07 Mar 2016

Achieving exceptional airtightness

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At an architect’s new timber frame home in Cork, Ireland, high racking strength and airtightness were crucial in the internal lining specification.

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When architect Boris de Swart was presented with the opportunity to build his own four-bedroom home in Cork, Ireland, he could not turn it down. A plot had become available in his desired location which possessed a dilapidated house asking to be re-built. “I am an architect by professional,” explains Boris, “and most, if not all, architects dream of building their own home. We are also renowned for being our own worst clients – being very hard to please on both the design and the technical build aspects. The plot, for instance, took three years of searching.”

Boris’ vision consisted of an elegant, transparent house, daylight filled and open to the east, south and west. He also required generous space inside for him and his family to live comfortably. Aside from the regulatory requirements, he also demanded a property with a high level of energy efficiency – well in excess of current regulations.

“The design brief was simple,” explains Boris. “A four-bedroom house plus study. Two living spaces – one main are with kitchen and another as a separate space for when the children are a little older. A family-size bathroom and an en-suite.

“Thankfully, obtaining planning permission for this modest, but spacious, home was relatively quick,” adds Boris “but this was helped by there being an existing house on the site.”

Going it alone

Boris took the decision to manage his build and act as the main contractor. “I already knew, even if I appointed a main contractor to the project, I would be there full time just to make sure he was doing his job right. So after some hesitation I decided to act as main contractor myself.”

In spite of his vast expertise and experience within the industry, Boris encountered several unavoidable problems, as he explains: “The site seemed generous, but for construction it was very tight. Also it turned out that articulated trucks were not able to enter the narrow access lane. So we had to use a nearby commercial yard and a number of additional smaller trucks for delivery of the timber frame and the large windows. The main challenge really was to manage the build. It would have been my first time to be in charge for a full build.

“I was also conscious of remaining within budget, but like many people we did exceed it. The additional costs were mostly unlucky. Bad weather when erecting the timber frame meant four extra days crane hire, which is an expensive outlay. The no-access for articulated trucks meant hire of additional smaller trucks to bring the timber frame to site. The site sewage connection was not quite at the level that we had hoped, which meant a much longer trench. Costs like project insurance are a multiple of what a main contractor would pay.”

Excellent airtightness

Designed and built to passive standards by specialist manufacturer Shoalwater Timberframe, the completed, stylish two-storey house incorporates a range of ecological materials and systems. But with its large glazed areas and two cantilevers at the rear and side of the building, the project required a structural panel that combined racking strength with exceptional airtightness – for which SmartPly VapAirTight proved ideal.

With the installation of 240 sheets of the new SmartPly VapAirTight OSB3 panel, the house achieved an air change rate (n50) of 0.09 air changes per hour at 50Pa – six times better than recommended by the PassivHaus Institute.

“Developed from our OSB3 system, SmartPly VapAirTight has integrated vapour control and unrivalled air barrier properties and will help to close the gap between design and as-built performance,” said David Murray, Innovation Manager at SmartPly. “We monitored the system’s performance at every stage of the process and upon completion it far exceeded PassivHaus standards for airtightness.”

SmartPly VapAirTight is easy to handle and can be readily cut and fixed using standard timber frame fixings. Being robust, there is minimal risk of damage during assembly, transport or erection, which means the airtightness is not compromised. It is suitable for renovation as well as new build projects and applications include modular manufacturing as well as the production of SIPs and prefabricated roofing systems.

Testing conditions

“We insist on the highest quality materials in every timber frame we design and build,” said Donal Mullins of Shoalwater Timberframe. “With work on-site starting in January 2015, the site and the panels themselves endured every type of weather imaginable – providing perfect testing conditions for the new VapAirTight panels.”

Due to the confined site and its challenging location, the issue of double handling provided additional testing for the panels and one which it passed with flying colours. Donal Mullins added: “Everything that happened gave the boards the opportunity to fail and they didn’t. And with SmartPly VapAirTight installed for approximately 98% of the internal linings, the system has certainly proven to deliver outstanding airtightness under real and challenging site conditions.”

The Shoalwater timber frame structure also made use of Coillte’s Medite Vent breathable MDF panel product as part of the roof construction. With SmartPly VapAirTight installed on the interior, over 230m² of Medite Vent was used on the roof’s exterior to ensure external vapour diffusion and reinforce the roof’s racking strength prior to the installation of the cellulose blown-in insulation.

Seek a professional

“The timber frame arrived on 15th January last year and we were able to move in on 9th August, so it took just short of seven months to complete. I had a six-month timeframe on my original schedule,” explains Boris. “It is a fantastic experience. But also an experience that can drive you over the edge. If I was to offer any advice to fellow self-builders it would be to acquire the services of an architect or design professional who has an interest in a similar type of build. Their work will be quite different to what they would normally do with a main contractor. Ideally plan ahead with costs and timeframe to make sure you have these tools to work with. And keep a decent amount of money aside for unforeseen items.”

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