Battens are the base of the roof: they carry the snow and wind loads and set the plane the sheets will lie on. A mistake in the spacing or in the board thickness shows up right after installation, as gaps and a wave along the slope. Below is the order of work, step by step, for Classic metal tile with a 350 mm tile pitch.
What you will need
- Edged board 25×100 mm or 30×100 mm, calibrated (thickness difference no more than 2-3 mm)
- A starting board 10-15 mm thicker than the rest, to match the height of the step
- Counter-batten timber 50×50 mm
- A waterproofing film for a cold loft, or a super-diffusion membrane for a habitable attic
- Galvanised nails (ring-shank or screw-shank), twice as long as the board is thick
- Antiseptic and fire retardant
- A long straightedge or a string line
Order of work
Step 1. Check the timber
The board must be calibrated: a thickness difference above 2-3 mm throws off the plane and the sheets lie crooked. Moisture content should be 18-20%: freshly sawn board twists as it dries and pulls the roofing with it. Do not use unedged board with bark at all – that is a guaranteed bark beetle.
Step 2. Treat the board
Before installation treat every board with an antiseptic against fungus and insects and with a fire retardant. Once the battens are up you will not reach all the surfaces again.
Step 3. Lay the membrane and fix the counter battens
The film is rolled out over the rafters, then 50×50 mm timber is nailed along the rafters on top of it. That is the ventilation gap: condensate runs down the film instead of rotting the boards. Battens are fixed only over the counter battens – never straight onto the rafters.
Step 4. Nail the starting board
The first board at the eaves must be 10-15 mm thicker than the rest, matching the height of the metal tile step, otherwise the edge of the first sheet sags. If all boards are the same thickness, nail an extra strip of the right thickness onto the first one.
Step 5. Set out the spacing
From the lower edge of the starting board to the centre of the second one is 280-300 mm – less than the rest. After that the spacing between board centres is exactly 350 mm, the tile pitch. Set out the whole slope at once rather than measuring by eye from the previous board: the error accumulates.
Step 6. Nail the remaining boards
Use galvanised nails twice as long as the board is thick. Two nails go into each joint with a rafter, at the edges of the board, otherwise it bows. Do not use black phosphated drywall screws: they are brittle, do not take shear and snap as the timber expands with temperature.
Step 7. Check the plane
Lay a long straightedge against the slope: every board must sit in one plane. A difference above 3-5 mm and the sheets will not meet in their locks. Make sure every nail is driven fully home – protruding metal scratches the polymer coating during laying.
Which membrane to choose
For a cold loft a classic micro-perforated waterproofing film is enough. If the attic is habitable, use a super-diffusion membrane: it lets vapour out from the room and blocks moisture from outside. Battens are never installed without a membrane.
Common mistakes
- Spacing wider than the wave. The sheet bends under snow and under the installer.
- Fixing not under the step. The screw must go into the lowest part of the wave, where the metal sits tight on the board.
- Unedged board. Bark means bark beetles, even after chemical treatment.
- Screws instead of nails. A black screw snaps under shear.
- Fixing straight onto the rafters. Without counter battens there is no ventilation and the boards rot.
Bulat metal tile comes with a written warranty, and sheets are cut to your dimensions, so there are fewer offcuts. Calculation from your dimensions: (067) 077-56-77, Mon-Fri 08:00-17:00. Catalogue: metal tile · profiled sheeting.