In the mid-1960s R Riley of Caernarfon Crown Slate Quarries Ltd proposed a system of slating which is the same as oversealed Patent slating.  His objective was to be able to sell the cheaper smaller slates which arise naturally during production but are unpopular because of the greater labour cost of laying them.

Two trial roofs were constructed on Anglesey: on a private house at Llangefni and a coastguard building at Cemaes Bay.  Both buildings still exist but without their Riley roofs.  Presumably because they were not successful.  This was most probably because the slates and the cover strips were top fixed and were lifted by the wind.  This was confirmed at least in Cemaes Bay in a report produced by the Building Research Station in 1964. Note IC17-1964.pdf Thanks to BRE for permission to reproduce it here.

The house at Llangefni during construction.

Five photographs of Mr Riley’s model roof

The photographs are part of the National Library of Wales

Geoff Charles collection.  They are embedded here under a creative commons licence