Nick King, Portfolio Manager (UK) at Klober, explains why eaves ventilation systems are so important and how to avoid common installation issues.
While eaves ventilation systems are an integral part of a roof, contractors often don’t pay as much attention to these systems when compared to roofing membranes. Although they typically make up a smaller section of the overall roof, eaves ventilation systems are still essential as failure to provide sufficient ventilation around the eaves can lead to condensation problems. To achieve optimum results, sound knowledge of how such products work and should be installed is a must.
Ventilation requirements
The need for adequate roofing ventilation is covered under BS 5250 (Code of Practice for Control of Condensation in Buildings), which stipulates minimum ventilation requirements depending on the type of roof build up. To meet these requirements, there are a number of ways to ensure that adequate roofing ventilation can be achieved, with eaves ventilation forming a crucial part of this.
It is often the case that eaves ventilation is overlooked entirely when a breathable membrane is selected. Why is this? It is a common perception that all breathable membranes can be used without additional ventilation – however this is not the case. Therefore, it is important to still consider additional forms of ventilation in such scenarios.
Eaves ventilation is a more traditional method of introducing roof ventilation, and is often used alongside other methods, such as breathable membranes, to ensure continuous ventilation of the roof void. This is important to stop condensation which can then result in rot and mould growth. The amount of ventilation required is dependent upon the roof type and pitch, but ventilation equivalent to a 10mm continuous air gap is a common scenario for cold pitched roofs. To achieve the required levels of eaves ventilation, a fascia vent and roll out rafter tray is the preferred method, often alongside a felt support tray.
The fascia vent is a ventilating unit 1m in length and is fixed to the fascia to allow airflow into the roof space. To protect the eaves, a felt support tray is then used to support the roofing membrane that’s on top of it. Finally, a roll out rafter tray is used to prevent the loft insulation from being pushed up to the underside of the roofing underlay and maintain a clear ventilation path into the roof void from the eaves.
Best practice installation
Working together, the fascia vent, felt support tray, and roll out rafter tray provide all the necessary components needed for effective eaves ventilation. In fact, Klober offers a three-in-one Eaves Vent Pack so that roofing installers have everything they need to get on with the job at hand. It is important to remember, however, that without the correct installation these products will not perform.
Common installation errors include pulling the roll out rafter tray too tightly. The rafter needs to be left castellated to ensure adequate ventilation through the insulation into the loft space. Similarly, the drape between the rafters providing a drainage channel, must be a maximum of 15mm, and membranes should also not be pulled taught. If the construction beneath doesn’t allow, due to insulation or boarding, then counter battens should be used.
Allowing the membrane to sag down into the guttering can be another problem but is easily avoided by stopping short of the gutter and allowing the underlay support tray to ensure safe passage of water to the gutter. Modern day membranes are not permanently UV stable, so exposure like this should be avoided.
Overall, inadequate installation of these products could allow water ingress from wind driven rain and snow to reach inside the void of the eaves, which in colder weather can result in repeated freezing and then thawing. Over time this will deteriorate the roofing system and potentially lead to water damage through the roof and into the property.
The importance of quality
While eaves ventilation systems are generally viewed as commodity items, the quality and performance guarantees of these products should be carefully considered. Not all systems will have the same levels of testing, guarantees or manufacturer-led training capabilities to support roofers.
To this end, all of Klober’s products come with a 10-year guarantee against manufacturing defects and conform to the relevant Building Regulations and British Standards. Training is also offered and allows plenty of time for valuable practical experience fitting the products on training rigs.
For further information about Klober’s three-in-one Eaves Vent Pack visit klober.co.uk/product/pitched-roofing/eaves-ventilation/3-in-1-eaves-vent-pack
For further information on the range of training offered by Klober visit https://klober.co.uk/training-and-events
