Highdown Court Extra Care scheme in Worthing for Saxon Weald, designed by The Tooley & Foster Partnership. Highdown Court is built with insulation levels significantly better than the requirements of the Building Regulations, and the SBEM energy calculations give a heating performance approaching the Passivhaus standard using conventional construction. The client has reported that only two of the six boilers in the building’s boiler room have been used over the last three years.
Most people’s idea of a Passivhaus is a single family home, often built for the owner and located in Germany and Austria. As the Passivhaus approach to low-energy building design is based on building physics it is not restricted to houses and can be used for larger structures as well, including schools and offices. However, as Peter Ranken discusses, there is one type of larger building for which Passivhaus is ideal – accommodation for elderly people.
We all know people who feel the cold more acutely, and often they are elderly, not very mobile or with medical conditions. Many of these people live in sheltered accommodation, extra care or assisted living developments, care homes or in their own homes, where internal temperatures are kept much warmer than ordinary housing. If these homes are the typical British house, a converted Victorian property, or even some more modern buildings, the fuel costs to keep vulnerable residents comfortable enough can be daunting.
This fuel-cost problem will become more acute as easily accessible fossil fuels become more scarce, and fuel costs rise. With the Baby Boomers approaching retirement, demographic change is driving a greater need for specialist care accommodation, whilst fossil fuels become more expensive.
The core of the Passivhaus approach is to provide scientifically proven levels of thermal comfort, with very low energy use – making this design approach ideal for a building type where maintaining comfort is critical for health and well-being, whilst fuel use needs to be reduced.
A window on comfort
A Passivhaus care building will deliver high comfort levels, with consistent internal temperatures and no draughts.
That is why the windows are triple glazed – in Britain it is theoretically possible to meet the Passivhaus energy standards with double-glazed windows, but the internal surface temperature would be too low, thereby creating cool down-draughts. The internal third layer of glass in triple glazing is warmer and therefore more comfortable. Similarly, the high levels of air tightness required in a Passivhaus building eliminates through draughts, improving comfort. The elimination of cold spots (thermal bridges) in building construction also reduces draughts and heat loss.
The windows are important as they insulate, but also allow the sun to warm the building. The windows are also openable, and therefore a Passivhaus care home can still have opening windows and balconies that allow residents to sit in the sun and feel the air from the outside.
A warm feeling
A key component of a Passivhaus is the mechanical ventilation system that provides a continuous supply of warmed filtered fresh air, recovering heat from stale air to pre-warm the fresh air before it reaches the inhabitants. This is included to save energy, but it also has other benefits for care buildings. Stale air and odours are quickly removed, improving air quality, and in some designs extra filtration can be provided to reduce allergens with benefits for people with breathing difficulties or allergies.
Passivhaus houses are renowned for their low energy costs – about a tenth of the average British house, and about a third of a typical new-build house, and these benefits will also apply to Passivhaus care accommodation. For a typical extra-care two-bedroom Passivhaus flat of 65sq m, with electricity at 14p/kWh, the annual heating cost would be £136.50, or £2.63 per week. This is approximately a third of the energy use of an equivalent flat assessed to achieve Level 3 of the Code for Sustainable Homes – itself a standard 25% more efficient than 2006 Building Regulations requirements.
As the Passivhaus standard originated in Germany, the peak heating load target of 10W/m2 is set on the coldest day when temperatures are at -10 oC, in contrast to the British standard of -3 oC. For a typical extra-care two-bedroom flat of 65sq m, the peak heating load would be 650W, equivalent to seven 100W lightbulbs. For most of the year, the heating demand could be met by a heated towel rail in the bathroom, with an additional heater in the living room.
This gives future proofing against increasing fuel costs – utility bills are often a big worry for retired people on fixed incomes, particularly those with private pensions which may not be as generous as those in the past.
Costing it all up
With all these advantages, what are the risks for those developers and clients who wish to build a Passivhaus care building?
If you have seen photographs of a single-family Passivhaus with external walls half-a-metre thick, you may be concerned at the extra cost of a Passivhaus care building. However, as a building shape, care homes and extra-care developments are already very efficient, with a lower ratio of external wall (heat loss) to floor area compared to detached houses. Therefore the step change to achieve Passivhaus performance is smaller than other building types.
As British building regulations require ever-increasing energy efficiency over the next few years, the cost difference between conventional construction and Passivhaus decreases. This has already happened in the education sector – in Wolverhampton two schools have been built to the Passivhaus standard at no additional cost over the standard local authority budget.
For care buildings, construction costs are still a little higher than ordinary construction, but the fuel savings offset this relatively quickly. The first Passivhaus care home in Britain is reported to have cost six percent more, and the anticipated cost savings will pay this back in eight years. Historic monitoring of Passivhaus buildings over the last 20 years has shown that actual performance is close to that calculated.
In our experience, the extra cost includes a risk factor, particularly for building services – Passivhaus needs very little, but contractors are not used to this, so in Design & Build contracts an additional allowance for building services can sometimes be included in tenders. With better knowledge of Passivhaus and earlier building services design, tenders should reduce.
When Passivhaus construction costs the same as conventional buildings, the reasons for choosing Passivhaus are clearly many. However, where the cost of a Passivhaus care building may be at a premium, the decision to build to this standard will depend on who owns the building and who pays the fuel bills.
For care homes, where energy costs are included in the fees for residents, and the care provider owns the building, there is a medium-term financial benefit for building to the Passivhaus standard, as the reduced running costs of a Passivhaus new build can reduce overheads.
For extra-care and assisted-living projects, where residents pay for their energy use, the very low space-heating costs in a certified Passivhaus reduce the worry for pensioners on fixed incomes as future fuel-price increases will be less of a concern, and can give a competitive advantage for landlords over other providers.
For publicly subsidised care buildings, the lower energy bills of a Passivhaus building reduce the financial pressures on tenants, thereby increasing the likelihood that the rent will be paid on time.
Scoring highly
Where planning conditions require a BREEAM or Code for Sustainable Homes Assessment, a Passivhaus care building will achieve a very high score in the Energy section.
To achieve a certified Passivhaus building, and assurance that the new building achieves the comfort and energy savings planned at design stage, a certified Passivhaus designer or consultant will calculate the heat losses and heat gains for the proposed building, based on the climate of the site to ensure that the design achieves the Passivhaus technical criteria. The Passivhaus designer will also advise the design team on the details of the construction to minimise thermal bridging and achieve the stringent air-tightness standard.
Whilst the Passivhaus design approach challenges design teams and contractors to think differently about achieving comfortable buildings with very low energy use, the end results are very popular with residents. There are now 30,000 certified Passivhaus buildings across Europe. The first Passivhaus care home was built in Germany in 2003 and is popular and fully occupied.
Peter Ranken is an architect and Certified Passivhaus Designer at The Tooley & Foster Partnership, who designed New Cranes Court, winner of the Development of the Year at the 2013 sustain’ Magazine Awards.
Tooley & Foster is currently working on a Passivhaus Extra Care project in the Midlands, and has a new Passivhaus division www.accreditedpassivhausdesign.com
