything being wrong was the discovery of a fruiting body on the external corner of a skirting, followed by deflection of the flooring this resulting in her vacating the room and her subsequent contact with ourselves.

Dry rot fruiting body on skirting board

On arriving at the property and commencing our survey the first observation made was that the attack was well away from any obvious internal sources of water (bathroom, kitchen etc) although could have been the result of a radiator pipe leak below floor level, although this may have become obvious to the occupants.

External inspection again confirmed no obvious down pipes or drainage systems adjacent to the decay and the property had a physical damp proof course and walls tested (using a moisture meter) detected no dampness to be present or to adjacent joinery, other than the skirting board above. One observation made however was that new sub floor air bricks had been fitted on to all elevations.

Why has the property got new airs we asked? We had cavity wall insulation installed about 3 years ago …………… alarm bells started to ring.

To cut a long story short having lifted the flooring within the front bedroom we discovered an extensive outbreak of fungal decay which extended through the internal wall into the rear bedroom covering around two thirds of the floor area in each room and evidently starting close to the location of the external wall and an air vent.

Dry rot in subfloor void

Dry rot mycelium growth

Dry Rot attack

The extent of the attack exposed following removal of the floor timbers.

Upon closer inspection however we discovered that the internal vent apertures had been blocked with cavity wall insulation and also found that the internal aperture didn’t align with the air vents located on the external wall.

Insulation materials evident in air vent aperture

Cavity brushes used to prevent insulation blocking air vents, although aperture clearly does not go through the wall.

During our initial survey we broke out several of the external air vents establishing that whilst the new vents installed had apparently been sleeved across the cavity (to prevent the materials blocking them) on removal they were not sleeved, but  fitted with cavity brushes, which served no practical purpose. Therefore the insulation had blocked the cavities, preventing air flow to the sub floor timbers, thus changing the environment within the sub floor void, creating damp conditions, sub floor condensation, thus resulting in the wetting of timbers and eventual development of the fungal attack.

Having established the cause and extent of the decay a specialist timber treatment contractor was appointed, undertaking the repairs and treatment of the floors, walls were re-plastered (where removed for cavity clearance) and new joinery fitted. Once the floors had been opened internally and aired and the cavities cleared etc the entire area dried down quite rapidly.

More importantly however was that every air brick fitted to the bungalow had to be individually broken out and subsequently replaced with sleeved vents directly through the walls to the sub floor area, thus reinstating the original sub floor ventilation, if not improving it!

From the point of discovering the decay to the re-occupation of the bedrooms took around 6 weeks and we are pleased (on this particular occasion) to report that the original contractors responsible for the installation of the cavity wall insulation have accepted full liability for the fungal decay as well as all costs.

How to avoid future problems? We at Premier have inspected and reported on numerous cases where Cavity Wall Insulation materials had caused bridging of moisture through the cavities, resulting in internal dampness and spoiling of decorations etc. Whilst our own evidence suggests that installers have tightened up on their pre-installation procedures in recent years, property owners still need to be aware of the potential issues that can cause future problems and expense (particularly if the installer is no longer trading).

Energy conservation is now government lead and more and more homes are being insulated, but it is important that prior to installing Cavity Wall Insulation  pre installation checks are undertaken by the installer which should include the most important factor, its suitability for cavity wall insulation i.e. the building’s construction (porosity of building materials) and its exposure to the prevailing weather.

Other checks should include visual inspection of the actual cavity at Damp Proof Course level, checking the cavity trays for debris and also for dirty wall ties, all of which are capable of transmitting moisture through a wall. More importantly check that the system (installation and materials) are covered by guarantees, preferably insurance backed.

From October 2008 all domestic buildings (being built, rented or sold) were required ‘by Law’ to have an Energy Performance Certificate (EPC) to help improve the energy efficiency of the building. The EPC provides an ‘A’ to ‘G’ rating for the building, ‘A’ being the most efficient and ‘G’ the least and to-date a ‘D’ rating is currently being banded as the average.

It is claimed that around a third of heat loss in a house is through its roof and walls and currently there is a government drive (supported by television advertising and the offer of Home Improvement Insulation Grants) to encourage home owners to increase loft insulation and also to fit cavity wall insulation, as it is claimed this can save on average around £180 per annum on heating costs!

However were you aware that by installing cavity wall insulation, whilst you may well be saving some money on fuel costs, you could also be creating a major expense for the future……..damp!

Example of cavity wall insulation

The cavity wall (as we know it) dates back to the early 1900’s and is commonly found in the coastal areas around Britain, used to reduce the risk of rain penetration. In the 1920’s, local building by-laws encouraged the construction of the cavity wall and by the 1940’s it had become the Industry Standard. The familiar cavity wall (as we know it) is two leaves of brickwork, forming a 60mm cavity and tied together with metal wall ties.

Even back in the good old 1970’s concerns were being expressed over Energy Conservation and home owners were then being encouraged to introduce loft insulation and it wasn’t long after that cavity wall insulation was also being recommended.

Fill your cavities with foam, polystyrene, mineral wool or any other material you can introduce through a small hole in the wall and you will save energy and loads of money. Sounds good, but what if by introducing this insulation you increased the risk of damp to your property, which in turn would cause internal decorative spoiling, plaster damage, fungal decay to  structural and joinery timbers and also accelerate the risk of corrosion to the metal wall ties.

Could that really happen? Well the answer is yes and it is.

Paul Carter, the principal of Premier Heritage, has investigated hundreds of buildings over the past 20 years of so, where damp has affected internal decorations etc and found that the damp present was due to bridging of the cavity by the earlier installed insulation materials. Whilst some of these cases were wrongly diagnosed by others as rising damp, most of these buildings (if not all) retained a physical damp proof course, the newest being a 1980’s brick built bungalow in Hampshire.

Ok, lets put this into perspective, there have been thousands of cavity built houses within the UK that have been insulated and a good majority of these don’t currently have nor will ever have a problem with damp. But there are a great number that have and no doubt more will be affected in the years to come! 

Increased rainfall in past years has resulted in a noticeable increase in damp problems affecting conventional cavity-constructed housing, due to moisture penetrating / bridging the cavities and in particular on the weather prevailing elevations and this isn’t a problem relating to current rainfall, but a gradual build of damp over many years.

Rainwater driving into the masonry of a building can penetrate the outer leaf brickwork leading to the wetting of the insulation materials, increased damp penetration and a reduced thermal performance of the material. Poor construction methods, mortar and perp joints, debris within the cavities, dirty wall ties and poor installation procedures by installers all contribute to the overall problem, which generally will result in the need to remove the insulation, which is not only expensive, but will almost certainly cosmetically scar the building when finished. Unfortunately it doesn’t come out through the same hole through which it went in!

So how do you avoid this problem? Well there’s no easy answer to this other than to look carefully at the building’s construction (porosity of building materials) and its exposure to the prevailing weather conditions. If having then decided to proceed, ensure that the chosen contractor / installer, during the survey, checks the cavities  and cavity trays for debris and dirty wall ties, but more importantly offers a system and material that guarantees (preferably insurance backed) that the materials being installed will not transmit / bridge moisture through and into the internal wall!

Alternatively, if you’re still unsure then don’t install.

Examples of Cavity Wall Insulation causing damp:

Cavity Foam Insulation

1970’s block constructed bugalow with poorly installed cavity foam insulation and debris bridging moisture via wall ties, cost around £800 to remove and rectify internal damage caused.

Polystyrene bead cavity insulation

Polystyrene bead cavity insulation 2

1920’s brick constructed house, south facing elevation with polystyrene bead insulation and poor quality mortar. Caused extensive damp to internal decorations and accelerated corrosion of wall ties (rusting ends just visable), cost in excess of £3,500 to remove insulation and install new wall ties.