the right is an interior shot of the great hall at the Pioneer Centre.
One of the lodges that sleep ten at Badaguish, near Aviemore
A detail of the roof structure of the Lee ValleyYouth Hostel.
The entrance to one of the Badaguish lodges at Aviemore.
A detail of a building at the Frontier Centre.
Golfer's rest at the Eastwood Golf Club
Entrance to the Osprey Centre, Loch Garten.
Conference facilities at Irthlingborough
Coverede walkway,Pioneer Centre
Erecting a timber building is a statement of intent. It signifies awareness that climate change is definitely manmade. Thinking big will dictate the smallest of actions.
materials from renewable resources are the software of a non-renewable
planet. Finite resources are the hard wiring.We
take satisfaction in providing structures that people enjoy using. Working
with wood is a pleasure, and living and earning in a timber building
should be fun too! It
says something about not being brash and intrusive, but seeking to live
in harmony on the only planet we have. We must strive to keep our ecosystem
All-timber construction can provide cost effective solutions to most requirements. The two basic concerns we tend to find about it are fire resistance and maintenance/durability.Well, the larger section timber we normally use does not burn easily, and it is actually the contents of a building that usually starts a fire. Fire retardant lacquer has to be applied to the timber wall and ceiling surfaces, but that is mainly to ensure ready means of escape in the event of fire.
Durability has much to do with design, and we design for it! Good detailing should shed, drain or vent any moisture ingress and if protected wood can dry out, it will not degrade. All structures need some upkeep, and life-cycle costs encourage designing for minimal maintenance. Labour costs have increased substantially in relation to those of materials.
It has always been possible to construct long-lasting low-maintenance timber buildings using carefully selected timber, but this tended to be expensive. Modern coatings are more durable. They are more able to accommodate movement in the wood due to heat and moisture variation, while maintaining a breathing seal.
While lacquered internal timber finishes are robust and hardwearing, external finishes, due mainly to exposure to ultra-violet light, usually require more frequent maintenance. External timber can be protected by overhangs or screening. Good quality micro-porous stains can be applied, or, alternatively, the nature of the wood itself can be changed.
Heat-treated softwoods can behave like the tropical hardwoods traditionally used to provide low-maintenance durability. These can be coated, or left to weather naturally.Cladding can simply be regarded as sacrificial, lasting 20-30 years before being replaced. Modern external stains may only require a maintenance coat at up to ten year intervals.
Timber Structural Solutions
The Natural Selection
Natural timber is pretty good stuff, but many of its properties can be further exploited by combining them in another form. For example, taking veneers off a log, like sharpening a pencil, and sticking them together produces not only plywood, but very strong, light, beams. Taking slices of sawn timber of uniform thickness, mixing them up, and then gluing them together again produces "glulam", i.e. glued, laminated timber. Because the grain is not all running almost exactly in parallel like it was in the original tree, this provides a much stiffer section. Whereas the tree wanted to bend without breaking, a glulam beam will be just as light, but have much reduced deflection under load.
Timber selection, drying and grading has always been done, but now it is usually mechanised. There is always a trade-off between sourcing local trees and sawing them on-site, or processing to make the optimum use of the wood. Specialised processing does bring benefits in terms of efficient use of materials although it will almost inevitably embody more energy due to transport requirements. The traditional stacking and covering of boards and battens to air dry for a "season", i.e. a year, may not often be feasible these days, so kiln drying, frequently fuelled with residues, is the means of providing a more precise component. Machine stress grading can do in an hour what would manually take months!
There are almost no limits to the structural solutions now available. Computer modelling can satisfy almost any requirement, although cost may be a factor, not least in how the erection can be carried out. We enjoy the challenge of producing elegant, affordable structural solutions, and doing so with the minimum of fuss. We are not in the business of producing hyperbolic paraboloid roofs or non-rigid structures. Anything else tends to be based on beams, albeit primary, secondary or tertiary etc ones. This may sound limiting, but it isn't. For a start, you can do amazing things with glue!
The load on a timber connection needs to be spread. This was originally done using timber dowels, but these were rapidly replaced with iron. Nails, screws and bolts are used in patterns to transfer and spread load. Suitable glue takes connection a stage further by maintaining uniformity of contact, similarly to the original tree, but using the grain to resolve and support the load requirements of a manmade structure. Perhaps human ingenuity will eventually allow the micro-processing of local materials to the same degree of sophistication available at large, specialised processing facilities.
Substructures and Floors
A foundation or substructure supports the superstructure and keeps the timber clear of the ground, with damp-proofing (usually a strip between courses of bricks or blocks, and a membrane under poured finishing or structural concrete slabs or screeds). While we tend to favour suspended timber floors (usually with strip foundations) for houses, it is desirable with public access buildings to keep the floor level as low as possible to minimise the length of access ramps.
"Floating" timber floors can be constructed directly on structural slabs, and these can be useful for installing wiring and pipes generally or for forming ducts for computer cabling. They are also a good way of putting in under-floor heating. The design loads for commercial and public access buildings are naturally higher than for domestic buildings, so joists may need to be larger and more frequently located with suspended timber floors, and floor boarding thicker unless support centres are closer.
Sometimes strip foundations need to be reinforced, or are not suitable for the ground conditions. A "raft" may be necessary. This is a reinforced structural slab sometimes laid at a lower level to support foundation walls, or used to form a slab to take the superstructure directly off of, but with a down-stand round the edges to maintain stability and prevent frost penetration. Where there is heavy clay or such like, piles may have to be used to support a slab or ring beam. Peat can be dug out or literally floated on!
Timber structures can generally be divided into three categories - panel; post & beam, and space-frames. Almost any timber structure has at least a degree of pre-fabrication. Even where just the loose materials go on site (this is sometimes called "stick building"), there will still has to be partial fabricated before erection commences. More site assembly of components may sometimes take place simply because it reduces transportation requirements by making the loads more compact.
In designing any structure, it is essential to plan out how it can be safely erected and transported. It is also advisable to work out how it can be safely maintained. One of the advantages of timber is its relatively light weight compared with steel and masonry - its strength to weight ratio is very good. Timber and steel both have tensile strengths similar to their compressive strengths, whereas masonry has little tensile strength, but plenty of compressive strength, so it is good for foundations but not roof structures.
Because steel is
so much denser than wood it is usually the best means of making connections
if glue is not used. Glue needs to be applied using good quality control
procedures and so if it is acting structurally, this may best be done
under factory conditions. Where steelwork, often in the form of plates
or brackets is exposed, we seek to give it a durable galvanic coating.
The other thing to watch out for with metalwork is that it will not
cause "cold-bridging" or attract condensation where it may
Stonehenge is post & beam, and there is evidence of timber being used in a similar fashion about the same time. Architects tend to like this form of construction because it requires layouts to be designed on a grid pattern. It can be suitable for larger structures, but not generally for domestic ones. The reason being that panels provide enclosure whereas post & beam requires infilling, which usually requires framing and sheeting or boarding anyway, or masonry. The range of wood derived sheet materials available now usually make these the most structural and cost-effective solution in the form of prefabricated panels.
Prefabricated "trussed" rafter roof components are now very common. These are remarkably efficient in providing low-cost roofs, although bulky to transport and awkward to handle, but lightweight given their load carrying capacity. High grade softwood, often with small cross-sections, are fixed together with nail-plates to produce precisely designed components, and are almost always the cheapest means of providing a roof structure. I-beams made from timber and sheet materials are increasingly being used to provide wider intermediate floor spans with less deflection than natural timber joists.
Space frames tend to simply be a development of post & beam. We usually supply them where large, open to pitch spans are required, and often incorporating arch portal glulam frames. These are an attractive and efficient means of creating a "wow" factor that provides good acoustics and a quality environment. People feel at home with wood, although we don't hesitate to use hidden steel posts or metal sheeting, laminate faced panels, bonded insulation etc. We do try to build sustainably, although this must reflect current conditions and what is available anyway.
We recommend pitched roofs where practicable, although the actual slope can vary enormously. Steeper pitches mean faster water run-off, and therefore less likelihood of water creeping through the overlap of the covering. Generally, the smaller the slate or tile etc used, then the steeper the slope required on the roof. With new natural slates, we suggest battens rather than the direct fixing to sarking traditionally done in Scotland. Very few roofs are actually "flat", but may be constructed with a very shallow slope so that rain and melt-water can be drained off.
Roof coverings are subject to large temperature fluctuations, and severe ultra-violet exposure from sunlight. Tiles were specified for NASA's space shuttle to cope with vast temperature variations, and the same logic probably applies to the durability of roof finishes. Membrane finishes are almost certainly less durable than rigid ones, and therefore are often best protected by another covering. Shallow pitches can be accommodated with profiled metal sheets, although a good membrane can work with suitable tiles at low pitches. Wooden shingles can provide a very attractive finish.
Turf roofs are traditional on some log buildings, and are normally constructed with a strong and durable membrane underneath. The turf provides additional insulation, but it is heavy, and thus tends to be used only on smaller buildings where there are plenty of log partitions to provide intermediate support. The pitch needs to be carefully considered to ensure the turf won't dry out too much, or slump if too wet. The dead load from any roof covering has obviously to be supported by the structure, and therefore lighter coverings can produce structural cost savings, although wind uplift can often be the most onerous design load condition.