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In general, if one building element is thermally different from another within a dwelling, they are to be measured individually so that their respective areas can be calculated, the appropriate U-values can be assigned, and then values can be entered separately into the DEAP software.
Many dwellings have one or more extensions of a different construction or insulation standard added to the main part of the dwelling (such as a cavity wall construction with an extension constructed from hollow blocks) or have parts of the original dwelling with different constructions or insulation standards although built at the same time (for example, the front of the dwelling is constructed from stone and part of the rear is constructed from brick). In these cases, dimensions, and constructional details of the main part of the dwelling and the extension are recorded separately (including year of construction), to allow the assignment of different U-values to the original and to the extension. Occasionally, there may be two or more extensions whose details need each to be recorded separately. DEAP allows the user to record the presence of an extension for existing dwelling BERs.
In addition, dwellings may comprise a different construction for some parts of the walls (for example, a timber-framed bay window or panel in an otherwise masonry construction). These are recorded as separate constructional elements.
Regardless of whether a dwelling’s floor (or floors) loses heat, the floor area for each level of the dwelling is needed to calculate both the total floor area and the dwelling volume. The floor area includes the habitable dwelling and parts of the habitable dwelling accessed from within the dwelling at each level. Floor areas do not include unheated garages, coal sheds, external unheated storerooms, thermally separated conservatories, or thermally separated porches.
The assessment of an existing dwelling is also concerned with assessing and measuring the building elements that lose heat from the habitable dwelling. Non-heat loss areas (such as party walls, a floor, or a ceiling wholly above or below another apartment, or walls adjoining a heated circulation space) are ignored altogether as heat loss elements.
To simplify the measurement process:
All heat loss areas and all floor areas are based on internal measurements. On-site measurements may be internal or external, provided they are converted to internal measurements when the respective heat loss areas are calculated for entry in the DEAP software.
Storey heights are entered into the DEAP software in accordance with the DEAP methodology, that is, for a one storey dwelling, the storey height is the height from the topside of the floor to the underside of the ceiling. For dwellings comprised of more than one floor, the lowest floor is calculated in the same way, that is, the lowest floor height is from the topside of the floor to the underside of the ceiling, with subsequent floor heights calculated from the underside of the ceiling below to underside of the ceiling on that level (that is, the upper floor includes the allowance for the intermediate floor). It may not be possible in an existing dwelling to measure the thickness of the intermediate floor, therefore, measure the topside of the floor to underside of the ceiling height on each level, and add 0.25m to each upper floor level to calculate the storey height to enter into the DEAP software.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 5.3 | 5.5 | 7.0 | 8.3 | 11.0 | 13.5 | 15.5 | 15.2 | 13.3 | 10.4 | 7.5 | 6.0 |
Source: Met Eireann data
As indicated in Section 1, the areas of building elements are based on the internal dimensions of surfaces bounding the dwelling.
Window and door area refers to the total area of the openings (windows, doors, rooflights), including frames. Wall area is the net area of walls after subtracting the area of windows and doors. Roof area is also net of any rooflights or windows set in the roof. Losses or gains through party walls and floors to spaces in other dwellings or premises that are normally expected to be heated to the same extent/occupancy as a dwelling are assumed to be zero as detailed here.
BER assessors should allow for elements of differing U-value (for example some windows single glazed and some double glazed, masonry main wall and timber framed wall in an extension, main roof pitched and extension roof flat).
DEAP allows for the selection and entry of default U-values for all heat loss element types for existing dwellings.
On the Building: windows tab, the following data is required for each window:
DEAP calculates the overall heat loss rate for glazing (W/K), the effective collecting area on each orientation for solar gain purposes (m2), a glazing ratio to floor area for daylighting purposes, and a solar gain rate (W/m2) for summer period overheating calculation purposes.
For doors, walls, roofs and floors, the following data is required:
A thermal bridging factor is entered in the Building: global factors tab. The default value of 0.15 W/m2K must be chosen unless contrary evidence is available as defined in Thermal Bridging.
The “Results” section details the overall heat loss rate, or heat loss coefficient (W/K) for the dwelling, composed of fabric (including glazing) heat losses and ventilation heat losses (from the ‘Ventilation’ tab). The ratio of heat loss coefficient to total floor area is calculated and termed the heat loss indicator (W/K m2), also called the HLI. The HLI is also displayed on the Results tab. The heat losses are used to calculate the overall heat demand for the heating season and cooling demand for the cooling season (where a fixed cooling system is installed).
U-values for the floor, walls and roof should be calculated when construction details are known. This applies to new dwellings assessed using information gathered on site and from building plans and specifications. The use of non-default values may be applied to existing dwellings where sufficient evidence is available, alternatively, the use of default U-values for existing dwellings where sufficient evidence is available to use non-defaults is not available. This is further expanded on in other tabs.
U-values for walls and roofs containing repeating thermal bridges, such as timber joists between insulation, etc., should be calculated using methods based on the upper and lower resistance of elements, given in IS EN ISO 6946.
IS EN ISO 6946 gives the calculation for components and elements consisting of thermally homogenous layers (including air layers) and is based on the design thermal conductivity or design thermal resistances of materials and products used. The standard also gives an approximate method for inhomogeneous layers, except cases where an insulating layer is bridged by metal.
Thermal conductivity values for common building materials can be obtained from Table 2.9, Building Regulations 2022TGD L (Table A1), I.S. EN ISO 10456 or the CIBSE Guide, Section A3[6]. For specific insulation products, data should be obtained from:
Certified data from other sources can also be used, bearing the following text in mind (taken from Building Regulations 2022 TGD L): “For thermally homogeneous materials, declared and design values should be determined in accordance with I.S. EN ISO 10456: 2007. Design values for masonry materials should be determined in accordance with I.S. EN 1745: 2012. For insulation materials, values determined in accordance with the appropriate harmonised European standard should be used.” U-value calculations should only use certified data as described here.
Note that Table 2.10 may be used for insulation products' conductivity for design purposes (such as provisional ratings) and for existing dwelling assessments where no further information is available. Insulation thermal conductivities from Table 2.10 may not be used for final BER assessments for new dwellings.
Where insulation thickness varies across a building element, the insulation thickness used should be the average insulation thickness (weighted by area). In the case of roofs where the attic hatch is part of the roof heat loss area, the attic hatch insulation thickness is also accounted for in this calculation. In some cases, the attic hatch should be considered to be a heat loss door rather than part of the heat loss roof area, particularly when it is used to access a floored attic acting as an unheated storage area.
These should be calculated using the procedure described in IS EN ISO 13370, or in the CIBSE guide, Section A3. TGD L Appendix A outlines a procedure for a building with more than one ground floor dwellings, (i.e., semi-detached houses or apartment block), where the U-value can be calculated for the total ground floor area. This U-value can then be applied to the floor area of the actual building being assessed. Further details are available in BRE 443[6].
Software packages to perform U-value calculations for different building elements in accordance with the relevant standards are readily available. Details such as element thicknesses, thermal conductivities, and resistances, used in carrying out U-value calculations, must be retained in the BER assessment records by the BER assessor.
The exposed perimeter of a ground floor is the total length of the external wall dividing the dwelling ground floor from the external environment or from an unheated adjoining space. The part of the dwelling perimeter that adjoins (for example, by a party wall) other heated properties (residential or commercial) is not included.
For example:
The DEAP calculation includes thermal bridging, at junctions between elements and around openings. If linear thermal transmittance (Ψ) values are available for these junctions, they can be multiplied by the length of the junction concerned, and the total added to the transmission heat transfer coefficient. The calculation includes an allowance based on the total exposed surface area if specific Ψ-values for thermal bridges are not known.
In the case of a dwelling that is part of a larger building where the remainder of the building is used for non-domestic purposes, the elements between the dwelling and the remainder of the building are considered:
The u-values section in the walls tab of Building Fabric provides guidance on default U-value for walls in this case in existing dwellings in the absence of supporting information for a non-default wall U-value.
The u-values section in the floors tab of Building Fabric applies a default U-value of 1.0 W/m2K for floors in this case in existing dwellings in the absence of supporting information for a non-default floor U-value.
Where the BER assessor is unable to determine the nature of the neighbouring premises, conservative assumptions should be made. For example, if it is unclear whether a neighbouring heated premises is commercial or residential, it should be assumed to be commercial.
The following table outlines the documentation required for different parameters for New-final, New-provisional, and Existing dwelling BERs, where those parameters are not accessible during the site survey.
Guidance on re-use of data can be found here
| Item | New-final | New-provisional | Retrofit to existing |
|---|---|---|---|
| Insulation thickness |
As-built drawings/specifications signed off by the person responsible for building regulation compliance sign-off, e.g.:
|
Drawings/specifications signed off by one of,
|
Invoices/ receipts (or DOW in uniform insulation thickness scenario) showing address |
| Conductivity of insulation |
Agrément cert or other certified sources. NB: Don’t use DEAP table 2.10 unless all other avenues exhausted |
Agrément cert or other certified sources preferable. Otherwise use DEAP table 2.9 | Agrément cert or other certified sources preferable. Otherwise use DEAP table 2.9 |
| Construction of element | As built drawings or specification | Drawings or specifications | Not needed for default U-value. As built drawings/specifications needed to support non-default U-values |
| Conductivity of element (e.g. Plaster, concrete) | CIBSE Guide A / DEAP table 2.10 | CIBSE Guide A/ DEAP table 2.10 | CIBSE /DEAP Table 2.10 acceptable if calculating full U-value |
| Area of element meeting non-default | Survey used to verify as built drawings or specification | Drawings or specifications | Invoices/ receipts (or DOW in uniform insulation thickness scenario) showing address |
U-value may be calculated for entire retrofitted element or add resistance of new insulation to the default resistance of original building element (See example here) depending on level of availability of supporting evidence.