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Perfectly PitchedA GUIDE TO THE VALLEYS: PITCHEDROOF VALLEY CONSTRUCTIONIn his latest Consultant Case Study, Pitched Roofing Consultant John Mercer focuses ontiled valleys and dispels some myths around mortar, plus offers some key guidance onan area that, in his experience, presents “some of the most common causes of roofleakage.”In this next case study, I turn my attention totiled valleys. In my long experience, some ofthe most common causes of roof leakage Ihave come across on tiled roofs are related tovalleys. Many people think that the mortar isthere to make the junction watertight, whichcould not be further from the truth. If you stopand think about it, slate and many plain tilevalleys are constructed without mortar and inScotland, even clay and concrete single lap tiledvalleys are constructed without mortar.“The contractor washoping that expandedfoam would keep thewater out, with just athin layer of mortarpointing at the edges”Above: An extreme example of a poorly constructed valleythat John recently encountered on site.The photo below shows an extremeexample of a poorly constructedvalley I came across recently;the lead has been laid flatover the valley boards, withno upstand or welt. Thecontractor was hoping thatexpanded foam would keep thewater out, with just a thin layer ofmortar pointing at the edges. The tilebattens have been extended over the lead towithin 10mm of the outer edge of the pointing. Tomake matters worse, the lead has been cut bywhat I presume was the disc cutter as tiles werecut in-situ.Lead-lined valleysThe main elements that keep the water out arethe upstands and welts at each side of the valley.The most common open width for a traditionalvalley is 125mm and this is generally satisfactoryfor normal domestic roofs. There are exceptions,such as low roof pitches and/or long rafterlengths and further guidance for these isavailable in the Lead Sheet Training Academy(LSTA) manual.A lead valley lining must be supported on timberboards which can sit on top of the rafters ifcounter battens are being used, or be fitted flushJohn Mercer, Pitched Roofing Consultant.with the tops of the rafters,supported on timber noggins,with a 4mm plywood liningover the top.25mm deep tile battens can beused to construct the upstands asthese will finish flush with the tops ofthe tile battens.The valley boards should be at least 225mm wideeach side of the valley to allow for a 125mm wideopen valley, with timber upstands set 150mmfrom the centre line of the valley and enoughwidth left to support the ends of the tile battens.If the open valley needs to be wider than 125mm,then the valley boards must be widenedaccordingly.Code 4 lead is suitable for most domesticbuildings, with Code 5 sometimes used on largerbuildings, laid in maximum lengths of 1.5 metres.The width of the lead sheet will depend upon theopen width of the valley, plus 200mm on eachside to allow for the width of the mortar bedding,25mm gap, the tilt fillet, a 25mm gap, and thewelt on the outside edge.The lead should be dressed into position with thecorrect amount of lap with the sheets above andbelow it. The headlap will depend upon the truepitch of the valley. At 30 degrees and steeper thelap should be 150mm. At lower pitches, the lapwill increase to, for example, 220mm at 20Continued on page 2422 TC OCTOBER 2020
RIVENDALE FIBRE CEMENT SLATESRIVENDALE FIBRE CEMENT SLATESCedral: proud to have been puttingCedral:roofsproudoverto haveheadsbeenfor decadesputtingroofs over heads for decadesCedral Rivendale slates are designed to reflect the qualities ofnatural Cedral slate, Rivendale at a fraction slates are of the designed cost. Available to reflect in the Blue-Black qualities or ofCromleigh natural slate, Graphite, at a fraction Rivendale of the slates cost. have Available a beautifully in Blue-Black textured orCromleigh surface Graphite, and dressed Rivendale edges, combining slates have the a beautifully benefit of textured modernsurface and dressed slate technology edges, combining with the the look benefit of a natural of modern slate.slate technology with the look of a natural slate.Rivendale Blue-BlackRivendale Blue-Blackmore at cedral.worldmore at cedral.worldTel 01283 501555 Email infouk@etexgroup.comEtex Tel 01283 (Exteriors) 501555 UK, Email Wellington infouk@etexgroup.comRoad, Burton-upon-Trent, Staffordshire DE14 2APEtex (Exteriors) UK, Wellington Road, Burton-upon-Trent, Staffordshire DE14 2AP
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