Weatherproofing Penetrations

At any penetration in the pre-finished steel sheet, there will be an exposed cut-edge, and also an area where water may ingress into the building. This area will need to be protected in order to prevent this. Site cut edges should be protected with a suitable clear lacquer before the weatherproofing is done.

Potential solutions

• Rubber gaskets can be used on vent pipes or other small penetrations. These consist of pre-formed EPDM or silicone rubber bellow gaskets with a pliable aluminium strip around the periphery, which can be worked around the shape of any profile. The edge is bedded with a gun grade sealant such as silicone and fixed with sealed rivets or stitcher screws. Rubber soakers are adaptable to most profile shapes and provide a good solution if applied well. Water must be able to drain from behind the soaker, meaning that large diameter pipes may need to be sealed with a rubber gasket to a flat apron flashing taken back to the ridge.
• In the case of profiled cladding, profiled soakers are used, consisting of factory-made Glass Reinforced Polyester (GRP) or aluminium soakers, which provide a transition from the profile shape to a flat leading to the upstand. These lap into the profile, with laps being sealed as with normal end or side laps. These are not suitable on very low roof pitches less than 4 degrees. Note that if profiled soakers are manufactured from a different material and have a different topcoat from the roof, they will cease to have the same appearance after time, because of differential fade and ageing.
• Apron flashings are flat sheet soakers, at the level of the crown of the roof sheet profile and are laid over the roof sheet, providing a convenient method of weathering openings, particularly with concealed fix profiles at very low slopes. The wide, flat lap between apron flashing sheets should be sealed with twin lines of sealant and stitched with sealed rivets or screws atm 75-100 mm centres. Longitudinal laps should not be used, and edges should be turned down over the profile ribs. The use of rigid insulation board, such as Polyurethane (PUR) or Expanded Polystyrene (EPS), in the profile pans between the apron and roof profile, will help support the apron and resist accidental damage.
• On-site application of Glass Reinforced Polymer (GRP) can also be used to weatherproof an opening. This is another specialist operation in which the advice of an expert applicator should be sought. Corus has carried out tests into site-applied GRP used with Colorcoat HPS200® Ultra, and is satisfied with material compatibility. The designer will need to consider drainage around the opening, the long-term durability of GRP, support to the bond area and differential colour ageing. Again, a specialist should be used to carry out the complete procedure.

With all methods of weathering openings, it is the early planning of opening positions which will allow the best detailing. Trimmers need to be introduced and the vapour control layer needs to be sealed to the opening surrounds to ensure continuity. Openings should ideally be positioned as close to the ridge as possible, in line upslope. Penetrations installed after completion of the roof area will need a trimmer to provide support to the surrounding area, and continuity of seal of the vapour control layer. Attention should be paid to the prevention of cold bridging and to the continuity of insulation.