Wooden roof framing in the Netherlands
Roof framing in the Dutch-speaking region have their origin in the northwest European common rafter roof, in which the roof is supported by common rafters which are connected in pairs by collars. The pairs of common rafters are at right angles to the longitudinal timbers of the roof. Originally, the pairs of rafters were not connected at all, with the result that the roofs often became lopsided. The oldest examples of which traces remain date from the 11th and 12 centuries.
In the second half of the 13th century, constructions were developed in the Netherlands to make the frame more rigid. These took the form of trusses, which were also placed laterally across the building, to carry the plate purlins which in turn supported the rafters.
The craftmen's guilds played an important part in the process whereby these constructions spread. Because knowledge was communicated in the guilds largely by word of mouth, these roof constructions became current almost exclusively in the area where Dutch was spoken, which in the middle Ages also included parts of northern France and western and northern Germany. In German-speaking areas, the northern part of France and in England other forms of roof support developed from the original common rafter roof. Carpenters travelled less than stonemasons and even though roof frames may have been built relatively far from the construction site, they were always, as far as we know, still prepared within the Netherlands or Belgium.
There were no guilds in rural areas and here the original simple methods of construction sometimes remained in use up until the beginning of the 20th century.
The purlin roof, which is of southern European origin, influenced Dutch constructions in the Late Middle Ages. Elements of this variant were in general use after about 1500.
In the extreme Southeast of the Netherlands the influence may be seen of the post roof, which was particularly common to Central Europe.
An important development in the study of roof constructions in the Netherlands was the rediscovery of the system of assembly marks which featured on all the elements of medieval roof constructions. This was a decimal system of marks scored in the wood, which, after 1300, included a symbol to distinguish elements on the left side of the roof from those on the right side. This was extremely important given that the constituent parts were often made by hand miles from the construction site and then transported by boat or cart. From 1500 onwards the marks were cut in the wood with a chisel.
he use of marks cut in the wood heralded the beginning of the period in which assembly marks were used less systematically. A variety of factors led eventually to carpenters virtually abandoning the use of marks with figures indicating numbers over 10.
The assembly marks often provide an indication of the time of construction and even, in some cases, of the part of the Netherlands in which the different elements were constructed. Using the assembly marks it is possible to discover the order in which the different elements of the roof of a building were assembled. Assembly marks are thus extremely important for studying the history of a building's construction.
For centuries, roofs with free-standing coupled trusses and supported rafters remained the most common type in the Netherlands. Since the second half of the 13th century a number of variants have been developed, for example using a central support and king-posts, but ultimately a single principal form remained, in which the pairs of rafters are supported by longitudinal timbers (plate purlins) resting on trusses placed laterally. The upper face of the purlins is horizontal. The rafters are in principle not fixed to the purlins and are not supported at the apex of the roof. The uppermost beam of the truss rests on the principals.
Numerous variants of this type of truss are to be found; they are explained with the help of the illustrations. The number of parts comprising a roof truss depends, among other things, on the width of the building. There are no essential differences between churches and secular buildings. In the case of private houses the parapet is important, because space is thereby created under the collar beams in the attic for people to walk upright and for goods to be stored. For this reason trusses were usually made using curved oak principals.
An unusual variant, found mostly in the southeast of the Netherlands, is the truss with an upper beam placed between the principals. This is perhaps related to the tie-beam truss found in rural architecture.
A form which originated in the south was the purlin roof, a roof supported by longitudinal purlins, which rest on trusses and whose upper surface is parallel to the pitch of the roof. There is also a ridge purlin at the apex and rafters fixed to the purlins. The pure form of purlin roof was combined in the course of the 15th century and early 16th century with the Dutch common rafter roof with trusses.