Un-insulated roofs with single-skin metal sheeting are likely to suffer from condensation when the metal sheeting is cooled during the winter, or on cold clear nights.
When warm air within the building cools on contact with the metal sheeting it can not support the same quantity of water vapour and may
become saturated, with any excess water vapour condensing on the underside of the sheeting. The condensate can drip from the roof, wetting the building’s fittings and/or contents, or may run down the roof and collect elsewhere within the building fabric where it can cause rust, rot or
damage to fittings.
Condensation is the most common form of dampness encountered in buildings and Part C2 of the building regulations requires designers to prevent harmful condensation forming on or within building elements. Guidance is given in BS 5250:2002.
Made from interlaced PES fibres, Drain Dripstop slows the formation of condensate by insulating the sheeting and prevents dripping from
the underside of the roof by absorbing the moisture and draining it down through its fibres to the gutter.
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Drain Dripstop is suitable for use on roof slopes greater than 7° and the greater the roof slope the faster the moisture is drained from the sheet. Drainage performance of the material per hour for a range of roof slopes is shown on the right.
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| Property |
Roof slope |
Water drained out |
Outflow of water
after 1 hour |
7°
15°
25° |
>10%
>15%
>25% |
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Drain Dripstop controls condensation in an environment where it appears cyclically (it can’t prevent condensation). For the membrane to work properly the building has to be adequately ventilated to allow the material to dry out between the cycles (see diagram on the right).
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Eaves ventilation required = 2% of roof slope area
Ridge ventilation required = 5% of total roof area
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In buildings with poor ventilation or humidity levels greater than 80g/m²/hour roof sheet lengths should be reduced to control the amount of moisture handled by each sheet.
The table on the right gives recommended maximum lengths for a range of roof slopes.
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|
| Roof inclination |
7° |
14° |
21° |
| Recommended Max panel length |
3m |
5m |
7m |
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The table opposite shows moisture levels produced by livestock and the area required by each animal to keep humidity levels below 80g/m²/hour.
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|
| Animal |
Weight |
Moisture
produced |
Area req.
per animal |
| Cows |
500kg |
361gm/hr |
4.51Sq/m |
| Horses |
500kg |
361gm/hr |
4.51Sq/m |
| Sheep |
100kg |
83gm/hr |
1.04Sq/m |
| Pigs |
100kg |
83gm/hr |
1.04Sq/m |
| Chickens |
2.2kg |
5.5gm/hr |
0.07Sq/m |
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Temp 16°-18° 80% relative humidity |
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Installation of sheets fitted with Steadmans Drain Dripstop condensation control fleece is the same as standard sheets. However, when humidity levels are greater than 80g/m²/hour or ventilation is poor, velcro packers or similar are required at fixing screw positions on purlins and in end lap joints to allow the moisture from each sheet to drain out onto the sheet below. |
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Note: due to its composition there is no need to cut back or lacquer Drain Dripstop at the lower end of roof sheets.
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| Weight |
140g/m² |
| Thickness |
1.5mm |
| Colour |
White/black mix |
| Water absorption |
>1500g/m² (installed) |
| Fire classification |
B - s1, d0 |
Drain Dripstop has good resistance to most acids, hydroxides and sulphides and does not support the growth of bacteria or mould. |
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When used in livestock buildings Drain Dripstop should be pressure washed at least once a year with a solution containing fungicide. |
