Cavity Wall Insulation Causes Dry Rot Attack

Nov. 8, 2011 - PRLog -- This has 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.

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.

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.

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 Heritage (http://www.premier-heritage.co.uk) 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.