Lead-lined roof gulley

[colinturner]

I need to replace the lead flashing which forms a 12m gully between the tiled roof of a single story building and the vertical wall of the main part of the house. The original flashing is in three sections (the longest being about 6m) and is admitting water through the joints which have been patched with various layers of bitumen and flashband over the years. The pointing where the flashing is wedged into the wall is also in poor condition and there are places where the flashing is not really wide enough to ensure complete waterproofing on the roof side.

I am proposing to replace the flashing with 600mm wide code 4 flashing which will allow me to go one course of bricks higher on the wall side and allow a good lap onto the battens supporting the tiles.

QUESTIONS
All the literature (from Wicks and Calder group) insists that lengths should be no longer than 1.5m, which means that I will end up with 8 lengths and 7 joints. In theory, I should form a step or \\\"drip\\\" at each joint and avoid an overlap or welt. This is impossible as there is not enough fall to accomodate it.
If I use overlaps, will it be sufficient to seal them with Calder\\\'s lead sheet sealant? This is intended for pointing lead/brickwork joints but I don\\\'t know how it will perform in lead/lead joints.

I have considered reinforcing the overlaps with strips of self-adhesive Flashband but don\\\'t know whether this will prove to be a \\\"bodge\\\" that will cause problems in the future.

Any advice or observations would be welcome - especially if received before the rain-clouds return!

 

[ChrisR]

Full answer would tale too long, but you use 4ft/1.5m sections to avoid the thermal movement tearing the lead, or the sheer weight of the gulley sheeting dragging it off down the gulley. Overlap the lengths a good length, say 1ft, but don't seal at all - no need and it would give you problems as the sheets moved relative to each other. Work from the bottom up and secure the upper ends as the books say.

600mm is wide for flashing, but if that's what you need, OK. You can get springy things to use instead of lead wedges in the mortar lines, which are much better.

"good lap onto the battens supporting the tiles.
"
Eh? the flashing goes over the tiles, not under, unless I've got the picture wrong (eg round a chimney stack... but that's different anyway!) Assuming its over the tiles, use lead hooks to support the lower edge of the flashing at intervals.

 

[colinturner]

Thanks Chris.
I think you're visualising a pitched valley gutter with a steep fall. In my case, the gulley is practically horizontal, with the highest point about a third of the way along and only a slight fall towards the two ends. The floor of gutter is supported on thin planks resting on the top of a narrow brick wall. This results in a certain amount of "pooling" and in rainy weather the standing water percolates through the patches I mentioned. Without sealant on the new lengths of lead, rain water will simply creep back under the overlaps. At the moment, I suffer from 3 leaks, but using 1.5m lengths (and I appreciate the good reasons for doing so) will mean 7 potential leak points instead of 3 javascript:emoticon(''), so I need to find a watertight solution.

The roof tiles are concrete with a "wavy" profile and a rough textured finish. The flashing needs to go under the tiles so they will shoot the water onto the lead. Putting it over the tiles will direct the water under the flashing and down my interior walls. Wish I could add a couple of photographs to illustrate the problem.

 

[masona]

Have you got room to build it up with exterior plywood like a ramp then lead on top or could you not remove bottom row of tiles then build your new fall into the rafters via your next row of tiles as you got more room to play with.Also do not nail lead down as it need expansion.Have you thought about using glass reinforced polyester coverings which come with a 25 years warranty.See this.

 

[colinturner]

Not a lot of room to manoeuvre. This is the sort of situation where remedying one problem tends to throw up several more. The part of the building which is roofed over is a long, single-storey ex-cowhouse or dairy which was converted into 3 rooms 50 or more years ago. Increasing the fall by lowering the ends of the gulley will involve a fair bit of structural work and could bring the gulley below ceiling height.
There is a limit to how far I can raise the central "hump" as there are only a few cms to play with before reaching the point where heavy rain will run off the side into the roof-space and through the ceiling. This has already happened where the original installer used flashing which didn't quite reach the battens supporting the bottom of the tiles, allowing water to go over the edge - hence my decision to use 600mm flashing to cover this vulnerable point.

Think I'm stuck with replacing the lead and waiting to see what happens.

BTW I tried the StormshieldUK link, but couldn't access the site. Google threw up several links to Stormshield but none of them worked, either.

BTW2 For UK readers - Travis Perkins proved the best local buy for the lead as they quoted me a price which was £100 less than Ridgeons

 

[masona]

Have a look at this. I have done 600mm lead flashing and it's extremely heavy !

If not can you post a drawing or photo?

 

[colinturner]

Thanks for the SLE link - well worth investigating and may be the ultimate solution. Having lifted the flahing away from the wall I'm committed to going ahead with the original plan and seeing what happens.

Yep, 600mm is heavy. I can lift a 3m roll so anticipate that 1.5m lengths will be just about manageable.

I was disappointed to find that my local Ridgeon's don't yet stock Borra flashing clips (a better alternative to lead plugs) and Travis Perkins have never heard of them.

The sun's shining, the weather forecast is good and my muscular son is home for the weekend - so I'd better get back up that ladder!

 

[masona]

Borra flashing clips are normally only available from roofing supplies,have look at your local Yellow Pages.

For those who want to know what Borra Flashing Clips is,see this.

 

[colinturner]

Ridgeons told me they had put in an order for Borra Flashing Clips and were expecting them to arrive in a week or so - I'd have bought 30 without hesitation if they'd had them in stock.

Back to the snips and rolled wedges.

Old flashing is coming off and revealing the horrors underneath - this is getting interesting.

 

[colinturner]

Have now stripped off all the lead, including generations of patches, and discovered that it was supported by an assorted collection of planks and offcuts of fibreboard. Lifted these to reveal what I had begun to suspect. The roof is not supported on its own wall - instead the ends of the rafters are supported in holes cut into the wall of the adjoining part of the house. The end of one rafter has completely rotted away and a couple of others look shaky. I've also had to open up a hole in the plasterboard which is now admitting a refreshing breeze.

I'm thinking of repairing the rotted rafter by bolting new timber on either side, extended to fit in the original socket in the brickwork.

After that, I'm a bit baffled. All I can think of at the moment is to make a series of 1.5m longitudinal steps with planking, overlapping them until I have a "summit" at approximately the mid point.. This would give the recommended "drips" between the sections of flashing.

Does this strike the experts (masona in particular) as the right approach, or should I consult a builder first thing on Monday morning?

If anyone cares to contact me by e-mail I would be able to take some pictures and send them to you.

 

[masona]

When bolting new timber on either side of the rafter don't forget to put timber connector in between rafter to stop it twisting & slipping + square washer on both side of the bolt.See this.


Can you not put the picture or drawing on the post for others to see?

Also no e-mail address on your 'Viewing Profile'

What area are you from?

 

[colinturner]

Can you not put the picture or drawing on the post for others to see?

Also no e-mail address on your 'Viewing Profile'

What area are you from?

I have put 6 pics here http://www.colinturner.glowinternet.com/gulleypics.htm

E-mail address should now be available from my Viewing Profile

The Cambridgeshire Fens

 

[masona]

Well done!

Right what you do now is,start at the end where you want it to fall from say approx 2" depending on your length.Make a firring out of 2"x2" sawn timber (firring is like a long wedge like they used to put it under flat roof for rain fall) Any good timber yard can make one for you.Put the 2 length side by side apart firring on top of your level wedge shape which is already sitting on top of the rafters,then use exterior plywood on top of the firring,(make sure you think you got enough fall,you test this with a golf ball!)then lead on top up to the wall and under the roof tiles as much as you can.Before you put the lead down put in a bottom batten (2 thickness) at the bottom of the tiles then lead over it.This will slow the rain down onto the gulley and also stop the water going back under the tiles.Put the bottom row of tiles back in position and cut the tiles to the new shape to the gulley & make sure the bottom of the tiles not rubbing on the lead..

 

[colinturner]

Thanks for the moral support - I need it!

The pictures may make the job look more straightforward than it is. The roof is a shade over 12m long and undulates a lot. The distance between wall and roof is not constand, either. Also, using 1.5m lengths of flashing on a shallow fall (minimum recommended gradient is 1:80) introduces the problem of water running back under the joints - which is why we've had leaks in the first place. Don't yet know how effective Calder Lead sealant is at making a waterproofa lead-to-lead seal.

After much deliberation we've adopted this solution: starting from the lowest point , at the narrow end, we're building up a series of timber steps to accomodate 1.5m lengths of flashing, allowing for a small (about 2cm) "drip" at each joint. We will take this just short of half way along the house wall and repeat the procedure from the other end. This will give

a) a fall in both directions (Gutters and downpipes are already in place to accept the water

b) a gradient of at least 1:80 in either direction (possible more at the right hand end)

c) the opportunity to take the lead up over the sloping roof as you suggest.

The bottoms of the tiles are already supported on a double thickness of batten. We intend to put longitudinal boards and extra battens on the bottom part of the roof slope and take the lead as far up as the 600mm will allow.

At the moment we're spending what seems like an excessive amount of time cutting wedges and fillets to give the necessary support to the gulley boards. It should be worth it if we getter a better fall, though.

Will try to get some pics to post on the net, but may not have the opportunity. Thanks again for shedding light on the problem.

 

[masona]

Just a thought,did you know you can get wide & deep gutter which come out in a roll machine with no joint.We have it at our Bowling club (approx 12" wide & 6" deep ! ) Just wondering if it would be easier to rest it on your rafters & tiles on top with lead flashing on the wall side on to the gutter.This would do away with lead altogether.The next question is no-one can remember who the company or manufacter is or if it costy!