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Engineered to impress

From learning how to work with cross-laminated timber to crafting joinery with mathematical precision, builder David Campbell talks about how he brought the highly experimental design of the Seed House to fruition.

Engineered to impress

From learning how to work with cross-laminated timber to crafting joinery with mathematical precision, builder David Campbell talks about how he brought the highly experimental design of the Seed House to fruition.

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By his own admission, HIA member David Campbell is always working on something ‘mad and crazy’. From raising a Federation house to dig out a four-car garage beneath it, restoring inner city heritage homes, or dedicating nine years to a ‘spectacular’ build on Sydney’s Cottage Point, he has seen and done it all since establishing David Campbell Building Pty Ltd (DCB) 20 years ago. 

Specialising in the construction of prestige, architect-designed homes and renovations, mainly in Sydney’s eastern suburbs and northern beaches, DCB tackles highly complex projects with a fearless, can-do, solutions-oriented approach. Tricky sites, out-there designs and experimental methods – these are the challenges DCB thrives on. 

The Seed House, located on a bushy bayside outcrop on Sydney’s lower north shore, is a stunning showcase of the company’s technical flair. Innovative and highly experimental, the house was designed by architect James Fitzpatrick (partner of fitzpatrick+partners) to be his family’s ‘forever home’. Inspired by the distinctive form of the seed pods of the surrounding angophoras, the structure comprises a cluster of interconnected ‘pods’, which emerge from the hillside layer-upon-layer, stretching out towards the water beyond in gravity-defying cantilevers. 

Gabrielle Chariton

Author

Contributor to Housing

The Seed House comprises a cluster of interconnected ‘pods’, which emerge from the hillside layer-upon-layer. Image: supplied
The house took three years, and more than 400 drawings to design, and two years to build. Photo: Ben Guthrie
The Seed House took three years (and more than 400 drawings) to design, and two years to build. Constructed primarily from cross-laminated timber (CLT), it sets new benchmarks in terms of materials use (and re-use), sustainability, aesthetics and construction methodology. 

‘It was only the third time CLT has been used in residential construction in Australia,’ David says. ‘So we weren’t familiar with working with it at all.’ 
The intensive learning curve that followed began with hands-on research – David travelled to New Zealand and the US to view homes that have been built with CLT, and visited the NZ manufacturing plant where the Seed House panels would be made.

The building may appear deceptively simple, but its large spans (up to nine metres) and 4.5-metre cantilevers take the structural qualities of CLT to the absolute limit. Onsite construction was preceded by an extensive engineering phase, involving hundreds of hours of computer analysis and modelling. As all internal walls and ceilings were prefabricated, David says that every fixing detail, service route and assembly sequence had to be considered before the first panel was manufactured. 

The Seed House’s sustainability mandate meant that substantial parts of the site’s existing home (which the architect and his family had lived in for eight years) were repurposed into the new structure, including the foundations and some of the walls. The demolition process presented a particularly unique challenge: ‘We spent a lot of time pulling the existing house apart by hand,’ David explains. ‘The architect told us to keep an eye out for a tree python he thought was living in the house. Well, we found the first snake and then we found about 50 more after that, all hiding inside the wall cavities.’ 
All internal walls and ceilings were prefabricated. Photo: John Gollings
The vast, timber-lined rooms follow the angle of the pods – narrower at the rear and opening out to take in the views of Sugarloaf Bay via floor-to-ceiling, flush-mounted glazing. Photo: John Gollings

The site was steep and access somewhat limited on the curved, narrow suburban street – ‘but that’s our normal’, David says. ‘When we realised what we were dealing with, the reaches involved and the time period we were working within, we decided to install a tower crane.’ Once the CLT panels were delivered to site, they were craned into position. ‘I think the biggest panel was about nine metres long and weighed 2.7 tonnes. It was pretty easy once we got the hang of it.’ 

The Seed House is at once imposing and reticent. Despite their impressive scale, the glass-fronted CLT pods, clad in black aluminium and topped with green roofs, sit harmoniously within their bushland surrounds. Inside, the 658-square metre home is a bold celebration of the nexus between the built form and the materials used: pale swathes of natural stone (including sandstone collected onsite) and native timbers (Huon Pine, Radiata Pine, as well as Celery Top Pine and Blackwood salvaged from the bottom of Tasmania’s hydro lakes) are punctuated by black steel. 

The vast, timber-lined rooms follow the angle of the pods – narrower at the rear and opening out to take in the views of Sugarloaf Bay via floor-to-ceiling, flush-mounted glazing – with raked ceilings soaring overhead. Again, the apparent visual simplicity of the interiors is the result of complex detailing and technically demanding joinery. 

‘The walls are all on an angle and the ceilings are on an angle so we’ve got a compound mitre cut on all the junctions,’ David says. ‘In two of the pods, we had to work out well in advance what width the boards had to be so that when the floorboard hit the wall board, which is on an angle as well, and then hit the ceiling board, all the edges lined up.’ 

Stepping down the hillside in a series of interconnected spaces, the home is anchored at the rear by a spectacular timber spiral staircase, which elegantly winds down three floors inside a capsule of curved glass and aluminium. It’s an architectural masterpiece in its own right, but achieving the fantastical finish was something of a mathematical nightmare for the DCB team. 

‘It’s made out of slabs of CLT, put together in a CNC machine in New Zealand and shipped over,’ David explains. ‘We did a 1:1 printout of the treads, the top part was already predetermined and the mid-flight was already predetermined…so where we started on the bottom, it had to be right.’ The treads were fitted individually, threaded up and over a six-metre post. 

‘As we fitted each tread, each one had to be glued and screwed [using hidden screw locations], and then as we went up, the column had to be grouted, so it was a long process.’ 

This mammoth project was completed in 2019 and David says the architect is ‘very proud’ of the finished home, which has already attracted plenty of industry recognition. Visionary in both design and execution, it illustrates what can be achieved when possibilities are tested. 

‘A lot of what we did on this home had never been done before,’ David says. ‘Our amazing staff embraced the project and had the dogged determination, endurance and skill to overcome every obstacle.’ 

The Seed House was only the third time CLT has been used in residential construction in Australia. Photo: John Gollings
The apparent visual simplicity of the interiors is the result of complex detailing and technically demanding joinery. Photo: John Gollings
The treads were fitted individually, threaded up and over a six-metre post. Photo: John Gollings
Visionary in both design and execution, the project illustrates what can be achieved when possibilities are tested. Photo: John Gollings

Seed House at a glance

Builder

David Campbell Building (DCB)

Architect

James Fitzpatrick, fitzpatrick+partners

Location

Sydney

Materials

  • Timber: XLAM cross-laminated timber panels; Huon Pine (ensuite), Blackwood (kitchen) and Celery Top Pine from Britton Timbers (floor, external walls and internal wall lining)
  • External walls: aluminium sheet cladding, Copper and Zinc Roofing Company
  • Windows: aluminium by Facade Innovations; double-glazed steel frame by L’Officina by Vincenzo
  • External: polished concrete paving, recycled brick paving from The Brick Pit
  • Kitchen: Watermark and Sussex Taps tapware; custom-made stainless steel sink; custom Quasair rangehood
  • Bathroom: Greek Travertine bathtub by Stoneface NZ; custom concrete vanity from Concrete Benches; Sussex Scala tapware and Watermark Designs tapware
  • Lighting: Unios