A 1940s semi which has become only the second building in the UK to be certified to the Passivhaus retrofit standard is in line to win a national award for low carbon engineering consultancy Encraft.
Encraft was appointed by housing association Orbit House of England to retrofit one of its 14,000 homes as part of a pilot scheme to see how adapting existing properties to Passivhaus and other low carbon standards will help slash tenants’ energy bills.
The semi in Elliott Drive Wellesbourne, Warwickshire, is expected to see heating consumption drop by around 85% as a result of the £100k project.
Not only is it the second building in the UK to achieve EnerPHit (Passivhaus retrofit) certification – it is also the first Wimpey no fines (sand free concrete) construction house in the world to achieve the standard.
Encraft is aiming for top prize in the retrofit category of the Passivhaus Institute’s UK Passivhaus Awards, which are aimed at highlighting that the standard can be applied to any kind of building to achieve a dramatic reduction in heating bills.
The Elliott Drive house was one of a number of speedily built properties built to tackle the post war demand for new housing whose construction is well known for creating condensation, providing poor insulation and thus generating high heating bills.
A 70 sq m house of this type would typically costs around £1,100 a year to heat, and Encraft estimates the transformed building should now cost just a couple of hundred to run.
The Passivhaus principle is to construct or retrofit a house to minimise its need for heating and cooling by maintaining a constant temperature through effective insulation, airtightness, triple glazed windows and the installation of a mechanical ventilation heat recovery (MVHR) system.
Constructing a property from scratch is more cost effective than retrofitting, and can cost only 5 – 10% more than traditional build, as its position and shape have a major impact on the property’s energy efficiency.
The project saw Encraft oversee the installation of improved insulation in the walls, roof and floor which involved digging out the floor to install 200mm of under concrete insulation and 200mm of insulation around the foundations to minimize thermal bridging. It also required raising the roof level to accommodate thicker insulation, installing new triple glazed windows and doors, attaching airtight rubber grommets around soil, gas and water pipes, installing Mechanical Ventilation and Heat Recovery and a small gas heating system. Although they were not a requirement of Passivhaus, the project also involved installing a new kitchen and bathroom, It also involved installing a new kitchen and bathroom and fitting solar PV tiles.
Energy reduction is being monitored by Coventry University and the savings are being compared with those achieved by the other half of the pair of semi detached houses which Encraft also retrofitted but in a less extensive, more affordable manner.
Orbit is one of a growing number of housing associations keen to explore the benefits of Passivhaus construction and retrofit to enable tenants to reduce their heating costs and avoid or escape fuel poverty.
Orbit is also working with Encraft on a newbuild site in Coventry where it is building one house to Passivhaus standards and another to code level 6 on an infill plot donated by Coventry City Council and comparing the costs and savings of the two approaches.
Encraft Passivhaus consultant Helen Brown explained: “This project marks a turning point in the UK Passivhaus and EnerPHit sector. Not only is it the second EnerPHit project, and the first to be certified by a UK-based certifier, it has also achieved higher air tightness results than those required by Passivhaus standards, thus dramatically reducing energy bills for tenants.
“58 Elliott Drive was the first Wimpey no-fine house in the world to be retrofitted to this standard. It shows what can be achieved with this kind of building and how it can be applied to the rest of the UK housing stock.
This gives us hope that in these times of austerity and fuel poverty, we can really make a difference to thousands of families on a limited income, in a cost-effective way and with respect for the environment.
“Because the triple glazed windows remain at 17 degrees even if it is below zero outside there is no need for traditional heating such as radiators under the windows. The temperature remains constant and additional heat can be delivered via the MVHR system which has ducts to every room. Background heating can be fitted as an additional source of warmth but a 100 sq m house only needs a 1kw boiler compared with a 12 to 20 kw model required in a traditionally constructed home.”