The architect specialising in energy-efficient window retrofits

When Catherine Waltham first climbed a ladder to inspect the original cedar-framed windows of a 1908 home in Fremantle, she had no idea the visit would redirect her entire career. The client wanted the timber replaced with modern aluminium frames, a quick swap that would have erased a century of craftsmanship in a single afternoon. Waltham refused the job, then went home and began sketching something different: a way to keep the heritage fabric intact while lifting the window's thermal performance to meet contemporary benchmarks. That afternoon, in her small studio tucked behind a café on High Street, the seeds of her retrofit practice were quietly sown.

Nearly two decades later, Waltham runs one of Perth's most quietly influential studios focused on the upgrade of existing window systems. Her work sits at the intersection of conservation, climate response and the everyday economics of running a household in Western Australia. In a state where summer temperatures routinely push past forty degrees and winter mornings bring a sharp coastal chill, the humble window has become the focus of her most ambitious thinking.

A path shaped by Australian housing stock

Waltham trained at the University of Western Australia in the early nineties, an era when sustainability was still a fringe concern in most architecture schools. Her early work included residential commissions in suburban Joondalup and a community centre in Mandurah, projects that taught her how quickly homes absorbed and trapped heat under flat-roofed extensions and minimal eaves. She began noticing the same pattern in older homes: timber frames that had warped over decades, single panes that sweated with condensation through July mornings, and ducted air conditioning units running overtime to compensate.

The turning point came when she was asked to restore a federation bungalow in Subiaco. Rather than replacing the timber sashes, she developed a method for retaining the original frames while inserting slim-profile vacuum insulated glazing into the existing rebates. The technique preserved the home's street-facing character, satisfied the local heritage officer, and reduced the household's heating and cooling load by a measurable margin. The project drew the attention of several preservation-minded homeowners who had previously assumed that energy efficiency meant sacrificing period detail.

Why retrofit matters in the Australian climate

The case for retrofitting rather than replacing runs deeper than sentiment. Australia's National Construction Code now imposes stringent thermal performance requirements on new builds under Section J, yet the vast majority of dwellings standing today predate these standards. In Perth alone, roughly seventy per cent of the housing stock was built before energy efficiency became a regulatory consideration. For homeowners, the practical question is how to bring older windows up to current benchmarks without launching a full demolition.

Retrofitting also answers a question of scale. The embodied carbon of an existing window frame, particularly one crafted from old-growth jarrah or early twentieth-century cedar, represents decades of accumulated environmental investment. Replacing it with a new aluminium unit, even one filled with argon gas, releases that stored carbon and demands fresh extraction, smelting and transport. Waltham's approach treats the existing frame as a reservoir of embodied energy worth preserving, then layers in discreet upgrades: draught seals along the sill, low-emissivity films applied to the interior face of the glass, and in some cases a secondary glazing panel fitted inside the original frame.

The technical craft of upgrading heritage windows

The process Waltham has refined is closer to conservation joinery than to standard glazing work. Each project begins with a detailed survey of the existing frame, measuring moisture content, checking for rot, and documenting the original putty work. Where timber has failed, she sources replacement sections from salvaged WA hardwoods, often pulled from demolition sites in Fremantle and Northbridge. New glazing is selected to match the visual rhythm of the original panes, particularly important in streetscapes protected by local heritage overlays.

The hardware is also reconsidered. Original brass hinges and sash fasteners are retained wherever possible, refurbished in a small workshop she shares with a metalsmith in Osborne Park. New components, when required, are sourced from the Australian Window Association's certified manufacturers, ensuring the finished assembly meets the country's performance standards. The acoustic benefits are often unexpected: a well-retrofitted sash window on a home facing a busy Beaufort Street intersection can cut interior noise levels by a third, a quiet gain that residents consistently mention in follow-up conversations.

Perth's regulatory and community context

Perth presents a particular mix of conditions that shapes this kind of work. The city's Mediterranean climate, with long dry summers and mild wet winters, means that windows must manage both solar gain and heat loss across most of the year. Many of the homes Waltham works on sit within heritage areas managed by the City of Perth or the Town of Cambridge, where any visible change to street-facing windows requires council approval. Her studio has developed a close working relationship with local planners, often preparing detailed submissions that demonstrate how a proposed retrofit preserves the appearance of the original building while lifting its thermal performance to comply with state and federal guidelines.

The economics of the work also reflect local conditions. Households across Western Australia pay some of the highest electricity prices in the country, and the cost of running ducted air conditioning through a long Perth summer is a familiar line item on family budgets. Waltham's clients frequently tell her that the decision to retrofit came down to a desire to reduce those ongoing bills while staying in homes they love. Several have also spoken about preparing their properties for a future where minimum energy ratings will become a precondition for sale, a shift already visible in some eastern states.

Industry recognition and peer exchange

Word of Waltham's practice has spread through the local design community, partly through her involvement in industry events that bring architects, builders and suppliers together under one roof. She has spoken at gatherings alongside other Western Australian practitioners, sharing the technical detail of her joinery-first approach. These conversations often lead to informal collaborations, and she points to a growing network of builders in Cottesloe and Mosman Park who now routinely refer clients to her when a heritage window needs more than a straightforward replacement.

Her profile has also grown through her work with industry organisations across the country. She frequently points newcomers to the current list of exhibitors at major design events as a way to source high-performance glazing, draught-sealing products and certified timber specialists. For Waltham, the exhibitor floor is one of the most efficient ways to compare what the Australian market currently offers, and she encourages emerging practitioners to make the rounds each year.

What comes next for retrofit practice

Looking ahead, Waltham sees several shifts that will reshape retrofit work in Western Australia over the coming decade. State government incentives aimed at improving the thermal performance of existing homes are likely to expand, mirroring schemes already operating in Victoria and New South Wales. She is also watching developments in glazing technology closely, particularly the local production of triple-glazed units and the gradual availability of electrochromic films that respond automatically to changing light. The next phase of her practice, she suggests, will involve more work on small commercial buildings, including corner stores in inner-city suburbs and community halls in places like Albany and Geraldton, where the same logic of preservation and performance can apply at a different scale.

She has also taken on a public-facing role within the design community, joining the roster of ambassadors supporting the upcoming edition of Contemporary Wine In Design. The role suits her studio's ethos of slow, considered work and quiet advocacy. Through it, she hopes to widen the circle of practitioners thinking seriously about the existing building stock, from small heritage homes in Fremantle to larger civic structures that have waited decades for proper thermal care.

Above all, she returns to a simple conviction that has guided her work since that first Fremantle inspection: that the most sustainable building is often the one already standing. The frames are already there, the timber already seasoned, the glass already settled into its reveal. The task of the architect, as she sees it, is to listen carefully to what a building needs, then intervene with as little disruption as possible. In a state where heritage streetscapes and a warming climate meet on every suburban block, that quiet discipline may prove to be one of the most consequential forms of design practice in the country.

If you're working on a retrofit project, attending an industry gathering, or simply interested in connecting with the people shaping Western Australian design, keep an eye on the Contemporary platform for upcoming events, profiles and editorial coverage. Subscribe to the newsletter, explore the latest features, and join the conversation as the local architecture community gathers to share work, ideas and a glass or two.