High Access Roofing offering Lead Flashings across London, London.
Parapet gutters have horizontal flashings on the parapet side.
The flashings are secured by being wedged into joints in the parapet or screwed into the joints. This results in the lead not being able to freely expand or contract along this side. Lengths of flashing should therefore be kept short to avoid excessive movement, with laps every 1,5m. Movement in longer lengths will result in a crease forming when the material expands. Over time fatigue lines form and eventually fracture from repeated expansion, allowing water ingress. In such circumstances it is not necessary to renew the entire flashing, as a small piece of lead can be wedged and pointed into the flashing joint, lapping over both sides of the crack.
Further problems can occur when a flashing that is turned into a masonry joint springs out, allowing water ingress. This can happen through inadequate fixings or because the turn in to the masonry joint is too shallow.
Deep Flashings and Vertical Flashing
A flashing of 250mm width can have anything up to 150mm of unprotected substructure behind it. The installer should always check that the lap is slightly more than equal to the exposed substructure, to ensure that the flashing protects from wind driven rain. This is usually an unseen potential failure point, but easily checked by lifting the overcloak and measuring the lap.
It is essential with vertical cladding to ensure the fixing is correct. As the codes of the lead increase, the weight increases and a common fault is the head fixing, which should be determined by the size and weight of the panel. Normally Codes 4 and 5 are used for vertical cladding, and panels under 500mm high can be adequately secured with one row of nails fixed 50mm apart. For larger panels two rows of nails are required, 75mm apart with staggered centres. Panels using Code 7 or 8 should be fixed with three rows of nails.
Where vertical cladding has been inadequately fixed at the head, problems present themselves in the form of slipped. Over-fixing results in bulging panels where movement has been restricted.
Clips are an essential element of vertical cladding and should be fitted to the bottom edge to prevent wind lift. The lower 2/3 of a vertical cladding panel must be left free to expand and contract with natural thermal movement. Vertical clips should therefore be turned so that a minimum gap of 6mm is left to allow the panel to expand.
A clip that is fitted without this gap is easy to spot. If it is a lead clip, the panel will simply push the clip open. If the clip is of a hard metal, such as copper, then a bulge will form in the lead immediately above the clips, clearly showing where its movement has been restricted.