Batten gauge for slates

The batten gauge is the distance between battens. To calculate it, subtract the lap from the length of the slate and divide the result by two:

Batten Gauge = (length of slate – lap) / 2

For example, for a 500 mm slate installed with an 80 mm lap:

(500 – 80) / 2 = 210 mm

Note: Ensure that nails are not long enough to puncture the membrane or roofing felt.

Nails should be made from aluminium alloy or copper. Silicone bronze or stainless steel should be used in coastal areas.

Battening and slate installation

Enter your slate length and headlap to get the batten gauge, holing gauge and battens per m².

Slate length (mm) Headlap (mm) Don't know your headlap? Get it for your postcode and pitch

205 mmMaximum batten gauge

310 mmHoling gauge (from tail)

4.88 mBatten per m² of roof

Batten gauge = (slate length − headlap) ÷ 2. Results use nominal slate sizes and are for guidance only: the headlap must meet BS 5534 for your roof pitch and exposure.

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Holing gauges

This table allows you to determine the holing gauge (distance from hole to tail of slate) for your chosen slate length and lap.

*Measurements should be taken from the tail of the slate.
Holing Gauges in mm
Slate Size	Lap mm
(Nominal) mm	50	65	75	80	90	100	110	115	120	130	140	150
600	340	348	353	355	360	365	370	373	375	380	385	390
500	290	298	303	305	310	315	320	323	325	330	335	340
400	240	248	253	255	260	2265	270	273	275	280
350	215	223	228	230	235	240	245	248
300	190	198	203	205	210	215

Battening and underlays

The maximum rafter or truss centres for new-build projects are 600 mm. Some older structures may have rafter centres of 400 mm.
The minimum batten size for slating is 25 × 50 mm.
Once the battens are fixed, it is recommended that every second perpendicular line is marked to help position the slate joints.
Slates should be laid with the thicker end at the tail and should be of a similar thickness within each course. The thickest slates should be used in the lower courses, with thinner slates towards the ridge.
Slates should then be fixed following the perpendicular lines, with the tails aligned. A 3–5 mm gap between adjacent slates is recommended.

If you have any questions, our experienced team on slate is at your disposal.