Photo of the rear  of a Victorian semi-detached townhouse with a new timber-clad extension - detail shot
Detail of the outside cladding - 'organowood' © Rick McCullagh
Detail of the outside cladding - 'organowood' © Rick McCullagh

Victorian Townhouse Meets Passive House Standards in Zetland Road

Demonstrating that historic buildings can be made highly energy efficient, these adapted Victorian townhouses have met the demanding PassivHaus standard.

The aim for this project was to take a pair of typical ‘hard to treat’ Victorian townhouses in Manchester and prove that it was possible for them to meet the world's highest performance standards set by the PassivHaus Institute, and that this could be accomplished without compromising the buildings' heritage. They have now been retrofitted to become Europe’s first Passivehaus Enerphit Plus standard homes.

From the street the buildings keep their Victorian appearance with the original brickwork incorporated into the design to provide thermal mass. The technologies used enable the house to achieve the Enerphit Plus standard of generating 60 kilowatt hours of renewable energy each year for every square metre of floor area. This is produced by 60 square metres of photovoltaic cells on the roof. The insulation and ventilation allow the house to maintain comfortable temperatures and air quality year round without a central heating system.

The approach adopted by the developer was to use natural materials as far as possible and minimise the use of petrochemicals. Internal insulation of the brickwork is achieved using timber ‘I’ joists with blown cellulose and wood fibre board. The original building footprints were kept, avoiding the need to add further embodied carbon by adding extensions.

The back of the buildings have been treated with an external cladding of ‘Organowood’, a novel approach to wood preservation using silica to partially fossilise timber without the use of biocides and resisting rot and ultraviolet degradation for 30 years. Windows are angled towards the sun to maximise passive solar gain. Each layer of the walls, roof and floors is highly breathable to allow drying both inside and out should moisture get in.

Treatment of the sides of the buildings reverses the approach used on the street face, with the insulation on the outside of the brickwork. Sustainably sourced timber ‘I’ joists support cellulose insulation covered in wood fibre with a lime based finish. Lime has been a critical material in the project, providing the breathability that is central to the project’s design philosophy.

A benefit of the high levels of insulation is soundproofing.

…even if you get quite a lot of people, you get a crystal-clear conversation because there’s so much insulation and so much thermal mass that it’s just total sound absorption.

Kit Knowles, the developer

The Zetland Road PassivHaus project was always intended as a valuable case study that would not only inspire others to follow suit, but also to share information on how it can be achieved. The push to meet the world’s highest standards has led to the creation of techniques, details and products that can be shared with the construction community.