green wood in construction

[Fumanzoku]

I saw some green oak used in the construction of a house on Grand Designs last year. I have a freshly felled chestut tree that would be ideal to use in the the roof structure of a garage I'm building. Has anyone any experience or advice on working with green wood ?

[Teamedup]

I believe that you should check that green wood has not been treated with CAA's as there is a health risk involved.

[Idealfrance]

Be careful. Green oak does not mean oak that is freshly cut; It's a variation of the species.

*Never* use fresh wood for construction. Get it dried out first. Depending on the type of construction, wood should have a humidity of between 12 and 20%.

The risk is that your wood will shrink by a huge amount with catastrophic results for your construction.

Ben Symons
http://www.idealfrance.com

[Nick Trollope]

[quote]Be careful. Green oak does not mean oak that is freshly cut; It's a variation of the species. *Never* use fresh wood for construction. Get it dried out first. Depending on the type of construction, ...[/quote]

I'm not convinced, I'm afraid, nor am I sure that I am right, but;

Green Oak is indeed "green" because of fungal action. It is also green because it is freshly cut when used. Oak dries (in air) at a rate of as low as 1/2" per year (to 15%), making air drying impractical and kiln-drying expensive (because of the size of kiln and the amount of time needed). Heat weakens all timber. Oak is a stable timber when new - stable, at least, relative to pine, say (I have no idea about chestnut).

All timbers shrink across the grain when they dry, not along their length. American timber-framed (oak) buildings are virtually always built with fresh, or green oak.

I have seen new oak used in timber roof construction.

I would be fascinated to know, if there are any real experts here (present company included), just what can be used.

[Idealfrance]

There's possibly some confusion here between green oak (mycelium stained) and green oak (evergreen) - http://fr.wikipedia.org/wiki/Ch%C3%AAne_vert .

In any case, for oak, the tangential shrink rate is up to 8%, and the radial rate is up to 4% from green to dry (6% humidity) state.

This means that a freshly cut 8cm by 23cm beam could, once it's dried, measure 7.7cm by 21.1cm depending on the orientation of the cut. Axially, of course, there is no shrinkage. Imagine if you'd used it for some parquet? (not 8*23, obviously, unless you like your floorboards on the thickside )

The idea is to use a wood that's at approx the same humidity as the environment it's going to be used in. That's why wood for interior is dryer than wood used on the exterior.

I've never heard of any professional using green wood. The idea is almost absurd to me... I'll ask our charpentier compagnon tomorrow.

The Châtaignier (chestnut - edible kind) is an excellent wood for construction. Very expensive to buy.

Ben Symons
http://www.idealfrance.com 

[Nick Trollope]

OK, this is interesting! I take your point about shrinkage rates, but I wonder if, in terms of a lintel or roof truss whether a tangential shrinkage of this amount is important? Isn't this what causes the checks and cracking in a beam as it dries?

Just how do they dry large oak timbers? At 12mm/year (at best) a 12" lintel would take 10 years to air dry! No jokes about watching oak dry, please... Even in an oven you are talking months, I believe.

I have need of some timbers for our latest build project, although, subject to closer woodworm inspection, I am intending to use timbers from a demolition. I may need some new timber. Perhaps I'll use softwood!

I have vague memories of wonder-boy Ben Huggins cutting up trees on Discovery H&L, with a chainsaw, to produce roof timbers.

I'd be interested to hear what your carpenter has to say.

Ta!

[Piprob]

Older building structures often used materials that were 'to hand', including green timber. They were designed and built to do so. Modern methods, fixings in particular, do not allow components to shrink, stretch or flex to anything like the same degree; consequently, unless for example, you nail, dowel, or joint, instead of screw or 'glue', your construction is much more likely to break.

The speed of building work today doesn't help. It's interesting to see old and complex roofing structures clad in cedar shingles, slate, and even stone that resemble a rolling hillside, yet they survive. If the tiles had been laid to chipboard, and the unseasoned trusses held with galvanised plates and screws, they would have fallen down years ago.

[Caterham7]

Green or freshly cut oak is definately used in new construction.Part of my new house in the UK is constructed from green oak,designed by myself.Some members are 300mm square and up to 6 metres long,they have dried out nicely developing shakes with shrinkage of up to 12mm across the width.

The house I will be building in France will have much more of an oak structure,it really does look superb exposed.

Visit www.borderoak.co.uk for examples of new oak framed buildings,I have visited their offices and some of their houses and in my opinion they are real works of art.

I do hope the recent interest in new oak buildings continues as they certainly are more aesthetically pleasing than concrete or brick boxes.

Regards Tony

 

 

v

[Fumanzoku]

Specifically I want to use it for the ridge - length about 6 metres - and nail the rafters to it. Though it'll be a lot of work trimming it down to size and shape.

[Caterham7]

Quite often the structural significance of ridge beams/boards is misunderstood.If your rafters are tied at the feet by a joist or a chord at a higher level the ridge board is a redundant member and no load is carried by it.On the other hand if no tie or chord is provided to the rafters,the ridge beam carries approximately 50% of the roof load,but as this load is applied the beam deflects and can push out the external walls (rafter spread),it is therefore important to check the deflection of the ridge beam and the theoretical spread of the rafters.

Unless the roof structure is a simple triangulated rafter/ceiling joist arrangement,I would recommend you seek advice from a competant carpenter or structural engineer.

Cutting the chestnut will be difficult without professional tools or rather time consuming,but hey,get that axe sharpened and have some fun.

Regards Tony

[Bobc]

Ben,

To quote your posting:

"I have never heard of any professional using green wood - the idea is almost absurd to me".

Perhaps take a look a some of the reference books that I have mentioned in the Reference Materials for Restoration Forum:

Building the Timber Frame House The Revival of a Forgotten Craft
Tedd Benson & James Gruber Simon & Schuster ISBN 0-684-17286-0

First-class reference book with detailed drawings explaining how to cut by hand every type of joint used in timber framing, although an American book, the joints and methods are the same as though used on the timbers in French barns.

The Timber Frame Home Design, Construction, Finishing
Tedd Benson Taunton Press ISBN 1-56158-129-1

Tedd Benson is probably the world authority on timber frame construction and this book provides comprehensive information on building with wood. Invaluable for the chapters on methods of concealing wiring and plumbing within buildings with open timbers.

Timberframe The Art and Craft of the Post and Beam House
Tedd Benson Taunton Press ISBN 1-56158-281-6

Not a technical manual but an study of 29 timber frame homes with superb pictures and drawings. For anyone with a large open French barn with exposed timbers and who needs inspiration on how to create a living space within it.

These books are by authors with certainly more experience in working with green wood than either you our I and so probably their views are valid.

Perhaps do some research before posting misleading replies.

Regards,

Bob Clarke
http://perso.wanadoo.fr/grindoux

[Alane]

Green oak definitely IS used in timber frame construction in France. Our local sawmill sells tonnes of the stuff every week to local artisans. I have used such timbers for repairs in my barn, they are not necessarily newly felled trees but even if one or two years old, they are sappy and wet much over an inch under the surface. On a 30cm square timber I worked the sap stained my fingers black and I had to clean the tools and drill bits regularly. Three years later the timber (which is on a sheltered south facing wall and consequently will have dried significantly in the outer face) has developed shake in the dimension where it was free to move but along the length has shown no movement. As it is pegged into a timber frame it has accommodated the movement by developing shake rather than shrink in overall dimensions, the daub wall infill we put in after the repair is still reasonably tight up against the edge of the timber.

15cm timbers I used for other framing work which was also contained plenty of sap has barely moved and only has very fine shake present after a similar period.

I'm not sure about chestnut although the carpenter we used for earlier work suggested using chestnut for floor joists. The Society for the Preservation of Ancient Buildings in the UK publish leaflets on this sort of thing but I would suggest talking to a local carpenter or at your local sawmill. I can't recall if Ted Benson mentions chestnut in his books - certainly worth a look as Bobc has said, Ted Benson's books are a treasure trove for anyone working on a timber frame building. In our area in Normandy there are mobile "sawmills" that will visit and shape up trunks and branches into square timbers.

 

Best Regards

Alan.

[Peter72]

If you look at the construction and repair of old houses they used whatever wood could be found. I have removed bits of Chestnut, and reused it, and even bits of Birch which the bugs loved and was only fit for the fire.

The problem with green timber is cutting it, you can cart it off to the local sawmill, ours has a bandsaw with about a 1.5M throat, or attack it with a chainsaw as my French neighbour has recently done. I also saw the chainsaw method used on an arched green oak(ie freshly cut) beam for one of the Grand Designs. The oak I have bought in France for mantel pieces and to rebuild the Lucarne was certainly not seasoned it was quite green but is drying out and splitting gently.

My carpentry with home grown green (Freshly cut) oak has been confined so far to making garden seats, the oak is very easy to work and saws and planes easily. However after a year or two it gets very hard but still keeps its shape. During this years firewood cutting season I intend to cut some larger oak beams to see how they work out and I also want to try shaping them with an adze.

It would be interesting to hear from someone who has actually done this. So get the saw out and go for it.

Regards

Peter 

[Anton Redman]

If and only if you know what you are doing the joints are stressed so that drying tightens rather than weakens them. One of the pleasures of working with green oak it the ease with which mortice and tenon joints can be cut. A quick look through and off the French House magazines will show how often the main mortice and tenon had dropped on the centre span.

The best book on carpentry I have ever read is Japanese and the translators introduction begins with a debate about whether the best translation of carpenter from Japanese in Naval Architect. North British / American English certainly distinguishes between Ships Carpenter and House Carpenter.

For the last 6 years I have bought pine from my local builders merchant and then stacked it over winter to dry out. I do not have the experience to build in green wood, If you are using modern mechanical roof tiles then build roof first superstructure and allow to season before installing tiles

Sorry not much practical help

[Pantouflard]

Perhaps do some research before posting misleading replies.

Good grief Bob if everyone on here abided by this before expressing their view there wouldn't be many responses.  A bit more tolerance.  It was an opinion.  Comment if you disagree but why all the attitude?

 

[Bobc]

Dear Ben,

My apologies if I have offended you but you are posting misleading information.

In one of your earlier postings on this topic you say " never use fresh wood for construction". This is completely incorrect.

As regards using green wood for construction, I can only conclude that you and your architect are out of touch with the real world.

Attached below are two extracts from books by experts in the field of timber- frame construction.

"The Shrinkage Factor

Timbers shrink as they dry. That’s a reality. For the most part, air drying and kiln-drying are not terribly practical. Air-drying requires too much patience (two to five years) and kiln-drying too much money (two to four months in the kiln).

Therefore, most frames are built with timbers that will eventually shrink to a somewhat smaller dimension and different shape.

Even when the timbers are essentially dry, in most cases there is likely to be some shrinkage as they move from the ambient relative humidity of the exterior conditions to the warm and protected environment of a house".

The Timber Frame Home - Design . Construction . Finishing

Tedd Benson Taunton Press ISBN 1-56158-129-1

"Working with Green Timbers

Of course we all do our best work and walk away from the frame with perfect tight joints and smooth check-free faces. We have plenty of photos, and memories of tight joinery and clean beams that will remain unchanged forever. But, if green timbers are used, no matter how perfect the joinery may be, or how well we surveyed the timbers, changes will take place.

Unfortunately, aside from recycled or dead standing timber, timbers come to us from the sawmill in one state and one state only - green.

There is simply no satisfactory way to quick-dry a fresh-sawn timber over 4x4. When timbers are subjected to rapid, artificial drying, the fibres become brittle and difficult to work and robbing a great deal of the strength naturally inherent in the wood fiber. Assuming that thoroughly dry timbers are virtually impossible to obtain, we should learn the best approach to working with green timbers".

A Timber Framer’s Workshop

Steve Chappell Corn Hill Books ISBN 1-889269-00-X

There are enough other postings on this thread that may lead you to believe that your postings are incorrect. If you seriously want to get involved in work using wood then perhaps consider purchasing some of the books that I have suggested.

Kind regards,

Bob Clarke

http://perso.wanadoo.fr/grindoux

 

[Bobc]

"Good grief Bob if everyone on here abided by this before expressing their view there wouldn't be many responses.  A bit more tolerance.  It was an opinion.  Comment if you disagree but why all the attitude?"

I am not sure what you are really adding to this thread.

The original question was regarding using green wood in construction.

The posting that I replied to was completely inaccurate.

Regards,

Bob Clarke
http://perso.wanadoo.fr/grindoux

[LesLauriers]

[quote]Perhaps do some research before posting misleading replies. Good grief Bob if everyone on here abided by this before expressing their view there wouldn't be many responses. A bit more tolerance. ...[/quote]

Pantouflard said "Perhaps do some research before posting misleading replies."  "Good grief Bob if everyone on here abided by this before expressing their view there wouldn't be many responses."

Quite right - but it would make the board much more useful!

[LesFlamands]

Don't really want to get embroiled in the argument about the massive amount of mis-information posted on this forum - I can only offer information based on first hand experience and observation of techniques and materials used for hundreds of years.

Most of the timber we use is green/freshly cut. We use mainly oak for framing:

This is a photo of part of a stairwell and first floor constructed entirely of green oak beams. All beams are cut to our dimensions at our local timber yard - the vertical posts here are 5.6 metres long. We are also just building a complex roof using green planed (as the entire roof structur will be visible from the inside) Douglas fir. Shrinkage (lateral) is about 5% in oak and has to be allowed for but otherwise it is a fairly straightforward process but does require some specialist equipment and a strong back.

[Caterham7]

[quote]Oh dear. Now who's misleading who? Were you planning on addressing my other points? Are you going to recommend using green wood? Maybe "never" was a strong word. I'll concede that. But I'm convinced...[/quote]

Quote,If you try to use green(fresh) oak for a roof truss,then it won't even be able to support it's own weight.

Thanks for this advice Ben,I have notified my professional indemnity insurers of the imminant potential collapse of dozens of roofs that I have designed over the last 17 years.I have ordered a dozen acro props to prop up my roof tommorrow,I am so pleased to be informed of this prior to the roof collapsing and anybody getting killed.

I am considering sueing all the professional bodies that I subscribe to,for keeping such a fundamental structural flaw in green oak a secret.

Once again thanks,I may owe you my life !

Regards Tony BSc CEng MIStructE

ps I think I'm with Bob on this one.

[Bobc]

Charles & Tony,

Thanks for your comments on this subject. I thought I was banging my head against a brick (oak) wall.

Also, welcome back Charles - thought you had vanished!

Kind regards,

Bob Clarke
http://perso.wanadoo.fr/grindoux

[Fumanzoku]

Meanwhile...I went out and bought a couple of pine madriers to do the job. From what I've read here and elsewhere I could've used the chestnut but it would take too much time to trim it down and also haul it into position. I'll keep it for other uses.

Thanks for the input.

[Idealfrance]

I have notified my professional indemnity insurers of the imminant potential collapse of dozens of roofs that I have designed over the last 17 years.

Glad to see you're taking responsability for your actions. Bravo. I hope it's not too late. By the way, I can think of a much better place you can put your accro props.

Bob, still no recommendation forthcoming?

Ben Symons MEng CEng ImechE
http://www.idealfrance.com

[Bobc]

"Bob, still no recommendation forthcoming?"

Ben,

Given the number of posts to this thread, in particular the two last ones, I felt that you might perhaps think that you had got it wrong and let the subject die.

As you have asked for a reply, then I would say that building with ‘green’ wood is a perfectly accepted standard. I am not sure what you mean by recommending it.

You asked me to find someone who says that using green wood is better than using dry wood in normal climates. I have provided you with these references from experts in the field.

Other than your own postings, all of the others have endorsed the use of green wood. In particular, the postings of Charles and Tony, who probably have far more technical knowledge and experience than I do.

If I was one of your clients I would be a little worried that you have an architect who feels that building with green wood is not a good idea. Worse still a charpentier who believes that a roof truss made from green oak will not be able to support its own weight. This is complete nonsense.

For me, the best part of my work is learning new things every day and having an open mind regarding building and restoration techniques.

Without wishing to labour the point, perhaps you should invest in some new reference material that would benefit you, your architect and your charpentier:

Nature Rules

A timber frame is made of wood, and wood - especially in timber dimensions shrinks and twists. Any timber above 4" cannot be reliably or economically be dried in kilns because it takes too long. Air-drying is also impractical for the same reason.

Even when it is possible to make the frame from old, dried, timbers, seasonal shrinkage and swelling results in dimensional change or surface checking.

We have made frames from timbers that were dried in a kiln and a few that were re-sawn from larger timbers over a 100 years old. In both cases there was not as much movemennt as in frames built from green wood, but there was visible change as the frame adjusted to its new environment.

It is the nature of wood.

Tedd Benson The Timber Frame Home Design - Construction - Finishing

ISBN 1-56158-129-1

Tedd has built over 500 homes and commercial properties using green oak. I think that this probably makes him more qualified than you, I, your architect and certainly your charpentier.

If you only buy one new book, buy this - it might open your eyes to other techniques.

Regards,

Bob Clarke

http://perso.wanadoo.fr/grindoux

 

[Caterham7]

For those of you that are interested in the extent and diversity of green oak frames the following sites have provided me with inspiration.

Grand Designs,you can see the houses from the previous series by going to www.channel4.co.uk/life/microsites/0-9/4homes/grand_designs

Click on The houses or The houses archive.

Argyll-Oak frame by Carpenter Oak

Berkshire Series2-Oak frame by carpenter oak

Herefordshire-Oak frame/SIPS panels by Border Oak,and to a certain extent the inspiration for my french project.

Sussex-very interesting hand made woodsmans cottage from Sweet Chestnut,with bale insulation/oak cladding.

www.ehbp.com English Heritage Buildings

www.carpenteroak.com Good current projects photos

www.greenoakcarpentry.co.uk check out the innovative museum gridshell

www.oakmasters.co.uk

www.oakwrights.co.uk

I would like to think these buildings will be around long after we are all dead and buried.

I hope this inspires some of you to build something similar in France.

Regards Tony