Felt, Batten and Fixing Specification to BS 5534

Felt, battens and fixings are the parts of a roof developers and QSs most often treat as commodities, yet they decide long-term performance and warranty exposure more directly than almost anything else on the roof. Specifying them correctly at design stage costs little. Specifying them weakly costs money across the warranty period and beyond, with batten failures often arriving five to ten years after handover.

Within our new build development roofing division, we treat felt, batten and fixing specification as a contractual review, checked against each site's wind exposure, each plot type's pitch and the tile specification before installation begins.

Underlay selection, overlap and staggering

On a modern UK roof the underlay is part of the controlled ventilation strategy under BS 5250, working with the eaves vents, ridge ventilation and vapour control approach. Breathable, vapour-permeable underlays are standard on most pitched roofs. Some require a specific overlap depending on pitch, some need taped joints at low pitches, and some are zone-rated for wind uplift and cannot be swapped between regions without revalidation. Felt and batten are laid and staggered correctly, with treated batten ends, because underlay overlap and tensioning are among the first items checked at mid-build inspection. A like-for-like substitution on site can quietly invalidate the design's wind uplift calculation, so we make no substitutions without an engineering check. See how felt and batten specification affects long-term roof performance.

Batten grading and spacing

Battens must meet BS 5534 for grading, treatment, dimensions and moisture content. Non-compliant battens can pass a visual check on the day they are fixed, then twist, split or pull through their fixings years later. Batten gauge follows the tile or slate specification, and the number of nails per batten, their spacing and the rafter centres they fix into have to reflect the wind load calculation for the site. Issues caught at batten stage are simple to put right and issues found after tiling are not, so we check each plot at batten stage rather than only at completion.

Manufacturer fixing schedules

Every project starts with the fixing specification generated from the manufacturer's technical portal or technical department, using the site location, building height, roof pitch, exposure category and substrate we submit. The issued document sets fixing type, fastener gauge and length, fixing centres and substrate requirements, and it forms part of the roof system as tested and approved. It is briefed to site teams at pre-start, and if conditions change we request a revised specification before proceeding. The reasoning is set out in the importance of fixing specifications and why adhering to them matters.

Perimeter double-nailing and centre patterns

Wind uplift is not spread evenly across a roof. The highest pressures sit at eaves, verges, ridges, hips and corners, so specifications call for tighter fixing centres, additional clips and heavier restraint in these perimeter zones than across the central body. On slate, double-nailing is common on exposed sites. On concrete interlocking tiles the centre of the roof may rely on the interlock while the perimeter is mechanically fixed. Treating the perimeter the same as the centre is one of the most common reasons a plot fails inspection, and our supervisory checks concentrate on exactly those zones.

Wind uplift and BS 5534

We carry out site-specific wind load calculations at pre-start for every new scheme. Location sets the basic wind speed, height, surroundings and topography modify it, and pitch, tile type and exposure zones set the fixing requirement. Coastal, hilltop and open sites need heavier schedules than sheltered inland plots. The schedule is documented, briefed at induction and verified internally before the NHBC visit, so the inspection confirms work already known to be compliant. Our article on wind uplift compliance and what NHBC inspectors actually check explains where avoidable issues come from, and the tile choices that drive these schedules are covered on our roof tiling and slating page.

Reviewing the roofing specification on a development? Contact Globe Roofing, email enquiries@theglobegroup.co.uk or call 01223 890727.