The stunning low energy seaside home that's built from clay

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Building: 320 sqm detached home
Build method: Clay block with external insulation
Location: Portmarnock, Co Dublin
Standard: Low energy building
Completion: June 2015
Budget: €600,000
€161 per annum estimated electricity costs for space heating

A low energy house in Portmarnock, Co. Dublin makes full use of sea views while maintaining a high grade thermal envelope that doesn’t overheat.

Architectural technologist and designer Des Crabbe of OA Studios is a veteran of several passive and low energy builds. He explains that the client was living in a poorly insulated 1950s era house which was both difficult and expensive to heat.

“The brief was not to build something fully passive in this case, but they did want a warm, energy efficient home. The other big challenge was that the house was less than 100 metres from the sea, and so would be subject to driving sea winds. We had to make sure that all of the materials chosen would be able to deal with that.”

The planning authorities gave the go-ahead for the demolition of an existing house onsite, and granted permission for the new build, subject to maintaining the views enjoyed by neighbours on both sides. Keeping the new house to the same footprint as the old, Crabbe consulted with neighbours to ensure the project went smoothly. In addition, the client’s son, architect Paul Murray, worked closely with Crabbe to arrive at the best possible design.

“We wanted the house to have a full 180 degree panoramic view of the sea, so we subdivided the building into three sections. We used stone spine walls to separate those areas as they run front to back, plus we included a fully glazed area in the centre of the building to the front in order to maximise the view.”

This large glazed area had to face east, Crabbe explains, which was suboptimal in terms of passive solar gains. However, the use of high performance glazing minimised heat loss issues.

He was also concerned about the possibility of drafts as a result of convection currents as the air circulated across the glass. For this reason, and to provide radiant heat throughout the house, he specified underfloor heating used in combination with a low temperature air-to-water heat pump.

The house itself is built using Juwo poroton clay blocks, and externally insulated with graphite EPS. Crabbe initially looked at using 215mm concrete block on flat with external insulation, but the contractor, Pannoncelt Ltd had extensive experience with poroton.

“The poroton block was slightly more expensive but it’s one of the best products on the market for controlling relative humidity inside a building. Also, because it is itself an insulator, it helps to limit thermal bridges,” Crabbe says. The enhanced thermal properties of the block also allowed Crabbe to reduce the external insulation from 200mm to 100mm.

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Airtightness is of course a priority in creating an efficient thermal envelope. Moreover, in order for the specified heat recovery ventilation system to perform at 90% efficiency, it was necessary for the house to have a sub 1.0 air change rate. Crabbe considered using the internal wet plaster finish as the airtightness layer but decided instead to go with a membrane used in conjunction with a battened service cavity internally.

“The way I see it on airtightness, you need to keep trades away from it and keep it as simple as possible,” he says. In the end, the building achieved an airtightness score of 0.9 ACH at 50 Pascals – an impressive result for a building with a relatively complex design. According to Crabbe, the quality of the main contractor was critical here, and in the general quality of construction: “The building and detail achieved was only possible because Pannoncelt were dedicated with the highest level of workmanship I have ever worked with.”

In order to reduce the risk of excessive solar gains (and thus overheating) from the extensive glazed surfaces, Crabbe specified openable windows at the front and the back of the house to allow for cross ventilation.

Given the coastal location and the exposure, there’s never any shortage of wind to facilitate house cooling when needed. Additionally, electric blinds on the south-facing windows helps to limit solar gain during the summer months.

Crabbe acknowledges that humidity was an issue in the early stages of occupancy, but as the house dried out, air quality improved dramatically. The house is thermostatically zoned, and – again in the early stages – there was some confusion with the client about how best to use the system. Crabbe produced an operation and maintenance manual to address that issue.

Homeowner Tony Murray says the house’s energy bills are one-quarter that of his and his wife Yvonne’s previous home on the site, which had a D1 BER and was of a similar size.

“Our main priority was to have a cosy and snug house with no drafts and at the same time plenty of fresh air,” says Tony. “This has been a great success with many people commenting on the quality of the air.”

“We are delighted with the result of all the effort that went into the design and build of the house. Particularly the specific finishes which make it such a unique house but yet a very comfortable home. It is great for entertaining with guests always commenting on the comfort and ambience.”

“The location is amazing but the house enhances that even more. We are very lucky to wake up every day in such a wonderful house, and delighted to share it with our family and friends.”

1 The walls of the house were constructed with Juwo Thermoplan poroton clay blocks; 2 the poroton walls are visible here rising up from the strip foundation, which was insulated with 150mm Xtratherm PIR board; 3 taping around joist ends for airtightness; 4 installation of the Webertherm XM graphite EPS external insulation system; 5 the large east-facing expanse of Velfac triple-glazed windows, which looks out over the Irish Sea; 6 rigid ductwork for the ProAir heat recovery ventilation system seen here in the ceiling service void, with the Intello vapour control and airtightness membrane visible on the inside of the wall build-up.

Image gallery

• Site plan Site plan
• Plans Plans
• Elevations Elevations
• Contiguous elevations Contiguous elevations
• Ground floor plans rev A Ground floor plans rev A
• FF plan FF plan
• Roof plan Roof plan
• Detailed section Detailed section
• Section BB Section BB
• Section AA Section AA
• Window schedule 1 Window schedule 1
• Window schedule 2 Window schedule 2
• Window schedule 3 Window schedule 3
• Lighting plan rev B Lighting plan rev B
• Foundation details door schedule Foundation details door schedule
• Elevations rev A Elevations rev A
• Window junctions Window junctions
• Landscaping Landscaping
• Stairs rev A Stairs rev A
• Jamb detail Jamb detail
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