Spruce up your Sprockets 27th June 2018

Peg-tile roof

Look up at an old peg-tile roof and you’ll find them there carrying out their role in life responsibly. Have I lost the plot you might be wondering! On the contrary, I’ve just found it, and the answer is Suffolk rooflines, sustainability and prolonging the life of these ancient buildings.

Medieval pitch

Typically a medieval roof has a steep pitch. Look closer at the bottom end of the rafter and you’ll find it has been extended, and this extension is called a sprocket. The rafter has not only lengthened but the angle changed. The bottom rows of an old roof kick out and extend some way beyond the wall.

Why am I rabbiting on about rafter extensions in such an excited way? Well the answer lies in understanding the purpose of the humble but intricate sprocket which serves a timber frame building in two distinct purposes.

Harvest more rainwater

Firstly by altering the angle of the roof the sprocket slows down the pace of rainwater and enables more of the water to be channelled into a gutter and thereafter directed into a water butt. Harvesting and using ones’ own rainwater can only help increase green brownie points.

Secondly, the extended roof overhang protects the wall from getting wet. Bearing in mind that these walls were essentially mud plastered onto sticks in between studs, the invention of sprockets was a very good modification. Sprockets enabled walls to stay drier and therefore last longer.

Protecting an Earth Wall

At Orchard Barn we have a third reason to utilise sprockets. Our craft room roof is supported by a 15” wide earth wall. Sprockets are vital to protect this earth wall. Look closer at the gable end and you’ll notice it’s lop-sided. No, that’s not just me being careless with the height of the shingles. The roof is designed to look that way - the overhang is needed at the back whereas the open front of the craft room cart lodge has no need of water protection (and sprockets would impede entry there).

It was a tricky business fashioning those sprockets because the rafters they are fixed on are in the round! Many heads were scratched in working out the best way to make and fit the round wood sprockets, but that’s a tale I’m going to save for another day.

Beautifully shaped sprocket on peg-tile roof that may date back to the 1400s

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