The situation

Sefton House is a compact, highly considered family home set on a steep, established site in Grey Lynn. Designed by Ashton Mitchell, the home terraces down the slope to maximise sunlight and frame elevated views, creating an open feel within a tight urban footprint. Its design excellence was recognised with a 2025 Te Kāhui Whaihanga Auckland Architecture Award.

At roof level, a plywood terrace sits directly above habitable space, demanding a waterproofing system capable of managing mixed materials, close junctions, and a level deck finish.

“This is a welcoming family home that manages to overcome its steep and constrained context… Plywood wall linings and timber floors make for a warm and glowing interior, offsetting the more recessive and prosaic metal exterior cladding.” — 2025 Te Kāhui Whaihanga Auckland Architecture Awards Jury

The challenge

The terrace required absolute watertightness in a location where transitions between plywood, metal saddle flashings, and tight architectural details left little margin for error. The waterproofing layer also needed to support a floating deck system while maintaining clean, durable interfaces that matched the precision of the design. Access constraints on the steep site added further complexity.

The solution

A CodeMark-certified Nuraply 3PM two-layer membrane system was chosen for its durability, versatility, and ability to bond seamlessly with both timber and metal substrates. Its robust detailing ensured clean junctions without the need for additional components.

To create a level, accessible terrace, self-levelling Nurajack pedestals were installed above the membrane to support the floating timber deck. This system protects the waterproofing layer while delivering a clean, finished surface that performs well in all weather conditions.

This approach provides a robust yet streamlined system that ensures long-term waterproofing performance and integrates smoothly with the home’s architectural detailing.