Specification of Lead Flashings
Lead Flashings are the first and frequently the only form of defence against water penetrating the horizontal and sloping junctions formed where a roof meets a wall or a parapet. However these abutments are generally amongst the most exposed parts of a building so they have to withstand all that nature can throw at it.
With Annandale Roofing you can feel safe with the knowledge that any leadwork that is being installed is to the highest specifications. We follow the guidance set down by the Lead Sheet Association to ensure that all leadwork is being carried out in a consistently high quality manner.
There are many situations where a lead flashing would be used for example around chimneys, windows, abutments or pipe outlets.
Example of inadequate specification of lead flashing
We were at a job recently where the leadwork was sub-standard. It was a newly built extension and there was a apron flashing in place where the head of the pitched roof met the adjoining wall. The flashing should have an upstand of at least 75mm and extend 150mm over the surface of the roof covering (200mm in severe exposures) and the lengths of flashing should be cut no longer than 1.5m (code 4 or 5). These aspects of the flashing were done correctly so to the untrained eye it would seem that everything was in good order.
Flashings must be turned-in to joints by a minimum of 25mm and secured by folded wedges or (as we prefer) fixing clips at 450mm centres. The flashing in question had nothing to secure it in place and was only turned into the wall by a meagre 5-10mm. The flashing should overlap at joins by 100mm minimum, in this case the end-to-end laps were only 20-50mm which would have caused water ingress. There were also no clips in place to secure the free edges of the flashing, these clips should be placed at 300 to 500mm centres with lead clips being used for sheltered exposures and tinned copper or stainless steel for most other situations.
pointing can be carried out with mortar but we use lead sheet sealant which provides a long term flexible joint which can absorb temperature changes and is quicker and cleaner to use than mortar. In rainy or damp conditions new lead will quickly develop an uneven powdery white coating of lead carbonate which will run and stain the roof tiles. We always use patination oil to minimise this which gives a more pleasing appearance to your new leadwork.
As you can see from this short example leadwork is not exactly straight forward but when installed correctly lead sheet is a proven, long life building material. As mentioned before, here at Annandale Roofing we follow the basic steps to ensure that any leadwork we carry out will last the test of time.