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Roof ventilation

Our flush fitting slate roof vent provides high levels of ventilation into the roof space

Modern buildings offer better energy efficiency; however, this makes it more difficult for moisture to escape. Take a look at the reasons behind roof ventilation, the different types, and if you need it.

Why is there a need for roof ventilation?

As modern construction techniques continue to place more emphasis on energy conservation, minimising the heat loss from buildings, insulation thicknesses have increased and air tightness is constantly improving. Although this is a way of achieving good energy performance certification, there is now far less opportunity for water vapour to be dissipated through fortuitous ventilation in the property, and therefore a higher chance of condensation build up and potential damage.

Few new buildings contain open fireplaces, single glazed windows and solid floor construction has become the norm. The increase in levels of moisture being created has gone hand in hand with more heating and greater insulation levels creating greater temperature differentials within the fabric of the building.

Water vapour in the air causes a vapour pressure, the warmer the air, the greater capacity there is to contain moisture. The greater the moisture content, the higher the vapour pressure becomes.  This vapour pressure acts in all directions and will cause the water vapour to pass through the smallest of gaps to anywhere where the vapour pressure is lower until equilibrium is achieved.

Pitched, cold and warm roof ventilation

First of all, what type of construction is the roof? You may have heard of the terms cold roof and warm roof construction, but what do these actually mean?

In pitched roof construction, the insulation can be placed horizontally above the ceiling level forming a ‘cold roof’; it can be inclined above, between or below the rafters forming a ‘warm’ or ‘hybrid’ roof, or positioned in the roof structure in different ways where a ‘room-in-roof’ is to be created that can result in warm and cold roof construction types. Cold roof voids are generally always required to be ventilated; however, where vapour permeable (or Low Resistance, LR) underlays are specified, the levels required may be reduced. The enclosed void of a warm pitched roof may not require to be ventilated, but this is usually subject to the requirement to install a fully sealed Air and Vapour Control Layer (AVCL) in conjunction with an air-open roof covering.

Understanding the roof construction of any new build or refurbishment is essential to determine what products are required for the job.

Ventilation & building regulations

Roof ventilation is essential to avoid the harmful effects of condensation in roofs. To comply with Building Regulations in England and Wales and the Building Standards in Scotland, it is recommended that the roof be constructed and ventilated in accordance with the British Standard BS 5250:2011+A1:2016 ‘Code of practice for the control of condensation in buildings’.

Roof ventilation installation

To provide ventilation, opening points can usually be provided on the following areas of a pitched roof:

  • Roof surface
  • Ridge line
  • Eaves, soffits and fascias

For each of these areas, there are numerous products to suit different applications and construction details. They are also vital to meet the appropriate requirements and regulations by providing adequate ventilation levels into the roofs space. Our expansive range of ventilation products can deliver the ideal solution to these common issues.

Our independently tested flush fitting tile and slate vents provide some of the highest ventilation levels on the market in addition to being used for soil pipe ventilation and as terminals for mechanical extraction. Our universal dry fix ridge and hip system provides for full mechanical fixing of tiles while being compliant with BS 5534 and BS 5250.

For more general information on roof ventilation requirements, why not invite us to come and present our RIBA approved CPD ‘Ventilation for Pitched Roofs’.

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