Southwest TAS 7139
Australia
Overview
Lake Tahune in the Franklin-Lower Gordon Wild Rivers National Park is one of the most spectacular locations one might spend a night. A new unserviced hut was required to safely accommodate bushwalkers below the summit of Frenchmans Cap.
The complex brief incorporates protection from wild weather and bushfire, minimal impact on the sensitive local landscape, a robust interior to endure high levels of public use, prevention of condensation, a healthy indoor climate, and longevity.
The construction crew only had a narrow summer weather window in the brunt of the Roaring 40s, with some of the most challenging alpine weather, at 980m above sea level and a two day hike to the nearest road. Hyper-insulated timber SIPs were prefabricated in the workshop in northern Tasmania, trucked to the South West
World Heritage Area and heli-lifted into the site.
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Structure
Sustainability
The new Lake Tahune Hut is built on the footprint of a dilapidated, uninsulated, condensation-ridden previous hut, which was heated with fossil fuels. It could no longer accommodate the growing number of visitors seeking shelter here. The new hut sets a new benchmark in sustainable design. The climate zone 8 site with frequent snow falls prompted an unusually high demand for insulation (R5.5-7.5), with triple glazed argon filled windows, and special attention paid to the avoidance of all cold bridges in the building envelope.
High internal heat gains combine with passive solar gains (large north-facing windows) to cover most of the hut’s heating requirements. In the coldest periods the hut is heated by a 0.7kW heater running off micro hydro power from a nearby creek. Condensation is prevented by the permeability of external surfaces and a small heat exchanger, which expels humidity but retains heat.
In order to minimise impact on the site, the footprint is simplified, while still accommodating up to twenty-six bushwalkers comfortably in two rooms on approx. 60m². The compact floor plan enables the most efficient use of materials. A system of filters ensures only clean greywater is returned to the sensitive karst landscape.
Off-site prefabrication reduced the erection time on site, and enabled zero on site wastage, a problem in the
inaccessible World Heritage Area. Lifting panels into their final position by helicopter preserved the tight building area between Myrtle trees. No vegetation was removed for lay-down.
Structural insulated panels
The eSIP panels that have been manufactured for the Lake Tahune hut by Valley Workshop and Warren French Architect were engineered from first principals. The premise of the development of the panels has been to build a hyper-insulated, strong timber panel free of petrochemicals. Timber is a renewable resource, it's low in embodied energy and sourced locally in Tasmania, not imported. 90% of the panel is plywood. The manufacturing of plywood makes use of smaller diameter logs that can be problematic in the forestry industry. Through the supply chain the product is support sustainably managed forestry practices in Tasmania. The structural insulated panels being light weight and hyper insulated with earth wool insulation batts, were the ideal solution for the challenges that the alpine site at Lake Tahune presented. The plywood used on the outer of the eSIP was the same product used for the internal wall linings.
Australian Certified Timber
EWPAA certified plywood, AFS/FSC certified pine framing and blackbutt decking was used in the project. Locally grown Tasmanian timber was used for structural members, plywood cladding and plywood and solid Tasmainan oak joinery. As there is no Tasmanian timber available which is both durable in wet conditions and complying with Bushfire Attack Level 29, Victorian Blackbutt was uses for exterior cover boards and decks.
No imported timber was used. 90% of the floor and roof panels are made of Tasmanian hardwood ply. The ply we use is certified EWPAA with an A bond glue and a formaldehyde rating of Super E0, which is low VOC or low emissions.
Tasmanian hardwood structural ply (Tply) makes up for 90% of the roof and floor panels. The company that supplies us with the ply is committed to sustainable development including only sourcing logs from forests that are independently certified. Ta Ann Tasmania does not harvest forests. It purchases its wood supply from Forestry Tasmania under long-term Wood Supply Agreements which have allowed us to gain Chain of Custody certification for our Tasmanian eucalypt veneer under the Australian Forestry Standard and the Program for the Endorsement of Forest Certification schemes (PEFC).
Interior
Floor System
Occupants of the hut leave their (frequently wet) boots and coats in the foyer, which has a drying facility. Popular in Tasmania, and a traditional hut flooring, Tas oak is a warm surface to feel underfoot. The timber theme is continued to the outside of the hut, where a large deck offers space for relaxation after the strenuous hike, opens to valley views and facilitates social interactions.
The tactile surface facilitates an emotional experience of warmth and protection from the elements. A sense of arrival is achieved at the door step – a destination at the end of an immersive, physically demanding and visually elating walk. The floor may not only be experienced by tired bare feet, but some walkers may make themselves comfortable on the floor when the hut is fully occupied. The hut is a home for the night and offers encounters with likeminded people.
The floor system is a Tasmanian Hardwood ply and solid timber grillage to which is applied a Tasmanian hardwood ply structural stressed skin. R5 insulation is enclosed within the plywood skin. The floor covering is Tasmanian Oak (Obliqua).
Interior Panels
All wall and ceiling cladding is 12mm Tasmanian Oak plywood, in 1200mm x 2400mm standard size. There is a 8mm shadow gap where sheets join. The skins of the structural insulated panels are also 12mm and 17mm Tas Oak plywood. The same material is used for the internal cladding as for the structural skin of the ply SIP.
In the harsh Southwestern Tasmanian Climate, a mountain hut needs to not only provide physical refuge, but also an emotional sense of warmth and protection. The timber interior is a modern interpretation of traditional Tasmanian bush hut finishes (originally trees of the immediate location, split on site). The light tactile wall surfaces, together with the quotes engraved in some panels, give the space an uplifting and poetic note, which enhances the experience of the walk, and the sense of arrival. Users have commented that from the beginning, this hut has had 'soul'.
The structural insulated panels (SIPs) are a structural member built offsite in the northern Tasmanian workshop. They are considered to be award winning for the following reasons:
Innovation: the SIPs are engineered from first principals. Invented by architect, engineer and builder.
Structural performance: the spans of the ply sips are award winning. Their capacity to span is double what a conventional bearer/joist system offers. The offers the opportunity to reduce the amount of footings, thus reducing the amount of high embodied energy concrete being used.
Reduced time onsite: large prefabricated members going together onsite thus reducing time onsite. Time taken on the Lake Tahune job to place the 2.4m wide x 8m long (45m2) floor system was just 4 hours including helicopter mobilisation. A similar time was quantified for the roof panels.
Onsite wastage: there was no onsite wastage for the subfloor for the hut, or roof structure for the hut. When working in a sensitive World Heritage listed area, this is important
R Values: the R values for the SIPs are double the R values when compared to a conventional system. The R values can be viewed on the PDF for 'Energy Efficiency'. There is very little thermal leakage as insulation is sandwiched between the ply skin. At the end of its service life, the hut can be disassembled with simple tools, and the plywood panels, like most other elements, reused.
Roof System
The roof system is a Tasmanian hardwood ply and solid timber grillage to which is applied a Tasmanian hardwood ply structural skin. R7 insulation is enclosed within the plywood skin.
