There is a long tradition of building roofing of wood in the Nordic countries. Today you can find these on historic monuments, such as medieval churches, some museum buildings and more widely in open air museums. Roofing of thin shingles was common on outbuildings of farms still some fifty years ago but these have been replaced with more durable and less fire hazardous materials over the years.
When we look at historic wooden details they make best sense if we know the tools and fixtures that were available at the time of execution. The first and foremost tool was the axe. Drills, planes and hand saws did not become standard equipment in a builder’s tool box until the 19th century in Finland; somewhat earlier in Estonia and Sweden. It is also worth remembering that the sawmill industry started as late as the second half of the 19th century.
There are many different ways of using wood as roofing:
- birch bark between two layers of tightly laid thin rafters (required tools: axe and knife)
- thick shingles (axe, knife)
- concave and convex planks (saw, axe, chisel)
- profiled planks (saw, plane)
- thin shingles (saw, axe, knife—or mechanical 20th century shingle plane)
A birch bark roof is laid without a single nail and even plank roofs could be laid without many nails. Thick shingles are either hung on wooden pegs or fixed with handmade nails. Fixing thin shingles on a roof requires a lot of nails and this is why thin shingles did not become popular until the end of the 19th century when mechanically produced cheap nails appeared on the market.
The sustainability of a wooden roof—like any roof—depends entirely on its maintenance. If thick shingles and profiled planks are tarred regularly they will last decades if not a century or two. Birch bark can last a century if it is kept from harmful UV radiation by changing the top layer of rafters every 20–30 years. Thin shingles will last some 25 years.
During the intensive course Wooden Roofs and Traditional Surface Treatment of Wood (Sustainable Heritage report No. 5) in April 2013 a plank roof was laid on a historic building in Ekenäs, Finland. After learning about different kinds of wooden roofing at the open air museum in Helsinki students concentrated on the work of nailing specially made boards on the roof of the listed storage building. Handmade nails from Estonia and Finnish tar were used on the roof and finally the whole building was painted with red earth paint which had been cooked by the students themselves… more documentation, program and images on Hands–On Work in Spring 2013.