As things stand, we know from talking to funders that construction is seen as the riskiest investment option by far.
Taking a 200 m2 house, (10 m x 10 m x 2 storeys, 40 % WWR) as an example, Bryden Wood has done a rough estimation of the impact that Passivhaus distinctive strategies have on embodied carbon:.Adding triple glazing instead of double glazing would increase carbon around 6 kgCO2/m2 over its lifetime.
Adding a MVHR and ductwork would increase carbon by 6.5 kgCO2/m2.Adding a heat pump would increase carbon by 3.5 kgCO2/m2.Adding insultation (rockwool) thickness in walls from 150mm to 250mm of rockwool would increase carbon by 3.6 kgCO2/m2.
Adding insultation (rockwool) thickness in floor and ceiling from 190mm to 370mm of rockwool would increase carbon by 6 kgCO2/m2.Reducing the boiler size from a 15kw electric boiler to a 3kw boiler would reduce carbon by 1.69 kgCO2/m2.
Reducing the number of radiators from 10 to just one would reduce carbon by 10.7 kgCO2/m2.
Reducing the size of the photovoltaic array from 24 to 12 units would reduce carbon by 12 kgCO2/m2.Bryden Wood’s strategy to achieve net zero carbon building is based on the adoption of a clear hierarchy for operational and embodied carbon..
In order to substantially reduce operational carbon, our designs will adopt the following hierarchy:.Be Lean (passive): minimise the use of energy via passive design measures such as optimised form, orientation and window-to-wall ratio (WWR); design energy efficient facades that incorporate thermal insulation, high airtightness, external shading and solar control glazing; use of natural ventilation and thermal mass and design transitional spaces and low thermal expectation spaces.. Be Lean (active): minimise the use of energy via energy efficient lighting (LED, daylight and presence control sensors) and ventilation systems (demand control ventilation, low SFPs, heat recovery); use technologies such as waste-water heat recovery and specify energy efficient lifts and appliances/equipment.. Be Clean: connect to district heating networks that have plans for decarbonisation; explore plans and feasibility of local hydrogen district networks.. Be Green: use onsite low and zero carbon technologies such as air source heat pumps (ASHP), ground source heat pumps (GSHP), photovoltaic panels, solar collectors for domestic hot water and wind generation among others.. Be Smart: implement innovative technologies such as electric batteries, heat storage, post-occupancy evaluation and develop smart-metering systems..
Offset: any remaining carbon should be offset via Power Purchase Agreements (PPA) or recognised carbon offset schemes.Offsets used should be publicly disclosed.. An example of specific design strategies that Bryden Wood have adopted follow the proposed operational carbon hierarchy is shown in Figure 5 and is demonstrated with examples below..