Not all tree houses are quite so rudimentary, and some are far from ephemeral. The finest example of urbane arboreal architecture is 450 years old and sits in a lime in the grounds of Pitchford Hall in Shropshire. The half- timbered, Grade I listed tree house is Elizabethan, but benefits from later additions: 18th-century Gothic ogee windows, elaborate rococo plasterwork and 20th-century steel reinforcement. This charming private tree folly is famed for having amused the youthful Victoria in 1832.
A good example of contemporary design is the architect Christopher Beaver's tree-house in Exmoor which is clad with cedar shingle, fixed to a platform spanning two larch trees and raised 14ft from the ground. The use of two supporting trees caused tricky movement problems. "When trees blow, they don't blow in unison," says Christopher, who called in engineers to help with the dynamics of the construction. A degree of flexibility was built in by using "movement joints" of a type used in bridge building.
Now 15 years old and beautifully weathered, the Beaver tree house is large enough to accommodate four sleeping children and has a pitched roof, four triangular windows and a rope ladder that can be hauled up and down through a trap door. Christopher estimates that a similar structure would cost roughly pounds 2,500 to design and build. For nationwide list of architects, telephone the Royal Institute of British Architects (0171-580 5533) and ask for the Clients Advisory Service.
A much cheaper kids-only option is the self-assembly tree house kit produced by TP Activity Toys. The packs include a Pirate's Deck (4ftx4ft platform with safety rails) at pounds 199.95; and a Log Cabin (which can be combined with the deck) at pounds 199.95. Accessories include rope ladders, scrambling net, slide and flagpole. For catalogue and stockists' list, ring 01299 827728.
In his book Treehouses (now out of print, but available through public libraries), Anthony Aikman suggests that English oaks and fruit trees are ideal tree-house hosts, while beech and elm should be avoided. But Derek Patch of The Tree Helpline refuses to be so clear-cut. "You can't make sweeping generalisations," he says. "Every tree is different; their branches don't have predictable properties like planks of wood."
Whatever the species, tree-house builders should choose a healthy, mature tree - if in doubt call in a tree surgeon to assess its condition. Tree houses should be lightweight and designed to co-exist with their living hosts without harming them (a few nails and screws are less damaging than abrasive fixings). For further information on tree-care call the Tree Helpline on 01420 22022. For a nationwide directory of tree surgeons telephone 01794 368717.
Any tree in a conservation area is subject to planning controls and harming a tree that has a preservation order is an offence which can carry a fine. Planning permission is not usually needed for tree houses unless they are sited in a front garden, in a tree overlooking a neighbour's house, or would be over four metres above ground level. If in doubt, seek advice.
For information on the Eaglehart DIY tree house concept, telephone Tom Eaglehart on 01556 600200. For copies of the anti-roads campaigners' book, "Dear Tree... ", contact Reclaim the Streets on 0171-254 2290.