Timber Wall Cladding SystemsTimber Wall Cladding SystemsIn Residential BuildingsIn Residential Buildings

Timber Cladding Systems allow

• Design freedom – not regimented – almost anything goes!

- Traditional styles- Modern styles, and- Unique personal styles

• Ease of handling – light and user friendly• Large range of finishes, plus• The natural beauty of timber!

Other Benefits

• Timber claddings have built in flexibility – helps to resist the stress and strains of foundation movements due to reactive soils and mine subsidence, wind storms and earthquakes!

• Can be designed with excellent thermal properties

• Have natural sound damping properties

Cladding Selection

Today’s designers can choose from a wide variety of timber cladding products. When choosing the type to use, there are a number of points which must be considered:

• The appearance required by architectural style

• Availability and cost

• Ease of installation and maintenance

Cladding Selection (Cont.)

• Prevailing climate and thermal performance required for a building, including buildings in a

bush-fire prone area

• The importance of additional strength given to the structure by some types of cladding

• Local government regulations or statutory requirements

Timber in Bush Setting

Looks Great!

• Structural – i.e. designed to carry loads e.g. bracing, as required by the BCA– e.g. structural plywood

• or solely as decorative - not carrying loads

Timber claddings have the option of being:

Sarking• Sarking is a waterproof material

that is fixed to the studs directly behind external cladding

• The primary function of sarking in walls, is to direct any water that may have penetrated the cladding back to the outside of the structure

• It also provides a draught proof barrier to keep wind driven rain or dust out of the wall cavity

• Wall sarking is fixed on the outside of the studs, from the top plate down and over the bottom plate and flashing, and/or in accordance with the manufacturers instructions

• Only vapour permeable, fire-retardant, building paper should be used as sarking behind timber cladding – don’t use aluminium foil type sarking - as trapped vapour may wet the back of the cladding and then cup and distort the cladding

Sarking (Cont.)

Vapour barriers

The need for a separate vapour barrier depends on the:– type of construction,– the intended use of the

building– and the climate at its location.

Note: Install vapour barrier Note: Install vapour barrier on warm side of all insulationon warm side of all insulation

Vapour barriers (Cont.)

Note: When large temperature differences exist between indoor and outdoor environments there is potential for condensation of water vapour within a frame

Showers, baths, dish-washers, clothes-washers, driers, cooking, indoor plants - and even people - generate large amounts of water vapour within a building

Vapour barriers (Cont.)

Some of this vapour will move outward through plaster, wood and other permeable materials until it either:

• disperses into the atmosphere (this could be the wall cavity)

• reaches an impermeable barrier • or meets a surface cold enough for it to

condense into liquid

Flashing

• Flashing over wall openings, at corners and vertical joints is essential water proofing

• Ensure flashing is fixed at least 25 mm under the sarking/cladding

• Over openings flash over the ends and the framing of the opening

Flashing (Cont.)

Moisture Content• All kinds of timber will take up or lose moisture,

and adjust dimensionally, in keeping with changes in the local humidity

• The actual timber equilibrium moisture content (EMC) will vary from place to place and from season to season, so that timber in service may have a moisture content ranging from about 6% to 18%

• Timber cladding will usually be supplied as “dry”, “kiln dried” or “seasoned” and will have a moisture content in the range 10-15%

Moisture Content (Cont.)

• Chamferboard and ship-lap cladding profiles will usually be supplied as seasoned

• However, cypress and hardwood weatherboard profiles, as well as some western red cedar profiles may be supplied unseasoned

• Unseasoned boards wider than 200 mm should not be used

Moisture Content (Cont.)

• Wider unseasoned boards may develop slight cupping across the face unless restrained

• Unseasoned hardwood boards should be fixed as soon as possible after delivery to reduce the risk of cupping or splitting

• As unseasoned cladding will shrink as it dries, an allowance must be made for shrinkage by increasing the overlap of boards (see AS2796 for details)

Moisture Content (Cont.)• When machined profiles are produced from

seasoned timber the design of the edge-joint will allow for movement due to seasonal changes in equilibrium moisture content

• Other than exercising proper care and good workmanship during installation, no special precautions need be taken to compensate for light expansion and contraction in service

Moisture Content (Cont.)

• When fixing, it is important that nails are placed so that movement of boards caused by changes to equilibrium moisture content during different seasons (or the drying of unseasoned boards after installation) does not create stresses sufficient to cause splitting of the timber

• Individual boards must not be nailed together at the lap

Storage & Handling• It is important to keep cladding clean and dry -

dirt marks and stains can’t be hidden by stain finishes, + any wetting may cause problems with movement at a later stage

• Make sure cladding is kept covered, stacked level, well clear of the ground, and that stacks are evenly supported at 450 mm intervals to prevent bowing and sagging

• Some cladding e.g. western red cedar, is relatively soft and require care in handling to prevent minor denting

Pre-Finishing

• Depending on the final appearance required, a priming coat of either water repellent, stain or paint should be applied to all surfaces before fixing

• It is also advisable to apply an undercoat colour matched to the final coat so that movement lines will not be apparent after any shrinkage or movement

Solid Timber Cladding

• Sawn timber weatherboards are available in a wide range of species, sizes and profiles

• Fixing can be horizontal, vertical or diagonal with a large variety of profiles and widths

Species Range & Profiles

• Hardwood• Cypress pine• Preservative treated

pine• Imported timbers• Numerous profiles!

Stained or painted

Installing Horizontal Cladding

• First - choose a method of joining the timber at internal and external corners.

• Usually it is timber stops - external corners boards can either be cut in neatly to a stop or left to run through - then cut off to a straight edge later - then fit the stop.

• Or cladding can be mitred at external corners and scribed at internal corners - time consuming method and requires precision

• Where cladding abuts masonry - leave clearance to prevent moisture from masonry entering the boards – or seal cladding ends and protect joint with a cover strip set in mastic

Installation Details

• Select the first board to be fixed

• If using weatherboards, undercut the bottom edge to an angle of about 15 degrees so that water will be shed readily.

• The first board should be laid to a string line, mark out the width of one board on both corners of the wall to be clad - partly drive a nail at these points and run a string line between them

• Partly drive nails into every third or fourth stud along the string line - remove the string line - the first board is placed against this line of nails and fixed

Installation Details (Cont.)

Installation Details (Cont.)

• Chamferboard and ship-lap profiles are laid similarly with the tongue facing upwards - rebate or tongue & groove are brought tight together using a chisel as a lever

• Weatherboards will require a full-length packing piece under the first board and as necessary over openings

Installation Details (Cont.)• Weatherboards are fixed with only one

nail per stud. This nail should be driven as closely as possible to the butt of the board but it must miss the thin end of the board underneath

• Lap hardwood and treated pine boards 30 mm and nail them 35 mm from the butt

• Lap western red cedar boards 20 mm and nail 25 mm from the butt - a gauge block can be used to keep the boards at the same spacing.

• Apply a primer to all freshly cut ends and seal all joints, including the stopped ends, with a paint/stain compatible mastic or silicon sealant

• Place the mastic on the ends of the boards before fixing them

• Nails should be driven with care - heavy and excessive nailing distorts the wood and may cause splitting during weather changes

• Some cladding boards may require pre-drilling of the nail holes at the ends to avoid splitting.

Installation Details (Cont.)

• Joints are placed over studs

• Tight fitting joints are achieved by cutting a board slightly over-length, bowing it to get it into position and then snapping it into place.

Installation Details (Cont.)

• Progressively, take measurements at the ends of walls, beside openings and at 1800 mm centres along the wall to ensure the cladding is still runs parallel - very important either side of openings if the cladding continues above the opening

• If necessary to correct this – it is best to catch up over a number of boards if the difference in parallel is great

• Cladding around window and doorframes need not be stopped if the butt jointing is neat

• When fixing cladding on the next wall around a corner, make sure the boards are in the same line

Installation Details (Cont.)

Fasteners• Hot dipped galvanised or other non-corrosive nails

(of suitable shank size and length) should always be used to fasten timber cladding

• Plain steel nails should not be used - as rust makes unsightly stains + causes gradual deterioration of timber around the nail

• Flat head nails are recommended to provide additional restraint for treated pine and Western Red Cedar cladding

• Silicon bronze nails (although expensive) produce a superior appearance when Western Red Cedar is coated with a natural or stain finish

• When fixing weatherboard profiles ensure nails are placed so movement of boards caused by wetting and drying do not create stresses sufficient to cause splitting of the timber

• Thus one fixing per stud is best - ensure individual boards are not nailed together

• Edge-joint design in seasoned cladding profiles usually allows for minor seasonal movement thus two nails per stud may be used

• Spacing of supports (studs) should not be more than 650 mm centres measured along the board

Fasteners (Cont.)

Finishing• After fixing, one or two

finishing coats of stain or paint should be applied - where cladding is to be painted, nail holes may be punched and filled prior to application of the finishing coats.

• Filling of nail holes in cladding that is to be stained is not recommended.

Plywood CladdingApart from the style and warmth of timber structural plywood has:

• Cross laminated strength – resists impact and edge damage

• Choice of face veneer to suit application

• Durable glue bond

• Can be bent to suit curved finishes

• Good acoustic properties

• Efficient thermal performance

• Guaranteed quality and safety

Other practical advantages of structural plywood cladding are:

A Lightweight Insulated System

• Most structural plywood claddings have machined faces

• Either vertically grooved or flat face

• Provides structural bracing to building

Stained or painted

Installation of Plywood Cladding

Butt Corner Detail

Corner Board Detail

Batten Corner Detail

Vertical Joint Alternatives

Horizontal Panel Joints

Modern - Stylish

Hardboard Cladding• Reconstituted, natural hardwood

• Environmentally friendly - only sustainable new growth hardwood used

• Contains no knots, gum veins, cracks or splits

• 25 year guarantee not to rot, split or crack

• Hidden joining system suitable for on and off stud joining

• No scarf joining

• Limitless cladding and lining design solutions

Panel Sizes

• 3660 x 1196mm• 3050 x 1196mm• 2745 x 1196mm• 2440 x 1196mm• Thickness: 9.5mm• Available in smooth of rough sawn

Traditional

Interesting

Modern

Timber Shingles

• Shingles (taper sawn) or shakes (split along natural grain) provide individual and striking style

• Common in USA & Europe

OR

Hardboard Shingles

Timber cladding apart from being a natural product is extremely versatile!

Interesting

Yet very practical

Acknowledgement

This educational resource has been prepared as part of the Forest & Wood Products Australia

Technical Resources Program – Supporting Timber Education & Training

Prepared by: James MacGregor Consulting