In the first part of our focus on Marley JB Red Battens, Kevin Taylor, the manufacturer’s Training and Technical Support Manager, highlights the key areas to consider for successfully setting out tile battens across a variety of roof areas.
Setting out battens for the roof eaves and ridge
As with any roof tile, it is critical to establish what is known as the hanging length of the tile. Most manufacturers share the tile’s hanging length in their product information. But if on site, builders should simply turn the tile over and measure from the underside of the nib to the tail of the tile.
Once this measurement is established, contractors should place a tape or rule at least 50mm over the edge of the fascia board or leading edge (measured on the rake) and mark off the hanging length onto the rafter. This first datum point represents the top edge of the eaves batten. The overhang may need to be extended for wider gutters or gutters which project off the leading edge.
The important point is to ensure that there is effective drainage into the gutters, so it is always advisable to check this with a roof tile before moving on to the next step.
The top course of roof tiles should finish high enough so that the ridge tiles cover them by no less than 75mm. Normally this means setting the top edge of the top batten down from the ridge (or the ridge brackets if using a dry ridge system) by the depth of the tile nib plus 5-15mm.
For variable gauge, single lap roof tiles, it is important not to exceed the maximum batten gauge recommended by the manufacturer, this can vary depending on the minimum headlap specified, which normally ranges from 75mm up to 100mm depending on the roof pitch.
The maximum batten gauge
To understand the maximum batten gauge when on site, roofers should measure the full length of the tile, and deduct the minimum headlap (for example: 420mm – 75mm = 345mm).
Starting at the first datum point (the eaves course), mark up sets of the maximum gauge until you are close to the ridge, and check where the top batten would fall in relation to the required datum point.
In most cases, the maximum gauge will need to be reduced to ensure that the batten gauges are even, and the minimum headlap is maintained. For example, to ensure an even gauge, a maximum gauge of 345mm may need to be reduced to 340mm to ensure that all the gauges are even, and a 340mm batten gauge would result in an 80mm headlap (420mm – 340mm = 80mm).
Whilst it is technically not incorrect to install most of the battens at the maximum gauge and then adjust the last few, this can result in poor diagonal alignment with profiled tiles (known as doglegs) and as such should be avoided.
It is also bad practice to exceed the maximum gauge (often referred to as stretching or pulling the gauge) because this results in insufficient headlap, which may affect the weathering properties of the roof covering, and void any guarantees or warranties offered by the manufacturer.
The battens, which should be 50mm x 25mm in size, factory graded to BS 5534 and ideally third party accredited, can now be set out and installed to ensure that the positions at the eaves and ridge are correct, that the batten gauge is even, and that the minimum headlap of the roof tiles has been maintained.
For more information on Marley’s JB Red Batten, as part of its full roof system, visit JB Red Batten – Roofing Batten | Marley.
