Sod Roofs, Norway

Erosion at the verges was in some districts prevented by means of similar logs, sometimes joined crosswise at the gable top. More common was a row of rocks gathered from the fields. Verge boards were not a feature of ancient log buildings with sod roofs, but were introduced during the 17th and 18th centuries through influence from urban architecture with tile roofs.
In modern turf roof construction bitumen roofing felt combined with dimpled plastic drainage membranes are usually used in place of birch bark. Bitumen roofing felt is nailed to the sarking and a dimpled cavity drainage membrane is laid over the top (dimples face down) to form a drainage layer. The turf is then laid over this drainage layer.