For over 50 years the A. Proctor Group has served the construction industry with an extensive portfolio of technically advanced thermal insulation, specialist membranes and vapour control layers, providing an extensive range of superior high-performance products suitable for modular and offsite construction.
The basis of best practice in modular construction comes from an understanding of the relevant building regulations and a holistic approach to the building design. In doing so we consider six core aspects in the process related to the balance of Heat Air Moisture Management (HAMM): building, weather, occupants, heat, air and moisture.
Building - the first area to consider is the type of building fabric involved. Concrete, steel and timber-based buildings all respond differently to moisture and contain different amounts of construction moisture that must be allowed to dry out. For example, buildings with a lot of in-situ concrete can take several years to fully dry out, this excess moisture load must be accounted for at the design stage.
Weather - construction moisture can also come from the weather and this must also be taken into account, along with the weather conditions the building will be subjected to once complete. Being weathertight earlier in the construction process and generally being composed of drier materials, offsite construction has an important hygrothermal advantage. Occupants - by reducing the initial moisture loading on the building fabric, the design can be more precisely tailored to manage moisture associated with the occupants of the building and the uses the building will be put to, leading in turn to a more efficient fabric envelope and building system.
The influences of these three aspects can then be assessed in terms of the heat, air and moisture movement within the building. This takes into account the heating of the building, as well as the air leakage effects and response of the building fabric to the absorption and desorption of moisture. Factors such as the position and performance of the fabric insulation can also be considered.
To ensure our design adequately manages these complex interactions, we undertake a hygrothermal analysis of the building fabric using software called WUFI. This breaks the building elements into individual layers and calculates the temperatures, moisture flow and degree of water storage at any point in the building fabric. This detailed analysis allows us to consider solutions that may mean that the internal vapour control layer can be removed altogether without creating a condensation risk.
This is made possible by the use of an external vapour permeable air barrier membrane. The Wraptite® membrane self-adheres to the external face of the sheathing and provides a robust airtight layer without compromising moisture movement through the wall assembly. By removing the vapour control in favour of an external air leakage solution we remove the associated material and installation costs, and more importantly, we remove the need to seal all the service penetrations, meaning we have a more reliable air barrier and can reduce the air leakage rates applied at the design stage.
To read the full article, go to Offsite Magazine Issue 19.
