CHAPTER THREE THE BASELINE DWELLINGS
Overview
3.1 The baseline dwellings used as the basis of this project are based on typical examples of recent Scottish social housing projects with which Davis Langdon and/or Assist Architects have been involved. Where necessary, the baseline projects have been adapted to ensure compliance with the energy standards in the 2006 amendment to the Building (Scotland) Regulations 2004F and the 2007 Domestic Technical Handbook.
Description of the baseline dwellings
3.2 The key characteristics of the seven baseline dwellings are summarised in table 3.1 below:
Table 3.1: Overview of baseline dwelling types
Dwelling type A: 2 bedroom house | 2-storey semi-detached house 73m 2 floor area Timber frame structure, masonry outer leaf, pitched concrete tiled roof, softwood windows, gas fired central heating & hot water |
Dwelling type B: 3 bedroom house | 2-storey semi-detached house 88m 2 floor area Timber frame structure, masonry outer leaf, pitched concrete tiled roof, softwood windows, gas fired central heating & hot water |
Dwelling type C: 1 bedroom bungalow | Semi-detached bungalow 56m 2 floor area Timber frame structure, masonry outer leaf, pitched concrete tiled roof, softwood windows, gas fired central heating & hot water |
Dwelling type D: 2 bedroom bungalow | Semi-detached bungalow 82m 2 floor area Timber frame structure, masonry outer leaf, pitched concrete tiled roof, softwood windows, gas fired central heating & hot water |
Dwelling type E: 1 bedroom flat | Mid-floor flat as part of a 4-storey, 8 flat block 56m 2 floor area Masonry cavity wall structure, aluminium standing seam roof, concrete upper floors, softwood windows, gas fired central heating & hot water |
Dwelling type F: 2 bedroom flat | Mid-floor flat as part of a 4-storey, 8 flat block 61m 2 floor area Masonry cavity wall structure, aluminium standing seam roof, concrete upper floors, softwood windows, gas fired central heating & hot water |
Dwelling type G: 3 bedroom flat | Mid-floor flat as part of a 4-storey, 8 flat block 85m 2 floor area Masonry cavity wall structure, aluminium standing seam roof, concrete upper floors, softwood windows, gas fired central heating & hot water |
Note: Mid floor flats were selected for the baseline flat types, as improving the CO 2 performance of these is less straightforward than for ground or top floor flats, where quite substantial improvements can be made through thermal insulation enhancements to the floors or roofs respectively.
3.3 Key specification information for the baseline dwellings is summarised in table 3.2 below.
Table 3.2: Specification of baseline dwellings
Building Element | Specification | Applies to |
|---|
Ground floor (U-value: 0.22 W/m 2K) | 150mm concrete ground bearing slab, 100mm rigid insulation, 22mm chipboard flooring. | All |
First floor | Timber joists, 15mm plasterboard, 22mm chipboard flooring. | Houses |
First floor | Precast concrete planks, 12.5mm plasterboard on metal framing, floating timber floor with battens on resilient pads, 22mm chipboard flooring. | Flats |
Roof (U-value: 0.16 W/m 2K) | Concrete roof tiles on battens on felt on plywood sarking, timber trusses, 240mm mineral wool insulation, 12.5mm plasterboard. | Houses Bungalows |
Roof (U-value: 0.16 W/m 2K) | Aluminium standing seam roofing system, 250mm insulation, 12.5mm plasterboard. | Flats |
External walls - Type A (U-value 0.25 W/m 2K) | 20mm cement render, 100mm concrete blockwork, 50mm cavity, metallised breather membrane, 9mm oriented strand board ( OSB) board, timber frame with 140mm insulation, vapour barrier, 12.5mm plasterboard | Houses Bungalows |
External walls - Type B (U-value 0.25 W/m 2K) | 100mm brickwork, 50mm cavity, metallised breather membrane, 9mm OSB board, timber frame with 140mm insulation, vapour barrier, 12.5mm plasterboard | Houses Bungalows |
External walls - Type C (U-value 0.25 W/m 2K) | 20mm cement render, 100mm concrete blockwork, 50mm cavity, 55mm partial cavity fill insulation, 140mm concrete blockwork, 12.5mm plasterboard | Flats |
Windows and doors (U-value 1.8 W/m 2K) | Double glazed, timber framed windows with trickle vents. Insulated doors with glazing. | All |
Heating and hot water | Low temperature hot water system ( LTWH) gas condensing combi-boiler 7, 90% efficiency, radiator space heating system, programmer, room thermostat, thermostatic radiator value ( TRVs) and interlock. | All |
Thermal bridging and airtightness | Thermal bridge 0.08 x exposed surface area. Airtightness 10m 3/m 2/h at 50Pa, based on the use of Accredited Construction Details (Scotland). | All |
Ventilation | Extract fans for kitchens and bathrooms. Natural ventilation elsewhere, via opening lights and trickle vents. | All |
Lighting | 50% low energy lamps. | All |
Compliance with the Scottish energy standards
3.4 Compliance with the 2007 Scottish energy standards was demonstrated by way of the Government approved SAP 2005, using BRE approved SAP-based calculation software.
3.5 The 2007 Technical Handbook states that the calculated carbon dioxide emissions for a dwelling (the Dwelling Emissions Rate, or DER) are not to exceed those of a notional target building of the same size and shape (the Target Emissions Rate, or TER), which is based on packages of measures described in the table to clause 6.1.2. The DER and TER figures used in this study are derived from the SAP-based calculation software for Scotland.
3.6 The DER and TER figures, along with the primary energy demand 8 (primary and secondary heating, heating pumps, fans, electrical lighting) for the seven dwelling types are as follows:
Table 3.3: SAP-modelled energy performance of baseline dwellings
Dwelling Type | TER (kg/m 2/year) | DER (kg/m 2/year) | Primary Energy (kWh/year) |
|---|
Dwelling type A: 2 bedroom house | 22.68 | 21.41 | 7064 |
Dwelling type B: 3 bedroom house | 21.83 | 20.47 | 8291 |
Dwelling type C: 1 bedroom bungalow | 26.37 | 25.17 | 6502 |
Dwelling type D: 2 bedroom bungalow | 24.78 | 23.79 | 7596 |
Dwelling type E: 1 bedroom flat | 22.59 | 19.34 | 5174 |
Dwelling type F: 2 bedroom flat | 21.95 | 20.89 | 5492 |
Dwelling type G: 3 bedroom flat | 19.30 | 16.38 | 6564 |
3.7 The modelled energy performance for all of the baseline dwellings used in this study is slightly better than the minimum guidance in the 2007 Technical Handbook, with the Dwelling Emissions Rates being slightly less than the Target Emissions Rates. This is largely due to the fact that the baseline dwellings reflect the current preference in social housing developments for highly efficient combi-boilers rather than system boilers, which are more costly due to the need for hot water storage.