In the first in a new series of articles from A. Proctor Group, we look at the true cost of simplifying the roofing detail.
Traditionally in pitched roof construction in the UK, a ventilated cavity was required below the underlay to ensure no condensation in the building. This ventilated cavity allows air to be drawn in at the eaves and carried up through the roof and out at the ridge, carrying the moisture-laden air with it.
The drive to improve energy efficiency and increase insulation and airtightness has resulted in introducing higher levels of insulation along with a vapour permeable underlay that could be airtight or air permeable.
Developed and manufactured in the UK over 25 years ago, the A. Proctor Group’s Roofshield underlay is highly permeable to water vapour and is also air permeable. its air permeable design means that there would be airflow through the roofspace, comparable to that of traditional ventilation, so a roof with insulation at ceiling level would function in the same way as a typically ventilated roof.
Roofshield roofs do not require ventilation openings at the eaves or ridge, regardless of the roof ’s size, shape, or layout. Omitting low-level ventilation means loft insulation can be placed further into the eaves, making it simpler to detail the junction between the roof and wall insulation, minimising heat loss in this area.
As Building Regulations demand lower U-values, up to 500mm of insulation may be needed at the ceiling level, so ensuring a ventilation path at the eaves becomes harder. Simply pulling back the insulation could lead to a “cold bridge” at the ceiling level at the eaves. This could lead to condensation and or black mould on the ceiling.
It is essential to emphasise the potential savings that can be realised in terms of simplified design, installation, and the reduced likelihood of condensation-related problems and customer-related callbacks. in addition, the extra-over cost of material and labour for cutting in, fitting eaves vents, installing vent tiles, and having to dress these from inside the rood is unnecessary when using Roofshield.
