A house transformed by Passivhaus retrofit - 34

A 1940's semi has become the first building in the UK to both reach the Passivhaus retrofit standard and be certified by a UK based certifier. Low carbon engineering consultants Encraft were appointed by housing association Orbit House of England to retrofit one of its 14,000 homes as part of a pilot scheme.

The housing association hope to learn how adapting existing properties to Passivhaus and other low carbon standards will help slash tenants’ energy bills.

The 1940s 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 first building in the UK to achieve EnerPHit (Passivhaus retrofit) certification from a UK certifier– it is also the first Wimpey no-fines (sand free concrete) construction house in the world to achieve the standard.

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 cost 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.

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 strictly a requirement of a Passivhaus, 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.

A growing number of housing associations are keen to explore the benefits of Passivhaus construction and retrofit to enable tenants to reduce their heating costs and avoid or escape fuel poverty.

Encraft are also working with several other housing associations on Passivhauses and on a newbuild site in Coventry as part of a project to compare Passivhaus standards to Code level 6 on two adjacent properties on an infill plot donated by Coventry City Council.

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-fines 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.”