Case study: Howgate Close

With average daily energy bills of only 24p, the cottages at Howgate Close have earned a reputation as possibly the UK’s most energy-efficient homes.

The Project

With average daily energy bills of only 24p, the cottages at Howgate Close have earned a reputation as possibly the UK’s most energy-efficient homes*. Built by farmer Dr Chris Parsons, the row of nine, single storey cottages exploits a range of passive solar design principles** - including a southerly orientation, a high thermal mass and a earth-bonding (external walls partially covered in soil) - to create homes which are exceptionally energy efficient and comfortable to live in. The homes are also truly affordable as no artificial heat source is required to deliver a stable internal temperature averaging 21-23 degrees Centigrade.

The cottages instead use a mix of passive heat sources, created by people and appliances, and solar gain generated through VELFAC triple glazed aluminium / timber windows. As a result, the energy consumption of a two bedroom cottage is 94% less than the average UK household.

The architecture of Howgate Close is based on designs created by sustainability housing experts Hockerton Housing Project  with performance further enhanced by Dr Jerry Harrall  a consultant in the design and adaptation of fossil-fuel-free buildings.

‘Describing Howgate Close as a development of eco-homes is to understate its performance,’ states Dr Harrall. ‘In fact all nine properties operate beyond zero-carbon, and instrumental to the success of Howgate Close is the installation of VELFAC composite triple glazing, specified for its excellent thermal performance.’

VELFAC triple glazed windows and doors

A key feature of every cottage is a large, white framed VELFAC composite window screen installed on south facing facades. The screens combine fixed units and a sliding patio door, and with dimensions of up to 3m x 5m occupy almost the entire wall. ‘The VELFAC windows play a crucial role in achieving a SAP rating for each cottage of around 143, potentially the highest group of SAP rating’s in the country and a significant improvement of the average rating of 63,’ says Dr Harrall. ‘VELFAC triple glazing has a U-value of 0.8W/m²K which reduces the rate of heat loss while bringing more natural light into each home, thereby reducing the need for artificial light,’ says Dr Harrall. ‘Across the development, the windows are actually net gatherers of heat, and contribute to an annual energy surplus which we estimate will be enough to power another similar dwelling.’

Unwanted solar gain is minimised by the exceptional insulation afforded by the triple glazed units, enhanced by low emissivity coatings applied to inner glass panes. Ventilation is primarily mechanical but supported by trickle vents within the window frames, and by cross ventilation using additional, smaller VELFAC windows installed in the rear facade. ‘Triple glazing also delivers excellent acoustic insulation,’ adds Dr Harrall, ‘which is important, as the cottages are located within actively cultivated farmland, and are near a busy road and wind turbines.’

Research and monitoring project at the Nottingham Trent University

Howgate Close is now a model development for affordable, ultra-low energy homes and is also the focus of a two year research and monitoring project, co-run by Dr Harrall and Professor Anton Ianakiev, Professor in Sustainable Energy Systems at Nottingham Trent University (NTU). ‘I have also co-authored an academic paper on Howgate Close,’ adds Dr Harrall, ‘which aims to show that it is possible to design, construct and live in buildings without resort to fossil fuels.’