Timber framing for dummies - Part II (slip tenons)

What do you do when parts of a timber frame are missing and you need to reinsert them using traditional mortise and tenon joints? Given that you have an existing wall plate above and sill beam below if you’re on the first floor or, on the ground flooor, a floor plate and sill beam, it would be impossible to insert a new stud with tenons into an existing frame.

How to insert a stud using slip tenons

How to insert a stud using slip tenons

You can’t put it in diagonally and then slot it home without cutting an greatly elongated tenon which would cause excessive damage to the existing plate or sill. And you can’t just bolt it in without tenons and hope for the best.

The answer is that you use slip tenons wherever possible. You cut mortises both ends of the stud or member you’re going to replace, then cut tenons and insert those into the original mortises in the existing frame members, slide the new stud in and hammer home the pegs. Simple!

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At Hazel Grove Cottage, the process has been complicated because parts of the sill beam have become heavily decayed meaning that new oak has to be scarfed in before slip tenons are inserted.

Timber framing for dummies - Part I

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Nine months after our conservation experts walked out on our restoration project - a 16th century half hall house in Kent - and after several plaintiff but fruitless calls to timber framers, we were at a loss. Our house - built 500 years ago and the subject of a still-unknown catastrophe some time in the last 150 years which saw it lose more than half ot its original frame - was a wreck.

It should have been so simple - take the bathroom out of the former coal bunker lean-to on the side of the main building and put it upstairs, a bit of replastering, a new window and … hey presto … renovation part I complete and the house starts to become habitable.

But we’re romantics we Williams people and we never could get that image of the house as it would have looked in 1550 out of our heads. So when it came to removing the window from the dilapidated bathroom-to-be we just had to have the missing bits of frame restored before the wall went back in. Missing bits of frame, by the way, equals two braces, two major studs and the top half of a principal post inexplicably sawn off at first-floor level.

The last timber framer we’d contacted had told us that it would be at least 18 months before he could even come to look at our cottage. So what do you do?

The answer, of course, is you learn how to do it pretty damn quick, purchase the relevant mortise chisels, get the scaffolding up, make the templates for the oak members, order the oak and get on with it.

Inserting new green oak members into an existing frame is not the easiest DIY job we’ve ever undertaken - at over 100kg apiece you can’t just toss these things about like a piece of kindling - but it is … as we discovered … doable and just about the most satisfying bit of restoring a building you could undertake.

I’ve included some pictures from my Flickr stream at the top of the page and I’ll be plotting progress on this project in future posts, including some how-to stuff for anybody else mentalist enough to be in the same position.

If, in the meantime, you’re wondering how this is done then you need to get your hands on a copy of Conservation of Timber Buildings by FWB Charles. This is not an easy book to come by - you can try the shop at the Weald and Downland Museum in West Sussex or buildingconservation.com may have a few in stock.

It’s just about the most fascinating building manual I’ve ever read.

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