Built from traditional
stone and slate, Preston Springs, a four bed home in Leyburn, North Yorkshire,
may look like a typical new-build property, but it is far from it.
Designed by architects
LEAP, Preston Springs is a Passivhaus, meaning it is ahead of its time in terms
of air quality, comfort and reduced energy use. It is one of the only
properties of its type in the local area, with just over 1,000 Passivhaus
properties in the whole of the UK.
Passivhaus is a
voluntary standard for designing and building very low energy properties that
offer high levels of comfort for their occupants. To achieve this, the levels
of air tightness and thermal performance far exceed those mandated by building
regulations.
To meet planning
constraints, Preston Springs has been built using a conventional cavity wall
construction. The 300mm cavity was fully-filled using two layers of Knauf
Insulation Earthwool® 150mm DriTherm
34 Cavity Slabs. Manufactured from Glass Mineral Wool, DriTherm is specifically
designed for cavities and uses a water repellent additive to prevent water
ingress, making it ideal for its exposed location close to the Yorkshire Dales.
DriTherm 34 was chosen
over rigid board insulation. Its structure meant the stone masons could cut and
fit the insulation easily on site to ensure it fully-fills the cavity, touching
both leaves continuously. This prevents undesirable air gaps that reduce
thermal performance. It is worth noting that masonry construction with
partially-filled cavities are particularly prone to air gaps between insulation
boards or breaks in contact between the insulation and the wall surface.
Secondly, because
detailing at junctions between the building elements and the openings meant
thermal bridging was virtually eliminated, a more cost effective insulation
specification could be chosen.
Principal architect
Mark Siddall was confident that DriTherm 34 would deliver the 0.1 W/m2K U-Value required to help the project
achieve Passivhaus certification.
For the loft, Supafil
Loft Blowing Wool was specified after extensive consultation with Knauf
Insulation’s Technical Support Team. While Supafil Loft is very popular in
Scandinavian countries, it is not widely used in the UK. However, Siddall
believes that blown insulation has a distinct advantage over other insulation
types when working towards very high levels of thermal performance.
He said: “The
advantage of Supafil Loft insulation is that it can get it into all the nooks
and crannies very quickly and easily. This makes it a low-cost solution as far
as labour is concerned because installers don’t have to cut and scribe around
individual trusses at 400 and 600mm centres – something that would take a huge
amount of time. By avoiding these air gaps the roof can be expected to deliver
the thermal performance that was specified.”
It was not just the
use of Supafil Loft that was unusual on the Preston Springs project, but its
depth; 700mm of Supafil Loft was installed, delivering a U-Value of 0.06, which
Siddall believes makes it one of the most highly-insulated lofts in the UK.
Siddall explains that
to achieve Passivhaus standard, installation is hugely important. He said: “The
only way to close performance gaps is through high quality workmanship. I have
used the same construction team on several projects. I ensured that the installer
had received the necessary training on how to install the Supafil Loft
insulation correctly, so I had the quality assurance that it would perform as
specified in practice.”
Steve Wise, Programme
and Product Development Manager at Knauf Insulation added: “It is always
exciting to work on projects that feature products not commonly used in the UK
or in applications that differ from the norm, such as the 700mm Supafil Loft at
Preston Springs.
“Passivhaus projects
allow us as manufacturers to explore what is possible. Preston Springs
demonstrates how environmentally-focused design, high performance products and
high quality installation can deliver and meet even the strictest thermal
standards in a real-world environment.”
Typically, Passivhaus
properties achieve a 75% reduction in space heating requirements, compared to a
standard UK new build. While monitoring is ongoing, anecdotal evidence from the
owners show that Preston Springs is performing as designed, maintaining a
temperate climate throughout the year. During ‘The Beast from the East’ the
internal temperature was a reported 19°C without heating, while the external
temperature plummeted to -6°C.
Furthermore, the
owners report they are delighted with the low energy bills thanks to the very
high thermal performance of the insulation combined with the heat recovery
system.
