downspout planning

Hi friends!

We're over half way through working with a contractor to build a home in middle TN (40 minutes west of Nashville). We had to give up on gray water as part of the build (the county water guy didn't just say, "No." He said, "Hell, no!") So we're trying to do as good as job as possible of using the rainwater off our garage and house roof. I have learned through this build process that each subcontractor has a way they alwaysdo things, and I want to be ready to direct a different way, if needed.

The site is a gentle slope, with the house and garage on the uphill side. We don't anticipate doing much on the north/drive side of the house. The to-be-dug pond or series of pondlets will be to the west of the house. Not a lined pond or anything. Just places to hold water and slow it as it moves down the hill.



The house will definitely have gutters on all four corners, and at the breezeway roof. We hadn't thought about having any ponding to the west of the house, but perhaps that would be better than the contractor's idea of burying hoses to take water to the west side of the house.



The garage rainwater should mostly go into a cistern on the north side of the garage. That is the highest point in our site, and we're hoping gravity will do most of the work to water gardens below. I haven't sized the cistern yet - any tips on that would be very helpful. Here in middle TN we tend to get about an inch of rain a week, 50+ a year, with some drought in the summer (2-6 wks, depending).

If you can install a round tank it will cost vastly less than those hog system tanks.
When you say the bloke will not do what you asked, can you give more details.
Tank size needs to be calculated based on the roof area draining to the tank times rainfall amount times weeks of capture.
So you have about 80 sq m of roof [ 780 sq ft ] x 10 weeks x 25mm
= 80 x 250mm
= 80 x .25M
= 20 cubic M which is 20,000 Litres or about 5000 gals.

So if you have 6 weeks of no rain you have about 830 gals a week for watering. [ 3200 L]

In normal times you could capture about 2000L a week.

BUT if you use some if the rainfall each week in the house itself
You would never have enough to keep watering over 6 dry weeks,

With a family of 4 your use could be;
If you can use that same water in the toilets you would use  per person a week 350L........................................1400L
Machine machines between 40 -130L per wash front loader / top loader. times say 1 wash per person = 130 L.....560 L
Garden watering is dependant on many things, but say 1100L per week.........................................................1100 L
Giving a total usage of garden and house af about ....................................................................................  3060 L

So you could think about capturing water off other parts of the roof.

If you have town water, tanks are expensive, if you dont then whilst its still expensive its better than no water.

If you have a well, then there are other large expenses as well.

I hope I have been clear.

My source of water quantities used in households
water usage

John C Daley wrote:If you can install a round tank it will cost vastly less than those hog system tanks.

I'll look at that. The hog tank system was drawn in by the architect,  but we definitely haven't picked a tank. Thanks!

When you say the bloke will not do what you asked, can you give more details.

He's the county official who approves septic permits and does final plumbing inspections. Seems to be fairly overworked and also hard to move.

Tbe tank size info is so helpful, John. And very clear. We do have county water piped in, so the plan is to use the rainwater for outside. But I get that the rainwater will be a resource we'll have if the county water fails.

It is wise to let the official do it his way, there will be rules about the environment that are out if date.