Low Energy Extension Design

Architect Simon Hoe outlines the stages through which a house extension is designed from the initial meeting to planning application.

This extension is a great example of low energy building. The completed extension (shown at the bottom of this page) has considerably increased the family living space. However, throught careful sustainable design which made the most of natural light and heat, the energy bill for the house has been reduced.

Stage 1 - Client Wish List

A meeting with the client produces their wish list. They wish to extend 1 storey to the rear, 2 storeys to the side, to provide the family with:

• 1. One additional bedroom.
• 2. More family space.
• 3. A utility room.
• 4. Expanded entrance hall.
• 5. A modern, spacious well lit design with glass and timber.

Stage 1 - Assessment

The first step is to assess the house through photographs and drawings.

Existing front view of house.	Existing rear view of house.
Existing house plans.

Stage 2 - Initial Sketches

Various options are sketched out. A further discussion with the clients covers preferences on how the family space will be used, whether the kitchen should face the front or the back, the styling of the new house, how the garden is addressed, how light is brought in and so on. The specific qualities of the southern aspect are discussed. The risk of excessive solar gain against the potential use of the sun's energy for economic heating

Ground Floor, Option 1	Ground Floor, Option 2
Garden Elevation, Option 2	Side elevation, Option 2

Stage 3 - Refining The Design

Following a discussion of the initial options, it's back to the sketch pad to pull together all the strands. A new plan emerges, providing a large, flexible family space. A glazed extension with an atrium to the landing catches the last of the evening light. Heat is collected by the glass, stored by the high mass floor and convected around the house. Design work continues on the modelling of the rear, and the treatment of the front. Sometimes a basic card model is produced to illustrate the spaces and their natural lighting.

Stage 4 - Converting Sketches To Drawings

The design is agreed in broad terms, and so it is time to convert sketches to drawings and to consider each area in detail.

Front elevation.	A canopy provides shelter at the entrance, and a shallow bay provides vital space for the office and hall.
Ground floor view. The furniture indicates the scale of the rooms	First floor view.
North elevation.	South elevation. The elevations come together. A welcoming front, light and space to the rear with heat from the sun convected around the house.
A section view. The stair landing offers a view over the double height family room.

The work has much improved the house in terms of living space, sleeping accommodation and storage.

The rear of the house faced south onto an angled garden. By angling out the glazed extension so it addresses the garden full square, the clients are able to enjoy the maximum evening sun. A double height glazed element ensures that the sunlight penetrates deep into the room and provides an airy dining area. The space is warmed by solar gain, the heat is stored by the insulated high-mass floor, and warm air is convected through the open landing to the rooms above. In fact, a major add on benefit of this extension is that despite adding considerable additional space, heating costs are actually reduced.

The 'family room', whilst one space, divides naturally into sitting, dining, kitchen, and play areas. A floor level eaves window in the converted loft space gives the impression of a floating roof, and dispels the cramped feeling so often experienced with loft conversions. Simple roof-lights give the surprise bonus of a previously hidden view of the Sugarloaf.

Exterior view of extension with glazed atrium.	The new kitchen-dining area is bright and naturally warm.
Front of house with new double height side extension.	View of loft area which is used as a children's play area and exercise room.

Summary

The preceding summary constitutes only a small percentage of all of the drawings and discussions that went into creating a practical design out of a wish list.