 However, by the outbreak of the First World War, the industrialised timber construction system had become more widespread.Also a comparatively recent "import" to Finland is the use of wooden shingles for roofs, dating only from the early 19th century.Previous to that, the traditional system had been a so-called birch-bark roof (in Finnish, "malkakatto"), comprising a wooden slat base, overlaid with several layers of birch-bark and finished off with a layer of long timber poles by weighed down in places by the occasional boulder.