Cosgriff House

By Christopher Polly Architect

Susan Street, Annandale

By: Christopher Polly Architect

Cosgriff House, photograph by Brett Boardman

How does the project respond to its context, contribute to the public domain for example street or neighbourhood?

The project retains its original envelope as part of its environmental, economic and planning values. A substantial lower ground living volume is sensitively inserted beneath the original fabric to harness the fall in the site towards the rear, extending deeply beneath the existing dwelling and outwards towards the garden to transform it - while a re-crafted rear ground floor above enfolds the existing rhythm of front rooms over the new lower ground below.

Both levels accept a modestly-sized lightweight addition which maintains existing wall alignments, gutter levels, wall heights and southern roof plane - extending and subverting existing geometries to present an interpreted mirrored slice of the vernacular hipped form attached to the retained rear fabric, for strengthened access to sunlight, ventilation and connections to its setting.

What problems did you have to solve?

The transformation of a two bedroom dwelling with a single living space into a 4 bedroom dwelling with two living spaces has provided significant additional freedom for the owners and their three young children to grow into. Enlarged kitchen and laundry facilities, substantial storage and two bathrooms tightly planned into a narrow-width lot have amply improved their daily lives.

What was the contribution of others, including engineers, landscape architects, artists, builders and other specialists to the outcome?

Three structural portal frames embedded within the fabric were pivotal in enabling the unobstructed, expansive volume of the new lower ground beneath the original house, while a composite steel and LVL-frame permitted the new folded roof form to be elegantly expressed internally and stitched without visual support to the old house, to execute the entire folded ceiling concept. The builder’s skill is noted in having achieved the well-drained, flush door channels integrated within the slab, finely detailed steel stair framing and crafted steel handrails with pinned supports as intended.

How would you describe the value of design in relation to the cost of the project?

Carefully crafting the majority of the project within the retained masonry and hipped roof envelope formed part of its overriding economic strategy, while added footprint is sustainably modest and lightweight-framed. Inexpensively framed vaulted ceilings and skylights carved within the original roof form enable a volumetric expansiveness, permitting access to light and sky within the middle of the ground floor. A concrete slab provides a durable, thermally efficient long term outcome, while consciously surrendered floor area permits a generous stair void that spatially expands to the lower level below, and upwards to sky and tree views.

What are some important sustainability aspects of the project?

a. New work is substantially embedded within the existing footprint, with only a modestly-sized 20sqm addition to the rear footprint to meet spatial requirements of the brief.

b. Fenestration placement improves natural light access and promotes passive ventilation, assisted by ceiling fans and a roof venting system to exhaust trapped heat out of the original roof space.

c. External fabric and louvre blinds enable solar penetration to be tempered or maximised when required.

d. Heavily insulated walls, ceilings and roofs further optimise the thermal performance of the envelope to stabilise internal temperatures and comfort levels.

e. Demolished sub-floor bricks were salvaged and re-used to rebuild the downward-extended enclosing masonry walls of the original envelope to minimise carbon input - reinstating and increasing thermal mass in combination with a lower ground floor slab.

f. Products and materials selections were all integrated for their life-cycle durability and performance in their respective applications - while also incorporating concealed rainwater capacity for garden use, harnessed solar energy for gas-boosted hot water, water-saving fixtures, appliances and fittings and energy efficient light fittings.

What do you consider to be the benefits of the project for the client, users and the community?

A conceptually rigorous form carves connections to light and sky within numerous spaces and enables access to its previously disconnected rear grounds - with a controlled material palette and colour scheme providing an appropriate counterpoint for the clients' lives.