Non Slab Floors
The New Zealand building industry is transitioning to meet the changing demands of the market and building regulations. An increasing amount of construction is occurring off-site, contributing to a reduction in build time and increasing the quality and efficiency of the finished house. Clients are also demanding their houses to be warmer, drier, and more energy efficient than ever before.
A company is currently building their first house using a cross-laminated timber floor instead of a traditional timber floor with joists and floorboards. Cross-laminated timber panels are engineered to span between walls and support a load, allowing us to eliminate a lot of the structural timber usually required for a floor or roof. This will enable us to save time during the start of the project since the floor will be installed on the bearers in less than half a day. There will be a similar time saving with the roof, making a total time saving of between two and three weeks. There will also be a cost and time saving at the end of the project since there is very little preparation required prior to decorating – the ceiling is delivered prepared ready for sanding. This allows for a reduction in labour costs and the cost of finance during construction.
The design a contemporary New Zealand beach house which will fit well in the local environment. They have also added some extras such as increasing the insulation to 36% above the legal requirement in order to maximise energy efficiency with a minimal increase in building costs. There is a large informal living area with direct access to the west facing deck. We have also incorporated a separate family room, computer nook, scullery, and an entertainer’s kitchen.
We have decided to document the progress of the house on this website using a weblog. We will be regularly updating progress so interested people can follow the construction.
Cross Laminated Timber (CLT) is a proven and fast growing engineered timber panel construction system, well established overseas and now in use in Australia and NZ. CLT can be used for roofs, floors and walls in both residential and commercial construction. CLT is by far the most environmentally sustainable form of building construction available, recyclable and with a negative carbon footprint. CLT is currently being used for building projects up to 3 storeys in NZ and 10 storeys in Australia. CLT has a high strength to weight ratio. Reducing the mass of a building decreases both seismic and gravity loading on foundations. CLT buildings are much faster and safer to erect than steel and concrete alternatives. Factory prefabrication of CLT panels means less of the site is taken up for working space. CLT has proven performance in severe earthquakes and is easy to remediate. CLT has proven performance in fire – the char rate can be accurately calculated. CLT is manufactured in NZ in accordance with the ISO standard to the NZ Ltd Quality Assurance Framework audited bi-annually by NZ Government‐owned inspection company AsureQuality. CLT has been rigorously tested and endorsed by engineering laboratories at the University of Canterbury and SCION. To date, CLT has been accepted by 7 different consenting authorities throughout NZ as an alternative solution under the NZ building code.
What questions do you need to ask your professionals?
What happens if I have got a difficult site to deliver the panels?
Suitable site access is required for delivery by truck, ideally to a point clear of traffic where the truck can be stationed during placement of the panels.
Alternative means of transport are practicable for remote sites with no road access. Panels have been barged to the outer Marlborough Sounds and placed by helicopter on Waiheke Island.
Maximum CLT panel dimensions will generally be within road transport size limits. Limits are prescribed by the NZ Transport Authority. Maximum loaded dimensions for a heavy rigid vehicle are 12.6m long x 2.5m wide x 4.25m high. Unpiloted over-dimension loads up to 3.1m wide are permitted within the parameters set out by the NZTA which prohibit transportation from 7-9am and from 4-6pm. For more information seehttp://www.nzta.govt.nz/resources/factsheets/53/docs/53-overdimension.pdf
Panels may be containerised for long haul transport within NZ and for export (Port Nelson has a direct shipping link with Melbourne). Container volume can be fully utilised by flat-packed CLT panels. Internal dimensions and load capacities of standard dry containers are:
20ft container 6.05m long x 2.44m wide x 2.59 high, 21,640kg
40ft container 12.19m long x 2.44m wide x 2.59m high, 26,500kg
Indicatively, a 20ft container would accommodate all the CLT floor, wall and roof panels for a 100m2 home or apartment.
Loading and Unloading
The supplier should be notified of the panel loading sequence to suit the required order of panel installation. Panels will be labelled at the factory to suit the sequence.
Care is required during unloading operations. If possible, work should be arranged so that panels are lifted into final position directly from the truck.
Are these panels protected?
If on-site storage is required, panels must be evenly supported clear of the ground on timber gluts placed at 2m maximum centres and securely covered from the sun and rain. Any factory applied protective wrappings should be left on until immediately before panel placement.
If exposed to prolonged wetting the timber will absorb moisture and because of its mass the drying process can be slow. Unless requested otherwise by the customer, the panels are supplied with a factory-applied water-repellent sealer to all faces.
The speed of building enclosure with CLT construction will normally limit exposure to rain and sun to a brief period. However the exposed outer layer of boards can be expected to show expansion and contraction before closing in and cladding. The glue line inhibits moisture from penetrating beyond the outer layer. The strength of the CLT is not impaired and the wood will dry and stabilise.
The work sequence should be planned to keep weather exposure of the panels as short as possible. Continuity of work should be maintained until the building is closed in.
Water ponding on floors should be prevented, and should it occur, water should be broomed from the panel surface. Where it is inevitable that floor panels will be exposed to weather for more than 30 days, the floors should be given immediate protection with heavy duty polythene sheet securely taped at the joins.
Architectural Appearance Grade
CLT surfaces which are to remain exposed for clear finishing should be given additional care to avoid visual damage from weather exposure, temporary fixings, staining by metal fixings etc.