Green Oak Framed Buildings Question - Warping?

[Tetsuaiga]

Recently I was saw that some buildings are made with freshly sawn oak timber. It's my understanding wood will tend to warp as its moisture content changes.

How is it that huge timber buildings can get away with using timber that's not even kiln dried?


I'm wondering if I must have misunderstood and that maybe it wasn't really green oak timber being used.
So i'm just curious about this really. Anyone know about this?

 

[bugbear]

Recently I was saw that some buildings are made with freshly sawn oak timber. It's my understanding wood will tend to warp as its moisture content changes.

How is it that huge timber buildings can get away with using timber that's not even kiln dried?


I'm wondering if I must have misunderstood and that maybe it wasn't really green oak timber being used.
So i'm just curious about this really. Anyone know about this?

Yeah - they warp!

One exception is when a beam is made from "most of" a single trunk,
simply slabbing the sides off. In this case, the beam tends to not warp, since the forces
are symmetric. They split and shake a fair bit though.

BugBear

 

[Tetsuaiga]

I suppose with the moisture content decreasing it will shrink which isn't so much as a problem as expansion would be.

 

[Tetsuaiga]

One exception is when a beam is made from "most of" a single trunk,
simply slabbing the sides off.

BugBear

Ah yes, that makes sense.

 

[matthewwh]

The joints are made and assembled accurately and then pinned with dry dowels. If it is done right the twisting forces counteract each other, lock the joinery and pull the whole structure tightly together.

It's a very clever craft requiring a good knowledge of how the timber will behave. Green wood furniture uses similar techniques on a smaller scale. If you pick up a copy of Living Woods magazine there are usually a good selection of courses, articles etc about green wood crafts.

 

[RobinBHM]

All of the original tudor oak framed buildings around the country will have been constructed with green oak.

There are quite a few companies around building green oak frames, some using sophisticated equipment, producing structures to very accurate dimensions. Oak frame kits are popular with self builders.

The timber will move significantly, requiring specific detailing to cope with the movement, for example fitting windows and doors. Plastering and rendering can be a real problem.

 

[RogerS]

And then you have the cowboy builder who made our timber-framed outbuilding (are you reading this ColinT from Ledbury?) but who didn't bother to tie in some of the roof trusses :evil:

 

[Sgian Dubh]

How is it that huge timber buildings can get away with using timber that's not even kiln dried

Adding to what others have said kiln drying large oak beams would be enormously expensive for two reasons. The first is the time it would take, and the second being the strong likelihood of the wood (oak being especially refractory) developing drying faults that would make it unusable.

Where large timbers of this type are used for construction they are generally nowadays Wet Graded for strength as opposed to Dry Graded which takes place for almost all other construction timber under 100 mm thick which will almost always be kiln dried to a target MC of 20%. Wet Grading allocates a lower load bearing capacity to beams than an equivalent dried and Dry Graded beam. However, the bonus is that as these wet beams dry out in many structure over years their strength increases because dry wood is significantly stronger than wet wood, and the structure generally gets stronger as it ages. So, if a typical structure is overbuilt in the first place with wet wood, then it becomes even more overbuilt as time passes.

And, as others have said, there are well established techniques used to make buildings with green wood, e.g., joinery, allowing for shrinkage, warping and splitting, pegging, etc. Slainte.