The A. Proctor Group Ltd has been at the forefront of roofing membrane technology for over 25 years working with our partners across the construction industry, helping to evolve standards, and delivering quality results on projects across the UK and around the world.

After 25 market-leading years, the A. Proctor Group continues to push the future of roofing membrane technology forward by embracing and developing next generation products that can be used in warm and cold roofing applications.

Condensation Control and Ventilation As Building Regulations demand ever-higher thermal efficiency, today’s buildings are becoming increasingly airtight. While this is undoubtedly beneficial for building energy performance, architects and contractors must understand the implications for moisture and vapour management when considering roofing membranes.

Condensation control should be considered as part of the design process. Successful control will depend on factors such as prevailing winds, room layout, number of storeys and type of heating system as well as the more usually accepted aspects such as construction, heating, ventilation and moisture production. All these aspects, therefore, should be considered carefully and, as they are interdependent to a greater or lesser degree, they should be considered together.

The fundamental principle in designing to minimize condensation is to maintain a balance of the three factors 1. Thermal and vapour properties of the structure 2. Heat input and 3. Ventilation to achieve either low vapour pressure and/or high structural temperature.

The building fabric, typical weather conditions and anticipated occupancy patterns and uses will all interact to define the moisture risks associated with the construction. These “ground rules“ form the basis of a good hygrothermal design strategy. Once an understanding of the building, weather and occupancy are achieved, the designer can then focus on ensuring the heat, air and moisture movement within the structure is properly balanced. This ensures both a healthy environment for the occupants of the building and long life for the building.

The A Proctor Group have been supplying construction membranes for over 30 years, and then, as now, most of the mainstream housing in the UK was built using truss rafters with insulation placed across the ceiling. This type of construction, a “cold pitched roof”, leaves a large, unheated, and uninsulated void above the habitable spaces.

Prior to the common usage of trusses, which began in the 1960s, these roof spaces were made from a frame of cut timbers, which allowed a relatively easy path to convert the loft space in the future, as is the case in many older properties. Trusses make this process all but impossible, but at the time this space was still a useful storage area, often floored, but not really useful as living space.

The increased adoption of solar photovolataics (PV) on pitched roofs has led to the introduction of new and updated guidance to ensure roofs continue to perform as intended. However, as Pamela Howat, Senior Technical Advisor at A. Proctor Group, explains, the terminology used in the updated guidance is causing confusion about the types of underlays that can be installed on roofs featuring PV panels.

Permeability is a term used in relation to two distinct parts of a pitched roof build-up: the underlay and the external roof covering.

The permeability of a pitched roof underlay – installed over the rafters and below the external covering – impacts on the provision of ventilation to the roof space. The permeability of the roof covering itself impacts on whether there is a requirement for a ventilated batten & counter batten cavity below it.

A typical tile or slate roof finish is the first line of defence against the weather. As water can get into the space below the tile or slate, the chosen underlay must also be capable of resisting water ingress.

What is an appropriate standard of water resistance, or water hold out, for a pitched roof underlay? What testing should be carried out on an underlay, and could timber treatments used for products like tile battens affect the performance of an underlay? This month’s FAQs explain all.