MortarThePoint Posted October 7, 2020 Share Posted October 7, 2020 I'm trying to work out where the flashing and cavity trays will sit on a roof abutment. I don't have the rafter to put in place and measure off, but I do have a drawing of the bay window roof exterior surface. I need to work all this out so I can get the positions of the stepped cavity trays correct as they get built in to the wall now. Their corners align with the corners of flashing, so it's lead me to try to understand this (excuse the pun). I can see NHBC recommend at least 85mm (some of their docs have 65mm min) between the roof surface and water line which defines the positions of one set of corners of the flashing. What I can't work out is what sets the position of the other set of corners. Is it just set by the height of courses and drawing a line perpendicular to the roof slope? I've seen something that suggests they sit on a line 150mm from the roof slope. I have attempted to draw this below with the lead shown in grey and the reference lines at 85mm from roof slope and 150mm from roof slope. The red rectangles show coursing and would be the positions of stepped cavity trays. Wider lead flashing or moving it off the roof slope slightly (so up the soakers a bit) would create a tighter angle on the 'saw teeth'. I imagine these must never result in the cut line sloping the other way. Is there a minimum amount of overlap on each step? Finally, can you stop when the lead goes past being vertically above the end of roof slope or is there a minimum amount it has to go past the end of roof slope. In the example below, could I have stopped one brick course higher at the bottom? Lots to understand so thank you if you made it this far. Link to comment Share on other sites More sharing options...
Mr Punter Posted October 7, 2020 Share Posted October 7, 2020 You may be overthinking this. Make sure the cavity trays are higher than the top of the roof and have a decent weep hole at the end. It is sometimes tricky as you may have the brickwork up a long time before the sloping roof. On existing buildings BC sometimes just allow a coat of silane / siloxane on the brickwork above. Lots of connies get put on existing houses and stepped cavity trays are out of the question. I don't hear too many horror stories. 1 Link to comment Share on other sites More sharing options...
tonyshouse Posted October 8, 2020 Share Posted October 8, 2020 I don’t like stepped flashings any more , angle grinder cut angled slightly up 85 to 100mm up. Then secret gutter under the tiles with or without cover flashing Link to comment Share on other sites More sharing options...
MortarThePoint Posted October 8, 2020 Author Share Posted October 8, 2020 1 hour ago, tonyshouse said: I don’t like stepped flashings any more , angle grinder cut angled slightly up 85 to 100mm up. Then secret gutter under the tiles with or without cover flashing Thanks, do you have a drawing or photo of this as it's difficult for me to get my head around. Do you still do the same thing as in my first post with stepped cavity trays though? Link to comment Share on other sites More sharing options...
tonyshouse Posted October 8, 2020 Share Posted October 8, 2020 Yes, much easier and less lead Link to comment Share on other sites More sharing options...
tonyshouse Posted October 8, 2020 Share Posted October 8, 2020 (edited) For me the lead goes in too far on this detail, 20mm plenty, also should go in slightly uphill to direct any water outward imagine a cut running up at the same angle as the roof but 80mm above the tiles - I call it a cover flashing Edited October 8, 2020 by tonyshouse Missed phrase 2 1 Link to comment Share on other sites More sharing options...
Temp Posted October 8, 2020 Share Posted October 8, 2020 5 hours ago, tonyshouse said: Yes, much easier and less lead Although stepped flashing does look good when done right. Link to comment Share on other sites More sharing options...
tonyshouse Posted October 8, 2020 Share Posted October 8, 2020 I think the straight cover looks more modern and cleaner. Link to comment Share on other sites More sharing options...
MortarThePoint Posted October 11, 2020 Author Share Posted October 11, 2020 On 08/10/2020 at 12:43, tonyshouse said: For me the lead goes in too far on this detail, 20mm plenty, also should go in slightly uphill to direct any water outward imagine a cut running up at the same angle as the roof but 80mm above the tiles - I call it a cover flashing So you end up with a constant with band of lead on the wall at the same slope angle as the roof. What's done with the cavity trays then? Link to comment Share on other sites More sharing options...
tonyshouse Posted October 11, 2020 Share Posted October 11, 2020 I have never use cavity trays for roof abutments nor had any problems, They can still go in if you want weeping out onto the face of the brickwork. Link to comment Share on other sites More sharing options...
MortarThePoint Posted October 12, 2020 Author Share Posted October 12, 2020 13 hours ago, tonyshouse said: I have never use cavity trays for roof abutments nor had any problems, They can still go in if you want weeping out onto the face of the brickwork. Surely you have to over bay windows or any enclosed spaces? Link to comment Share on other sites More sharing options...
makie Posted October 12, 2020 Share Posted October 12, 2020 4 hours ago, MortarThePoint said: Surely you have to over bay windows or any enclosed spaces? If you want to do it properly. Link to comment Share on other sites More sharing options...
tonyshouse Posted October 12, 2020 Share Posted October 12, 2020 Yes, but very close under a window sill is low risk, to each side of the window above a bay, yes , minimum is to tray the water sidewards And downwards and out to the face of brickwork with a welt at the bottom end Link to comment Share on other sites More sharing options...
MortarThePoint Posted October 20, 2020 Author Share Posted October 20, 2020 I'm still not convinced I have made the correct decisions with all this, but the roofers have said they can work with it so fingers crossed Link to comment Share on other sites More sharing options...
MortarThePoint Posted October 21, 2020 Author Share Posted October 21, 2020 I'm considering lead alternatives for the flashing. Perhaps Zinc, but a supplier has quoted to use Wakaflex. Are the rubber type flashings any good? How well do they stand the test of time? Link to comment Share on other sites More sharing options...
tonyshouse Posted October 21, 2020 Share Posted October 21, 2020 One I did earlier https://www.dropbox.com/s/93ov68omfwzd00v/cover flashing.JPG?dl=0 1 Link to comment Share on other sites More sharing options...
Onoff Posted October 21, 2020 Share Posted October 21, 2020 12 minutes ago, tonyshouse said: One I did earlier https://www.dropbox.com/s/93ov68omfwzd00v/cover flashing.JPG?dl=0 Are you intending to weld that top lap? Love a bit of lead welding. Link to comment Share on other sites More sharing options...
PeterW Posted October 21, 2020 Share Posted October 21, 2020 That is a very long piece with no breaks. Do you not find that sort of length wrinkles when it gets too warm ..?? Link to comment Share on other sites More sharing options...
tonyshouse Posted October 21, 2020 Share Posted October 21, 2020 (edited) Not on the North side of a building, yes, over the limit for code 4 but no problem yet. I normally do 1.2m long = 1/5 th of roll cheated on this porch 1/2 3m roll top lap will be cut to the left a bit and plumb Edited October 21, 2020 by tonyshouse Sp 1 Link to comment Share on other sites More sharing options...
makie Posted October 21, 2020 Share Posted October 21, 2020 2 hours ago, tonyshouse said: Not on the North side of a building, yes, over the limit for code 4 but no problem yet. I normally do 1.2m long = 1/5 th of roll cheated on this porch 1/2 3m roll top lap will be cut to the left a bit and plumb 1.5m is fine with code 4. It's the max recommended by the LSA. Link to comment Share on other sites More sharing options...
tonyshouse Posted October 21, 2020 Share Posted October 21, 2020 I know but you can get wrinkles in it especially if it is in the sun, I often see cracks in 1.5m long stepped flashings Link to comment Share on other sites More sharing options...
MortarThePoint Posted October 23, 2020 Author Share Posted October 23, 2020 (edited) On 21/10/2020 at 15:58, tonyshouse said: One I did earlier https://www.dropbox.com/s/93ov68omfwzd00v/cover flashing.JPG?dl=0 Looks smart. Is this over a non-enclosed space (e.g. porch)? Edited October 23, 2020 by MortarThePoint Link to comment Share on other sites More sharing options...
tonyshouse Posted October 23, 2020 Share Posted October 23, 2020 Yes, but I would do the same even if not Link to comment Share on other sites More sharing options...
tonyshouse Posted October 23, 2020 Share Posted October 23, 2020 (edited) And on my own house like this, can you work out what I did? https://www.dropbox.com/s/fvpm7gh2tespz75/Porch .jpg?dl=0 Edited October 23, 2020 by tonyshouse Wrong link Link to comment Share on other sites More sharing options...
MortarThePoint Posted September 16, 2021 Author Share Posted September 16, 2021 (edited) On 21/10/2020 at 15:58, tonyshouse said: One I did earlier https://www.dropbox.com/s/93ov68omfwzd00v/cover flashing.JPG?dl=0 I've come back here after however many months and it's time for the roofers to tuck in their lead. Still think yours looks very nice. Looks like the vertical height of the flashing is about 130mm so at 45 degrees was it a 100mm strip of lead tucked in around 10mm? [90mm/COS(45) = 127mm] Or have you tucked it in much further ~50mm? Edited September 16, 2021 by MortarThePoint Link to comment Share on other sites More sharing options...
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