Mild Steel
Types and Durability
| Description
Mild Steel |
Expected Lifespan
(Years ) |
Adjustment Factors |
| General | ||
| Hot dip galvanized steel to ASTM E 1514-98 or BS EN 10142 or BS EN 10147, minimum 275 g/m² zinc coating weight. PVC/ Plastisol coating, 200 microns nominal thickness [1] | 25 | 1st stage adjustment factor:
In industrial areas (heavy polluted): -15% years In urban areas: -10% years In suburban areas: -0% years 2nd stage adjustment factor: Within 20m from express way: -20% years Within 20m from major arterial road: -10% years Within 20m from light traffic road: – 5% years Within 20m from sea water/ area prone to salt spray: -15% years Test certificate from approved local testing authority : +15% years |
| Hot dip aluminium-zinc coated steel to ASTM E 1514-98 or BS EN 10215, minimum 150 g/m² zinc coating weight. Acrylic/ polyester/ silicone polyster/ PVDF/ PVF2 coating, 25-50 microns nominal thickness [1] | 20 | |
| Acrylic/ polyester/ silicone polyster/ PVDF/ PVF2 coating to ASTM E 1514-98, 25-50 microns nominal thickness [1] | 15 | |
| Hot dip galvanized steel to ASTM E 1514-98 or BS EN 10142 or BS EN 10147, minimum 350 g/m² zinc coating weight [1] | 10 | |
| Mild steel not relevant to BS, or coating/ surface protection less than above specification [1] | <10 | None |
Source: BPG Building Fabric Component Life Manual, Building Performance Group; London; 1999 [1]
Related Test Method:
- Dry Film hardness to ASTM D 3363
- Chalk resistance test to ASTM D 4214
- Detergent resistance to ASTM D 2248
- Alkali resistance to ASTM D 1308
- Humidity resistance to ASTM D 2247
- Salt spray resistance to ASTM B 117
Combination of adjustment factor (1st stage and 2nd stage) should be added to obtain the durability values. Refer to durability calculator.
Assumption: Expected life spans depends on coating as coatings may deteriorate during the lives quoted. Recoating is feasible but is not normally practical and is rarely carried out. [13]
The life of the metal coating depends on the colour, orientation and environmental condition. TERNE coating may be applied for decorative purposes only.
Design and installation in accordance with ASTM 1637: 1998 or BS 5427: Part 1, BS 8200 and in strict accordance with manufacturer’s instruction.
Adequate provision for movement to be made in the system installed
Any ferrous metal fastener assemblies used in roofing shall be tested to ASTM D 6294: 1998 for corrosion resistance. Fixings to be plated carbon steel or stainless steel to BS 1494: Part 1, or proprietary fixings in accordance with manufacturer’s guidance, and to be compatible with other metal used. Type and spacing of fixings to be protected, eg by push on caps or integral plastic heads. Aluminium to be fitted with austenitic stainless steel fixings (which must be isolated from the aluminium in marine or heavily polluted environments due to risk of bimetallic corrosion). [13]
To prevent bimetallic corrosion, aluminium sheets shall be separated from steel purlins/ rails, eg with PVC tape, zinc chromate paints, where 2 or more metallic are used , they should be either compatible or be separated. [13]
Spacing of supports and spacer bars in accordance with manufacturer’s load span tables. Spacer bars, channels, supporting purlins etc to be minimum 275 g/m² galvanized steel or no less durable than the cladding.[13]
Provision of vapour control layer, breather membrane and ventilation to built up systems with test method according to ASTM E 1646: 95 or E 2140-01.
Sealants to side and end laps (where required by BS 5427: Part 1) to be non-setting gap filling, or preformed tape, and compatible with the metal and its coating, and UV resistant if exposed to sunlight with standard specification toASTM C 509: 2000 [13]
Provision of movement joints in accordance with BS 5427: Part 1, Table 5
In external/ damp locations, avoids direct contact between aluminium alloys and timber treated with copper, zinc or mercury based preservatives, Oak, Sweet, Chestnut, Douglas Fire, Western Red Cedar, copper alloys (or rainwater runoff from), concrete, mortar or soil.
Where the roof is designed for regular access, special walkways should be provided to prevent damage to the cladding.