"FABRIC
FIRST"
Whatever You Have Learned,
Put It Into Practice
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.
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.
PASSIVHAUS
PassivHaus buildings provide a high level of occupant comfort while using very little energy for heating and cooling, leaving other topics for designers to decide whether they should be included or not.
Outline Specification of the PassivHaus Standard
The PassivHaus standard is a comprehensive low energy standard intended primarily for new buildings. The following energy performance targets define the standard and must be met in order for certification to be achieved.
Energy performance targets and air changes per hour
The standard requires that the Primary Energy demand target is met in all cases, this figure must include the space heating, domestic hot water, lighting, fans and pumps and also all of the projected appliance consumption.
In addition to the primary energy demand the standard permits that either the Specific Heating Demand or the Specific Heating Load must be met.
Energy Balance
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The energy balance of the proposed building must be verified using the Passive House Planning Package (PHPP) using the appropriate regional climatic dataset. Either the monthly or the annual method may be applied.
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If the Specific Heat Demand is ≤ 8kWh/m2.yr or the ratio of free heat gains to heat losses is greater than 0.70 it is recormended that the monthly method is used to ensure accuracy.
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The standard provides limiting backstop values for the glazing specification, ventilation system, air tightness levels and thermal-bridging as these factors should not exceed these limits in order that the thermal comfort criteria can be maintained.
Further information
The following table illustrates the elemental backstop values which should not be exceeded in order for the Passivhaus certification criteria to be met.
*please note opaque U-values are only recommended targets and are not critical to certification
The backstops above apply to moderate weather regions only, for warmer climates the performance values could be reduced. Please consult your building certifier for more information.
Comparison PassivHaus versus Code for Sustainable Homes
One can not directly compare the PassivHaus standard with the Code for Sustainable Homes. PassivHaus is an energy performance standard whereas the Code is an environmental assessment methodology covering the overall environmental performance of a building including for example construction site management, consideration of the materials used in construction, water consumption of the building, provision of recycling bins etc. The PassivHaus methodology is a tried, tested and successful approach to designing and constructing very low energy buildings, with thousands of examples built over the last 20 years all over Europe. The energy performance and carbon saving criteria of the Code for Sustainable Homes are based on SAP. Choosing between PassivHaus and the Code for Sustainable Homes can be a difficult choice, as making the wrong choice could infer costs not required for the development. Thir13en is available to assist in this regard.