Large-format tiles
Wall tiles above 3 m needing mechanical fixing (BS 5385-1:2018)
- where
- face area of one tile (m²)
- tile length and width (mm)
- tiled area above the fixing height (m²)
- width of tiled wall (m)
- height to the top of tiling (m)
- height above which mechanical fixing is required (3 m)
- tiles needing mechanical fixing (approx.)
Explain this equation
Use this when tiling tall walls with large tiles, such as stairwells, atriums and commercial washrooms, to see whether BS 5385-1 calls for mechanical fixings and roughly how many tiles are involved.
At is the face area of one tile. BS 5385-1:2018 applies the rule to tiles over 0.1 m². Aab is the tiled area above Hf, the 3 m line. Nt is how many tiles fit in that area.
The area above 3 m is the wall width times the height of tiling above the line, and never less than zero. Dividing by one tile’s area and rounding up gives the tile count. Tiles of 0.1 m² or less are outside the clause, so the count is zero.
A 4 m wide wall tiled to 4.2 m with 1200 × 600 tiles has 4.8 m² above 3 m, about 7 tiles needing fixings. Swap to 300 × 300 tiles (0.09 m²) and the clause no longer applies.
Watch out: tiles that straddle the 3 m line count too. The type and number of fixings per tile come from the fixing maker or a designer.
Flags when large wall tiles are high enough to need mechanical fixings and estimates how many tiles are affected.
Enter your values to see the result.
Good to know
BS 5385-1:2018 asks for secondary mechanical fixings on tiles larger than 0.1 m² fixed more than 3 m above floor level, so a falling tile cannot injure anyone below. On tanked walls agree the fixing method with the membrane maker. Large tiles also need solid bedding and a background able to carry their weight.
Common mistake
Treating the 3 m line as the top of the tile; any tile whose upper part is above 3 m is in the zone.
Limits
Area estimate for a plain rectangular wall; count tiles from the setting-out drawing for the final figure. Fixing type and number per tile come from the fixing manufacturer or a designer. External walls follow BS 5385-2.
Sources
Results are calculations from the published methods and manufacturer figures shown, and depend on the data you enter. Always follow the tile, adhesive and grout manufacturers’ instructions, BS 5385 and the Tile Association guidance. Coverage rates vary by product and substrate. Check prices and VAT rules with your own records and HMRC.