Europe
Airtightness
for
NZ's
First
Straw
Bale
Passive
House
The home is the Southern Hemisphere’s* first Straw Bale certified Passive House.
Jessica Eyers of Hiberna designed this three-bedroom straw bale house which her husband Ben built. The build utilises natural, low-tech, locally sourced materials and pairs them with high-tech scientific design and construction principles.
How was this project implemented?
The structure comprises a post and box beam wall system with straw used as in-fill. The airtightness layer is achieved using a combination of plaster on the walls and pro clima INTELLO® PLUS Intelligent Air Barrier in the ceiling. pro clima CONTEGA® PV, fleece tape for interior airtight plaster connections, is used to connect INTELLO® PLUS to the plaster and the plaster to the windows. Ventilation is supplied using a Zehnder Q350 heat recovery ventilation unit.
During their research into the heat conductivity of straw bales, they discovered that the orientation of the bale has a great impact on the insulation value. Bales on edge make for a slimmer wall but overall the U-value is greater.
A 3Kw PV system was installed in the roof which meets the home’s electricity needs as well as powering an electric car. Hot water is supplied from a heat pump while the home is heated by two 1KW radiators fed via a scavenging coil in the water cylinder.
Ben initially planned to make the windows himself but eventually decided to source the triple-glazed timber windows from a friend in Germany. He now imports these as a side business. Polystyrene was used to insulate the window jambs to help achieve the Passive House standard. Jessica specified timber fibre insulation in the future to fit better with Hiberna’s natural ethos.
Due to the two-storey structure and the plaster airtight layer, airtightness was quite a challenge, but they ended up just squeezing in at 0.59 AC/hour. The couple have learned a lot from this build and look forward to many more builds like this for clients in the future.
- Designer - Jessica Eyers, Hiberna
*There are approximately 15 certified Passive Houses on the database that include straw in their composition. The only other home pro clima is aware of that uses just bales and plaster (no membranes, linings, or cavities) for the walls is in the UK.
Intelligent Airtightness
Moisture damage to structures and protection measures
- Moisture can enter into building structures in many different ways, and it is impossible to prevent a certain level of moisture loading. However, if moisture levels are too high, moisture damage to structures can result.
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To ensure a structure is protected against moisture damage, the drying reserves possessed by the building component are much more important than the degree of tightness of the vapour check.
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Vapour barriers with high diffusion resistances allow for barely any drying from the component to the inside.
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A high degree of protection against moisture damage to building structures can be achieved with intelligent airtightness.
Airtightness Systems
Vapour check and airtight membranes with humidity-variable diffusion resistance provide the best protection against moisture and mould-infested components. In combination with moisture-active wind-sealing membranes on the exterior, they significantly improve the protection of building components and facilitate a healthier, mould-free indoor environment.
