How is a wall constructed?
Measure the inner leaf thickness, cavity width & outer leaf thickness. Birtley recommends the use of an additional cavity tray with all external cavity wall lintels.
• Single leaf face brick or block external walls.
• 200-215mm solid brick or block walls.
• 215mm fair face solid walls with two leaves.
• 100mm and 140mm load bearing walls
• 100mm Non-load bearing walls
Measure the cavity width & the outer leaf thickness.
How wide is the opening?
The opening that will contain the window or door.
The Lintel: Should be minimum 300mm wider than the opening (150mm at each end) Except when noted otherwise.
How much weight is above the opening?
To determine which load duty is required, the imposed load must be fully assessed and quantified.
Loads can be direct e.g. walls/floors/live loads, or indirect, from adjacent parts of the structure – for which a proportion must be taken into account. Imposed loads should be derived in accordance with PD6697/BS5977, and unfactored when compared with our published Safe Working Loads (SWL).