Thatched Roof Construction Techniques
For hundreds of years, thatchers have been plying a trade that has helped to create some of the most beautiful buildings in the UK. Thatch roof construction continues today, even though the number of skilled tradesmen capable of doing the work is a fraction of what it used to be just a hundred or so years ago. Perhaps a recent resurgence of thatch roof construction may entice a whole new generation of craftsmen to take up the trade.
Be that as it may, roof thatching is something that requires a tremendous amount of knowledge and skill. Craftsmen must create roofs that can withstand the weather, ensure the comfort of occupants, and last for decades. Today's craftsmen still practise most of the traditional principles of ancient thatching combined with new principles and techniques they have learned that will make their roofs even better.
Building the Foundation
To the untrained eye, it may seem as if a thatched roof is but a collection of straw or water reed laid randomly atop a structure. But there must be something underneath that natural material to hold the roof up. That underlying structure forms the foundation, if you will, for the thatching that will become the outer layer.
A typical thatched roof starts with an underlying structure constructed with timber rafters and battens spanning those rafters. The thatcher fastens the first layer of thatch to the battens and rafters using a variety of fasteners. In the old days, the preferred fastener was either rope or balers twine; today, metal and plastic fixings are used instead.
On top of that first layer goes the 'main coat'. This main coat is applied by starting at the eaves and working one's way up to the ridge. Bundles of material are placed strategically in an overlapping manner so that water runs down the roof instead of being trapped by the thatching material. Thatchers lay bundles of material side-by-side to cover the entire horizontal surface, then begin a new overlapping layer above the first. This process continues all the way to the ridge.
Ridge Design – Complex or Simple
Designing the ridge of a thatched roof is where the thatcher has an opportunity to truly showcase his craftsmanship. Ridges are the most complicated part of roofing, so they must be designed and implemented with care. Ridges are constructed using long rolls of thatch material bound together to create a continuous line from end to end.
Thatching and the Norman Era
Regardless of the chosen design, forming water-tight ridges involves pushing the ends of bundles together along their edges and tying them off at regular intervals. Thatchers must be sure that the ends of bundles are intertwined densely enough to create a strong water barrier. There are three basic kinds of ridges that thatchers base their designs on:
Wrap-over – A wrap-over ridge is constructed by placing a bundle of thatching material directly on the apex of the peak, pushing the sides of the bundle down over the apex, and then fastening it in place. Another bundle is pushed into the end of the first, and the process is repeated. This creates a rounded ridge that looks very similar to a more modern roof made with roofing tiles.
Butt-up – A butt-up ridge is constructed using bundles side-by-side that meet at the apex. They are bound tightly together on their butt edges to create a single unit and then attached to the roof via the outer edges. This construction creates what appears to be a concentric block that runs down the peak of the roof in relief.
Flush – A flush ridge is the easiest to install because it does not require any additional bundles or construction. With a flush roof, the last layer of bundles on either side of the peak are brought together at the apex, cut flush with one another, and bound tightly together. This creates a straight and seamless ridge with no additional height or depth added.
Ridge design offers the thatcher an opportunity to implement artistry into his design. Some of the most beautiful thatched roofs in all of Britain credit much of their appeal to the ridge design. Ridges span a full range of designs, from the incredibly complex to the unassumingly simple.
Shaping Eaves and Verges
One of the final steps of thatch roof construction is shaping the eaves and verges. During the construction process, eaves and verges have to be implemented in such a way as to maintain proper tension within the thatching material in order to create a water barrier. The amount of tension required is dictated by the materials used. Once a roof is fully constructed, eaves and verges can be trimmed to create the desired look.
A thatched roof constructed of wheat reed is often trimmed with a hook to create a straight line along the eaves and verge. The verge can then be cut from the underside to create an attractive overhang that will also serve the purpose of directing water away from the sides of the structure. Of course, eaves and verges can be shaped in many ways, according to the materials used and the intent of the design.
Dealing with Pests
Since thatched roofs are made with natural materials, there is always the threat of pest problems. What many people don't know is that such issues are rare these days. But when pests do cause trouble, the simple solution is to install netting.
The first examples of netting that appeared in the late 19th century involved nets made of wire. The nets were developed to protect thatch roofs from nesting rodents and birds. Modern netting is more likely to be plastic than metal.
Netting can be applied to the entire roof surface or just on the ridge. That decision is best left to someone with experience in thatched roof construction. It must also be noted that netting should not be automatically installed as part of a new build or re-roof project due to its tendency to trap various kinds of debris that can reduce the life of a roof. Netting should only be installed if pest problems are confirmed. Even at that, it should be installed with as little coverage as possible to solve the problem.
Finishing Interior Spaces
Most of what is normally discussed regarding thatch roof construction have to do with the outer layer that is exposed to the weather. But what about the underside of a thatched roof? What do property owners do with interior spaces?
Hundreds of years ago, it was rare to finish the underside of a thatched roof. Property owners were not as concerned about aesthetics as we are today, so they just let things be. Modern structures may or may not follow that same tradition.
Some buildings with thatched roofs remain unfinished inside. Property owners who choose to let things be enjoy seeing the rustic looking construction that adds character to interior spaces. Property owners who want a more finished look can obviously choose among multiple options.
Torching is one method of finishing the interior. It involves using some sort of mortar coating or plaster. Torching does not cover the interior space completely, but it does make for a cleaner look and reduced draughts. A property owner wishing to cover up the underside of the roof completely will generally choose a lathe and plaster ceiling or a ceiling finished with gypsum board.
As you can see, an awful lot goes into thatch roof construction. At the hands of a skilled craftsman, a thatched roof provides more than adequate protection against the weather along with an aesthetically pleasing look reminiscent of days gone by. There is so much to love about a well-constructed thatch roof that this ancient construction method is enjoying a renaissance in modern building – to the delight of historic preservationists and skilled thatchers alike.