Buildings PassivHaus
Learning from
passive action
The UK’s first PassivHaus school has opened in Scotland. Carina Bailey reports
on a project that could set a new trend in imported low-energy structures
D
ubbed the ‘Weetabix’, Acharacle Primary Air tightness
is believed to be Britain’s first school to be The structure is made from small bits of timber that are
designed and built with an external fabric that joined using wooden dowels instead of glue. This system
exceeds the low-energy PassivHaus standards. is called Brettstapel and its use on this scale is a first in the
The facility, located in Lochaber in the West Highlands of UK, Liddell says. The school’s windows are triple-glazed; its
Scotland, opened in May to replace existing Victorian and classrooms are south facing to capture passive solar gains;
add-on accommodation. The breakfast cereal reference it has super-insulation (280mm-thick wood fibre) in the
neatly sums up the fact that its heating derives almost walls, floors and roofs; partly uses local wood internally; and
exclusively from the energy given off by the pupils utilises rainwater in the toilets.
themselves. Using this system has given the school remarkable air-
The seven-year project was the brainchild of Gaia tightness, with just 0.2 m
3
/hr/m
2
.
Architects, a practice based in Scotland and Norway that “The guy who came to measure [the air tightness] brought
specialises in what it describes as innovative ecological two big fans. At the end, he said he could have done it just
design and community architecture. Gaia sees Acharacle by using a hair dryer. It passed first time. It’s astonishing.”
school as a key pilot project in the UK – one which, The result compared to the normal standard of 0.6 for
it hopes, will persuade UK manufacturers to offer PassivHaus standard building, and 10 m
3
/hr/m
2
to satisfy
PassivHaus materials. Section 6 of the Scottish Building Standards Technical We need to
The school’s purpose-built solid timber superstructure Handbook. “So we are talking pretty significant amounts.
get there very
was imported from an Austrian manufacturer, which It’s three times better than PassivHaus standards,” Liddell
could guarantee PassivHaus-standard construction. It was enthuses.
quickly – we
transported to Lochaber by lorry and built in six months. In a conventional building built to current building haven’t the
The structure’s impressive insulation means that the regulations the U-values have to be about 0.2W/sqm/K,
time to make
building needs no heating – except during the winter but this passive build has achieved a U-value of 0.125 for
holidays when a small wind turbine provides about 5KW the roof, 0.128 for the walls and 0.098 for the floors. The
mistakes and
of energy to provide heat. But it is this small heating building also achieves a U-value of 0.8 for the windows and to get feedback
requirement that actually stops the school being certified doors, compared with the expected 1.8 for normal building
from academia
as a true Passivhaus building, the definition of which methods.
requires no additional heating to be installed. These measures mean the building is predicted to use
20 years down
However, Howard Liddell, principal of Gaia Architects, about 93 per cent less energy, or 7.1 per cent of the energy the line.
argues that all the other PassivHaus measures used gives needed in an equivalent building regulations structure.
this school the highest build standards in the UK. “In
certain areas it certainly seems to be ticking some very Ventilation
important boxes,” he says. The school uses natural ventilation – except in the kitchen
He adds: “The wind turbine is just there for the most and toilets – aided by the use of hygroscopic materials, which
extreme situations, we don’t expect it to be on very much. have been used throughout the building to “iron out the
When it’s not generating heat for the school it’s actually peaks and troughs of moisture levels”. The walls are covered
clocking up a little bit of electricity into the grid so the by unburned clay plaster, which is extremely good at soaking
energy is not wasted.” up and releasing moisture, according to Liddell. Vegetable
The turbine also provides electricity for all electrical paints have also been used to make the building ‘moisture-
appliances, including heating the hot water, but the school open’, leaving the fabric itself to help to passively ventilate
is not zero-carbon. the building. >
www.cibsejournal.com July 2009 CIBSE Journal 29
CIBSEjul09 pp28-31 passive.indd 29 25/6/09 15:19:29
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