Box Gutter Construction Options?

[ashthekid]

In the middle of a complete conversion project whereby new box gutters are being created on either side due to party wall proximity.

What I would like to know, because the intended box gutter lengths are quite substantial - approx 10m then a step down, followed by another 7m.

Does it sound right that the box gutter would be constructed in ply and then treated/covered in some sort of rubber EPDM?

[PeterW]

Ply and GRP every day of the week ..! Don’t use rubber, it will leak eventually. 

[tonyshouse]

Design it out!

[joe90]

2 minutes ago, PeterW said:

Ply and GRP every day of the week ..! Don’t use rubber, it will leak eventually. 

+1, 

[makie]

42 minutes ago, PeterW said:

Ply and GRP every day of the week ..! Don’t use rubber, it will leak eventually. 

 

Not if done correctly it won't. You can buy it to size so there is no joints

[ashthekid]

I know you can get EPDM in very long lengths though so surely no leaks?

[makie]

6 minutes ago, ashthekid said:

I know you can get EPDM in very long lengths though so surely no leaks?

 

If it's done properly you will be fine, lead is obviously the best in terms of quality but EPDM will work fine.

[simon45089]

I recently made and installed two box gutters of 7 metres each. I made the box section in ply then lined it a full length aluminium square gutter. The aluminium has no joints, and was formed on site by a man in a van with the necessary folding machine. You can go as long as you like with no joints as the aluminium is on a roll. if it ever leaked- which is not expected, I could in theory draw it out of the ply boxing, and slide in a new one. The only limitation is the size of gutter required in width and height. The former makes them a standard size, around 140mm x 100mm , but as stated length is only limited by the roll of aluminium in the van !

 

[PeterW]

9 hours ago, ashthekid said:

I know you can get EPDM in very long lengths though so surely no leaks?

6m is the widest you can buy so you will either be buying a huge amount of excess if you want a single piece, or will be joining it. 
 

Lead would need to be done in multiple bays of 1.5m to allow for expansion, GRP can be done in a single length hence the suggestion. 
 

How deep and wide is it ..? Do you have good access to clean it as they are prone to catch leaves. 

[joe90]

18 minutes ago, PeterW said:

Lead would need to be done in multiple bays of 1.5m to allow for expansion,

Also you would need a step at every joint ( I believe) ?

[PeterW]

Or a 200mm overlap at 1:40 so that water cannot sit on the joints. 

[ashthekid]

Here is where the box gutter is going(in blue) and where there is substantial step down(in pink) but not joining steps as there is an internal RWP in each length, so 4x RWP’s in total because of party wall issues. 
 

As a side topic, I am considering installing a couple of water harvesting units within the large air gap we have that the RWPs are also going down into and directly connecting them to toilets which will be back to back to the air gap side wall. 

[PeterW]

Very poor design .. 

 

Water shedding at speed will hit the bricks on the top not the gutter. That also looks a very large roof - I think you will need to check volume carefully as your gutter isn’t very deep. 
 

Over 10m, even at 1:80 drop you will lose 80mm or more than a course of bricks. 
 

I would create a very deep gutter all formed in GRP. It would be minimum 150mm deep, and lap both sides of the gutter up and under the tiles / slates until level. Ideally then add a coping stone on top of the wall or make an aluminum capping to go over the lot. 
 

Very rough picture below ..!!

 

 

 

You will also need to insulate that corner properly under the edge of the tiles as that’s a horrendous cold bridge if you’re not careful. 

 

 

[makie]

10 hours ago, PeterW said:

6m is the widest you can buy so you will either be buying a huge amount of excess if you want a single piece, or will be joining it. 
 

Lead would need to be done in multiple bays of 1.5m to allow for expansion, GRP can be done in a single length hence the suggestion. 
 

How deep and wide is it ..? Do you have good access to clean it as they are prone to catch leaves. 

 

You can buy Hertalan in 20m rolls and they do them in widths perfect for gutters like this.

Lead would not be done in 1.5 m bays for this, code 4 is not meant to be used on gutters of that length. You can use an expansion joint to avoid the need for steps.

[ashthekid]

Update:

box gutter has been created with ply and now this product below is being used to line it. FlexiTec by RES-TEC.
Anyone used it before? 
Is this the GRP that was suggested?

 

Taken from their website:

 

The Flexitec 2020 System by Res-Tec is a flexible, single resin GRP system with full overlay and new deck capabilities. Combining the best elements of fibreglass with the versatility of overlay systems, no other flat roof solution performs at this level across so many applications.

Edited May 14, 2021 by ashthekid

[PeterW]

It’s a powder hardened GRP - are they also using mesh..?

 

Other option is Desmopol or similar - it is a rubber based product so more flexible but potentially less durable. 
 

How will you get to maintain this out of interest ..??

[SteamyTea]

The curing agent can come in may forms.  Usually a liquid, but often a powder.  This powder can be incorporated into the weave or mat.

Nothing special about it.

Edited May 14, 2021 by SteamyTea

[ashthekid]

@PeterW No mesh matting that I can see being used, just a RES-TEC primer onto the ply then the resin along with powder hardener. 
I’m assuming mesh only really gets used in larger flat roof type surfaces, rather than small box gutters like this?
 

Access and maintenance from a ladder either side. There is only approx 2m that would be trickier to access because of neighbouring property adjoining the party wall.