Creating a Passivhaus home

Balancing sustainability and style, Sort Trae is the culmination of a retired architect’s vision for a home and creative space that blends into a South Yorkshire hillside. HEM Architects helped the client to bring this dream to life, using Knauf Insulation’s glass mineral wool insulation to achieve the incredibly high Passivhaus standards for energy efficiency.

Low carbon and high comfort

The client envisioned a sustainable build using Passivhaus, a voluntary standard for designing and building properties with very low energy consumption, 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. 

FrameTherm® Slab 32 was friction-fitted within the 140mm thick timber frame walls on the first floor, while DriTherm® Cavity Slab 32 was used to fill the stone-clad masonry cavity walls on the ground floor.

“We try to specify fully filled masonry cavity walls where possible, sometimes up to 200mm wide, to maximise the use of mineral wool insulation. It pays dividends for the client”, explained Liam Seaman, Architectural Technologist for HEM Architects.

Thermal performance is critical to the Passivhaus approach. The FrameTherm® Slab 32 provided a calculated U-value of 0.137 W/m2K in combination with the black timber frame wall and cladding. For the masonry cavity wall on the ground floor, a fractionally higher U-value of 0.138 W/m2K was achieved using thermally broken wall ties and DriTherm® Cavity Slab 32. This has contributed to Sort Trae’s exceptional thermal efficiency.

Because glass mineral wool is flexible and fibrous, slabs knit together and adapt to minor imperfections in the substrate. This tight fit contributed to an overall air change of 0.54 ach (air change per hour), comfortably below the Passivhaus standard of 0.6 ach, meaning the property is air-tight while still providing good ventilation.

Sustainable practices

Liam explained his reasons for choosing Knauf Insulation, “The alternative products are often oil-based and the application of these is outweighed by the environmental impact of their production and lifecycle.”

Both FrameTherm® Slab 32 and DriTherm® Cavity Slab 32 are manufactured with ECOSE® Technology, Knauf Insulation’s unique bio-based binder that contains no added formaldehyde or phenol. The binder is made from natural raw materials that are rapidly renewable and is 70% less energy-intensive to manufacture than traditional binders.

Knauf Insulation’s glass mineral wool insulation contains up to 80% recycled content, mostly glass bottles and jars. It is also compressed so more product can fit per pack or pallet, and less packaging is used. This means there’s more product per truck, resulting in fewer vehicles on the road, and less packaging per m2 of insulation.

Achieving the Passivhaus standard

In collaboration with HEM Architects and other suppliers, the client has created a stunning home and an inspiring set-up for her loom-weaving workshop.

“It is general practice for us to specify Knauf Insulation as standard because we find the product information available to be really clear and useful”, Liam added.

Knauf Insulation’s practical, detailed product information made it HEM Architects’ first choice to achieve the Passivhaus standard for thermal performance.