Why is ventilation necessary?

All Buildings are built with ventilation in mind, with different types of vents which serve slightly different purposes, however broadly the vents are there to help achieve a few common goals. First the increased air flow provided by the vents should help prevent condensation build up in the home (which can lead to mould). Secondly, older open flue boilers and gas fires rely on good ventilation in the room to create the right environment for the fuel to burn – a lack of oxygen can cause the fuel to burn in a different way which produces harmful by-products. Homes with suspended timber floors will have ground level vents that allow the air to circulate around the floorboards to prevent the floor boards rotting. Finally good ventilation actually improves the quality of the air for the occupants – rooms avoid becoming too stuffy.

When cavity walls are retrofitted with cavity wall insulation, it is quite common for these vents to be inadvertently blocked – but depending on the type of vent this can result in dangerous consequences – so here we are going to look at the different types of vent and let you know which ones should be kept and which ones can be safely closed off.

Floor vents are critical to prevent rotting!

Firstly it is vital that the air vents which are 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 over time.

Always keep vents involved in combustion open!

Above floor level the vents do have different purposes, but the most important type of vent is the one involved in helping achieve necessary airflow for combustion – these cannot be blocked ever!

Normally these types of vent are sleeved – meaning that the vent is continuous from the inner skin of bricks to the outer skin – however this isn’t always the case. If the cavity is filled with insulation retrospectively and this type of vent isn’t sleeved then the vent can become blocked with the new insulation – and unfortunately this type of oversight is becoming more and more common from sloppy cavity wall insulation installers. This type of vent should never be sealed from the inside or the outside; the installer needs to perform a spillage test pre and post installation to ensure the vent is still working as intended once the cavity wall insulation gets installed within the cavity.

Likewise, vents that are used to help ventilate rooms with gas or wood burning appliances should always be sleeved if the appliance in question is situated within the room and has a rating of 5kw or more – this  includes open fires. It is the responsibility for the cavity wall installer to install new ventilation via a core vent if there is insufficient ventilation – this needs to be done by the installer prior to them getting on with their main job of filling the cavity with insulation.

Some vents can be blocked with little consequence!

There are types of vent though that are okay to be blocked when cavity wall insulation is installed. There are some vents that are simply there to ventilate the cavity, but obviously when the cavity gets filled with insulation, the ability for air to flow around the cavity is greatly diminished – it is okay for these vents to be blocked.

Likewise, larder vents found in many older properties can safely be blocked – these were commonly found in the kitchen area for preservation of fresh food however most homeowners will have replaced the larder with a modern fridge making this type of vent a little redundant.

Room vents we would recommend to keep open, as they aid ventilation in rooms, which will help avoid the issues highlighted in the opening paragraph, however they can be closed at the customer’s request.

If you feel your home has insufficient vents, or you are worried a vent has been blocked by cavity wall insulation that has been retrofitted within your property – call Extraction4Homes today on 0208 819 9152.