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2008 Archive

Carpenter Oak & Woodland’s blogs on timber frames, building, design, architecture and timber craftsmanship.

Design and Build

November 12, 2008  · Posted by Scott Fotheringham

The Roman Architect Vitruvus in his Ten Books of Architecture (circa 25BC), the oldest known text on the subject, defines the essence of architecture as a synthesis of "utilas, firmistas and venustas", variously translated as firmness, commodity and delight (Sir Henry Wotton 1624) and strength, function and beauty. For Vitruvius, architecture requires balance between intellectual and manual, between theoretical and practical, between design and construction. John Da Silva of Polhemius Savery DaSilva Architects Builders makes the point about traditional Architect and Contractor relationships where one can profit by proving the other wrong are rife with mistrust and contentiousness. Designing and making allows the integration of theory and craft providing the best chance at approaching Vitrivius?s balance.*

I liken John?s words to the business practices of our own organisation. We are passionate about serving our Clients through the understanding of their needs, with integration into the design team at the earliest stage of the project concept. This approach to construction removes entirely the potential opportunity to profit from the errors or omissions conveyed by a set of rushed incomplete drawings, further exacerbated by a rather pathetic attempt at descriptive text made up by inexperienced college graduates. When the specialist contractor knows more about the construction than the project procurement team, that knowledge is the power to profit.

I recently was advised by a dishonest procurement practitioner that if our company provided the information from which he could put together a meaningful contractual document, we would be "nominated" to carry out the works. Alarm bells rung, as we had no knowledge of this practitioner and he had no experience of working with us and, by complete chance, we learned that he had made the same promise to two other specialists. How did he ever think that this dishonest approach would ever produce a successful project?

* Architecture of the Cape Cod Summer by Michael J Crosbie

More blogs by Scott Fotheringham

UK Timber Supply

November 12, 2008  · Posted by Tim Burrell

I frequently find myself reflecting on the fact that there is such a clear and compelling case for building in timber, and that post and beam construction has so many advantages, but the forestry industry in Britain just doesn't support it.

Don't get me wrong, I like the Forestry Commission. I like their cycle tracks through forests and their maintenance of areas such as the New Forest. But what I do find disappointing is that as a supplier of timber to this industry, it just doesn't happen. It's not just that we often struggle to find a contact to source timber for one of their own projects, as reasonably specified. It's that there is no sign of them responding to the obvious demands for building materials in this country - at least not that we, or our British sawmills can see.

The French do this really well - oak is a commercially grown crop there, and organised harvesting and replanting is commonplace. Is it any wonder then that British oak is so expensive and difficult to find, but that it's readily available from the other side of the channel?

OK, so I'm ranting. But if we, as a commercial organisation (albeit one with a strong conscience) can operate net replanting schemes which won't benefit us financially, isn't it reasonable to ask others who operate with public money to have a serious look at this problem?

More blogs by Tim Burrell

The Longevity of Wood

October 06, 2008  · Posted by Scott Fotheringham

I don?t know about you, but I absolutely hate spending my precious free time hacking out rotten wood, scraping peeling paint, and trying to preserve my biggest ever investment. Any time I see fancy painted wood fascias I don?t think that looks nice, I think I?d hate to own that house.

I?m still reading Stuart Brand?s book "How Buildings Work" which kinda sums the issue up for me:

?As for wood, redolent with tradition, it is the best of materials from the standpoint of adaptability and one of the worst in terms of maintenance. It is fairly cheap, made of a renewable resource, easy to work, and it can be extortionately beautiful. But it wants to absorb moisture, and wherever the water content gets over 21 per cent, the wood turns into habitat and food for fungus, termites, ants, beetles, bees, borers and other wildlife. "What holds up that house?" one cynical carpenter asked me rhetorically, gesturing at a nearby standard stick build home. "Faith, habit, and the dead bodies of termites, same as all the houses around here." Who builds in wood builds a shack, adaptable now, gone soon.

The exception is timber framed buildings, because the wood structure is protected from the weather, it is massive, and it is exposed. Air and eyeballs can get at it to keep it dry and inspected. "According to government statistics," reports Gene Logsdon, "the average life of a conventionally built stud house is about 75 years. The life of a timber frame house is at least 300 years, and some over 1000 years survive."

The principals for longevity are very simple:

1. design, design, design - the best Architects understand the materials they are using

2. material selection - fast grown softwood is a very cheap building material, but not in the long term

3. whatever you use, keeping it dry or allowing it to dry out easily is the key

More blogs by Scott Fotheringham

Why timber can twist

October 06, 2008  · Posted by Tim Burrell

We were looking at a frame last week (not one of ours I hasten to add), where a considerable number of posts and studs had twisted, and we got to discussing why this was. 

Trees are both geotropic and phototropic - that is, they generally grow straight down by default, but also grow to the light. While this might imply that the obvious way for a tree to grow is straight up, and that therefore the grain in it should be straight, in reality this is rarely true.

To a greater or lesser extent, all trees have tension built in. As soon as we cut a tree down, the tension will try to dissipate. This means that spiralled grain will try to straighten out, causing twisting along its length. (It is this same principle that makes boards of timber distort and cup - the rings are effectively straightening out with nothing restrain it.) None of this affects the structural strength of the timber, but can, of course look unsightly.

For the purposes of timber framing, our specification does not allow for markedly sloping or spiralling grain, so problematic pieces will be rejected. However, even a small twist can become relevant over a long period, so that a beam of good quality which is perfectly square when it comes off the sawmill, is unlikely to be perfectly square by the time the joints are cut in it.

This twisting effect is why we use the manufacturing methods that we do. We physically lay out the timbers and mark them up in relation to the others so we can take this movement into account, rather than assume the whole beam is square and take the edges or centres at the separate end as datum points.

So, like shrinkage, which we seem so keen to keep talking about, twisting shouldn't be an issue provided that the milling process and the manufacturing process take it into account.

More blogs by Tim Burrell

Roman siege catapult for sale on eBay

September 29, 2008  · Posted by Andy Parker

I guess when I'm asked at parties what I do, I would say that I help to construct timber-frame buildings. The truth is that our skill - as a company - is really what we call 'timber engineering', and that our main business is constructing buildings.

We say timber engineering, because we are capable of doing things with timber that others would flee from, screaming loudly. For example, we can span far wider distances than many companies believe is even possible - and yes, our stuff stays up.

So we do get asked to do some pretty unusual things. Top of the list must be our slight excursion into building ancient war machines. I say slight, because it is slight for us, but we've probably got more experience of this than any other company - having built a few now, such as the trebuchet at Warwick Castle.

The ballista was built for a TV documentary - for the BBC and the Discovery Channel - called 'Building the Impossible'. Good title: many of the things built by the ancients are incredibly well-engineered and refined - and not at all easy to replicate. The ballista proved no exception.

Here's a short video showing the planning, design and construction of the ballista.

This video shows highlights of the building of the ballista - and its successful firing.

It took a lot of hard work, planning and construction to create the ballista. Along the way, we found out a lot that was - well, not new, but had been lost for thousands of years. A good example is the rope that is used to put the throwing arm under tension. It had originally been made from animal sinews.  It was understandable to think of this as antiquated, as it would be very time-consuming to make and require thousands of animals to surrender their muscle tissue. Plus, haven't we made great advances in similar materials? You would think so. So, a modern replacement was chosen - but was as similar to tensile strength as possible to the Roman sinew-rope. It wasn't until we placed the rope on the ballista, tightened it and left it overnight that we found out why - the real reason why the Romans had used animal sinew. All modern ropes slacken off in the cold of the night and damp of the early morning, rendering the ballista hard to fire - there's little tension left. Sinew rope performs in the opposite way - it tightens further, creating more tension and making the ballista fire further. Smart stuff.

That's just one example - the entire process was fraught with stumbling blocks that we weren't able to see in advance. A lot of what we knew was right, and enabled us to build the ballista, but a lot of what we knew was just plain wrong.

We had good people - great people, actually - working on this, so we resolved the issues and built it. We then successfully fired it, though firing it did cause damage to the timber that needs repair. (We saw after it was built that the damage would be caused due to an issue in the plans, but we decided to fire anyway - and we're glad we did!)

So now, we're selling it on eBay, to free up space in our Scotland timber yard. Our hope is that it is restored and goes to a good home - somewhere it can be appreciated by others; where we can marvel at the sheer genius of the thinking behind these awesome war machines.

Of course, if you want to lay siege to a neighbouring castle, it may be just the ticket too.


More blogs by Andy Parker

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