From timber frame to thatched roof

Until the seventeenth century, wood was the most important building material in both cities and rural areas. The inhabitants of the Kempen region also mainly used wood, daub and straw to build their homes. In timber framing, timber forms the framework and the walls are filled with twigs, reed and clay.

During the coming years, restoration of buildings at the Open-Air Museum will use existing techniques, including the timber framing method. If you would like more information about the restored houses and planned restorations, you will find it here.

A wooden puzzle

The wooden components were manufactured in the carpenter's workshop, but some were made on the construction site. The carpenter drew out the full-size timber framework on the ground. Then he laid out the components like a puzzle on the ground drawing. They would start with a tie beam (or crossbeam), which would remain on the working floor to serve as a template for the others. Once a particular component was ready, he would fit it together in the workshop and affix it temporarily. If necessary, he would make modifications until everything fitted properly. Once all the components were finished, he transported everything to the construction site.

Identification marks

The timber frame had to be assembled on the site. The carpenter put an identification mark on each component to make sure that every beam was in in the right position. Those marks allowed him to see which components belonged to each other and their locations. He applied the identification marks on the middle of the beam. They usually comprised straight stripes that represented a number. This system was already in use in the eleventh century. He scratched or carved the characters with a knife into the wood. From the nineteenth century, carpenters also used chalk.

The letter H

The beams formed a tie in the form of the letter ‘H’. Carpenters often used triangular shaped joints on the beams, which made the construction unbreakable and therefore more stable.

The timber frame, the framework, was the load-bearing structure of the building. The walls and wall-surfaces had no load-bearing function, unlike contemporary buildings.

Raising the building

When the framework sections were ready, one had to raise the building. You could not raise the timber framework into upright position alone. The neighbours would come to help. Using manpower, rope and hoist, the men raised the frame sections one by one and anchored them. They used a simple hoisting rig for the heaviest sections. One example is a derrick and capstan. That comprised two poles bound together at one end (to form an inverted ‘V’). There was a pulley block mounted at the point where the two poles meet. They shored the whole unit up with ropes anchored into the ground. The pulleys reduced the amount of force required. One end of the rope attached to the frame section to be raised, and the other end ran over the pulley block for pulling by the capstan. Using that method meant that just a couple of people could raise the frame section.

A new roof every 30 years

When the roof construction was finished, it was the thatcher’s turn. They mainly used rye straw in the Kempen region. A thatched roof was much cheaper than a tiled one. Roof tiles or slates had to be bought and transported from elsewhere. Thatch is lighter than roof tiles, so the roof construction can be lighter and thus requires less wood, which could be expensive. It also insulates better than roof tiles. And the advantage of a thatched roof lies in its hollow stems. They allow water to drain off fast, which means that the roof will not rot as quickly. The major drawback, however, is high flammability.

At Bokrijk today, we use reed. It insulates less well than straw thatch but it is more durable. The barn from Lommel-Kattenbos was newly thatched in 2014. A straw thatch roof weathers relatively quickly and can only hold its appearance for up to 15 years. In ideal circumstances, it can last 30 years. It requires replacement after a maximum of 35 years. A reed thatch roof will last 30 to 50 years in good circumstances, and even up to 80 years in exceptional cases. A tiled roof, on the other hand, easily lasts a century.

Wattle

Constructing the walls required filling in the wooden framework. This was done with a combination of daub and wattle.

A weave of woodwork, wattle, was required to fill in the spaces in the wall framework ready for daub application. The spacing between the timber styles was 1.8 to 3 metres. That is why there were horizontal battens (slats) on which the flattened-off vertical battens were nailed, spaced at about thirty centimetres. The horizontal wattle work then fitted between them. Daubers usually used willow for the wattle because it is easy to bend. The pliability was increased by first soaking the wood in water. 

Daub

They covered the wattle with daub. The daub is a fine-particle type of soil, comprising clay and silt. Daubers usually immersed the daub pits before winter. The daub contained organic material that required removal. The dauber would let it rot and freeze thoroughly before using it. Chopped straw was added to improve bonding and to strengthen the daub layer.

The daub was applied in different layers, first on the inner wall and then on the outside. The first layer contained a lot of straw and the dauber applied it with a plastering float. The thinner finishing layer (or skim) consisted of finely sieved daub and finely chopped straw, flax or cow hair. This process was applied to both the inside and outside. Commonly, lime but also animal blood, urine and droppings were added to the outer layer of the daub. That made the walls water repellent. It did not create a smell. The horse urine used lost its smell after just a few days.

White

A timbered house demanded a lot of maintenance. The outside walls were lime-washed to protect them against moisture. That is what made the walls white. The lime-wash consisted of hydrated (or slaked) lime and water, and sometimes glue or oil to increase the adhesion. The practice of lime-washing walls arose a few centuries later than the timber framing construction. We know this from paintings in which the walls of half-timbered houses are not always white. It probably became common practice when daub became scarcer. The scarcity would mean using lower quality daub, which would probably allow more moisture penetration. 

Black

The woodwork was not initially treated. Blackening wood to protect it from moisture only started around 1800. A natural black dye was used for that purpose. From 1900, a syrupy reddish chemical liquid was used. That liquid stopped the wood from breathing any more. And that did not do the buildings any good. 

A house on the move?

The timber framework of a building was often reused for constructing a new house. Possibly, the timber framework might have been moved in its entirety sometimes. The applied woodworking methods made that possible. The house was relatively easy to disassemble and reassemble elsewhere. Homes were rebuilt in that way, or at least many building materials were reused, especially in times of scarcity or when the wood price was very high.

The baking house located in Bokrijk today on the Heist-op-den-Berg house property is an example of a building on the move. Around 1880-90 this baking house was completely moved from the ‘Witte Cannaerts’ estate to Jan De Hoef and family’s property, a few kilometres away.