Lake District gem

A detached Passivhaus home, designed to fit in with its spectacular surroundings of Ullswater in the Lake District National Park. The home was built to a quick timescale, using off-site timber frame construction.

Tethera. Image credit: Hesketh Hayden

Key stats

Construction: Timber frame
TFA: 110 m²
GFA: 134 m²
Form Factor: 3.9
Completed: 2022
Certified: Passivhaus, 2022

Tethera under construction. Image credit: Hesketh Hayden

Having stability of temperature and humidity wherever you are in the home makes for a fantastically comfortable environment.

Russel Hayden, Director, Hesketh Hayden

Design

The new home replaced an existing uninsulated 1950s bungalow which had reached end of its life. Planning considerations were critical because of the project's location in a UNESCO World Heritage site. The planners required that the new house kept the same form and ridge height as the original bungalow and to use the same palette of materials as the neighbouring houses (white render and local slate roof). The design responded to these constraints, by creating a simple, modern 'low key' design to fit in with the local vernacular. The heating system for the project is provided by 2 x electric towel radiators.

Ventilation & summer comfort strategy

The building has been designed to have zero overheating in PHPP and has performed well during the summer. although there have been several warm days (but not classed as ‘overheating’ in the PHPP). Ventilation and summer comfort strategies include:

The MVHR system has been set to have automatic summer bypass
Openable windows & rooflights provide ample cross-flow ventilation when required;
Overhang ‘outriggers’ and trees provide passive shading
Glazing makes up 27% of the home's TFA

Construction

The house was built using pre-fabricated insulated timber frame panels. The panels erected on site and made the construction watertight in two days. The building envelope was weathertight, with windows installed within two weeks allowing internal finishes and services to proceed.

There was also a focus within the project on using low embodied carbon materials. Timber was used extensively, natural insulation (recycled newspaper and sheep’s wool insulation) were used throughout above ground, concrete minimised, materials were reused where possible (including the slates for the roof) and zero VOC coatings and materials were selected. PHribbon analysis was undertaken for embodied carbon.

The as-built home scored a cradle-to-grave embodied carbon figure of 351kg CO2e/m² GIA, satisfying the RIBA 2030 Climate Challenge target- The concrete slab was a major limiting factor to a better result, despite adopting 50% GGBS (Ground Granulated Blast-furnace Slag) as cement replacement. Concrete was required due to the project's ground conditions.

Designed energy performance

Airtightness n₅₀ (≤ 0.6ACH @ 50 Pa)

0.1 @ 50 Pa

Space Heating Demand (≤ 15 kWh/m².a)

14.2 kWh/m².a

Heating Load (≤ 10 W/m²)

10 W/m²

Primary Energy Demand (≤ 120 kWh/m².a)

108 kWh/m².a

Primary Energy Renewable (PER) Demand (≤ 60 kWh/m².a)

54 kWh/m².a

Primary Energy Renewable Generation

25 kWh/m².a

Lessons learned

This project deliberately adopted proven technologies to ensure the brief could be met for an affordable home built on a highly sensitive site without delays.

For instance,planning permission was obtained within five weeks of submission.The construction was well managed and stress free, and demonstrated that the approach could easily be developed at scale. In particular, panellisation of the envelope superstructure significantly reduced the build time, beneficial in the relatively wet Lake District climate.

The period from construction to handover was less than six months, helped by careful and thorough design detailing and the keep-it-simple approach.All tradesmen came from within 20 mile travel distance ofthe site and the frame was pre-fabricated 20 miles away.