Steel
Types and Durability
| Description
Steel – suspension grid and channel |
Expected Lifespan
(Years) |
Adjustment Factors |
| Pre-galvanized steel to SS 117: 1995, minimum 300 g/m² zinc coating weight. | > 30 | Life limited to 10 years if plain steel fixing is used.
Excessive exposure to steam and moisture or under category ‘Severe’ (S) to BS 8290:Part 1 : – 15% years Near overhead pipe: – 10% years. Test certificate from local approved testing authority : +15% years |
| Pre-galvanized steel to BS EN 10142, minimum 275 g/m² zinc coating weight. Polyester powder coating to BS EN 10161 or liquid organic coating to BS 4842, minimum 40 micron coating thickness. | 30 | |
| Pre-galvanized steel to BS EN 10142, minimum 275 g/m² zinc coating weight | 25 | |
| Pre-galvanized steel to BS EN 10142, minimum 140 g/m² zinc coating weight | 20 | |
| Steel not relevant to BS/ EN or less than above specification | < 20 | None |
In the case of 2 or more conditions of adjustment factor occur, the percentage of year shall be added.
Note: Life span quoted above are under category ‘Normal’ (N) to BS 8290:Part 1
BS 8290:Part 1 defines two categories of environment – Normal and Severe. These are used to assess the performance of protective finishes against corrosion for suspension system components, metal trays, etc. The conditions which these categories represent are:
- Normal (N): Relative humidity 30% – 70% at 10° – 30°C including occupied and heated buildings with no exposure to aggressive atmospheric conditions.
- Severe (S): Relative humidity and temperature conditions which are not covered by the Normal category environment. This category includes external and internal applications where high humidity and/or aggressive atmospheric conditions occur (e.g. swimming pools, or processing plants where ceilings are spray cleaned).
BS 8290 provides useful complementary information to this work section:
- Part 1 deals with design issues generally.
- Part 2 specifies materials, manufacturing tolerances and strength requirements for suspension grids.
- Part 3 deals with installation issues.
Other sources of information include the Specialist Ceilings and Interiors Association (SCIA) guides and Health Technical Memorandum 60.
Imposed loads
BS 8290:Part 2, requires manufacturers or suppliers to state the maximum uniformly distributed load (UDL) which their grids will sustain whilst keeping within prescribed limits of deflection. The BS 8290 load test uses a small number of assembled components for which loads and corresponding deflections are recorded for:
- Main and cross T members of exposed grids
- Primary support members for concealed grids with main runners (spring T, Z sections, etc.) included to impart stability only (i.e. not subjected to loading and deflection measurements).
The limits of deflection are:
| Span (between hangers) | Deflection (mid span) |
| Up to 1200 mm | span/400 |
| 1200 – 1800 mm | span/500 |
| over 1800 mm | span/600 |
Tests must include all variations in assembly and component details for which the ceiling grid is designed, including alternative:
- grid layouts and hanger spacing
- positions of spliced and expansion joints.
Information provided by manufacturers should include:
- Maximum loads relative to hanger spacing and grid layout. Additional hangers may be required for fittings (luminaires, access panels, etc.) which are to be supported via the suspension system
- Maximum distances of hangers from perimeters along main runners, primary channels, etc. necessary to prevent distortion of perimeter trims – normally 450 mm.
- Maximum distance of hangers from spliced or expansion joints – normally 150 mm.