V Joint Shiplap

V Joint Shiplap

Radial Timber Sales V joint Shiplap provides a stylish and strong alternative to traditional softwood or manufactured cladding systems. The shiplap cladding is profiled from durable silvertop ash hardwood boards that overlap to produce a continuous vertical or horizontal cladding system.

Shiplap cladding has been used as a feature on houses, commercial projects, apartments, high end fence finishes, visitor centers, lifesaving clubs, holiday homes & sheds. For images of Shiplap cladding visit: http://radialtimbers.com.au/gallery/shiplap/

Available Species

V Joint Shiplap is available in the following species:

Other Products



Shiplap cladding boards are generally sawn from naturally durable regrowth hardwoods such as Silvertop (Eucalyptus Sieberi), or sometimes Yellow Stringybark (Eucalyptus Muellerana) both of which are Class 2 durability.

NOTE: Silvertop is one of the approved species for use in “high fire danger” areas by Building Control Comm. Practice Note No. 46 (Dec. 2001) and AS3959 – Construction of buildings in bushfire-prone areas and has a BAL 29 exposure rating. Yellow Stringy Bark has a Bal 19 exposure rating

Grade & Moisture Content

All timber is supplied as standard and better grade (not select) and dried to maximum moisture content of 14%. Small tight knots, gum veins, splits, ambrosia and other marks are acceptable features that sometimes occur in boards. Timber is graded in accordance with the Australia Standard AS 2796.2-2006 Timber Hardwood Sawn and Milled Products/ Part 2 grade description. Also see examples of board colour and feature variations on our website

The moisture content of the timber depends on the relative humidity of the air and also its temperature, which is influenced by the colour of the surface coating. Dark coloured surface coatings absorb more solar energy, resulting in higher temperatures and lower moisture content. If the moisture contents are too low at the time of installation, problems can occur with rebated board profiles if sufficient expansion gaps are not left between the boards (see below for recommended spacing’s between the boards).


The natural durability rating of a timber species is a rating of the timber’s natural resistance to attack by wood destroying fungi and wood destroying insects. The natural durability rating applies only to the heartwood of a timber species and the Silvertop has a rating of Class 2 with approx above ground durability of 25 year plus.

Sketch / Sections

Virtual samples and auto cad files of profiles are available on the Radial website http://radialtimbers.com.au/products/v-joint-shiplap/

V Joint Shiplap boards in cross section

Show more.


Radial shiplap cladding is supplied in dressed 19mm thick boards with “V” shaped tongue and rebate joints (see Figure 1 above). Radial sawn shiplap boards overlap and have an effective cover approx., 90mm or 110mm.

Lengths and Availability

Boards are supplied in random lengths of between 1.2 and 5.4m but some shorter lengths may also be included (av. lengths approx. 3.6-4.0m. Set length boards may be available in limited quantities as a special request (a 30% surcharge is applicable to all set length orders and longer lead times apply).

Engineered Set Lengths (ESL)

Engineered Set Lengths (professionally finger jointed) boards are available in a special 85mm and 110mm cover and are mechanically glued joined boards produced to nominated set lengths. Special length ESL orders will only be available as supply allows, and availability should be checked at least 4-6 weeks prior to ordering. Shiplap boards can also be engineered up to 6.0 metres. With the correct handling these joins are guaranteed for external use and are much more water tight than butt or splayed joins and mechanically strong enough to span in between studs.


Timber Oiling or Staining

Timber oiling, coatings or staining will not stop the weathering process, but will slow it down and acts as a sealer and assists in slowing down moisture loss or gain. Differential weathering between protected and exposed areas can produce colour variations. This can result in marked variations in appearance.

There are a variety of timber treatments, stains and coatings available and most should be applied prior to fixing. Care must be taken to well coat any end grain to minimise water absorption or loss. We don’t recommend a film coating as this will generally not be breathable and will eventually peel and bubble due to UV and will trap in moisture.

When a true un-pigmented clear timber sealer is required and the owner is okay with allowing the timber to grey off naturally, Radial Timber recommends the application of an oil based sealer or quality penetrating timber finish, this will assist greatly in nourishing the timber during its early life on the structure. (http://preschem.com/architects-products/radial-timber-sealer.html)

Preventative Care To End Grains

All end joints of boards and end grain must be sealed to prevent moisture entry as the end grain is far more absorbent than the face grain. The end grain must be well sealed to prevent rapid moisture uptake and drying out which can cause splitting and movement of the boards. Critical end grain locations are at mitred corners (not recommended for exposed locations) or splayed joints and the top and bottom of vertical boards.  Horizontally butted boards into corner stops are also an area that needs special attention.

Where sealants are used with the timber cladding, they must be accessible for regular inspection because their durability is less than the cladding. Unnoticed leaks from sealant failure could result in hidden damage to the structure.

Finishing Points To Consider

Some of the points to consider about the coating selection and durability are: 1) Lighter coloured paint finishes generally last better, 2) Narrower boards reduce the amount of stress placed on the coating system, 3) Coatings on timber exposed to the north and west will deteriorate more rapidly than on south facing surfaces or in shaded areas, 4) Timber must be sufficiently dry when coated, 5) Timber partially sheltered by overhanging eaves will weather at a different rate to more exposed timber.

Recommended Cleaning

Iron stain, is an unsightly blue–black or grey discoloration and can occur on nearly all woods. The discoloration is caused by a chemical reaction between extractives in the wood and iron in steel products, such as nails, screws, and other fasteners and appendages. This often occurs the first morning after rain or dew, when water enables the extractives and iron to meet and react.

Problems have been associated with traces of iron left on wood from cutting or slicing; cleaning the surface with steel wool, wire brushes. Iron dust from metalworking and even plant fertilizers can be sources of iron. To clean off the majority of all staining it’s best to clean all boards down with a 5% solution of oxalic acid after installation to obtain a clear timber surface (Radial Timber can supply oxalic acid).



The long term performance of cladding is dependent on regular and effective maintenance. The frequency of maintenance will depend on the type of finish and the degree of exposure to the weather. Recoating and any further preparations should be carried out in accordance with the finish manufacturer’s specifications.

Seasoning & Weathering

Some minor surface checking may occur  when the  timber is exposed to the weather but these non-structural cracks are typical in most Australian hardwoods (NOTE: unprotected west facing walls may be subject to extreme temperature changes and therefore, timber is more likely to check or move. On these walls is best not to have any horizontal or vertical joins on the random length boards).

All exposed, externally fixed cladding will tend to fade to a silver grey colour if left uncoated. The degree of greying will vary depending on the amount of exposure to sun, wind and rain. The timber used in this above ground product has natural durability and when used in conjunction with good building practices, should generally not require additional treatment against decay.

Timber Leaching

It is also normal for hardwoods to leach red/brown extractives (tannins) during heavy rain periods. Extractives tend to be less prominent in lighter species but it is advisable to cover or protect walls and paving until all extractives have leached (can vary depending on rainfall but will generally continue for up to 6 months).The tannin staining can be cleaned with a diluted bleach/water mix.

Storage & Installation of Radial V-Joint Shiplap


Packs should be stored up off the ground on bearers and under cover or protected with an additional tarp to prevent swelling or water staining. When the cladding is delivered wrapped in plastic, it is important to check that the wrapping is not damaged and likely to allow water to be trapped within the stack. If wetting does occur, separate the timber with strips between each layer. Place in a well ventilated area under cover and allow a minimum of 48 hours for timber to dry before fixing. Radial Timber will not be held responsible for incorrect storing or drying of the timber.

Setting Up

Shiplap cladding is typically installed in a regular pattern with the tongues and rebates of adjacent boards fitted together (see Figure1). Seasoned Shiplap boards will exhibit minimal shrinkage and will actually swell slightly in wetter regions or exposed areas (especially the west side of a building) making it essential to ensure boards have an approved gap to allow for this movement. Noggings, fixing battens or studs should be spaced at max. 600mm centres. If shiplap is run vertically a fixing batten may make installation easier.

Try to have the tongues of the shiplap facing into the direction of the prevailing winds as this will minimise moisture pressure being swept sideways during high winds into the rebated board.

Installation & Layout

Preferably layout of the boards should be in a vertical position for better water runoff especially in very exposed locations such as near the coast. Boards can be fixed directly to breathable moisture vapour barrier clad walls however a better option is to use fixing battens on the studs. Use 75×35 treated pine batten fixed directly to the moisture vapour barrier clad stud walls, this also allows for good ventilation between the back of the boards and the moisture vapour barrier. It is also advisable to use a plastic horseshoe packing shim under the batten to alleviate build up between moisture vapour barrier and timber cladding (refer to technical drawings on our shiplap page on the website). Allowances must be made for the extra width cavity wall when it comes to windows, doorways etc.

If fixed horizontally, the tongues of each Shiplap board should face up to prevent water from being trapped inside joints. Try to have the tongues of the shiplap also facing into the direction of the prevailing weather as this will minimise moisture pressure being swept sideways during high winds into the rebated board. On long runs, walls can be butt or splayed joined over battens or broken up into smaller panels by inserting a flashing or vertical/horizontal timber stops between each panel. Special Aluminium or timber profiles can also be used on external and internal corners some of which are available from radial timber

Board Spacing’s & Weatherproofing

Boards must be installed with a 5mm gap (see Figure 2) on the front of the board for the 90mm &110mm cover. Radial Timber Sales will provide 5mm spacers in the packs for this to help with installation.

Boards exposed to the sun and rain (north – northwest elevation) will shrink and swell more than semi protected boards. Recommended expansion gaps are critical on these exposed elevations as is eliminating any butt joins (engineered set lengths might be a better option) and where possible provide some weather protection with eaves, veranda, or similar.

Do not allow rain or water to get behind boards during installation and always protect the exposed end grains of the timber during rainy weather. It’s important that all flashing around windows or other openings are adequately installed (refer to diagrams on our website) to allow for proper drainage away from the timber.

If the shiplap is run vertically at the bottom of the boards make sure the boards are undercut to form a drip edge or a suitable angled flashing is installed. Care and attention should also be taken to avoid pooling of water when fixing other structures such as pergolas to the cladding as well.

Fixing Recommendations

Boards should be fixed with 50mm long  10 gauge (4.8mm diameter) stainless steel (304, A2 or 316 grade) screws as these don’t degrade like other metals but care should be taken close to ends to avoid splitting. (Radial Timber can supply the self-drilling, self-countersinking stainless steel screws fixings). The recommended fixing rate for 90mm or 110mm boards is two face fixed screws per board per stud/batten.

Shiplap boards in cross section with spacing

90x20 Shiplap
V Join 90×20
Complete Details Secret Fixed Shiplap
Green Board 50mm
Radial Shiplap Complete Fixing Details
Green Board 50mm
Typical Radial Shiplap Details
Green Board 50mm
Shiplap Noggin Fixing Details
Green Board 50mm
Batten Fixing Details
Green Board 50mm
External Corner Details
Green Board 50mm
Internal Corner Details
Green Board 50mm
Window (Noggin Fixing) Flashing Details
Green Board 50mm
Window (Batten Fixing) Flashing Details
Green Board 50mm
Wall Pitch Roof Flashing Details
Green Board 50mm
Wall Skillion Roof Flashing Details

V Joint Shiplap SampleV Joint Shiplap SampleV Joint Shiplap Sample

Timber Finishes

Radial Timber Sealer

We recommend our product to be coated with at least an oil based sealer such as Radial Timber Sealer or decking finish on external timber. Radial Timber Sealer is required to repel and control moisture, hence minimises splitting, cracking and checking that can occur. It still allows the timber to grey off naturally while leaving it look and feel like timber. It can be applied to hardwoods used for external cladding, window frames, fences, trellis, decking and pergolas.

Radial Timber now has the option to have your timber pre treated with our Radial Timber Sealer, please enquirer about having your timber oiled when you get in contact with us.

Visit the Radial Timber Sealer page on Preschem website for more information about the product.

Radial Timber Calculator
_   X
Select Product:
Width of the deck
Length of the deck
Joist spacing on centre in millimetres (eg. 450)
Coverage of deck board in millimetres (eg. 75)
Gap between deck boards in millimetres (eg. 5)
Screws per intersection of joist & deck board (eg. 2)
Wastage Allowance
L of Aussie Clear
Please note that this tool is to be used as a guide only.
Outlast Timber takes no responsibility for the incorrect usage of this tool and advise that customers ensure that the quantities calculated are correct.
Deck and Screw Calculator Help