East Hampshire District Council - Quebec Park

Quebec Park in Bordon, East Hampshire, is a medium-size development of two, three and four-bedroom homes on the site of the old Quebec Barracks. We used our Assured Performance Process to review each house type planned for the site - at key stages of their design - and to identify a range of risks and recommendations.

The 100 homes on the Quebec Park site are being designed to the Zero Carbon Homes standard and use a timber-frame construction, with additional rigid insulation inside the frame. Some units have photovoltaic panels on the roofs and there is a mixture of house types ranging from detached houses to flats.

Both the developer and design team have considerable previous experience of sustainable buildings. The developer, Radian Homes, has a number of developments that achieved Code for Sustainable Homes Levels 5 and 6 (with Level 6 theoretically a zero-carbon home).

Radian also carried out post-occupancy evaluations of these past projects, with lessons feeding into their new developments.

Our Assured Performance Process included reviews of each house type planned for the site, at key stages of design. Using APP allowed us to identify a range of risks and recommendations including:

  • Orientating as many homes as possible south, with south-facing roofs, to make it easier to provide summer shading and to make the PV as efficient as possible.
  • Adopting better U-values than the minimum requirements of Part L of the Building Regulations.
  • Careful attention to the summer overheating risk (a particular risk for timber frame homes with low thermal mass), using shading and night-time ventilation to lower temperatures.
  • Moving the windows in relation to the insulation layer to reduce thermal bridging – by omitting planned spandrel panels (which pushed down the window sills) thereby creating an avoidable thermal bridge.
  • Extending a warm roof across a terrace of several homes to reduce thermal bridging.
  • Reducing boiler capacity to better suit heat losses and reduce boiler cycling.
  • Recommending that the design team appointed someone to be accountable for the final energy performance of the completed homes.
  • Publishing the expected energy performance of the homes in sales literature.

Inception and strategy

We made specific recommendations at a very early stage of design – particularly linked to massing and orientation on the site. We recommended:

  • Orientating as many homes as possible south, with south-facing roofs, to make it easier to provide summer shading and to make the PV as efficient as possible.
  • Adopting better U-values than the minimum requirements of Part L of the Building Regulations. We suggested following the fabric efficiency standards proposed by the Zero Carbon Hub.

Planning and early design

In addition, we made specific recommendations during the pre-planning stage, especially in relation to thermal bridges and overheating risks. We recommended:

  • Modelling thermal bridges at all junctions and improving on Enhanced Construction Details.
  • Giving careful attention to the summer overheating risk (a particular risk for timber frame homes with low thermal mass), using shading and night-time ventilation to lower temperatures.

Detailed design

We also made a series of specific recommendations in the detailed design phase, including:

  • Reducing the ‘timber fraction’ (the proportion of timber stud to insulation material) at junctions and lintels. These weaken thermal performance by increasing the average U-value, leading to thermal bridges and possible condensation points.
  • Moving the windows in relation to the insulation layer to reduce thermal bridging – by omitting planned spandrel panels (which pushed down the window sills) thereby creating an avoidable thermal bridge.
  • Extending a warm roof across a terrace of several homes to cut the number of thermal bridges.
  • Avoiding ambiguity in design drawings by drawing thermal bridge details.
  • Omitting planned weather compensators and zone controls for heating systems, because super-insulation, good airtightness and modest dwelling sizes mean that there will be no energy-saving benefit. We also suggested reducing boiler capacity to better suit heat losses and reduce boiler cycling. This will also result in savings in construction costs.

Construction

We have made regular visits to the site to examine energy related elements of the construction; checking on assembly of details, insulation type, thickness, and installation quality.  We have advised on detailing and best practice to avoid thermal bypass and ensure thermal bridges are reduced as per the design intent.

We have also examined the timber fraction and made recommendations to reduce the risk of underperformance as the site build out progresses.


Developer: Radian Housing


Contractor: Drew Smith Ltd


Architects: Architecture PLB


Planning Authority: East Hampshire District Council


Energy Consultant: Greenbox Associates


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Assured Performance Process

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