Roofing

22.5° pitched roofs with OSB sarking (Scotland) - lead valleys

Anonymous user 23/02/2024 - 3.36 PM

I am hoping some of the experienced roofers can advise on a few questions/problems I have. 1. Standard lead valleys (2 roofs at 90° to each other) installed straight on to the the 9mm sarking board, unfortunately nailed along lead edges so no expansion and lead has split, leading to rot in OSB. The lead is only 300 wide code 4. Should 18mm valley boards be used in Scotland or is 9mm OSB or 9mm ply on top of trusses sufficent. Additionally should lead be 425mm min width to suit (marley plain concrete tile, dry ridges/edges). 2. Existing underfelt is tar based (roof replaced 13 years ago). Some areas where slope meets tilting fillet at eaves edges are perished. Possibly due to the sarking at eaves edge being horizontal (no slope) and the valley issues as noted above. I intend to ensure slope on eaves edge and replace lower strips of felt. If possible, please recommend modern replacement non breathable felt for laying on sarking which can also be laid in strip under lead valley on top of boards. 3. Finally my biggest problem, I have a central valley gutter (tapered gutter) between 2 parallel roofs, with 3rd rood at one end also feeding in. There is a 6m long, 2 lead sections each approx 3m long by 1.2m wide (800 flat 200 tapered either side on pitched roofs) with a 25mm step between (both code 4). Needless to say it has split in numerous places from 2 years after fitting.. (thank goodness for Acropol+). After replacing the sarking/valley boards, I was thinking of replacing with either lead code 6, with 2 off 50mm steps (if I can fit in) and lead wood cored roll to split the upper 1200 wide section (as per LSA) or trying pvc (Sika Sarnafil was my first thoughts) or other bonding membrane. I would appreciate thoughts on this or alternative membrane which may be suitable. A few pictures of valley are here www.cmacd.org/pics Any advice on the above very much appreciated many thanks Cam

Joe furey roofing

Rating: 5 out of 5

5/512 reviews

Colchester

450 mm code 5 lead for Valley. 18 mm ply or osb board sufficient fixed to top of roof trusses will be fine . Tilting fillets to be fixed to ply board to act as water check for lead installation. Where you fix the tilting fillet to ply will be determined by size of lead used and the width u would like the finished tiled vslley to be. Minimum side lap of 100 mm on the side lap of tiled valley. (So finished cut and tiled valley must cover the lead by 100 mm both sides from top to bottom. A wide range of breathable membranes on offer varying in price. Don and low roof shield is the best membrane I've used. A lead box gutter can be done in code 5 lead . The longest span you can have in a box gutter is 1.8 m before you will have to step down to a new bay. The maximum width of a bay before you have to split it into 2 bays with a mop stick running down the center is 1 m. Everything else you explained is good practice on your end. Hope this helps

Answered6 October 2020

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AD Roof Specialists

Rating: 5 out of 5

5/5145 reviews

Wigan

Hi. Additionally, to the above advice, I would strongly recommend that, before any code 5 lead is installed, that you cover the timber boarded area with a geotextile fleece to eradicate any condensation from stone,concrete or timber, and this will also protect against any uneven nature of substrate and provide support against downward pressure. Good luck. Adrian AD ROOF SPECIALISTS

Answered27 June 2021

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