What is an open timber roof?
An open timber roof (in Dutch ziende kap) is a roof structure that can be seen from the room below, because there is no ceiling or loft floor in between. Trusses, purlins, rafters and roof boarding stay on show and give the space its character. Open roofs are found in early Christian churches, medieval halls and barns, and today also in homes and converted farm buildings.
Well-known examples are the Ridderzaal (Hall of Knights) in The Hague and Westminster Hall in London, with its famous hammer-beam roof.
Application
- Tall, spacious rooms: the space runs right up to the ridge, giving height and light.
- Heritage buildings and conversions: when churches, barns and farmhouses are converted, the existing roof is often deliberately left exposed.
- New build: homes with open lofts or galleries use trusses or glulam beams designed as exposed work.
Practical tips
- Insulate on the outside: to keep the structure visible, insulation usually goes above the rafters (sarking or over-rafter insulation). This changes the roof build-up and often the eaves and ridge height; listed buildings usually need consent for this.
- Vapour control layer: it must run airtight on the warm side of the insulation, including around timbers that pass through the envelope. Otherwise condensation can form in the roof.
- Timber quality: knots, splits and old saw marks are on show. Specify appearance-grade timber, or clean old timber rather than sanding it down.
- Structure: never remove a tie beam, collar or wind brace for extra headroom without advice from a structural engineer; they keep the trusses in shape.
- Acoustics and fire safety: a space open to the ridge is more reverberant. Also check fire safety requirements for the finishes.
Related terms
- Roof truss
- Rafter
- Collar beam
- Hammer beam
- Sarking over-rafter insulation
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