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In Building Regulations and within Building Standards (Code for Sustainable Homes or PassivHaus, for example) to meet specific requirements ‘Fabric First’ may be referred to as part of the ‘building envelope’ or the ‘thermal envelope.’
According to Wikipedia, ‘a building envelope is the physical separators between the conditioned and unconditioned environment of a building including the resistance to air, water, heat, light, and noise transfer. The three basic elements of a building envelope are a weather barrier, air barrier, and thermal barrier.’ Further, the thermal envelope, or heat flow control layer, is referred to as ‘… part of a building envelope but [this] may be in a different location such as in a ceiling. The difference can be illustrated by understanding that an insulated attic floor is the primary thermal control layer between the inside of the house and the exterior while the entire roof (from the surface of the shingles to the interior paint finish on the ceiling) comprises the building envelope.’
In simple terms, this means anything that separates the inside of the building from the outside, including the foundation. ‘Building envelope thermography involves using an infrared camera to view temperature anomalies on the interior and exterior surfaces of the structure. Analysis of infrared images can be useful in identifying moisture issues from water intrusion, or interstitial condensation.’
In the ‘Fabric First’ approach the design and means for preventing water intrusion, controlling air-tightness, ensuring healthy walls/roofs (the prevention of mould growth or other dangers, for example) and appropriate insulation becomes the most important aspect of a build, while internal water vapour and household odours must be managed by controlled ventilation.
In an appropriate thermal envelope, the ‘Fabric First’ approach allows the building to maintain a controlled micro-climate within the building envelope. Air-tightness is of the highest importance, as other factors may influence heat or cold performances, and must be detailed and clearly understood around apertures with windows and/or doors, and the air-tightness of this fenestration is where a building is most likely to fail as can be indicated by thermography or through air-tightness testing of a building.
The building envelope is all of the elements of the outer shell that maintain a dry, heated, or cooled indoor environment and facilitate its climate control. Building envelope design is a specialised area of architectural and engineering practice that draws from all areas of building science and indoor climate control.
Once a micro-climate is achieved in a building, it then becomes relatively simple to know the performance of the structure, through the use of Government accredited Code for Sustainable Homes, PassivHaus, Domestic On Construction Energy Assessor (DOCEA), Non-Domestic Energy Assessor (NDEA) or simply Building Codes assessment software.
Experience has taught us at Thir13en that life or projects is/are rarely that simple. It all sounds reasonable, logical and straight forward but in practice the issues that address these problems are rarely simple. Quality control of critical details such as that for fenestration is imperative, and the use of materials specified at the design stage is critical to achieve the intent of a design.
Builders, contractors, and even clients have been known to change material specifications for a variety of reasons, mainly because they believe substitution will achieve the same result but this is rarely the case. That is why the Integrated Design Process is critical to one’s project, not only to achieve the performance of the thermal envelope but to achieve the costs, and savings, identified by the Integrated Design Process.