climate data

Passive Attack by John Moorehead

Photo
Photo

All was not well when work began on this impressive Co Cork home and its architect had to pull out the stops to make the eco-home fit the brief

A problem with the design of a passive house in Co Cork made its designer, John Morehead, go hot and cold. A fault in the climate information, that was used to regulate the airtight, ventilated and draught-proofed house, meant the house was too cool. Passive house designs are so sensitive to the environment and climate that even heat from a plasma television can throw the controlled temperature off kilter.

Morehead, an architect with the Cork firm Wain Morehead Architects who specialises in designing passive homes, was concerned to get all the details right when he embarked on a new project on the shoreline of the upper Owenabue estuary, in Carrigaline.

Building had just started on the two-storey, four-bedroom family home and, while the greatest care had been taken to find ecological and energy-efficient materials, it was clear that everything was not as it should be.

“We commissioned the job of sourcing climate data to specialists in Britain,” says Morehead. “We were working off Dublin data, not local data, and suddenly we found we didn’t meet the passive-house criteria. By this stage, we were already on site. We didn’t eat for a week — it was that serious.”

It took three weeks for Morehead and his team to put the mistake right. Intensive research was carried out to try to find out what was putting the data out of sync. Readings put the house at a temperature that was far cooler than first anticipated. There was also less radiation, which can have a big impact on passive-house technology.

“It turned out there was a fault in the way the climate data was being generated,” says Morehead. “It operated on peak-data information — the extremes rather than the averages. To make the house passive again, we had to tweak the specifications. We did this with the help of a local climatologist, but it was three weeks before we were back on an even keel.”

The result, though, is an impressive and unusual contemporary house in a lovely setting with striking views. It is the home of Sally and John O’Leary and their three children. The couple approached Morehead about building an energy-efficient home in August 2008, and work began the following year. They had been refused planning permission to build a previous modern design on the site.

The refusal was based on context rather than aesthetics, and the fact it would be built on a sloping site that ran into the Owenabue estuary was also a concern.

Around that time a neighbouring house was being developed, so it was important for both the O’Learys and their new neighbour to maintain privacy and preserve views, as well as to keep the planners on side.

“Our brief was to design a four-bedroom family home and to be as ecologically friendly as possible while sticking to a budget,” says Morehead. “Our clients were interested in an energy-efficient home and one that would bring the outside space in, merging into the interior.

“The family also wanted natural finishes and a design that was relatively simple. There had to be a focus on food and cooking because that is what they love to do.”

Morehead came up with the modern yet simple passive house in Carrigaline, which was completed in April this year. It has almost 2,600 sq ft of living space over two floors. The home is at the cutting edge of passive-house design, and is one of six certified passive homes in Ireland. A name plate by the front door proudly displays its Certified European Passive House status.

The project did not begin with the intention of building a passive house. “It was originally intended to be an A-rated passive solar project and the decision was made to seek passive-house certification as late as the tender stage,” says Morehead.

Passive house certification is a quality-assured energy-performance and comfort rating that demands stringent control of both the design and construction process.

To make the most of the views and to accommodate the sloping site, the living area was put upstairs. It overlooks the estuary and contains a central winter garden, which enhances the notion of bringing the outdoor space in.

The area has become a multipurpose room, whose use changes with the weather and the seasons. “It is a busy spot, encouraging participation in activities by young children at the principle accommodation level, irrespective of weather,” says Morehead.

“The room is fully insulated from the remaining accommodation, so it can become an outdoor space without compromising the rest of the house or thermal envelope,” he adds.

“Both the expansive glass wall from this room to the hall and the screen to the deck fold away to make a versatile indoor/outdoor space penetrating deep into the bowels of the dwelling.”

Particular care was taken to ensure the home was as airtight and insulated as possible. A cement substitute made from the by-product of the iron and steel industry was used instead of conventional concrete, a decision that saved more than 16 tonnes of CO2. The walls were clad in panels of fibre-cement. It is a low-maintenance material, a consideration that was important in the coastal setting.

Because so much of the work was undertaken during the recession, Morehead and the O’Learys hired local tradesmen and builders when they could.

The upper walls and roof were made from closed wall timber-frames, also manufactured locally. “This construction had exemplary insulation and airtight characteristics,” says Morehead.

“These walls also assist with moisture transfer during periods of high humidity. The upper walls were covered with a rain screen of a carefully selected and detailed untreated Austrian larch cladding.”

To achieve a home that maximises heat gain, Morehead sought out technology to minimise heat loss. Triple-glazed windows with low-iron glass increase transmission of solar heat. The air temperature is controlled to such an extent that no internal surface temperature within the house deviates by more than 4C, even if it’s -10C outside.

The kitchen is an important feature for the O’Learys, who had stressed that they were keen cooks, and it has been given a linear corner window that not only frames views of the river, but also maintains privacy by preventing it from being overlooked by the neighbouring house. The room has direct access to the multipurpose area and the upper garden.

On the upper level there is also a guest bedroom, laundry, study and family room.

The brief had also asked that the needs of a growing family were taken into account. The house should adapt to the children as they grow. To meet this request, the children’s bedrooms surround a large, open multipurpose play area.

The kitchen, along with the living and winter garden areas, has an innovative infrared heating system that Morehead developed himself and is now patenting. “The infra-red emitters heat the occupant, not the air,” he says. “Therefore a level of individual comfort control can be enjoyed independently.

“As with the sun’s energy, 40% of which is infrared, the occupant and indeed any warm-blooded creature, absorbs and responds to this energy through their skin and their inbuilt circulatory system. Heat is then distributed evenly and at a pace to suit the comfort criteria of the body.”

Solar water heating comes courtesy of tubes at roof level and rain water is used for both sanitary and gardening use. While Morehead is coy about the overall cost of the build, he is keen to press home the savings that can be made on home heating, especially at a time when energy companies are raising prices.

“You can heat a home like this for just €150 to €200 a year,” says Morehead. “You are independent of all the price hikes and can live with consistent comfort levels.

“The project confirms that a carefully tuned passive solar design can meet the passive-house standards cost effectively.”

Welsh Passivhaus Social Housing Trials

In 2009 Bere Architects won a competition to design low cost houses for Wales which would showcase the Passivhaus concept and feature innovative measures for energy efficiency and eco excellence. The houses are now complete and open for visitors at Ebbw Vale (by appointment) Larch House and Lime House are the first Welsh Passivhaus social housing prototypes to be erected in Wales. both house types are certified with the Passivhaus Institute by BRE Wales. Larch House has been designed to achieve Code 6, 'zero carbon' of the Code for Sustainable Homes. It is a 3 bed Passivhaus designed to minimize annual heat demand (below 15kW/m2/yr) using extreme peak load climate data prepared by the BRE for this Heads of Valley site.

Much of the winter warmth in Passivhaus designs is derived from solar gains, but Ebbw Vale is 1,000ft up in the top of a valley, with cold and misty winters. The BRE's weather data for the site showed it was twice as demanding as both Manchester and Innsbruck, Austria. To keep winter heat inside, the insulation levels are very high (walls 0.095 W/m2K; floors 0.076 W/m2K; roof 0.074 W/m2K), and because of the relative lack of winter sun, compared to a lowland site, the windows are unusually large to maximize the solar gains from a bright overcast winter sky (55% of south elevation). This is the traditional design strategy for a Passivhaus, resulting in great comfort, tiny energy bills, and bright and airy interior spaces. However, for social housing, a solution to overcome the costs associated with large windows and retractable blinds were required, so subtle but crucial changes were made to the design.

Lime House achieves Passivhaus certification using a different method, based on keeping the heat load below 10W/m2 at any time. 10W/m2 is the maximum amount of heat that can be transported by a low energy heat recovery ventilation unit, and unlike Larch House, Lime House has no towel radiator backup heating. It results in a building that focuses on minimizing heat demand during the worst periods of misty, Welsh hilltop, winter weather with short, dark days and cold nights. In these conditions, solar gains are of little importance, and internal heat gains are more important. So south facing windows are reduced in size and the better insulation of walls dominates, with no more than 20% south facing glazing. A weather optimization graph determined that any more than 20% glazing would increase the peak heat load above 10W/m2.

Payback

If fuel costs go up 5% per annum, the Code 6, zero carbon Passivhaus, social housing prototype will be significantly cheaper after 50 years than when it was built (due to its negligible demand for fuel and the feed-in tariff), whereas a standard building regs house will have more than doubled in cost, due to fuel costs. Even with 2.5kWp photovoltaic panels, a Code 5 Passivhaus will have cost only £10,000 more after 50 years than when it was built. At today's fuel prices our Code 6 Passivhaus is calculated to earn the occupant £1,333 per annum.

Conclusions

Now, with some UK based cost data that shows how Passivhaus houses can be built to a low cost, with really attractive payback periods that make it look short-sighted not to spend a little extra to achieve a certified Passivhaus, compared to a basic speculative builder house. These Passivhaus buildings will also future-proof occupants and owners from high running costs and fuel poverty.

The house building system which rewards speculators (private householders and commercial developers) for greed, regardless of the financial and environmental cost to future generations and the timidness of successive government ministers to go further than skin-deep into the portfolios they hold, to understand and then to explain and legislate for the greater good.

Cost analysis

A cost comparison was done against the RICS/BCIS database for one-off detached houses on normal lowland sites (nearest comparison available):

• Cost of Larch House, Passivhaus built to Code level 6: cost of the one-off, 100m2, three bed house, with normal UK weather data (7-10% less than cost using Ebbw Vale weather data), and including £12,000 towards the cost of PV, a sprinkler system, large windows and external sunshade blinds = £ 1700/m2.

• Cost of the lime House (low cost) Passivhaus: 76m2, two bed Passivhaus: After adjusting the Passivhaus for lowland weather data (saving 7% costs) we found a Passivhaus built to the 2 bed Lime House spec costs £13641 (excluding PV) which is just 14% more than exact comparisons with RICS data for average ordinary one-off houses built over the last 10 years averaging a cost of £1171/m2, both excluding prelims and PV.

According to RICS figures, once built in quantities, ordinary estate housing, over the last 10 years, cost an average of £760/m2, excluding prelims and based on RICS data of the average price difference between one-off and estate housing. It should be possible for a large volume house builder to build Passivhaus estate housing of the (low cost) type, using the lime House design techniques for £886/m2. That means that for a 2 bed house of 76m2, the cost premium for a Passivhaus is £9,500.

The return on that investment is 14-17 years, based on assumptions of 5-10% annual fuel price increases, and the cost savings of the house over 50 years are likely to be more than £ 60,000, even with only 5% annual energy increases and without income from the feed-in tariff associated with photovoltaic's. For 10% price increases the figure would be £360,000.

Justin Bere