Horizontal Cladding

Vertical Cladding

Principles Of Exterior Cladding

Unless your architect, design professional or building Inspector has detailed otherwise and assuming that you have already chosen your timber cladding there are some basic design rules that need to be considered.

A. Think of your claddings function as that of a roof in that it keeps the elements off the interior of the structure, all detailing should shed water away from the building.

B. Airflow between the structural part of the building and the reverse of the cladding is critical to prevent trapped moisture. Although timber is a good insulator, cladding should not be fitted tight and sealed.

Typical Section Showing Fitting Of Horizontal Cladding

Softwood Battens 25 x 50 – Time and thought should be taken fitting battens to ensure they produce a level and flat surface for the cladding.
Batten spacing (unless specified by your architect or other professional) should be fitted at 400 mm centres and meet BS 5534 with a section of 25 mm x 50 mm.
For simple rectangular elevations a vertical batten providing air flow will be sufficient but on triangular elevations counter battening may be necessary for fixing at the perimeter.
Where possible try to start the cladding a minimum of 250 mm from the finished ground level. The area below this is considered a ‘Splash Zone’ where timber will weather quicker due to rain splashing back on to the wall. At this point consideration should be given to how the cladding will look once fitted. i.e.  The top of your doors and windows should be level, so use this as a datum to work from. The Red Grandis Channel covers 100 mm with the Cedar covering 130 mm. Measure down multiples of board cover to find a starting point. Check the margins (what you can see of the window) are acceptable/ equal and any opening or moving component will work with the trim fitted.

Stainless Steel Insect Mesh – Insect mesh prevents vermin and insects entering the void behind the cladding. There are many examples of insect mesh diagrams available on the internet. These all show straight sharp right angles fitted between the battens and the cladding. Whilst, as a detail, these look great in practise, these sharp corners and straight lines are hard to achieve. Our experience is to bend the mesh in half, fit it between the battens and force the corners in tight with an off cut of batten. The lower insect mesh should be fitted with the bend up and the upper insect mesh fitted with the bend facing down. With the insect mesh slightly proud of the face of the batten this can be compressed easily once the cladding is fitted. We do not put relief grooves in the back of our cladding as this makes the continuity of seal impossible.

Corner Post – Our corner post has a unique tongue and groove within the mitre. This feature allows both sides of the corner to be full width. This has the added benefit of being able to use different species if desired to match the elevation. Where oversize lengths are required, joints can be staggered to improve strength and continuity.
The T&G is the same size as the cladding so gluing is not strictly necessary but in some situations may prove beneficial for handling etc. Class D4 Polyurethane adhesive should be used and cleaned off when set.

Oil Finish – If you have made the decision to oil your cladding now is the time. Apply as per manufacturers’ recommendations using the specialised oil brushes.
Two sizes are available a 50 mm for smaller areas and a 150 mm for larger surfaces. The 150 mm brush is ideal for cladding faces as you are able to oil the entire face in one pass.
The entire board must be coated paying particular attention to the tongues and grooves and back as once fitted these will not be accessible. Finish brushing the face making sure you have no finger prints, brush marks etc.

Fit Corner Posts – Once oiled, start by fitting the  corner posts. This will set the starting point from the bottom and give a fixed edge to work from. You can fix through the face or secret fix by screwing the fixing through the edge although our fixings do not need a pilot/ clearance hole, in practice when fitting through the edge the use of a bradawl is ideal as its placement is more constant than a drill.

Fit Door/Window Trim– The door/window trim can fit flush or protrude from the face of the finished cladding. Treat the door/window trim as mini door linings. The head of the lining should go full width and be on the same angle as the sill. This will enable water to drain from the top of the cladding and create a drip at the lowest side on the front. Cut vertical jamb lining to length utilising the same angle as the sill, there should be a gap of at least 6 mm between the end of the door/window trim and the sill. This will reduce capillary action.
Seal perimeter of window using frame sealant, fit EPDM by removing self-adhesive backing tape and fix board through the face.

Screws – After many years of trialling various stainless steel pins, nails and screws we have found the Tongue Tite stainless steel cladding screw performs the best. These are endorsed by CladMark +.
Small headed pins and brads are not suitable as the gauge of the fixing is not strong enough to withstand movement.

Fit Cladding – By following the above sequence you should now have everything prepared and fixed points to measure from. Start at the bottom and fix the first board, check the level and take a moment to stand back and check that it looks acceptable to the eye with the whole of the building. TRADA recommend a minimum of an 8-10 mm clearance gap on end grain to reduce capillary action, this would be good practise on an unfinished board but for many this size gap would be unacceptable. If the board is oiled (with particular attention to sealing the end grain) this gap can be reduced. We find an acceptable size is 6 mm. A simple way of achieving this is by using an off cut of the tongue as a spacer. Butt joints should be avoided as the cladding will move during the seasons, not only will it encourage capillary action a joint that is flush today will ‘cup’ in 6 months.
Seal junctions between battens and trims with a good quality non silicone black sealant, once again this reduces the likelihood of capillary action and blacks out where a strong contrast in batten colour is present.

Typical Section Showing Fitting Of Vertical Cladding

BATTENS – Time and thought should be taken fitting battens to ensure they produce a level and flat surface for the cladding.

Batten spacing (unless specified by your architect or other professional) should be fitted at 400 mm centres and meet BS 5534 with a section of 25 mm x 50 mm.

For vertical cladding you will need to counter batten, this is where you put a vertical batten to the building, with a minimum thickness of 15 mm and then fix a horizontal batten to take the vertical board.

Where possible try to start the cladding a minimum of 250 mm from the finished ground level. The area below this is considered a ‘Splash Zone’ where timber will weather quicker due to rain splashing back on to the wall. At this point consideration should be given to how the cladding will look once fitted. i.e.  The top of your doors and windows should be level, so use this as a datum to work from. The Red Grandis Channel covers 100 mm with the Cedar covering 130 mm. Measure down multiples of board cover to find a starting point. Check the margins (what you can see of the window) are acceptable/ equal and any opening or moving component will work with the trim fitted.

INSECT MESH – Insect mesh prevents vermin and insects entering the void behind the cladding. There are many examples of insect mesh diagrams available on the internet. These all show straight sharp right angles fitted between the battens and the cladding. Whilst, as a detail, these look great in practise, these sharp corners and straight lines are hard to achieve. Our experience is to bend the mesh in half, fit it between the battens and force the corners in tight with an off cut of batten. The lower insect mesh should be fitted with the bend up and the upper insect mesh fitted with the bend facing down. With the insect mesh slightly proud of the face of the batten this can be compressed easily once the cladding is fitted. We do not put relief grooves in the back of our cladding as this makes the continuity of seal impossible.

OIL FINISH – If you have made the decision to oil your cladding now is the time. Apply as per manufacturers’ recommendations using the specialised oil brushes.

Two sizes are available a 50 mm for smaller areas and a 150 mm for larger surfaces. The 150 mm brush is ideal for cladding faces as you are able to oil the entire face in one pass.

The entire board must be coated paying particular attention to the tongues and grooves and back as once fitted these will not be accessible. Finish brushing the face making sure you have no finger prints, brush marks etc.

FIT DOOR/WINDOW TRIM – The door/window trim can fit flush or protrude from the face of the finished cladding. Treat the door/window trim as mini door linings. The head of the lining should go full width and be on the same angle as the sill. This will enable water to drain from the top of the cladding and create a drip at the lowest side on the front. Cut vertical jamb lining to length utilising the same angle as the sill, there should be a gap of at least 6 mm between the end of the door/window trim and the sill. This will reduce capillary action.

Seal perimeter of window using frame sealant, fit EPDM by removing self-adhesive backing tape and fix board through the face.

SCREWS – After many years of trialling various stainless steel pins, nails and screws we have found the Tongue Tite stainless steel cladding screw performs the best. These are endorsed by CladMark +.

Small headed pins and brads are not suitable as the gauge of the fixing is not strong enough to withstand movement.

FIT CLADDING – By following the above sequence you should now have everything prepared and fixed points to measure from. Start at the main focal point of the elevation this will either be a door or window. Decide whether the centre of the focal point is best suited to the centre or edge of the board. Temporarily mark out multiples of board widths to establish potential cuts as small strips are best avoided.  TRADA recommend a minimum of an 8-10 mm clearance gap on end grain to reduce capillary action, this would be good practise on an unfinished board but for many this size gap would be unacceptable. If the board is oiled (with particular attention to sealing the end grain) this gap can be reduced. We find an acceptable size is 6 mm. A simple way of achieving this is by using an off cut of the tongue as a spacer. Butt joints should be avoided as the cladding will move during the seasons, not only will it encourage capillary action a joint that is flush today will ‘cup’ in 6 months. Once again, cut on a slight angle to shed water to the outside.

Seal junctions between battens and trims with a good quality non silicone black sealant, once again this reduces the likelihood of capillary action and blacks out where a strong contrast in batten colour is present.

AROUND A CORNER – Cut board to required width and return around the corner. Try not to use less than 1/2 a width of board. As with the door/window trim remember to leave a 6 mm gap and seal the length of batten at the back of the cladding with black sealant to obscure the batten and seal the joint.

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