Chair Design © John Bullar 2005
A designer maker's view by John Bullar
Published in Furniture & Cabinetmaking Magazine
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Colin Eden-Eadon, the editor of Furniture & Cabinetmaking Magazine wrote " I think this is a lovely piece, simple with graceful lines and has some intriguing construction. It's a trend I would like to see more of."
I hate traffic jams, but they occasionally have benefits. Sitting in one a few weeks ago, I turned on the radio and caught a feature on the BBC's 'Today' programme about "That little known enemy of good posture - The Chair". Experts, interviewed for the programme, agreed that too much time spent sitting at desks, in cars and in front of the TV was causing weak backs, shortened leg muscles and reduced agility among the population. This makes falls and fractures more likely, with many elderly people dieing as a result. In addition to this, the cost to the health service of medical care for victims of falls is estimated at one billion pounds a year. If you add the cost to employers of time off work with bad backs then, as the programme put it "The bill from Chair Disease begins to look rather large!"
What other inflexible artefact makes such intimate contact with the body as a chair? If you tried on a pair of shoes, you might tell straight away if they were too small, but not much else about their comfort. Shuffling around the shoe-shop carpet in them for a few minutes, generally gives a clearer picture, but even then you can be caught out and find they are crippling a mile or two down the road. Is it any surprise then that chairs, which are often bought on appearance or if tried at all, only for seconds, can turn out to be disastrous?
In the jam I started thinking about the seat in my car. Although it is a very ordinary car and I had been sitting still for two frustrating hours, it was not physically uncomfortable. Car seat design has been evolving over the decades, building on successive experience, together with a massive investment in research and design by manufacturers. Car seats also have a number of adjustments to suit different sizes and postures. All this seems to have yielded results.
Now I am not saying that a good chair design - whatever that is - will solve all the problems associated with too much sitting, but it must be important. So how can we predict which chair designs will function well? Galen Cranz, in her book 'The Chair', addresses many aspects, including ergonomics, in remarkable detail. Professor Cranz explains that seat height should allow the heels to rest on the floor where they will carry 40% of the sitters weight. This avoids pressure on the back of the thigh muscles, which can prevent blood flow. A downward slope on the front edge of the seat also helps in this regard. However, if the seat is too low the knees will be higher than the hips, causing stress on the hips and discs in the lower back.
Seat tops are usually either padded, or else shaped from wood as in the case of Windsor chairs. Cranz says the sitter's weight should be distributed through bones, not flesh and this means that any padding should be thin.
Statistical graphs of height distribution across the population show two peaks, one at 5ft 6 inches (1676 mm) and one at 5ft 10 inches (1778 mm), corresponding to average women and average men. There are wide natural variations around these peaks, as well as a tendency for young adults to be about 3 inches taller than their grandparents are. Taking the average person's height as 5ft 8 inches (1727mm) and dividing by four gives 17 inches (432mm), which is normally taken as the optimum height for a standard seat.
The majority of the adult population fall within the height range, 5 ft (1524mm) to 6ft 4 inches (1930 mm ), so at worst they have to cope with chair seats that are 2inches (50mm) too high or too low for them. Of course, this provides little comfort to those individuals who are not in the majority of the population.
CHAIRS FOR BEARS One option is for people to have individual chairs made to measure, like the three bears that Goldilocks visited. This is a service that the individual furniture designer maker may be able offer as an extra advantage over the mass market. Of course, special small seats have always been used in primary schools, as those of us who have squeezed into them to watch school concerts, will be very aware!
It is possible to achieve a similar degree of lumbar support without a pronounced curve in the chair-back by providing an opening between the back and the seat to allow for the buttocks and coccyx.
My belief is that the main function of armrests is to aid the process of sitting down and standing up - something that the elderly and those with joint problems can otherwise find difficult. Maybe that is why many family dining set have two 'carvers' - dining chairs with arms, for the elder members. The arms also function as handles for moving the chair closer to the table during the process of sitting or moving it back before standing.
From the chairmaker's point of view, the armrests can also have the function of bracing between the front and back legs and restraining the upper stiles making the chair stronger. The normal height for armrests is about 8 inches (200mm) above the seat.
Many 'easy chairs' seem to defy all the rules. They have large amounts of padding with no real back support and are far too low for the feet to take any weight. Used together with a footrest they can function closer to beds than seats. Armrests are pretty near essential for these, otherwise getting out of them can be a struggle, even for the able bodied.
A popular stunt performed by some sitters is to rock their chair back on its rear legs. This results in the sitters weight being cantilevered off the rear seat joints. Fortunately the trick is mostly done by young children who are light in weight, but there are some adults who will attempt it.
Ideally the rear joints would be strong enough to cope with rocking but a heavy adult would put enormous strain on a joint, inevitably loosening it if they do not immediately break it. Traditionally these would be mortise and tenon joints, pegged to stop them working loose.
Another defence against compulsive rockers to design a chair such that the rear feet are well behind the seat, making it near impossible to rock. This also improves stability and avoids accidental tipping back.
TESTING
Having gone to the effort of building the prototype, it is worth giving it a thorough and critical testing, ideally by a range of people sitting in it for at least half an hour each. Then be prepared to act on the results and re-think the design where necessary.