Building the Eco-Extension

Building the modern eco-extension was very different to renovating the main house. The extension used the latest building materials and techniques for built-in eco credentials:- timber and steel frame, insulation, heating and ventilation, windows and glazing, roof and roof lights.

The modern eco-extension creates a stunning addition to the renovated Victorian house.

Built on the rear part of an extensive garden the area was levelled and foundations prepared before construction of the timber frame and steel building.


The existing waste drainage was upgraded from a 4 inch to 6 inch waste pipe system that lead to the main sewer system and we built new brick access manholes.. The upgrade was needed because of the additional house capacity and potential peak flow rates.

We dug-out the foundation trench and laid 300 x 300 mm reinforced concrete foundations up to ground level. Within this perimeter, once all earth was removed a concrete slab was laid.

This comprised hard-core of 100 mm, Visqueen damp proof membrane, 100 mm foil backed solid 'Kingspan' thermal insulation, and 100 mm concrete. This was poured and levelled to within 50 mm of ground levelto allow sufficient depth for the 'wet' underfloor heating pipes and screed covering.

The first 2 courses of brick were built up with Staffordshire blue engineering brick, which was chosen because it provides excellent damp resistance.

Extension Structure

The timber framed building had been prefabricated off-site.When delivered it was erected within 10 days. Each component has a waterproof breathable membrane on the external side to prevent damp; drafts and repel water.

Under the external finishing K-rend insulated render we installed an additional 100 mm 'Kingspan' insulation to super thermally and sound proof the property. Expanding foam was used to fill any gaps as a draft prevention measure.

A large reinforced sction of steel joists which formed a Rectangle frame was installed over the ground floor timber frame. This forms the structural component of the cantilevered balcony on the first floor.

In the groundfloor ceiling, once the electrical and plumbing work had been fixed we installed Rockwool insulation between the joists. This helps retain heat within the lower rooms.

Roof System

The roof system uses a seamless fibreglass and liquid plastic Decothane roof system chosen for its durability and strength. Over this, above the single storey connecting building we installed a 'green roof' and four Velux flat roof skylights and light wells designed to flood the room with light.

The main roof section also has the Decothane system. This is moulded around the chimney . The drainage system is designed to prevent ponding and channel rainwater into concealed drainpipes. We installed solar thermal panels that heat water, and CCTV security cameras at vantage points.

To maintain a clean design to the building, all drainage downpipes are recessed into walls.

Heating and Ventilation

The primary heating system is wet underfloor heating powered by a modern gas boiler. The heated water generated from solar thermal roof panels is stored in a thermal heat store cylinder and this supplements the domestic hot water system.

As a secondary heating system a contemporary gas fire is installed within the central chimney stack which is equipped with a flue liner.

Ensuring the internal environment remains comfortable in a well-insulated house is a heat recovery system. This draws warm, moist air from around the building and uses it to heat fresh air drawn in for ventilation from outside. The duct work is discretely installed in frames throughout the building.

Internal Design Elements

Boarshurst always strive to meet and exceed client's expectations by recreating design detail from plans. In this property individual design elements include the creation of window blind recesses in the ceilings above the windows following the minimalist clean lines of the design. A spotlight system in the lounge is similarly concealed.

In the kitchen we created a feature overhead light panel with a discrete integrated extractor.

Internal walls have been boarded and plastered to a very high standard of finish.

Recessed lights and switches are installed including internal led feature lighting and external feature lighting on balcony.

Windows and Glazing

The window frames and glazing are Low-E specification. This maximise sunlight and heat into the room and minimises loss by reflecting heat back into the room. The external surface is self-cleaning glass.

Boarshurst Experience

"The experience for Boarshurst has been a very positive one in architectural design experience and in use of innovative materials. Only a few years ago our various employee teams would have thought exceeding building regulations for insulation was perhaps excessive. Now they understand and are fully on-board when clients talk about underfloor insulation, insulated walls (interior and exterior) and insulated internal ceilings and roof spaces. 'Grand' projects like these this improve our eco credentials too."

Concrete Slab & Foundations
(below)Eco Extension Build
Extension Construction
Completed Extension
Contemporary Eco Build Extension and Traditional Renovation

Traditional Renovation Stages
House Renovation
Foundations Built Up
Brick Course
Timber Frame Erected
Cantilever Balcony steel Frame
Insulated Frame Walls
Plasterboarding Inside
Kitchen Installation
Final Stages of Eco-Extension

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