JeCC Award Winner

Jersey

The Dunes is a new 4 bedroom dwelling, designed and built using building physics tools (passivhaus methodology), Modern Methods of Construction, and largely natural or recycled materials - primarily timber. It’s heating/cooling energy demand is modeled at less than 20kWhr/m2 per year.

Architecture: MAC Architectural Services

Construction timelapse

Background

Nestled at the foot of the Sand Dunes in St Ouens Bay lies the recently completed property known as The Dunes. The Dunes is a new 4 bedroom dwelling set within large grounds at the bottom of Mont a La Brune. The property benefits from an elevated position in the bay which affords views over the whole of St Ouens Bay from Corbiere Lighthouse to L’Etacq.

Advanced Housing Systems Ltd (AHS) and MAC Architectural Services Ltd (MAC) were approached by the owner of the Dunes site with the brief to redevelop the existing site and provide a new purpose built family dwelling. The client provided a very detailed brief which included stringent sustainability criteria that were to be met. The new property was to be in the region of 5000sq/ft and was to provide a family home with sociable open plan living areas which maximise the views of the bay and the surrounding sand dunes. The client had a clear desire to make sure the new building would be designed in a fashion that would complement and nestle within the sand dune environment, rather than look to stand out from the bay below.

The design and construction team were directed to reduce the impact the construction had on the environment throughout the design and planning stage as well as the construction process. The heating energy consumed by the end user was targeted to be better than half that of the average new build in Jersey.

The client selected AHS partly as their in-house team included both a Certified European Passivhaus Designer and a Code for Sustainable Homes Assessor (BREEAM). Furthermore, Colin Smith Partnership had advised that the off-site Modern Method of Construction (MMC) build costs were comparable with local non-MMC builds. In this particular build, we used third-party insulated raft foundation and ICF system for the basement - just to make sure we stay ahead of the pack.

Construction phase gallery

The specific sustainability criteria relevant to the Award are examined here

The total energy used, energy use and energy saving techniques

The substructure, including a substantial basement, and superstructure of the building were engineering, manufactured off-site and installed by AHS. The construction incorporated both sustainable materials and passivhaus building methodology.

The design was in 3D and modeled using building physics software for heat loss, thermal mass and vapour transport.

The substructure was an insulated raft of 200mm concrete on 300mm EPS, giving a u value of 0.11 W/m2.K.

This Passivhaus specified base is thermal bridge free and was assembled on-site in 3 days. It is preloaded with underfloor heating and is inherently high thermal mass. The thermal mass absorbs passive gains such as solar during the day and releases the heat at night. This helps overheating as well. A power-float finish means that the floor finish can be installed directly to the base. The basement was integrated into the raft using EPS insulated concrete formwork (ICF).

The superstructure was also manufactured off-site in sustainable materials primarily using engineered timber I joists in the roof and floor cassettes. The remaining envelope was a closed panel system with pre-installed electrics and recycled glass wool insulation.

The overall u value is 0.13 W/m2.K.

The erection time was 4 weeks including installation of our triple glazed low profile glazing.

The mechanical ventilation and heat recovery (MVHR) system recovers around 90% of passive building heat gains and transfers this to fresh incoming air. This relies on exceptional air-tightness which is inherent in the closed panel timber frame/SIPS system, in addition to good site practice.

The speed and efficiency of construction cuts down substantially on site energy use during construction, as well as transportation costs.

The space heating and domestic hot water requirement is fulfilled by high COP air-source heat pumps.

Water use and water saving techniques
The property incorporates large surrounding grounds which have also been substantially redeveloped. The previous property occupying the site was surrounded by hard areas of paving with a concrete driveway and pebble dash white rendered walls. The new driveway and surrounding garden areas have been designed to mimic the surrounding dunes. The garden areas have been banked and layered with marram grass and the new driveway set within these rolling gardens, edged with large granite boulders, soft hoggin and gravel finishes provided. Set within the banked garden areas is a private fire pit (wood burning) seating area which connects to the main house through a sunken pathway within the rolling gardens.

The gardens reuse many plants, which were already mainly xerophytes (needing little water, being adapted to the sandy location). New planting was in low water requirement species and varieties. Rainwater largely percolates through to the garden.

This strategy minimizes the need for water or the transport of new soil, the sand/shale extracted during construction being reused in landscaping.

As well as visually complementing the neighbouring dunes, the environment created provides excellent habitat for some of the wildlife in the area, such as green lizards, which will thrive in the granite boulders forming the drive and sunken fire pit area.

Waste management and transportation
Waste was minimized through good practice, but, as mentioned above, 99% of waste by weight and volume was sand and shale reincorporated into the landscaping. This massively reduced transportation costs as well.

Construction materials
The building envelope is largely FSC certified timber; recycled glass wool insulation; engineered timber i-joists; local reused stone, sand from the site itself. These materials were selected for their low carbon credentials, light weight, recyclability, and ability to reduce waste and transport costs.