What is thatch?
Thatching is the craft of building a roof with dry vegetation such as straw, water reed, sedge, rushes and heather, layering the vegetation so as to shed water away from the inner roof. It is a very old roofing method and has been used in both tropical and temperate climates. Thatch is still employed by builders in developing countries, usually with low-cost, local vegetation. By contrast in some developed countries it is now the choice of well-to-do people who want their home to have a rustic look.
A combination of its compactness and the steep pitch of a thatched roof mean water runs off the roof by dropping from one end of a stem of reed to another. A new thatch will only ever get wet about 1" down from the surface.
The predominant thatching material in use in this country up until the 19th Century was straw but the main thatching materials in use today are water reed, longstraw and combed wheat reed. Sedge, a grass-like plant which grows in wetland areas, is also used extensively in ridging.
In the UK new water reed or straw is generally 12" - 15" thick although some properties with straw roofs have thatch thicker that this. Interestingly, it’ss not the thickness of the thatch, but the pitch of the reed on the roof that is the crucial element in shedding water. Often a thick coat of thatch will have a slacker pitch so isn’t necessarily any more effective. The length of the reed or straw also has a role to play in the efficiency of the thatch to shed water.
Generally because of the thickness of the thatch the bottom projects far enough away from the walls of the property to shed the water away from the walls without the need for gutters and downpipes. Water runs off the roof either into a soak-away trench - filled with small stones - or the water just finds its own way of soaking into the ground or drying on the surface of the ground.
As the final protective covering along the top of the roof, the purpose of the ridge is twofold: to conceal the last fixing rod and to provide an attractive finish to the roof.
Although a high quality ridge will only need replacing every 12-15 years, a poor quality ridge may only last 5-7 years. Sometimes, however, the ridge may look shabby, whilst still serving its purpose of keeping water out.
In the UK ridges are made from straw or sedge because this is easier to bend over and form a watertight bond at the apex.
Thatched roofs will have felt underneath. This is for 2 reasons; It keeps the property dry whilst thatching work is taking place and obviates the need for tarpaulins. Second it prevents dust and loose bits of reed/straw falling into the roof space after thatching has been completed.
Thatch will, of course, need to be replaced, but contrary to popular belief it can last decades – up to 40-50 years depending on the material used, the pitch and aspect of the roof and the quality of the workmanship. A new ridge will need to be fitted every 10-15 years though and at this time the whole roof can be dressed and cleaned and any moss removed.
Towards the end of its life, a thatched roof will require patching; however, regular inspection and maintenance of the thatch can prevent problems such as vermin damage or rot from shortening the lifespan of the roof.
Some thatched roofs will have wire netting on them. This is to protect straw roofs from birds (it is also fitted to ridges for the same reason) and it adds protection from strong winds etc especially in exposed sites.
What’s the advantage of a thatched roof?
Apart from its individuality and charm, the main advantage of thatch is that it has quite unique insulating properties meaning that the property stays cosy warm in winter and yet cool in summer. You can’t say this about more recently built properties!
If you are considering buying a property with a thatched roof then its important that you thoroughly check its condition.
Unlike a conventional roof, it is very obvious if a thatched roof is in poor shape, so take time to stand and look at the condition of the thatch:
o If fixings are exposed all over the roof, it indicates that the thatch is either nearing, or has reached the end of its life.
o If gullies are appearing (vertical deep patches of rot), these will require the attention of an experienced thatcher. Similarly, dark wet patches on the eaves close to the wall indicate the thatch is leaking.
o If the roof is covered in heavy moss, it could mean that the thatch is unable to breath and is therefore unable to dry out properly.
There are some common misconceptions about thatched roofs – which tend to put off first time buyers or those people wanting a low maintenance home. Perhaps for this reason, they tend NOT to sell at a premium (despite their obvious ascetic charm) as they’re not to everyone’s taste and people believe that they will be costly and time consuming to maintain. So what are the facts about thatch.
Facts about Thatch
1. Statistically, homes with thatched roofs are no more likely to catch fire than those with conventional roofs. If you try and set fire to a closed, thick book, you’ll find that it won’t burn very easily due to the lack of air and compactness of the pages. The same is true of thatch.
2. Thatched homes are not disproportionately expensive to insure - premiums are the lowest they've ever been; incorporating fire preventative measures makes insuring a thatched roof in the UK not much more than a slate or tiled roof.
About 75% of thatched properties are listed, so this brings extra considerations. Most external or internal repairs or alterations to listed buildings require listed building consent and you should talk to your local Building Conservation Officer before employing a thatcher to carry-out work on the roof.
With common sense and diligence, you can still have an open fire or woodburning stove in a thatched property.Statistically, homes with thatched roofs are no more likely to catch fire than those with conventional roofs; however, if a thatched roof does ignite, the results are rapid and spectacular, so owners of properties with thatched roofs should take precautions.
o You can have the thatch fire-retarded – either by being sprayed on completion or the material dipped in a fire retardant before being applied to the roof.
o Around 90% of thatch fires are caused by chimneys – they need to be swept regularly to prevent a build-up of soot deposits.
o The top of the chimney stack must be at least five feet above the thatch, allowing sparks to escape and die-out before they settle on the thatch.
o The chimney should be checked to ensure that the brick or stone work is in good condition and it should have an insulated lining fitted where the stack passes through the thatch. Having the chimney lined is a sensible precaution.
o When installing a stove, make sure you employ a professional with experience of thatched properties to do the job.
o Keep any eye on the flue temperature by fitting a flue thermometer and don’t burn wet or unseasoned wood, as this will leave greater deposits in the flue.
o Electrical wires in the roof space should be checked by an electrician regularly.
o The roof should be checked for signs of mice or other vermin as they can cause damage to electric wires.
o Locate smoke alarms and appropriate fire extinguishers throughout the property.
o If contractors are carrying-out work in the roof space, make sure they do not use blow-torches or other equipment which could create sparks. Plumbers for example should only use compression joints.
Owners of thatched properties are sometimes not the only ones who appreciate the warmth and beauty of their quintessential English roof - nesting birds, mice, rats and even squirrels can end up making a hole in your pocket as well as your thatch, so owners of thatched roofs should follow some simple guidelines:
o Walk around your property and have a good look at the roof once a week - if pieces of your thatch are sticking out in loose clumps, with holes above, this could indicate that you have guests.
o If you suspect your roof is playing host to mice, rats or squirrels, contact your thatcher or pest control officer for immediate advice.
o Wire netting applied all over the roof will prevent birds and vermin from gaining entry and is recommended on combed wheat roofs (long straw) and for water reed roofs if birds and rodents are a persistent problem.
o Birds are particularly fond of nesting under eaves - particularly if the thatch has not been properly fixed in place, or has become loose. To remedy the problem, call in a thatcher before the birds start looking for nesting sites in early spring and encourage birds to nest in your garden, rather than your roof, by providing a variety of nest boxes around your property.
o Watch out for squirrels in autumn and winter - they are particularly fond of hiding their nuts in thatch and also like to sharpen their teeth on the lead flashing around chimneys.
o The worst damage is caused by rats, which gain access to the roof space and then burrow their way out through the thatch. Make life difficult for them by feeding wild birds etc recommended feeders and avoid throwing food waste on your compost heap. Make sure bin bags are stored where rats and foxes cannot gain access to them.