CASE STUDY: Blackrock Street Housing, Manchester
22 dwellings in semi-detached format, a mix of 2b3p/ 3b4p and 4b5p accommodation. All dwellings are for social rent.
KEY SUSTAINABILITY OBJECTIVES/ OUTCOMES
- The dwellings are designed to Passivhaus standard of building fabric performance with third party assessment accreditation by Warm Associates / Passivhaus Institut. Dwellings to achieve Passivhaus PHLEB- Classic – Plus standards depending upon location.
- Two dwellings designed to true NZC based on operational energy and embodied carbon, verification to be sought in line with the UKGBC Net Zero Carbon Buildings: A Framework Definition.
- WLC of 362.25kgco2e/m2 without module D and 242kgco2e/m2 with module D.
- The houses are designed to be flexible, floor cassettes incorporate open web floor joists which form a service zone, external walls also incorporate a dedicated service zone for vertical service runs – this allows building services to be easily reconfigured to adapt to future needs (2b)*
- Design for adaptability – adopted narrow fronted plans which allow the floor units to span across from side walls; no loadbearing internal partitions which allows any internal walls to be easily removed or reconfigured; wall panels incorporate vertical service zones and the floors are a 300mm deep continuous service zone with open web joists, allowing easy rerouting of services throughout. (2c)*
- The building information has recommendations for end-of-life treatment of materials and a methodology for deconstruction. (2d)*
- The use of timber as a construction material and pre-insulated external wall panels and floor cassettes meant the houses were constructed in a standardised ‘flat pack’ Ikea type MMC approach. This meant the houses went up in days and were less costly than conventional build and volumetric MMC. (3)*
- The use of Low carbon materials such as timber are used within the houses. Timber as the primary construction material for the building shell created savings of 102kgco2e/m2 counting sequestration. (5a)*
- The use of 100% recycled plastic drainage, formwork and separating joints saved 17.3Tco2 by reducing the need for concrete. (A1-A3) (5b)*
- Waste has been designed out by avoiding composite materials to enable disassembly at end of life; formwork and separating joints are used to reduce the amount of concrete on site. (5c)*
- 75% of materials are locally sourced.
- The contractor, John Southworth Building, has operated a number of social value initiatives during construction: 75% of materials locally sourced; 75% labour local [within 10 miles of site]; 50% of subcontractors local [within 10 miles of site].
NOTABLE APPROACHES AND SOLUTIONS
Reducing whole life carbon:
- Whole Life Carbon Assessment – A WLCA including stages A-D has been carried out in accordance with the RICS Professional Standards and Guidance. Using recognised environmental impact software encompassing a database of verified EPD’s and measured quantities as the basis for calculation.
- Embodied Emission during operation – Based on a 60 year lifecycle emissions operational emissions associated with maintenance, repair, replacement and refurbishment have all been considered. In a building such as this, replacement forms by far the largest part of embodied emissions in use. Replacement lifecycles have been considered in accordance with industry and product standards. Energy in use (with excess exported energy included under stage D) has been considered separately as operational energy in the WLCA.
- End of Life Emissions – Initiatives to reduce End of Life Emissions include identification of recyclable materials, recommendations on the re-use and recycling of materials and a commitment to include information stipulating methodology for demolition / re-use as part of the building information pack. Key initiatives to reduce end of life emissions are the use of timber as a primary construction material for the building shell, avoiding the use of composite materials so at end of life built components are easier to disassemble and recycle/ upcycle.
- Embodied Carbon Metrics – The WLCA assessment of 242 KgCo2e/m2 for the NZC dwellings is within the best practice 2030 targets for domestic buildings as defined under LETI and RIBA 2030 Climate Challenge.
Reducing operational energy:
- Operational energy use reduced to minimum practicable by adopting Passivhaus design standards.
- The largest energy load is heating water for domestic purposes and sustainable energy technologies have been adopted to reduce this demand. Dimplex ASHPWH cylinders are incorporated to heat water.
- A key part of the design approach is to provide large, often full height window openings. This reduces the need for artificial light but also improves the quality of the internal space making rooms appear larger and a visual connection of indoor/ outdoor space.
- All electric lighting is LED based.
- Passivhaus PHPP calculations address potential overheating issues and window sizes are managed to satisfy these requirements.
- MVHR systems provide a continuous supply of fresh, filtered air to all habitable rooms and achieve 90%+ efficiency with regard to heat recovery. MVHR system complies with Passivhaus standards of performance.
- The choice of benign, natural materials in the construction process assists in delivering improved indoor air quality.
- NZC dwellings provided with web based energy data logger, energy consumption recorded at selectable intervals and stored on DataStream and automatically sent to central server. Information presented on Excel for analysis.
- Dwellings are all electric energy use as promoted by the forthcoming Part L ‘future Homes Standard’ 2025. Regulated and unregulated energy circuits monitored separately and sub metered to monitor lighting, equipment, power etc. Each dwelling provided with energy use display to inform/ influence occupants.
Increasing renewable energy supply:
MCS certified arrays of 4.08kWP South facing and 5.10 East facing have been implemented that annually generate 3,616kwh and 3,513kwh of electricity and offset 1,876kgCO2 and 1,823kgCO2 respectively. Operational energy is minimised by the use of ASHP hot water. ASHPHW saves 1,431 kWh / year over an electric immersion cylinder reducing the emission of 742kgCO2/ year.
Offset any remaining carbon:
The Whole Life Carbon Assessment indicates a nominal amount of carbon offsetting required to achieve True Net Zero Carbon for the NZC dwellings – circa 26,100 kgCO2e per dwelling. 26 tonnes over the life of the building. Offsetting will be entered into at practical completion using recommended Gold Standard 2019.
- All dwellings satisfy Nationally Described Space Standards.
- The project uses off site manufacture for the building shell.
- The KTS system complies with MHCLG Modern Methods of Construction – Definition Framework category 2b, primary structural systems – enhanced consolidation. The timber frame system uses closed, pre insulated wall panels complete with VCL and service zone battens. Pre manufactured open web floor cassettes.
- The importance of applying WLCA at the commencement of the design process rather than a measurement tool after the process.
- Clarification of how ‘one click’ software deals with biogenic carbon, at what stages and how this is assessed. Confirmation that this is in line with GLA/ RICS guidelines.
- Need to formalise the process of considering material choices in the context of WLC, properly integrate into the RIBA Plan of Work stages 2 to 4 – design and costing including VFM.
- Contractor also needs to be integrated into the decision-making process so they are comfortable with material choice decisions. Cost – availability – buildability.
- Once contractors are familiar/ comfortable with the construction process, offsite manufacture of the building shell and construction to Passivhaus standard, more willing to commit to reduced construction periods and the cost and carbon benefits of DfM become deliverable.
* This project is included in the “How circular principles impact Carbon and Value” report.