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Hidden gutter details - which to choose and is any one right?


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After 8 months of going very slowly on the main house build, returning to work 2 days a week plus a bereavement has not helped, I am approaching needing the hidden gutter detail. The architect gave me some ideas but after a lot of discussion with some of my materials colleagues I have concluded that zinc / grp / powder coated aluminium wont cut it and I have decided to go for lead. It is a hidden gutter and having looked at loads I have come up with a couple of ways of making it happen, see section images below. I think I like option 2 as I don't have the phaff with very short roof tiled section at the eaves. Both have a slight problem in that cannot see a way of getting a through draft under the supporting marine ply. I also wonder if I should give up on the second, upper, over lap of the lead with the VCL and take the lead all the way up to the underside of the tiles, this saving a problem with an insect guard. Anyway thoughts appreciated.

 

847389929_Leadgutteroptions.thumb.jpg.af6526702f644cc2da60d487224b256c.jpg

Edited by MikeSharp01
clarification
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TBH I don’t like either of those designs, have you looked at the capacity of both, what I don’t like is the angled bottom, I believe this decreases the capacity massively, all the ones we chose had flat bottoms. 13F13459-25EF-4BDF-905E-5C1759385980.thumb.png.a8d3b3a618a8b7d10341b2832aedf517.png

I know you are limited by your wall make up but I would personally go back to the drawing board. 

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I think the gutter needs to be finished in GRP or similar and needs a min fall of 1:200 to the outlets.  Make the outlets are lower than you think they should be as there is often a build up of material near them so the water does not drain.

 

Design it so if you block the outlets the gutter will surcharge down the outside of the building.

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Thanks for all the feedback. 

 

I am not sure of the flat bottom issue, many gutters are half round and the one I chose to measure is as shown in the drawing - so I need to look into that but otherwise both the designs have a cross section much bigger than a standard plastic gutter 7800mm2 as opposed to 5800mm2 and the weir, so excess water pours over the top and runs down the outside of the walls, means overflow is dealt with if there is ever a problem with a down pipe so I am not sure capacity is a problem.

 

I can deal with expansion, max run is 9m, by fixing in the middle and having falls both ways so limiting the fall total and the expansion at the ends. So expansion would be about 6mm per leg assuming a range between -5 and + 40 Deg C. The down pipes are in plenty of space so can move.  

 

Yes I will have to lean to solder lead but I can get that practice in. 

 

9 hours ago, Russell griffiths said:

I know you are limited by your wall make up but I would personally go back to the drawing board. 

 

The essential challenge for me is the space I have available the there is a space of 90mm running round  the main structure, which cannot be cut into, and this creates the space for the gutter.    

 

I will go back and see what I can do to improve things. The alternative is to forget the gutters and put drains under the walls and just let the water run down them.

 

 

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16 minutes ago, Russell griffiths said:

i was under the impression that lengths over 1.5m where frowned upon. 

I think that is the max distance between drips, but if you use expansion joints you can go much further.

 

I chose lead because it is easy to work, can be serviced and is one of very few 'metals' I could make it from an get close to a good life as close to the sea as we are. GRP is the only other option I think now.

 

 

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6 minutes ago, Russell griffiths said:

How are you proposing to make the expansion joint waterproof 

Using a few bits of this HERE.

 

Just now, the_r_sole said:

iirc the expansion joints have a guarantee of 10 years, wheras something like rheinzink has a 30 year guarantee if you use their standard detail...

 20 years it seems but my problem is proximity to the sea so all the metals have a much smaller guaranteed life, sometimes none at all.

 

Ok when I did my early work I based my thinking on the polypipe documentation HERE. I thought my gutter was basically the Ogee shape, although mine has a 34% greater area and I found that my effective roof area is 77m2. This means that I could get away with the standard Ogee section as this can cope with and effective roof area of 88m2 if I use a double end down pipe and this is for a zero fall gutter.

 

So looking at the cross section issue I found THIS paper which sort of tackles problem of the cross section and indicates that only at very low (not a problem) and very high - the weir takes care of it is the cross section an issue and for entirely different reasons. If I assume my section is a somewhat truncated V I can work out the various factors including the hydraulic depth and get an idea of its capacity and it looks like it is well over the polypipe limit recommended area for our roof. I need to check this through as I may have gone rather too quickly through such a relatively complex paper although it does come close to the polypipe calc for a similar area (their sovereign profile).

 

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4 minutes ago, the_r_sole said:

With a hidden gutter detail you want to oversize it to a huge margin imo! attaching a gutter onto a facia is very different to hiding a gutter on a wall head behind cladding.

I'm used to working in scotland so always a bit mindful about keeping water out... when you've seen rain climbing up a 35 degree pitch roof it makes you overthink gutters and flashings.

I agree, hence the over sizing by 35% and  weir height / detail to get the water out and over the wall in 1 in 10 year event. I do appreciate the blowing back in / up issue hence the two layers of VCL one above and one below the cross section so any that gets blown over the Lead end at its highest point is brought back down and out via the lower, and main VCL layer.

 

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it is a routine question, but I would be interested to hear how you will be maintaining it, Mike. 

 

Having lived in an old house with several valleys with no straightforward access, it was interesting and a  hairy when 3 ft of snow settled up there. One involved a ladder and then a crawler and a sweeping brush.

 

Ferdinand

Edited by Ferdinand
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Hi Ferdinand.

 

The gutters are right on the edge of the building although hidden and are only 2.9 and 3.9m above ground so maintaining then should not be a major problem I hope. One of the beauties of lead is that you can peel it back to loo underneath and it has the ability to be repaired, by soldering / welding (taking care of hot working around a timber framed building) as and when needed. GRP will be in situ for ever, although it can be repaired if needs be. For zinc I will have to work out a way of getting it out if it needs replacing and it has slightly worse expansion problems to lead.

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On 17/06/2019 at 22:29, PeterW said:

Lead doesn’t like to be perfectly flat and you’ll get creep on joints so you may want to build in a fall if you have a fairly long run. That way the laps are not under standing water. 

Thanks Peter I will bear that in mind - I do need to ensure that it does not walk out the end of the building so a fall both ways from the middle might be the best way to ensure this.

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