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Featured Article
EnerPHit |
While the principles of low energy building apply equally for new build and upgrades, the reality is that htting passive levels becomes much trickier when retrofitting. The Passive House Institute have taken this on board and created a retrofit standard that is ambitious but achievable.
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Official magazine of Easca
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Rise of the passive house |
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Wednesday, 01 February 2012 |
Page 8 of 20
One thing about passive house that’s frequently debated is the price —
how much extra does it cost compared to conventional build to go
passive? Figures of between zero and 20% are frequently thrown about,
though it’s usually stressed that with the extraordinarily low heating
costs, any extra outlay can be recouped.
Trying to make a passive house as affordable as possible, one Mayo-based
architect decided to build her own to the passive House standard.
“We’ve got Oak Barn Construction to do the main structural aspect but
we’re basically finishing it off ourselves in order to manage the high
specification within our budget,” says Cuala McGann of McGann Scahill
Architects.
“I’ve been interested in the passive house standard for quite some time,
and being a certified passive house designer, I’m seeing this as an
opportunity to put it into practice,” she adds.
The stick built timber frame structure
McGann says it’s difficult to know how much extra aiming for passive
will add to the final cost of the project. “When I finish this exercise
I’ll be able to put it in exact numerical form,” she says.
She reckons that if one stays true to the spirit of the passive house
standard by not installing a conventional central heating system, going
passive shouldn’t cost more than 5% extra.
McGann chose the stick-built timber frame system from local contractor
Oak Barn for the project. “We were basically looking to go with a
breathable construction, and we wanted to work with Oak Barn
Construction,” she says.
“She wanted to have her own house as passive, partly to show clients
that you can achieve this,” says Oak Barn’s Willie McDonagh. The company
stick-built the timber frame structure with I-beams. “The advantage of
that was that we were able to get wider walls [meaning more insulation],
and less cold bridging.”
Natural zinc roofing
The walls of the house feature 160mm of Gutex woodfibre insulation
externally, with 300mm of cellulose between the studs and an insulated
100mm service cavity. The roof includes 360mm of cellulose plus 170mm of
woodfibre insulation in the service zone. Optiwin triple-glazed Passive
House Institute certified windows also feature throughout.
“That’ll be the highest spec that we have worked to,” Willie McDonagh
says. “The walls were massive but it wasn’t difficult to work with.”
McGann plans to get the house certified by the Passive House Institute.
She says that this project has been “good in terms of professional
experience.” She adds: “We’re using it as an opportunity to apply the
passive house standard to an architectural design.”
Selected project details
Client: Cuala McGann & Olivier Bauduin
Architect: McGann Scahill Architects
Civil / structural engineer: Structural Design Services
Main contractor: Oak Barn Construction
Wall insulation, roof insulation & airtightness products: Ecological Building Systems
Windows and doors: Optiwin
Mechanical & electrical contractor: Ecowest
Project overview:
Building type
: 204 square metre detached two-storey timber frame house
Location: Westport, Co Mayo
Completion date: under construction 2011
Passive house certification: pre-submission
Space heating demand (PHPP): pending
Heat load (PHPP): pending
Airtightness: max. 0.60 air changes per hour at 50 pascals pressure
BER: pending
Ground floor: raft foundation insulated with 200mm Kingspan insulation under-slab, 35mm insulation over-slab.
U-value: 0.12 W/m2K
Walls: stick-built I-Joist timber frame: render finish on render
carrier board on treated SW battens on Solitex facade membrane, 160mm
woodfibre board, 302mm timber I-joists fully filled with cellulose
insulation, 18mm taped and sealed OSB, 100mm insulated service cavity
and 12mm plaster carrier board internally.
U-value: 0.07 W/m2K
Roof: natural zinc finish on 18mm OSB on 50x35 treated SW battens on
Solitex-Mento breathable roofing membrane, on 35mm Gutex-Multiplex
woodfibre insulation, on 360mm timber I-joists fully filled with
cellulose insulation, 18mm taped & sealed OSB, 170mm woodfibre
insulation service zone, plastered finish.
U-value: 0.07 W/m2K
Windows: Optiwin triple-glazed aluminium-clad timber windows, with argon filling and an overall U-value of 0.73 W/m2K
Heating system: wood insert stove (pending) supplying heating coil
on HRV and 300L buffer tank, plus solar vacuum tubes (pending) supplying
separate 300L domestic hot water tank
Ventilation: heat recovery ventilation system (pending) - Passive House Institute certified to have heat recovery rate of 92%
Green materials: timber frame, cellulose insulation, woodfibre
insulations, 50% GGBS cement, rainwater harvesting system & water
conserving fittings (both pending)
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