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Rolled Lead Sheet

Rolled Lead Sheet INSTALLING ROLLED LEAD SHEET: HOW MUCH DO YOU REALLY KNOW? Darren Tutt, Lead Sheet Association Technical Officer, offers some top tips to assist contractors when working on projects which involve Rolled Lead Sheet. The Lead Sheet Association has been providing technical advice and training for decades across the construction industry. Using that expertise, we have put together the top ten issues and queries we deal with on a day-today basis to help contractors get the most out of this material. All the advice and guidance provided here is in relation to Rolled Lead Sheet manufactured to BS EN 12588 and conforming to the Standard set out in BS 6915. More detailed information about the following issues can be found in the LSA’s Complete Manual, or if you want a handy guide to basic information when you are out and about, on our new App – search LSApp – it’s available for Apple and Android. We are also on the other end of the phone to support contractors with more complex enquiries where we handle thousands of calls a year through our technical enquiry line. We know that contractors have to contend with many aspects of roofing and often bring in lead or hard metal specialists, but by sharing the following we hope to give you some guidance on the things to look out for. 1. Ventilation The consequences of installing lead sheet on an unventilated substrate can be detrimental to the expected longevity of the roof in question. All lead sheet should be laid on a thoroughly ventilated substrate. That means that under the decking the lead sheet that actually sits on there should be a minimum 50mm through-ventilated path with no stagnant air pockets. Even vertical applications should be ventilated although here the ventilated path can be reduced to 25mm. “All lead sheet must be laid on a minimum fall of 1:80 which equates to a little under 1 degree” 2. Neoprene expansion joints Traditionally, lead gutters incorporate steps or ‘drips’ in their design. These are intended to break up the lengths of lead sheet used to ensure that thermal expansion is within guidelines for individual pieces of lead. In many instances this works wonderfully well, but in others there simply isn’t the height to allow for them. Our advice is simple really – wherever possible stick to traditional tried and tested methods and only use neoprene expansion joints as a last resort. With 46 TC MARCH 2018

new-build design, the inclusion of drips should always be considered first. 3. Lead sizing Getting the thickness of the lead sheet right for a particular application is essential. Lead comes in a range of codes (thicknesses) yet so many times we see the wrong codes of lead used or the individual pieces of lead sheet installed in too large a piece. Lead sheet is a metal of low strength but provision for this is made by sizing and fixing within certain parameters so that the risk of fatigue cracking or ‘creep’ is minimised. Check the Manual – or App – to make sure you get the right code and the right length, lead is incredibly reliable if you get these things right and will last an incredible amount of time. 4. Underlays When asked what underlay – if any – is required the answer is quite simple. If exterior quality plywood, penny gap softwood boarding, penny gap oak boarding, stone, concrete or brick is used, a building paper to BS 1521 Class A should be used. It is only with penny gap softwood boarding that geotextile fleece can be used as an alternative. In all cases there must be throughventilation present. 5. Flashing lengths Lead flashings should nearly always be installed in 1.5m lengths, however there are exceptions. Lead flashings to asphalt, bituminous felt, or single ply roof coverings are continuously bonded along one side, therefore it is essential to limit the lengths to 1m so that the thermal movement of the lead sheet is not affected when exposed to long periods of summer sun. “We see lead flashings or other edges of roofing, cladding and weatherings missing any form of restraint to their free edges” 6. Falls All lead sheet must be laid on a minimum fall of 1:80 which equates to a little under 1 degree. Anything less may encourage ponding water and a build-up of debris and dust or staining of the lead sheet which should be avoided. 7. Clipping There are so many instances where we see lead flashings or other edges of roofing, cladding and weatherings missing any form of restraint to their free edges. All such edges must be adequately clipped to prevent lifting and distortion in high wind conditions, and it is amazing to see how often these are missed out or not considered at all. Clipping of lead sheet varies considerably in both material used and the distances that they are set apart – this is covered in detail in the LSA Manual. 8. Laps A lot of enquiries we get assume that a flashing should lap over a pitched roof covering by 150mm. This is true for a 30 degree slope, but what a lot of people don’t realise is that the lap length is wholly dependent on pitch and can vary considerably. We usually end up referring clients to the 75mm lap diagram that we show in the manual. Laps can vary between 75mm to 395mm on pitched roofs or even more if the exposure of a particular building is considered severe. It is also worth noting that the lap should always be taken from the lowest row of fixings in whatever it is covering. 9. Fixing The fixing of lead sheet is carried out in many different ways, all of which are dependent on the particular application. For instance, a lead roofing bay on a roof with a small pitch of up to 3 degrees differs in the arrangement and position of its fixings when compared to the same roofing bay on a higher pitch. These differences are very important to ensure correct installation and future longevity. Above: Lead is a contemporary building product that has been used by architects in many different scenarios “The consequences of installing lead sheet on an unventilated substrate can be detrimental to the expected longevity of the roof in question” 10. Damp Proof Courses (DPCs) Lead DPCs and trays are designed to prevent moisture that penetrates brick or stonework finding its way into the building. Many of the calls we receive regarding these centre around mysterious staining appearing. In nearly all cases this is caused by failure to treat the lead that is built into the walls with bituminous black paint on both sides prior to fitting. This coating prevents free alkali in fresh Portland cement mortar and sulphuric acid vapours that are contained in the moisture in chimneys from corroding the lead sheet. Contact the Lead Sheet Association 01622 872 432 @LeadSheetAssoc MARCH 2018 TC 47

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