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Timber collar beam roof and roof coverings

Short answer

A collar beam roof uses wall plate (75x100mm), common rafters (50x100mm at 400-600mm c/c), collar beam (40x100mm), ridge board (40x150mm), and battens (25x40mm). Pitched roof coverings include thatch, clay tiles, slates, stone slabs, AC sheets, GI/CGI sheets, aluminium/steel sheets, plastic sheets, and wooden shingles, each with distinct properties like cost, weight, durability, and slope requirements.

Draw and explain different components of timber collar beam roof with their sizes. Explain different types of roof covering for pitched roof.

Components of a collar beam roof (with usual sizes)

A collar roof is a couple (or couple-close) roof in which a collar beam (horizontal tie) joins each pair of rafters at about one-third to one-half of the rise above the wall plate. The collar stops the rafters from sagging and spreading, and allows a slightly larger span (about 5 m) than a couple-close roof.

            ridge
             /\
            /  \
     collar/----\ collar beam
          /      \
         /        \
      __/__________\__
     wall plate   wall plate

The collar beam is bolted to the rafters; battens and the covering are fixed over the rafters.

MemberUsual size
Wall plate75 x 100 mm
Common rafter50 x 100 mm at 400-600 mm c/c
Collar beam40 x 100 mm (or 50 x 75 mm)
Ridge board40 x 150 mm
Battens25 x 40 mm at 300 mm c/c (for tiles)

Types of roof covering for pitched roof

CoveringMain properties and use
Thatch (straw, khar, reed)Cheapest, good insulation, high fire risk, needs 45-60 degree slope, short life
Clay tiles (country, Mangalore, Allahabad)Good insulation, durable, heavy, need close battens; slope 25-45 degrees
SlatesDurable, fire resistant, neat; heavy and costly; slope above 25 degrees
Stone slabs (patthar)Used in hilly Nepal; very heavy, durable, needs strong rafters
AC (asbestos cement) sheetsCheap, light, fire resistant; brittle, health hazard (asbestos)
GI / CGI sheetsLight, easy and quick fixing, durable if coated; noisy, hot, can corrode
Aluminium / coloured steel sheetsLight, rust-resistant, many colours; costly
Plastic / fibre / polycarbonate sheetsLight, translucent; low strength, UV ageing
Wooden shinglesGood insulation, attractive; fire risk, decay

✓ Answer checked by Claude Opus 5.5 (high effort)

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