Technical Booklet D Structure·Page 49·4B.14
Timber section sizes and processing for flat roof joists
Joist sections must be sawn to tolerance class 1 thickness and class 2 width per BS EN 336, or be CLS/ALS processed sizes to class 2, to provide level surfaces for ceiling lining and structural decking.
The section sizes are either sawn across the timber thickness in accordance with tolerance class 1 of BS EN 336 and processed in accordance with tolerance class 2 of BS EN 336 across the timber width (joist depth), or are CLS/ALS processed sizes in accordance with tolerance class 2, to provide level surfaces for ease of ceiling lining and the fixing of structural decking.
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