Re-thatching

In Britain, when a house is re-thatched, it is traditional for the thatcher to strip off only as much old thatch necessary to reach a sound base into which the new thatch can be fixed. This is known as 'sparcoating' or 'overcoating'.

In some parts of the country, for example in Norfolk, when water reed is used, the old thatch is completely removed, right down to the roof timbers, Water reed is also an ideal material for newly constructed housing or barns, However combed wheat reed should not be ruled out on new builds.

Most British thatchers today re-thatch by overcoating, whether they are using combed wheat reed or water reed. One of the benefits of this technique is to preserve old layers of thatch and historically important parts of an old roof.

There are exceptional cases where stripping back to the roof timbers may be unavoidable, perhaps because the thatch has been badly neglected. If you have a listed building and stripping is recommended by your thatcher, you should ask for advice from the conservation officer and check whether the work needs Listed Building Consent.

As with other thatching methods, the thatcher lays combed straw in courses, upwards from the eaves to the ridge, the fixings of each course covered by the course above. The pitch and the shape of the roof are essentially determined by the design of the roof construction, but can also be affected by the thatch and the way in which it been built up and laid.

Re-thatching can alter the shape of a roof and this should be discussed with the thatcher, who should be aware if you want the general shape of your roof to remain the same. A great depth of old thatch may, over time, flatten out the pitch by several degrees. Your thatcher may recommend that, for better performance, the pitch is made steeper to encourage rainwater to drain off faster. In some cases this can be achieved by reducing the depth of the old thatch at the bottom of the roof slope.