Most of us these days have a greater awareness of our impact on the environment and at the very least are conscious of the need to reduce it even if we don?t always feel able to. For this reason we are often asked where the timber for our oak framed houses comes from and if the source is sustainable. The other question that comes along with this is if we use English oak in our frames and what are the largest sizes we can get.
At one of our CPD seminars recently (these are seminars we run for industry professionals who have to demonstrate that they keep their knowledge up to date so that they can retain their membership of their professional bodies) these very same questions were raised.
I was speaking at the seminar at the time and one of the delegates; a timber miller in the UK, kindly suggested he show us some photographs of a parcel of forest he had recently been to see in France.
I?ve often explained at these seminars that there is a world of difference between managed oak trees in France and the oak trees we see in Great Britain. We stopped managing oak forest several hundred years ago but in France the practice continued. Oak sourced from the UK is from mixed forestation, limited in size and often of dubious construction quality (however it often has some wonderful characteristics for furniture making, turned bowls and so on). However the same species of oak (quercus robur) in France grows tall, straight and with good construction characteristics.
Hence a lot of the timber for the oak framing industry does, out of necessity, come from France. If you are concerned about the sustainability and impact on the environment bear in mind that the net stock of forest in Europe is increasing year on year and although it would be ideal to source the oak more locally even coming from France, the†use of†timber in construction is still significantly better than the energy consumed in using concrete or steel.
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In my blog about the In Touch with Timber conference recently, I touched on the building of large timber framed supermarkets. I assumed that retail giants like Tesco and Sainsbury were motivated by profit and nothing else in a very competitive market, so it pricked my interest that timber space frames are now more financially attractive than steel to the commercial sector, as is so often the case in continental Europe. Could this be the kick start for a major expansion of the timber engineering industry in the UK?
First and foremost it appears, getting people into the supermarket is the primary objective of the retail sector. Once people are in they spend. Everything the supermarkets do is customer led. Environmental or "green" issues are very fashionable. People feel good about helping the environment and want to be green, and look favourably on companies that are also trying to be green. So the supermarkets are now competing with each other to be greenest. Tesco announced plans to spend £100m on research into wind, solar and geothermal power, twice as much as Gordon Brown promised in the last budget. Interesting that Mark Soutar, Head of Environmental Construction for Tesco said that they got more publicity by sticking two little wind turbines on the roof of one of their stores which only powered the signage than any of their other environmental measures.
Anyway back to the engineered timber building. Apparently, with the massive rise in steel prices closing the gap, it is still more expensive to build in timber. So why is timber more attractive to large retailers? The timber trade says:†
All of which are true of course, but the supermarkets say:
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In response to my blog in July several people have asked how to achieve an externally expressed frame without continually breaking the thermal envelope of the building.
Our view is don't make the oak frame part of the thermal envelope because the only guarantee you'll get is that it will leak somewhere at sometime. In how many places and how often will depend on the skill with which a system is fitted but all the systems we see are extremely complicated with lots of components. In other words they're prone to human and component failure.
Although some 'purists' don't like the idea, the best way to achieve current building regulations and get the appearance of an externally expressed frame is to use air dried oak cover boards over a complete external thermal envelope.
There are a number of products to which one can apply render and if the cover boards are fixed to the panels first the render then 'fills' between the cover boards so that they aren't so obviously surface mounted. Be sure to use good thick cover boards to prevent cupping. Below are some pictures of a really well executed 'externally expressed' frame using this approach. This new oak framed house is in Twyford, Hampshire.
As an aside I find it difficult to see what's 'purist' about an oak frame that uses numerous modern components to try and make it meet current regulations!
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At some point every self builder is trying to pin down the cost of their project and they will get such varying advice that it must be enough to put many off the process altogether. We are frequently asked for guidance on the cost of an oak framed house but I fear that in giving it we only add to the plethora of information already swimming around in people's heads. Build It magazine regularly publish building costs for different build types and earlier this year Grand Designs magazine made comparisons between homes built in steel frame, brick and block, pre-cast concrete panels and timber frame.
In summary steel frame came in at £1,000 - £1,100 per sqm, brick and block at £900 - £1,100 per sqm, pre-cast concrete at £1,200 - £1,500 per sqm, conventional timber frame at £750 - £950 per sqm and post and beam timber framing at £1,000 - £1,200 per sqm.
Clearly this puts oak framing in a very favourable light with all methods of construction except conventional timber frame. However many people underestimate the proportion of their budget that will need to be allocated to interior fixtures and fittings.
If you're trying to build on a tight budget it's worth bearing in mind that you can spend £5,000 on a kitchen or £50,000 on a kitchen. Some self builders are choosing to spend some of†their available budget on an oak frame that will enhance their home for ever and install a low cost kitchen that they'll replace in a few years when they have more funds available.
On this basis you may be surprised to find that an oak frame is within your grasp!
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There seems to be some unrest in the market about warranties for new oak framed homes with some well established insurers starting to get the jitters! To be clear this is nothing to do with buildings insurance but, typically, 10 year building warranties. Companies such as NHBC are getting nervous about oak frames but they're muddying the waters because they're not being clear about what it is that bothers them. If you can get under the skin of it the real problem seems to be infill panels that try to emulate those used in period buildings.
With infill panels the oak frame punctures the wind and weather tight envelope dozens and dozens of times. Perhaps hundreds (typically four edges around every panel) of water tight seals have to be made and stay intact against oak that will move and shrink. Whilst some manufacturers claim to have a solution to this the insurance industry now seems to think otherwise.
So if you want infill panels in an oak frame and want a building warranty either use a builder who is accredited by the insurance company you want to use or get an architect who will do your working drawings, oversee the project and sign it off for you.
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