How Thatch Works

ABOUT THATCH | LONG STRAW | WATER REED

Thatch is best described as a thick insulating and breathable roofing membrane made from dry plant material that effectively sheds rainwater, sleet and snow, thatch has been valued and used for shelter ever since mankind emerged from caves.

All thatch works of sorts, but how well and for how long is important for thatchowners to understand when contracting a thatcher to thatch their roof.

With the combined knowledge and experience of generations of thatchers in East Anglia, members of the East Anglia Master Thatchers Association wrote and published the standards and specifications for thatching in East Anglia for thatchowners and professionals to better understand what thatch construction steps and measurements are required for an optimum long lasting high performing thatch. Master thatcher members of the EAMTA have to guarantee their work to these specifications for continued membership of the Association.

Unfortunately the thatching specifications are difficult to understand fully by anyone other than thatchers, this page hopefully will answer a lot of questions that you’ve wanted to ask.

• The secret to a high performing and longer lasting thatch starts with understanding how to slow down the surface decay of normal thatch to a minimum.
• A well-thatched normal thatch will only have noticeable surface decay of around 2-3cm, and the thatch beneath will be bone dry and have the same colour as when first thatched.
• Through the slow process of surface fungal decay the thatch wears down to the thatch fixings, sometimes over a period of 2-3 generations, it’s the top millimetre of dead fungal consumed thatch that turns to dust with some extra help of damaging affects of the sun. It is time to consider re-thatching when the main body thatch fixings are either near the surface or visible on the surface, it’s at this point that thatch can slip or blow away or rain and snow can get behind the thatch and leaking into the property.

These points below linked in with the EAMTA specifications will help with combating fungal decay and enhance the performance and longevity of thatch.

• The use of good quality thatch material from the outset is important, it should be of suitable length and relatively undamaged in it’s harvesting/storage production.
• The steeper the thatch the longer lasting the thatch will be, as a steeper thatch sheds rain and moisture that more quickly allowing the thatch surface to dry faster thus stopping fungal decay getting more established, always aim for a 50 plus degree pitch.
• The thickness of thatch serves a number of purposes; insulation to keep the warmth of the house in, to keep the heat of the sun out in the summer and the winter cold weather from penetrating into the house, good sound proofing, good breathable moisture regulator and not forgetting the traditional primary function of extra lifespan of the thatch.
• Good depth of thatch fixings beneath the thatch surface gives a good indication as to how long the thatch is likely to be effective for.
• Normal water reed thatch should not be excessively tight on the surface, as low moisture levels, primarily through diffusion can be slow to evaporate/diffuse away between the thatch surface and thatch inner fixings, that may encourage more aggressive fungal decay to establish in that inner zone of thatch. (Diffusion - movement of unsaturated water in semi-porous materials)
• Normal top coats of long straw thatch should not be excessively loose or thin as this can lead to ingress of rainwater and establishment of fungal decay between thatch layers.
• Ridge maintenance is important, good ridges need replacing every 15 to 25 years, ridges often appear worn out to thatchowners at the 10 year plus point as the hazel lattice patterning starts to look untidy, it’s a matter of choice for the thatchowner at this point, whether to go for a new ridge or not, but quite often the ridge will be effective for another 10 years? It is important not to let the ridge get to the point of allowing ingress of water behind the thatch, look for hollows under the ridge apex line.

A common myth that people believe is that thatch soaks up water like a sponge when it rains, and that the thatch is wet throughout its thickness, this is not true for circa 95% of all UK thatch, the EAMTA standards and specifications together with supplementary guidance given here will hopefully help you to choose a thatcher that does not give you a rotting poor performing thatch.