18th July 2016
2. Duffy/Allpress Residence - Engineering
In this second Duffy/Allpress blog we update progress on-site and broadly cover the engineering team’s solution to building a subterranean basement atop what was once a swamp.
The Duffy/Allpress residence, situated at the acclaimed Millbrook Resort, Queenstown, is a 850m2 (9,200 sqft) luxury home in the early stages of development. The site is located adjacent Millbrook’s Coronet Nine 9th Hole, formerly a vast swamp land which still contains water beneath the surface. The addition of water seepage from a local pond and hill behind the site meant the basements structural design had to be responsive and reliable. Local engineering firm Holmes Consulting came up with the solution.
Holmes design incorporates an extensive waterproofing membrane over a double concrete slab system. Unique to this design, instead of being locked into compacted ground the slab system floats on water, providing neutral support. Around the circumference of the slab are drainage channels which allow the water to freely disperse without causing pressure to the base of the slab. If the pressure wasn’t released the slab would crack and could break apart.
The double concrete slab system is vital. The outer wall contains no waterproofing allowing water to seep into the void area. This void works similar to a drainage ditch catching the water and allowing it to be pumped into the waste water system, reducing the water table around the basement by constant flow. The weight of the double slab is almost equal to the maximum expected water pressure under it, and therefore will not put any significant stress on the slab structure.
Approximately 45,000 litres of water a day is currently pumped from the basement area. The engineers expect a reduction in this flow rate as the water table subsides. Once the basement is complete, and the adjacent pond lined, the flow rate will be significantly less.
The basement slab system has been completed and the precast ground floor installed. The concrete masonry to the residence’s first floor living area is currently being installed by NJ Blocklaying.
The complexity of this home’s design means communication between all contractors is critical. The use of concrete slabs rather than timber framing means electrical and plumbing, for example, have to be well planned and flawlessly executed. In our next blog we’ll discuss the sub-contractors, how Project360 works closely with them, and some of the unique items the client has incorporated into their home’s fit-out.
Duffy/Allpress Residence
Owners: Paul Duffy and Loren Allpress
Architect: Michael Wyatt Architects
Engineer: Holmes Consultants
Builder: Summerhill Construction
Concrete Masonry: NJ Blocklaying
