Dr Jerry Harrall of SEArch architects describes how simple, low invasive design techniques such as using extruded polystyrene as external insulation transformed the cost of living and quality of life for residents of a 200 year old house in High Wycombe.

For some, the clock is ticking towards zero carbon goals. For others, it’s already become a reality. The good news is that it doesn’t require complex building methods or even high tech equipment to achieve significant improvements in the energy performance of existing building stock.

Greening-The-Box offers a suite of building techniques developed by SEArch (Sustainable Ecological Architecture Ltd) applying straightforward, low invasive design methods to enable existing buildings to operate without reliance on fossil fuels.

Greening-The-Box High Wycombe is the first private dwelling to benefit from such adaptation techniques, resulting not only in remarkable cost and energy savings but, according to the homeowners, an improvement in their quality of life too. When a client uses words such as “uplifting” and describes their new environment as providing “serenity and tranquillity”, you know you are on to something!

I believe the environmental and cost benefits are just as impressive, including:

100 per cent reduction in CO2 emissions of 18 tonnes/year (17,878kg CO2/year)

80 per cent reduction in running costs (a very considerable £2,000 reduction in the first year)

100 per cent reduction of fossil fuels use.

Providing further credence to the building’s enhanced performance, the Standard Assessment Procedure (SAP) produced a rating of 89A, a highly notable performance when most housebuilders are working to ratings of lower than 80 for new dwellings. The pre-design SAP rating was 49.

So how was this achieved? Let’s go back to the beginning. The High Wycombe project is a 200-year-old detached house. The owners were looking to reduce their reliance on fossil fuels, cut energy bills and at the same time have less of an impact on the environment. Their ambitions were to design out the need for an oil fired central heating system, and put in its place a naturally heated environment as well as a natural ventilation regime.

Perhaps surprisingly, just five key changes were needed to make the existing building fit for a low carbon future: enveloping the house externally with STYROFOAM-A extruded polystyrene insulation increasing internal thermal mass of walls and floors increasing the southerly glazed areas decreasing the northerly glazed areas modifying the layout to encourage natural ventilation.

In its pre-adapted condition, the absence of any external insulation to the solid external walls and below the ground floor slab meant that both building elements offered little resistance to heat transfer; it was a difficult building to keep warm. The average rate of heat loss, or U-Value, was calculated at 2.17W/m2K.

STYROFOAM–A insulation from Dow Building Solutions was specified for the project for both environmental and performance reasons. The material is not only UK-manufactured, but is blown with carbon dioxide giving it a Global Warming Potential (GWP) of less than five. The material also has an Ozone Depletion Potential (ODP) of zero and is ideal for external use where moisture resistance, rigidity and strength are key requirements.

Post adaptation, the introduction of 200mm of STYROFOAM-A insulation to the external fabric and below the floor slab reduced the rate of heat loss by a very considerable 620 per cent to just 0.35W/m2K. Thermographic images show minor surface temperature variations over the STYROFOAM-A clad external fabric and junctions with minimal heat loss detected. In comparison, thermographic images of the adjacent, twenty year old property indicate significantly higher levels of fabric heat loss with noticeable variations across different building elements.

Adding such high levels of insulation also contributed to the effectiveness of thermal mass within the structure. The pre-adapted, un-insulated thermal mass of the building was calculated as 0.68MJ/K/m2. Post adaptation, the property’s thermal mass marginally increased by 9% to 0.72MJ/K/m2, a small incremental increase.

Despite the small increase, the thermal mass acts as a highly effective heat-sink and helps to moderate internal ambient air temperatures throughout the year for both heating and cooling; introducing STYROFOAM-A externally means the thermal mass becomes that much more effective.

Residents now enjoy a relatively stable ambient internal air temperature of around 21⁰C without the aid of a central heating system. Instead, supplementary heat contributions are achieved with a low grade, self-regulating electric under-floor heating system, a wood burner and secondary heat from household appliances. The 35KW rated under-floor heating contributed 1200KWhr of heating load over the first twelve months; this is anticipated to reduce over the second year due to drying out.

To the south of the building, the potential for solar heat gains through the fenestration was increased by creating a larger area of direct south facing glazing which now measures 9.3m2 in total, an increase from 3.9m2. This represents a 72 per cent increase in south facing glazing areas with a net solar heat gain contributing to the overall heating load.

In contrast, the north elevation glazed area was reduced from 11.3m2 to 6.1m2. This 50% reduction in glazing combined with the higher specification replacement glass (24mm low–E double glazing), reduced the heat transmittance through the north windows collectively from 34 W/m2K to 11W/m2K. This resulted in a 68 per cent reduction in the rate of heat loss from the north windows alone.

As an additional touch, who would have thought that simple changes to layout could result in dramatic changes? Simply by putting bedrooms on the ground floor and principal occupation rooms on upper floors, solar receipts could be increased and elevated daylight levels enjoyed where they are needed most.

Finally, as well as relatively simple changes to the building structure, 5.5KWp of roof mounted photovoltaics (PVs) were added, generating 4,200KWhrs in the first year and displacing 3,106kg of CO2.

What has been created at Greening-the-BoxHigh Wycombe is a pragmatic, affordable and replicable solution which will no doubt be of great interest to those working hard to get the Green Deal out of the policy papers and into our homes.

A highly inefficient 200-year-old building has been transformed into a genuinely low carbon, low impact household which offers a perpetual environmental legacy. It’s been achieved by employing simple design techniques and by using materials which are already widely available in the UK, and as such offers a potential blueprint for the benefit of generations to come.