How to install roofing battens - 4 simple steps

When setting out roof tile battens, the correct batten sizing and spacing are important and will have a direct influence on how the tiles withstand the ingress of rainwater through capillary action – ensuring that the roof remains watertight. Batten sizing and spacing are also important for aesthetic reasons so that the tiles on the finished roof are evenly spaced.

Whilst setting out tiling battens on a roof should be a straightforward process, it is not uncommon to come across basic errors which result in time-consuming and costly remedial works, and in some cases, full roof elevations have had to be stripped off and re-installed. In this article, we will cover the various steps needed to avoid such errors.

Preparing for the roofing battens

Before installing the roofing battens, start with the underlay. Roofing underlays provide a  waterproof barrier to prevent ingress of any water that manages to get under the roof covering.

Underlays come in a variety of options. Marley’s underlays are lightweight and easy to install, with integrated adhesive strips for sealing at the laps. They meet the requirements of  BS 5534:2014+A2:2018, the code of practice for slating and tiling for pitched roofs and vertical cladding. They are also compliant for UK wind zones 1–5 and are BBA certified. Two options are available, depending on the roof requirements: vapour-permeable and non-breathable.

Choose your roofing battens

Next, it is time to select the roofing battens. BS 5534:2014+A2:2018 sets out the requirements for roofing battens, including dimensions, quality, preservative treatments and marking.

Marley’s  JB Red roofing battens are made from PEFC-certified timber, produced only from high-grade, slow-grown and kiln-dried sideboard timber for maximum strength and stability.

These high-quality roofing battens are machine-graded to meet the performance requirements of BS 5534 and are the only UK machine factory-graded roof batten with BBA certification and CCPI verification. They are suitable for all roofing applications and  can also be used as a foothold.

Determining timber batten sizes based on roof covering and span

Before setting out the tile battens, it’s important to ensure that the batten size is correct for the project. Kevin Taylor, Training and Technical Support Manager at Marley explains: “The right size will depend on several factors, including span, type of roof covering and whether the tiles are laid with a single or double lap.”

• Clay and concrete tiles can be installed double or single lap, and this will play a part in determining the timber batten size. The correct timber batten size for double-lap clay and concrete tiles is 38x25mm. Single lap installations should use 38x25mm batten for 450mmrafter spans and 50x25mm batten for 600mmrafter spans.
• Slates should always be installed double lap. Fibre cement slates require 38x25mm batten for 450mm joist spans and 50x25mm batten for 600mm joist spans. All natural slates require battens to be 50 x 25mm for all rafter centres.
• Timber shingles and shakes will need a timber batten size of 38x25mm for spans up to 450mm, and 50x25mm for 600mm spans.

 

Kevin adds: “For spans greater than 600mm, or other loading conditions, Annex F of BS 5534 provides structural calculations for strength and stiffness to determine the appropriate batten size.”

Tile battens compliant with BS 5534 typically come in two dimensions: 25x38mm and 25x50mm, with a ±3mm tolerance in the width but the depth must never be less than 25mm. These measurements should be taken with a reference moisture level of 20%.

“Marley’s BS 5534-compliant JB Red timber battens are machine-graded, certified by the BBA and CCPI verified,” Kevin says. “They are supplied in 25x38mm and 25x50mm sizes and can be provided in lengths of at least 3m, although lengths of 3.6m or more are typically supplied. When installed, they should be at least 1.2m long and span at least three rafters.”

General principles for setting out tile battens

Roof battens are nailed into the rafters (or trusses) and provide support and something to fix the roof tiles or slates to.

BS 5534 specifies a number of batten sizes based on the span of the rafters and the product being used. For example, 25 x 50mm battens are required for single-lap Modern roof tiles laid on rafters with a 600mm maximum span.

Guidelines for setting out battens

• Start at the lower edge of the roof, nailing the batten into place at the centre of the rafter.
• Battens should be fixed to rafters set at centres not more than 600 mm apart unless calculated and should span across at least three rafters. To ensure this, the battens should be at least 1.2m long.
• Not more than one in four courses of tile battens should be joined over one truss for gauges over 200mm. Below a 200mm gauge, there can be no more than three consecutive joints in any twelve courses.
• Battens should be nailed to the centre of the rafter and any joints should be directly over a rafter with the batten square cut, tightly butted and skew nailed.
• Where batten ends are cut at the verge, an appropriate timber treatment should be applied, this applies to both mortar bedded and dry fix verges.

According to BS 5534, the nails used to fix battens to rafters should usually have a diameter of at least 3.35mm. The nails should provide a minimum of 40mm penetration into the rafter.

With any roof tile, it is first important to establish what is known as the hanging length. Most manufacturers will state the hanging length in their literature but to find it on-site, turn the tile over and measure from the underside of the nib to the tail of the tile.

Once this measurement is established, 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 datum point represents the top edge of the eaves tile 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 effective drainage into the gutters, so it is always advisable to check with a roof tile before moving on to the next step.

Setting out tile battens at the ridge

The top course of roof tiles should finish high enough so that the ridge tiles cover them by no less than 75mm. Generally, this means setting the top edge of the top tile 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.

Determining the tile batten gauge

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 will normally range from 75mm up to 100mm depending on the roof pitch. To establish the maximum batten gauge on site, 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 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 tile 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 tile 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 where possible. It is bad practice, no matter how tempting, 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 factory graded to BS 5534, 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.

When setting out for plain tiles, the first course should be set at least 50mm over the leading edge to ensure effective drainage into the gutter, as with larger tiles. However, it is important to make sure that an under-eaves batten is also in place. To establish the position of both battens, check the hanging length of both the standard tiles, and the eaves/tops tiles and check that the tails of the two tiles align once laid, before moving on to the next step.

Remember to leave enough room at the ridge for the top course tile, an additional tile batten, and an eaves/tops tile. The gap which needs to be left at the ridge will vary depending on the manufacturer and whether the tiles are clay or concrete. Because there are so many batten courses per metre with plain tiles (10 per m) and the gauges so small, it is not realistic to establish an even gauge throughout. Instead, the main body of the roof can be battened at the maximum gauge of 100mm, with the top 15-20 gauges adjusted as required to ensure the minimum headlap of 65mm is maintained.

For fixed gauge clay pantiles and similar products, it is good practice to check the recommended tile batten gauge with the manufacturer and install a small area of tiles on temporary battens (or the first few courses) to ensure a good fit, before installing the rest of the batten courses.

While the primary purpose of roof tile battens is to hold tiles in place, they also provide safe footholds when working on the roof, providing the contractor walks where the battens are nailed to the rafters.

As experts in roofing products, Marley offers everything you need to successfully install  a roof – from tile battens and underlays to roof tiles and accessories – and our products are fully supported by our knowledgeable technical support team and a 15-year warranty.

More information about timber battens sizes, as well as batten grading, product information and BS 5534 can be found in our downloadable Roofing Battens Guide. If you need help determining roof batten size or would like to discuss any other aspect of your next roofing project, please get in touch.