Loading

Pen y Bryn Edern Three and Half Pin Slating with Shale valleys

Pen y Bryn is a C17 farmhouse said to date from 1603. There is an inserted plaque above the door dated 1790 with the initials of John and Mary Jones.

"Os barnasoch fy mod I Yn ffyddlawn I’r Arglwydd Deuwch i mewn I’m ty Act. XVI. 15. If you judge me to be faithful to the Lord come inside my house.”

RECORDING THE ROOF'S CONSTRUCTION AND DETAILING

A section of the slating was carefully dismantled and the slates' lengths, laps and the lath gauges were measured at each course. Most of the slates had slipped out of place. But by digitally moving them back into position in a photograph it can be seen that the slating has been set out in three and a half pin gauge. This is a technique which is well known in Devon and Cornwall and has been conserved. But on roofs In Wales they have almost always been simply discarded and replaced with modern slating. The majority of the original slating is in 11 inch / 279 mm long slates with just a few courses of 12, 13 and 14 inch (305, 330, 356 mm) slates at the eaves.

THE SLIPPED SLATE ON THE LEFT HAS BEEN DIGITALLY MOVED TO ITS ORIGINAL POSITION SO THE GAUGING AND LAP CAN BE MEASURED

For three and a half pin slating the lath gauges - their spacing on the roof - are the slates' lengths divided by 3.5 producing three margins of 2/7ths and a head lap of 1/7th. At each new course of shorter slates however, the gauge is reduced. It provides generous head laps for large slates and adequate laps for small slates. Because the laps are generous the side lap is not as critical as it would be in double lap slating. This is how vernacular slates which can be very narrow keep the rain out. Traditionally lath gauging is done with a slating stick which is marked out with slate lengths and gauges.

AN EAST MIDLANDS SLATER'S STICK

UNDERSTANDING THE SHALE VALLEYS

VALLEY SHALES

The shale valleys were dismantled to see how the parts fitted together to keep water out. This is difficult because once a slate is removed it's relationship to the other slates is lost. To overcome this the stripping was videoed so we could look back at how it was originally.

PARTS OF THE VALLEY
UNPICKING THE SHALES TO SHOW HOW THEY FIT WITH EACH OTHER AND THE CHEVRONS

HOW THE SHALES FIT AND WORK

The main slates butt against the chevrons from each side but this leaves a small gap which risks leaks. The shales cover this gap sitting under the chevron and over the main slate and the chevron below. Because the slating is three and a half pin with extra head lap each shale is also underlain by the shales below making sure no water can get in. Although this is an unusual valley, the way the slates fit together to prevent leaks is simply how all slating works.

RE-SLATING

RE-SLATING

SLATING A VALLEY

THE FINISHED ROOF

© Slate and Stone 2017

Report Abuse

If you feel that this video content violates the Adobe Terms of Use, you may report this content by filling out this quick form.

To report a Copyright Violation, please follow Section 17 in the Terms of Use.