Pepper Tree Passive House

Pepper Tree Passive House

Designed by Alexander Symes Architect, Pepper Tree Passive House is a small secondary dwelling to a young family’s home in Australia’s Illawarra region, perched on a steep site and elevated into the canopy of the site’s eponymous 60-year-old Pepper Tree.

The project was first envisioned several years ago by both Alexander Symes Architect and their client, a builder with a Passive House specialty.

After the initial concept and design were developed, the client/builder began to salvage and store materials from other projects that would have otherwise gone to waste, for use on this project.

This early coordination between architect and client/builder flows throughout the project; from recycled timber and pavers made from waste concrete, down to screws and fixings left over from other jobs, doing so allowed a massive reduction in virgin materials used.

While the existing home had a tired and thermally inefficient brick exterior, internally the home’s layout functioned perfectly for the young family.

As a response, the project brief developed into one where the existing home had its external envelope upgraded.

This included new insulation where practical, a ventilated timber screen facade, new skylights, a wrap-around deck, and a solar panel pergola.

A striking secondary dwelling was designed around the 60-year-old Pepper Tree in the steeply sloping and under-utilised rear yard.

The secondary dwelling was envisioned as a 24-hour space; used as a home office by the family’s growing business during the day and a short-term stay cabin at night.

Designed and built to meet the Passive House standard, the short-term stays allow visitors to experience the higher quality of space that the Passive House standard affords while creating a future-proofed studio with western views of Mount Kembla and the treetops outside.

Each wing of the secondary dwelling hosts an endemic-planted green roof, allowing the biodiversity of the site to be regenerated despite the extended building footprint created.

The two cantilevered wings each host a green roof, filled with native Australian plants, blending the building into the landscape.

And the works to the existing home improve the thermal comfort of the space and create new entertaining spaces throughout.

Between the natural and raw material palette including extensive timber use, endemic rooftop gardens, and tree canopy deck, the biophilic connection of the entire site is strengthened with its immediate environment.

Nestled into the tree canopy of the Pepper Tree, the secondary dwelling sits lightly on the steep site and elevates the natural ground via its green roofs, with the recycled Shou Sugi Ban cladding allowing the building to blend into its environment.

Previously exposed to the street corner below, the wrap-around deck to the existing home creates spaces for entertaining that provide both a noise and visual buffer to the street and direct views over the street tree canopies towards Mount Kembla.

The project adds much-needed usable floor space to the suburban site without overdeveloping or sacrificing biophilic connection.

By using salvaged and waste materials throughout, costs were significantly reduced without sacrificing material quality.

Passive House standard and 12kW photovoltaic panel system mean that the project’s overall grid energy consumption is only 14% of a comparably sized home (86% reduction), significantly reducing the lifetime cost to Alexander Symes clients.

As opposed to thermally upgrading 160m2 to the passive house standard, only 60m2 will actually be comfortable in future peak climatic conditions.

This approach provides a precedent for creating small future-proofed additions so that we can be climate adaptive without the massive cost of upgrading all existing dwellings.

Built to the Passive House standard, the project meets the five core criteria:

  • Well insulated (R5.4 Walls, R5.0 Floors, R6.5 Ceiling/Roof)
  • Airtight construction (2 layers – external vapour-permeable membrane and internal sealed Intello membrane, 0.51ACH @ 50Pa)
  • High-Performance Glazing (Neuffer triple-glazed, timber/aluminum composite framed windows)
  • No Thermal Bridges (carefully detailed and constructed timber structure with no thermal bridges between internal and external)
  • Heat Recovery Ventilation (Brink Reinvent Excellent 180 Heat Recovery Ventilation unit)

Naturally, a Life-Cycle Assessment was conducted for this project.

It revealed that despite the higher amount of embodied energy associated with the construction of Passive House, the building’s environmental footprint was 64% less than a comparable built-as-usual home in the same climate zone.

That was due to three main moves:

  • small, high-performance building envelope
  • low-embodied carbon material selection
  • significant on-site generated and exported renewable energy

Other sustainability attributes of the Pepper Tree Passive House project include:

  • Fully electric building (no gas)
  • Grid energy used is 100% accredited GreenPower
  • Heat pump hot water
  • Induction Cooktop
  • 12kW PV system, 14kWh battery
  • Triple glazed, alu-clad timber windows
  • 4,000L rainwater tank, serving Laundry and Bathroom
  • Construction waste material fully diverted
  • No internal paint, 0-VOC, and E0 finishes, and materials used where possible
  • Endemic and edible landscape

Project Details

Project Size – 60 m2
Site Area – 617 m2
Completion Date – 2021
Building Levels – 1

Project Team


Alexander Symes Architect

Alexander Symes combines a scientific approach to sustainability with a practical and poetic understanding of crafting a building.

Client and Builder

Souter Built

Souter Built provides a range of building services including residential, commercial, heritage restorations, and Passive House Construction.


Barton Taylor

Barton is an established commercial photographer specialising in architecture and design.

Photo Gallery

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Design © 2022 Alexander Symes Architect. All Rights Reserved.| Images © 2022 Barton Taylor. All Rights Reserved.

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