Not too long ago, timber frame construction was seen as a problem in this country. Any prospective buyer or builder using or choosing it was in constant danger of their timber frame house rotting, burning, or keeping them awake at night thanks to hopeless acoustic qualities — and often all three at once, if you believed some of the stories.
Timber buildings were dangerous wild beasts best left to braver folks than us Brits to tame, but this reputation is somewhat undeserved and careful design can help you avoid the feared pitfalls.
Given that timber frame is one of the earliest building techniques, and that a large proportion of our oldest houses were built this way, it always struck me as odd that we view this construction type as somewhat alien. It’s odder still if you consider that around 70 percent of houses in the developed world are built using timber.
Admittedly, there were some poor examples of postwar timber frame housing which displayed some of the problems it became associated with, but the hoo-ha and suspicion was disproportionate and perplexing.
Perplexing, of course, until you realise that various parties with vested interest were at play. I am no conspiracy theorist, but it suited many in the construction industry – from architects to brick makers – to carry on with the ‘tried-and-tested’ ways (blockwork) and keep timber frame as an outsider.
That time has passed, and timber construction is a reformed character — the scare stories have moved on to marauding straw bale homes, and the like. It is now accepted that well-built timber frame buildings have a huge role to play in providing sustainable housing. It has become incredibly popular with self-builders and increasingly so with developers, but just as it was never as dangerous as some saw it, neither is it the cure-all that others perceive it to be.
Timber Frame Design: Considerations to Make
As with all construction types, achieving low-energy timber construction requires very careful consideration in its design and detailing. Yes, it can be thinner, warmer and have less embodied energy than masonry-built houses, but (without wishing to sound like too much of an eastern mystic) these strengths are also its weaknesses.In designing timber homes, you will need to face up to these issues if you’re to get the most out of them.
Pros: Space Saving
With the pressure on land in the UK, a real draw of timber frame is that it can provide thinner walls than other forms of construction. Timber can reach high levels of insulation in less space for two principal reasons:
- the gaps between the structural timber uprights can be filled with insulation, so this layer can be both structural and insulative;
- timber has a thermal resistance four times that of brick/dense block, so is inherently suited to highly insulated buildings.
There is, however, a big ‘but’…
Cons: The Timber Fraction
The amount of timber stud compared to the insulation in a building’s layer is called the timber fraction. This must be carefully calculated to work out the thermal performance of any build up, because one of the things needed to reduce energy consumption in buildings is to reduce repeating thermal bridges (this is where your structure crosses or causes a thinning of the insulation layer and, in doing so, creates a path for heat loss). The problem is that most timber frames are calculated with an optimistically low timber fraction that uses a nice, simple, straight section of wall to calculate the U values. This is applied to all the building’s walls.
Over the last two years, I’ve seen around 20 timber frame houses while filming ‘Building the Dream’ for Channel 4, and many of these have had big lumps of timber at junctions, corners and doors. I doubt these are being factored in correctly at the design stage.
To reinforce this, at present, new houses in the UK use on average twice as much energy for space heating as they are designed to. This so-called ‘performance gap’ affects all forms of buildings and construction. Poorly considered timber fractions in timber frame houses (resulting in ambitiously thin walls) are a part of this under-performance problem. It need not be so.
Trees are the most incredible things. As they grow, they fix carbon out of the atmosphere so in using wood in buildings, it locks that carbon out of the carbon cycle for as long as the building stands — hopefully hundreds of years. Wood fibre also makes fantastic insulation, so it is possible to make a sustainable house almost entirely from wood.
The problem is that the amazing characteristics of wood’s lightness and strength means timber buildings are inherently lightweight — and while this is good for reducing energy associated with transportation, it can result in houses that are more prone to overheating.
Heavy masonry, on the other hand, gives thermal mass, which takes a long time to heat up and cool down, thereby moderating internal temperature fluctuations. A stone barn will be slow to heat in the morning but hold the heat into the cooler evenings and be more comfortable. A wood shed will warm up fast and cool down fast. It has a fast response with larger variations, with less margin for error in getting the perfect temperature.
When you consider our changing climate, it shows the challenge to ensure we don’t make new low-energy housing that works well today, but in 20 years’ time needs air conditioning!
Sail blinds have been used to control passive solar gain in this timber frame home
Getting the Design Right
Above all if you work harder at the design stage there is no reason why you can’t build timber buildings that meet the ‘Goldilocks test’ — not too hot, not too cold, but just right! Three essential considerations can help you get this right:
- High levels of insulation
- Careful orientation (in relation to the sun)
- Solar shading
To my mind, the debate is no longer about whether one kind of construction is better than another. It must focus on how well designed, detailed and constructed a building is — irrespective of what material it is made from.