There are two systems of roofing with Horsham stone-slates: the ‘normal’ double lap system and single lapping.  This article deals only with single lapping.  It isn’t known why the single lap system is used in this region but it is speculated that as the Horsham stone-slates became unavailable the batten gauge was stretched to make the available slates go further.  Eventually the gauge became so large that the slates were single lapped which left the perpendicular joints open allowing water into the roof.  To overcome this Welsh slate ‘soakers’ were inserted at each perpendicular joint and the whole system bedded in mortar.

Slating purists regard this system as an aberration but this is a narrow-minded view.  There are several similar systems in the UK and Europe.  They all work perfectly well and should be regarded as part of the wide variety of lapping systems used in the British Isles and elsewhere.  They include -

  1. Patent slating link >

  2. The under-seal system seen in Caithness and over-sealing in Orkney and Ireland - Lapping systems link >

  3. Nordic Helletekking Helletekking.pdf download >

There are more pictures of Horsham roofs here >


Re-roofing St Botolph’s Church