Slimline water harvesting unit inside wall cavity?

[ashthekid]

I’m currently in the middle of a conversion project whereby I’m having to create an unusually large cavity between the existing old wall and a newly created inner skin. I’m considering the use of some simple water harvesting systems like the super slim one tank that seems in theory a perfect fit inside that cavity. There are internal rainwater pipes coming down for a box gutter above that cavity as seen in the image below. 
Does that idea seem like a good idea?

my plan to to hook up 3 individual slimline tanks to hook upto 3 toilet cisterns that are directly connected to that newly created inner wall. Seems to make sense in my head. I just wanted to see what other people thought about this idea?

 

I cannot locate any tanks externally because it’s inside the neighbours garden. 

[SteamyTea]

Well it will certainly add some 'thermal mass'.  That should keep your house nice and cool.

What happens when it leaks?

How about condensation?

How about vapour control?

How about odour?

How about rigidity?

Will there be enough storage?

where will the overflows go? 

Edited March 12, 2021 by SteamyTea

[Bitpipe]

What happens if someone drills a hole in either wall and punctures it?

 

What do you do in a dry spell ?

 

RWH is of marginal benefit domestically given you need a lot of contingency to meet WRAS.  
 

You’re  better off using efficient appliances and reduce your consumption that way.

 

 

 

[markc]

Like many `green` ideas this sounds great in theory but the practicalities soon outweigh the benefits. All of the above points need to be considered, plus access for maintenance and inspection/cleaning/disinfection.

[ashthekid]

Yes access for maintenance was always a concern for me and providing some sort of hatch to do that would be vital but all those other points are very good and I hadn’t thought of most of them to be honest. 

In terms of efficient appliances like WC, are there any that come to mind that are substantially efficient compared to your standard WC? Seeing as that is where the majority of water is wasted in my opinion. 
Ignoring baths/showering of course. 

[markc]

Efficient appliances, washing machine, dishwasher etc are fantastic. WC`s need water to move the debris and keep the pipe clear. The low volume units often need a 2nd flush which to me negates the whole point. They are better if the tank has some head above the pan, but very low level cisterns are a pain, i now have mine adjusted so the water level is only just below the overflow.

[SteamyTea]

14 hours ago, ashthekid said:

I cannot locate any tanks externally because it’s inside the neighbours garden. 

Two ideas I have had, while doing something else creative.

 

Can you bury a tank and pump and filter/purify to where you need it.

Or fit storage in the loft and catch rainwater halfway down the roof (a second, but higher up, gutter), then filter and purify.

[Bitpipe]

5 hours ago, ashthekid said:

Yes access for maintenance was always a concern for me and providing some sort of hatch to do that would be vital but all those other points are very good and I hadn’t thought of most of them to be honest. 

In terms of efficient appliances like WC, are there any that come to mind that are substantially efficient compared to your standard WC? Seeing as that is where the majority of water is wasted in my opinion. 
Ignoring baths/showering of course. 

 

Modern dual flush systems are pretty efficient. I used the Gerbrit in wall system with wall hanging WCs and it works and looks great.

 

I looked into RWH deeply and there is a lot of cost if you want to go beyond watering the garden. You need a mains fed tank to compensate when there is insufficient rain water, a separate plumbing system for your loos plus health concerns about bacteria and virus in bird droppings washing into your system from the roof and being aerosolised when you flush. Legionnaires is also a concern for any standing water source.

 

It's a nice creative idea but one that I think will get over complicated very quickly and you probably have better things to worry about and spend your money on!

 

[Pocster]

I initially was going to have rainwater harvesting . It’s green and efficient. But the cost against the benefit ( return on investment could be decades ) just made it a non starter . That cash instead could yield better on pv / ASHP / battery etc. 

[Mr Punter]

Another dream crushing NO here I am afraid.

 

Rainwater that is collected is best done in a water butt and used for watering the garden.  Even then they can sometimes cause issues.

[Iceverge]

Just to add to your worries what are you planning to construct the guttering from as is?  It looks like a custom piece of metal/fiberglass? 

 

As is what happens when it leaks/overflows? I'd be suspicious that if it fills up with crud at the moment the only place for it to overflow is into the roof structure. 

 Maybe I'm paranoid but the idea of an internal RWP gives me the shivers! Is there any option to route it anywhere else? 

 

I echo the above comments, rainwater is best left for watering the garden in summer. 

 

 

 

[Temp]

My concern was that water running down the roof may impact the "Party Wall Header Course" rather than the side of the box gutter.

[Temp]

9 minutes ago, Iceverge said:

As is what happens when it leaks/overflows? I'd be suspicious that if it fills up with crud at the moment the only place for it to overflow is into the roof structure. 

 Maybe I'm paranoid but the idea of an internal RWP gives me the shivers! Is there any option to route it anywhere else? 

 

You want an "overflow wier" or spout at the each end. See below. Note how the end is 25mm below the bottom of the box gutter. That way any blockage in the down spout and water goes over the wier rather than the level rising until it spills into the wall/roof.

 

The following drawing is from this document that has other ideas, including an internal overflow arrangement..

https://www.vba.vic.gov.au/__data/assets/pdf_file/0005/98447/PlumbingFactSheet-Overflow-provisions-for-box-gutters.pdf

 

 

 

 

 

The devil is in the detail with hidden gutters. For example on a normal external down pipe you don't need to glue or seal joints, you just make sure the top section goes inside the bottom section. That's because if it blocks up water will just leak but its outside the house so it doesn't matter. On a concealed system that leak would be in your cavity wall!  Its pretty essential the installer knows what they are doing.

 

If an end weir isn't possible I would extend the box liner up the roof so that if the level rises it goes over the wall, or through overflow holes through the wall, rather than into the roof.