Thatched roof: construction, materials and thatching technique
From roof tile on battens to eaves — how a thatched roof is built up
The thatched roof is one of Denmark's oldest roof coverings and a living craft to this day. A good thatched roof stays tight for decades and gives the building a characteristic, soft expression that no other roof covering can imitate. Behind the calm surface lies precise craftsmanship, where layer upon layer of roof straw is built up and bound firmly so that water is always led outward and downward.
§The materials
- 01Roofing straw — the bearing cover material, harvested and sorted by length, thickness, and cleanliness
- 02Binding wire — stainless or galvanized wire that binds the pipes firmly to the battens
- 03Rod (thatching rod) — presses the pipe layers down and distributes the binding's pressure
- 04Ridge cap material — e.g. heather, straw or turf that seals the ridge tightly
- 05Lægter — det underlag, rørene bindes fast til
§Building layer by layer
Thatching progresses from bottom to top. The first layer is laid at the roof edge and each new layer is laid so it covers the binding in the layer below — the same way roof tiles are laid with overlap. The reeds are fastened to the battens with binding twine stretched over a rod so the pressure is evenly distributed along the batten. The thickness of the finished roof is typically in the range of 25-30 cm, built up of several slip courses.
§Thatching technique
The core of the thatching trade is the binding. Previously, the reeds were sewn down with thatching needles and yarn through the roof; today the reeds are usually screwed or tied to the battens with binding wire and screws in a technique where the wire does not go through the roof. After binding, the reeds are beaten into place with a thatching board (a grooved board) so that the surface becomes smooth and tight and the reeds lie at the correct angle to drain water.
§The ridgeline capping — the closure of the ridge
The ridge, where the two roof surfaces meet, cannot be thatched with roof reeds alone because the reeds here would stand too flat to keep the water out. Therefore, the ridge is closed with a crest — traditionally of heather, straw or peat — which is tied or held in place with stick and wooden peg. The crest is the most exposed part of the roof and typically needs to be maintained and renewed long before the rest of the roof is worn out.
| Element | Function |
|---|---|
| Roofing straw | Water-repellent covering material |
| Binding wire + stick | Binds and holds the pipe layers |
| Thatching board | Strike the surface smooth and compact |
| Ridgeline capping | Closes against water |
| Sliding layer | Multiple layers that give the roof thickness |
§Quality and lifespan
A well-executed thatched roof is recognized by an even, tight surface, dense thatching without thin spots, and a well-bound ridge. Lifespan depends on the roof's pitch, how exposed it is to shadow and moisture, and the quality of the straw—a steep, well-ventilated roof on the sunny side lasts much longer than a flat, shaded roof facing north. The thatcher evaluates all these factors when a roof needs re-thatching or repair.
“The thatched roof is bound, not nailed — and a well-bound roof sits tightly for a lifetime.”