Wet/Dry Rot Timbers
Cavity wall insulation can cause problems by trapping moisture within the timber and also blocking the air flow. Floor and wall timbers in a property rely on a lack of moisture, together with adequate air flow, in order to retain their integrity. This can lead to the timber frames rotting. More worryingly, once timber frames have started to rot, the spores will continue to grow and spread to other parts of the property, even if these parts have not been initially affected.
Rotting timber can cause serious damage to the structure of your house, so it’s vital to deal with the problem.
Is Cavity Wall Insulation Blocking Your Air Vents?
There are commonly two types of vents in cavity walls these will be visible in the outer leaf of the wall; those in the wall appearing above floor level are designed to ventilate the cavity. In properties that have a suspended timber floor, there will also be air vents located in the outside “leaf” appearing below floor level, these are installed to allow ventilation of the void below the floor.
You can check which ventilation your property has by looking at the house from the outside.
It is vital that the air vents installed to ventilate the area below the floor are not blocked. If these vents have become blocked by debris in the cavity, insulation or have been deliberately sealed using silicone sealant or similar, then the air flow beneath a timber floor will be restricted or completely removed, which can lead to floor timbers rotting.
When cavity wall insulation is installed in a property, air vents designed to ventilate the cavity can routinely be sealed by the installer – If the only sub floor air vents that your property has have been blocked by silicone or similar, then there is a risk that the area beneath the floor is not being ventilated effectively.
If your vents are blocked, damage may have been caused to your floor timbers. You may not be aware of this damage yet and it is vital that this is addressed to prevent further damage.
Blocked air vents can cause serious damage to your house so it’s vital to deal with them
Is Your Brickwork Being Damaged By Cavity Wall Insulation?
Cavity wall insulation should only be installed in properties where the exterior brickwork is in good condition. This means that the bricks should not have had frost damage, the pointing should be in good condition, and there should be no pre-existing damp problems. Similarly, if walls have been painted with paint that prevents moisture escaping back out of the brick, then cavity wall insulation should not be installed.
Problems can also be caused once cavity wall insulation has been installed due to the fact that the exterior leaf of the wall now becomes colder, as the insulation is keeping heat to the inside leaf of the wall. Any penetrating moisture in the external leaf can only evaporate back out to the outside, which means that the brick can take longer to dry out. This means that if there is frost, the wet brick can split. This can usually be seen through the front face of the brick breaking off as the water freezes in cold temperatures and expands.
Cavity walls were initially developed for properties in coastal areas, particularly in the West and South West of the UK. This was because these areas were subject to wind driven rain, which penetrates the walls of the property. The cavity was introduced to ensure that moisture being driven through the outer leaf would either drip down to the ground or would evaporate within the cavity, but would not reach the inner leaf and thus the house itself.
This made sure that the inside wall of the house remained dry.
High Exposure Leads to a High Risk Of Damp!
However, if the cavity is breached by debris or by sand then this allows a bridge for moisture to travel to the inner wall. Wind driven rain can penetrate the outer wall and use the cavity wall insulation as such a bridge. For this reason, properties in these areas of “high exposure” suffer a much greater risk of damp following the installation of cavity wall insulation.