Porcelain on pedestals
Pedestals needed for a terrace (corners shared)
- where
- tiles along the length and width, rounded up
- terrace length and width (m)
- tile length and width (mm)
- joint set by the pedestal tabs (mm)
- total pedestals
- extra (centre) pedestals under each tile
- pedestals per m²
Explain this equation
Use this to order pedestals for a raised porcelain or stone terrace on a roof, balcony or over a slab.
nx and ny are the numbers of tiles across each way, including part tiles, from the terrace size and the tile size plus joint. P counts every grid corner, where up to four tiles share one pedestal, and adds e centre supports per tile.
A grid of nx by ny tiles has one more line of corners than tiles in each direction, so corners are (nx + 1)(ny + 1). The 1000 converts metres to mm. The rounding up covers the cut tiles at the edges.
For 600 × 600 tiles the count tends to about 2.7 per m² on a very big area but is near 4 per m² on a 20 m² terrace because of the perimeter row. Adding a centre pedestal roughly doubles the count.
Watch out: cut tiles against walls and upstands often need extra pedestals under the cut edge.
Counts pedestals for a rectangular terrace: one at every tile corner (shared by up to four tiles) plus any centre supports.
Enter your values to see the result.
Good to know
A grid of nx × ny tiles has (nx+1) × (ny+1) corner points, so over a big area the count tends to one pedestal per tile, rising on small areas because of the perimeter row. Suppliers suggest a central pedestal on slabs of 600 × 600 and over where extra stiffness is wanted, and two for rectangular slabs 1200 mm long. Add pedestals where cut tiles need support along walls and upstands.
Common mistake
Ordering one pedestal per tile and running short along the perimeter, or forgetting extra pedestals under cut edges.
Limits
Rectangular area, tiles laid in a straight grid from one corner. Offset layouts and L-shaped terraces need a drawn plan. Check pedestal spacing and centre-support needs with the paving manufacturer.
Sources
- Plots-discount, Calculation of the number of adjustable pedestals (60 × 60 slabs: 4.0/m² at 20 m², 3.6/m² at 40 m²; 7.2/m² with a central pedestal)
- LABC Warranty Technical Manual, Section 12 Roof terraces and balconies (finished falls ≥1:80, design falls 1:40; support height within manufacturer maximum; loads to BS EN 1991-1-1)
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.