Withington Co-operative Eco-house - rainwater tank

Rainwater harvesting tank

Robert — Fri, 28 Feb 2014 22:59:10 +0000

After a break from the 'eco' aspects of the project, this week we completed the installation of the rainwater harvesting tank. It stores 3000 litres of water and measures 2.5m x 2.5m, sitting in a hole 1m deep:

Rainwater is often overlooked in eco-house projects (especially urban ones). The whole rainwater system was bought as a kit from http://www.rainwaterharvesting.co.uk for just under £2,500. If it saves a few hundred pounds per year in water bills, then it will pay for itself in 5-8 years - which is a better return on investment than pretty much any other eco-feature. That doesn't take into account the labour cost of digging the hole, the disposal of the waste, or of the extra plumbing work involved. However, in our case we are also using the tank to feed the sprinkler system, so we can allocate some of these costs to meeting our fire safety requirement instead.

The system hasn't yet been commissioned though. Next week we're putting the scaffolding up at the rear and continuing with the EWI all the way up the back wall.

Rainwater harvesting, and neighbours

Robert — Thu, 13 Jun 2013 17:49:57 +0000

The rainwater harvesting system we're going to use is from rainwaterharvesting.co.uk - they sell a complete system, in kit form. Because the tank is shared with the fire sprinkler system, I thought it would be a good idea to get it on-site ASAP, if possible. So I've been thinking about how to achieve this, given the road closure going on with the United Utilities works (The tank we'll be using measures 2.4m x 2.4m x 1m approx).

At the moment, UU have the side road (which gives us access to the rear garden) closed during the daytime, but then they open it to (small) vehicles before they finish work each evening. This is going to change in two weeks' time. So I came up with a slightly convoluted but workable plan: hire a 3.5t flatbed from Salford Van Hire, drive down to Peterborough, get the rainwaterharvesting.co.uk people to load the tank onto the vehicle, drive back to Manchester (by which time it would be after 5:30pm so UU would have finished work), and have a bunch of people ready to offload it into the garden (then return the van next morning). After making quite a few phone calls to confirm availability of both the tank and the vehicle, costings, ordering procedures, etc, I came to the conclusion that whilst I could get it in to the garden, this would be pointless unless we could get all the displaced earth out of the garden - and that we didn't have enough time to also achieve that, before the 24/7 road closure comes into force.

So we'll have to stick to Plan A: wait until the roadworks are finished before putting the tank in. I need to tell the sprinkler people about this; they sent through a CAD file following Wednesday's meeting, mostly OK but a couple of points to raise with them, which I'll have to do on Monday now.

I'm very eager to ensure that we have good communication, and good relationships with the neighbours. Both the adjoining houses are rented. I already know the owner of one of them, but yesterday I managed to speak to the other one on the phone for the first time. He seemed rather concerned, so there will be more work to be done to put his mind at rest. In particular, there are some Leylandii trees in the garden that we are going to get rid of, and what gets done about the boundary (ie do we build a wall, plant a hedge, etc) will need some careful negotiation. He promised to have a word with his tenants, and then we'd speak again next week.

Fortunately for this project, my time is not being charged for - but in other circumstances such time would have to be paid for, yet the above aren't things you can "see" in the finished result. I had no idea when I started that my time would be needed for these kinds of things - certainly something to bear in mind for future projects.

Going to see the window supplier on Monday morning, which I'm quite excited about.

Design approach: rainwater harvesting

Robert — Fri, 07 Jun 2013 18:00:00 +0000

Rainwater harvesting seems like an obvious thing to do to me - capturing the rain that is inevitably going to fall on top of our buildings seems like a even more of a no-brainer than capturing the sunshine that reaches our roofs. Ironically enough, the logistical difficulties we're having on this project due to road closure are because United Utilities are having to put in an enlarged sewer due to the original Victorian drain being unable to cope with today's increased water usage (as well as its poor state of repair); if every house on the street harvested its rainwater instead of dumping it down the drains, that would yield a reduction in wastewater volume of at least a third.

Rainwater harvesting systems are difficult to retrofit in anything other than a whole-house refurb, because you have to have a large underground tank (rainfall has seasonal variation of course, so you need to store a large volume to benefit from the system) and two sets of pipes running around the house, to keep drinking water and rainwater supplies separate. But if you are starting from scratch with your plumbing, rainwater harvesting seems to be a no-brainer.

There has been some criticism of the significant embodied energy in the rainwater tanks not being fully taken into account in assessing the environmental benefit of rainwater harvesing systems, compared to energy saving from reduced drinking water consumption. On this project, we're very aware that there is also significant embodied energy in the drainage systems that take rainwater away from buildings, if it isn't harvested. And for this particular project, because we've chosen to install a fire sprinkler system, we are going to use one shared tank for both the sprinklers and WC flushing. So it could be argued that, as the tank is required anyway for fire safety reasons, only the additional plastic in the increased sidewall area to accommodate the extra water for WC flushing would be included in a rainwater harvesting embodied energy calculation (by the way, we're not doing any quantitive embodied energy analysis in this project - not because it's not important, but due to lack of capacity).

The difficulty, for a mid-terraced house such as this, is that it's only really practical to capture rainwater from one half of the roof (the rear, presumably); a two-tank system and running large diameter pipes through the house were both quickly ruled out as not viable. For this reason, we're only using the rainwater for WC flushes - the calculations we've done are that it won't necessarily provide 100% of WC flush water, so it wuold be pointless to start plumbing in other things eg washing machine.

The chosen system is available "off the shelf" from rainwaterharvesting.co.uk, who supply the whole system in kit form. The things I like about their offering, compared to others I've seen are:

1. There is a header tank in the attic, rather than supplying appliances directly from the underground tank. This means that the supply is more reliable, and the electricity usage from the pump (already very low, we're promised) is significantly reduced, because pumps work more efficiently if run continously rather than stop-start.

2. The Rain Director control unit deals with switching over to mains water in the event that there's no rainwater left, and can cycle the water to stop it going stale if, for example, people are away on holiday.

3. The tank is shallow-depth, only requires a hole 1m deep.

I spoke to the supplier at Ecobuild, and again more recently on the phone. They are going to supply an adaptor to allow us to fit an upstsand pipe to the inlet of the submerged pump, so that the inlet will be physically part-way up the tank, thus guaranteeing that the WC flushes can't "steal" the water that is reserved for the fire sprinkler system (the sprinkler system will use a separate suction lift pump).

Starting off the project - and sprinkler system

Robert — Wed, 05 Jun 2013 18:39:43 +0000

It would have been a good idea to have started this blog right at the very beginning of this project. But, since that didn't happen, getting the funding through to be able to start the building work in earnest seemed like a good milestone at which to pick up instead. There's a fair amount of work gone into this project already, which I'll have to fill you in on as we go. The main things to know for now are: we've already bought a house for refurbishment (it's an Edwardian mid-terraced property in an inner suburb of Manchester); produced the design and specification of the eco-refit - which has Building Control approval; set up a not-for-profit legal structure for the project; and got the necessary funding in place (all loan money - we're not dependent on any grants).

I had a meeting on-site with the main contractor today. They want to get the scaffold up, and start work on the roof and repointing the front wall (with possible brickwork cleaning). The advantage of this approach is that they start off in their comfort zone, and I have a few weeks to get some of the more specialist "eco" stuff ordered and delivered.

Speaking of deliveries, one of my big challenges is to work around United Utilities, who have got the road closed to do a sewer replacement. We knew for some time that this would be happening; what we didn't know was that they would change their minds about which order to do the various areas in, just as we got our money through and wanted to start work! So right now we can get up as far as next-door for deliveries at the front, and we can get a small vehicle (car or Transit van) to the rear, but in two weeks' time both of these routes into the property will be blocked, for four weeks (if they keep to their schedule).

United Utilities road closure for sewer works - right outside the house

The other meeting I had today was with someone from the sprinkler company. Now I totally agree that installing sprinklers seems like a bizarre place to start with an eco-house! I'll write a separate article explaining the thinking - but first the meeting. The sprinkler guy spent quite some time on-site looking at pipe runs etc. They're expecting all holes and openings to be made for them in advance, which is something I need to go back to the main contractor about. It's really complicated to think through the interaction between sprinkler pipes (which are rigid), regular heating and domestic water pipes, electrical cables, and insulation. One particularly tricky area is the front attic room, where there's so little full-height ceiling that it's not possible to get full coverage just from ceiling-mounted sprinklers, so it looks like we will have to put one in the ceiling of the dormer - which is already a difficult area to treat because of complex roof timbers in confined space.

Dormer roof, with roof timbers exposed. This is a difficult area to treat, in every possible way!

We're going to put in a rainwater harvesting system - used for WC flushing - and the tank will be shared with the sprinkler system. Current thinking is to get the sprinkler first fix done first - so that any making good can be done in plenty of time. But this raises a scheduling issue, as the rainwater tank is big (2.4m x 2.4m) and difficult to get on-site whilst the road blockage is in place. So I realised after the sprinkler guy had left that I may need to ask them to make a separate visit to connect up the tank - or perhaps during the commissioning.

Withington Co-operative Eco-house - rainwater tank

Rainwater harvesting tank

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Rainwater harvesting, and neighbours

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Design approach: rainwater harvesting

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Starting off the project - and sprinkler system

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