Floors, wall cladding, roofing & joinery

We look at options for floors, walls, roofing and joinery with an emphasis on ensuring your home stays weathertight.

Types of floor

The type of floor put into a house depends on the design and construction methods. The common types are:

• Concrete pad.
• Wooden – either suspended timber strip-lined floors or pressed composite materials.

The advantage of a house built with a concrete pad is that the concrete floor can act as a thermal heat storage mass which, if used in conjunction with insulation in the walls and ceilings, keeps that stored heat inside.

In all cases the floor should be insulated.

Timber framework

Your designer and builder should know the current timber treatment requirements for the various areas in a house. But if you are doing some alterations and purchasing the timber yourself, make sure you buy the timber treated to the right standard for the situation. For example, framing for enclosed decks and balconies requires a higher treatment level than other wall framing.

You can find out about timber durability requirements in Paragraph 3.2 ‘Timber’ of Acceptable Solution B2/AS1, supporting Clause B2 ‘Durability’ of the Building Code. This Acceptable Solution requires designers and builders to follow the requirements in NZS 3602:2003 Timber and Wood-based Products for use in buildings.

NZS 3602 requires treatment and identification of timber to be in accordance with a further New Zealand Standard - NZS 3640:2003 Chemical Preservation of Round and Sawn Timber. This Standard clarifies the identification system of the types of timber treatment by use of colour, branding and/or chemical testing.

These standards can be purchased from Standards New Zealand, call 0800 782 632 or go to www.standards.co.nz.

See also Timber Treatment Requirements - Notes for Builders which you can view on Department of Building and Housing website.

Cladding for exterior walls 

Common options for exterior cladding include:

• Brick or masonry veneer – it may have a higher initial cost but the advantage is that it requires virtually no maintenance.
• Autoclaved aerated concrete which has good insulation properties and comes in blocks, reinforced panels, and lintels. Note: not all products are accepted by some BCAs - check before specifying.
• Weatherboards which can be made of timber or from composite materials. Some do not need painting. They have very good weathertightness properties. Depending on the weather tightness risk score a cavity may be required behind the weatherboard.
• Monolithic systems - for example, textured wall surfaces made out of plaster, polystyrene or fibre cement sheet - are promoted as providing a sealed and waterproof outer skin but must be installed strictly to manufacturer's instructions. The waterproof coating must be carefully maintained to ensure watertightness, and will require a cavity in most applications.
• Aluminium, for example, extruded aluminium weatherboard.
• Profiled metal. This requires careful detailing and workmanship.
• Plywood sheet.
• Concrete masonry blocks - they don't rot, can provide good heat storage, but they need to be installed correctly. Note: in some areas additional thermal insulation may be needed. All single skin masonry will require the application of a waterproof coating.

Installing claddings for weathertightness

Whichever cladding you choose, it is only going to be effective in doing its job, which is to keep water out of your home, if it is appropriate for the situation and used correctly. Your designer will be able to give you advice on the best claddings to use in your situation. This decision will depend on many factors but the Acceptable Solution for weathertightness limits the use of some claddings in some circumstances. It also specifies the use of a drainage cavity where the risk score for a building reaches certain limits. Manufacturers also place limits on where and how their materials should be used.

Problems occur when claddings are used outside their specifications or have been installed incorrectly. For information about how to use materials to ensure your home is weathertight see Leaky buildings.

Try to limit the range of different claddings used on one particular building, so reducing the number of unnecessary cladding joints. Joints in cladding systems are its weakest part – increasing the risk of leaking.

Roofing and roofing design

Common types of roofing include:

• Metal which comes in a variety of shapes, some already finished. Each profile will have specified minimum slopes that it can be used for.
• Tiles which can be made out of concrete, pressed steel, clay or wood.
• Synthetic rubber roofing membrane, which must be laid to fall to ensure water will run towards a gutter or drain.

Complicated roof designs, i.e. those with many roof planes at different pitches and levels, require special care when being built. All the junctions need to be properly flashed, and, as flashings don’t tend to last as long as the roof, they will require more maintenance during the life of the roof. This may not be easy or cheap.

Anything that penetrates the roof, such as pipes or flues, need special care to ensure weathertightness.

There are other technical considerations, for example, allowing for heat expansion and contraction, and making sure the pitch meets the various metal roofing profiles in the Acceptable Solutions to the Building Code. You should be able to rely on your architect or designer to advise you – choose your designer carefully.

To keep maintenance of the roof to a minimum:

• Have a simple roof shape.
• Have as few penetrations as possible.
• Make sure there is enough pitch to allow water to drain and not pool.
• Check it annually, clearing out downpipes and gutters, and making repairs where necessary.

Joinery

When selecting joinery, consider the architectural style of your home, and choose the joinery to complement, or modernise the look. The most common options for joinery around windows and doors include:

• Aluminium – this is commonly used in New Zealand but has some disadvantages. Low cost sections are thermally inefficient and often result in condensation forming on the frame as well as the glass. Double glazed options are available. There should be vents in the framing to allow for drainage and ventilation.
• Wood – less common these days because of the cost and the need for regular maintenance.
• PVC - this is commonly used overseas but is relatively new to New Zealand. Imported sections may suffer under the effects of New Zealand's strong ultra-violet radiation.