Last issue the erection of the big shed was finished. Now it’s time to organise stormwater collection and disposal, do the landscaping (what?… wait a moment) and get council approval in a final inspection.
In the planning stages it’s easy to overlook stormwater collection and disposal. After all, all that you have to do is run a few gutters and downpipes, right? Well, no. These days, planning authorities want to see detailed plans as to how rainwater will be collected and disposed of.
The first stumbling block came when my local council (the planning authority in this case) rejected my proposal to have “stormwater discharge within the block, flowing down the natural slope to a grassed area of approximately 800 square metres”. And that’s on a block on the edge of a tiny hamlet, with farmland in two directions and a river reserve in the direction of natural drainage…
After discussion with the council planner, stormwater handling changed to the installation of a 10,000 litre rainwater tank, with the overflow connected to an absorption trench 600 x 600mm x 10 metres long.
I bought a 10,000 litre plastic tank (AUD$1600 including delivery) and connected it to the standard gutters via two 90mm plastic downpipes (about $200 including pipes, gutter adaptors, bends, brackets and glue).
I’d already provided a flat pad for the tank during the shed earthworks, and had had sufficient crusher dust delivered to cater for the tank as well as the shed pad itself. (Tanks need to be placed on fine material like crusher dust or sand.)
I hired a small excavator ($500) and dug the 10 metre long absorption trench. To line the trench I bought geotextile cloth ($100), and to fill the trench had a truckload of very coarse gravel delivered ($200).
The absorption trench design is organised like this: the 90mm plastic overflow pipe (perforated along its length by a hole-saw) carries water into the gravel, which is wrapped sausage-like in the geotextile cloth. The water then percolates through the gravel and cloth into the surrounding soil.
The cost of handling stormwater added up to about $2600 – a large expense not budgeted for in the construction of the workshop.
I then chose to add a mains-powered rainwater pump ($150) and plumb it to the tank and a newly-installed outside tap ($50). This pump is primarily to allow the rainwater to be used to water a vegetable garden, but since it is a convenient source of pressurised freshwater, I’ll also later plumb it to a sink within the workshop.
Especially if the workshop is located on sloping land, it’s important that slopes be stabilised and surface run-off water be catered for.
My workshop is located on a site that has a fall of about 1.5 metres across its width. This necessitated a ‘cut and fill’ approach to gain a level shed pad, so resulting in sloped ‘batters’ around the pad.
During the planning process I slightly moved the proposed shed location, allowing the batters to be decreased in steepness from about 45 degrees to about 25 degrees. I went shallower in angle so water run-off is reduced – and that’s less water running towards the shed.
The batters were compressed by the bobcat that did the pad levelling, and then the slopes were covered in bark chips, protecting the surface from being washed away.
Around the base of the shed slab I placed a 1-1.5 metre wide path formed from gravel – in this case, the gravel comprised locally-available river pebbles. These pebbles allow water to easily infiltrate and give a low maintenance surface. The pebble surface was also used around the rainwater tank.
The pebbles cost $300 including delivery. The bark chips were already onsite and so were free.
No surface drains were placed around the shed – the amount of run-off flowing towards the shed is minimal and the upper level of the gravel is kept below the level of the concrete slab.
With the shed, stormwater handling and landscaping finished, it was time for the final council inspection. (Final? Two inspections had already been carried out – one of the prepared site, and another just prior to pouring the concrete. This third inspection was to be carried out by a different inspector, the original one now being on leave.)
With the last shed I built, which was in Queensland, the council inspection was quite thorough – the inspector spent about 20 minutes looking, measuring and noting. He had been particularly careful in comparing the built shed with the submitted plans, which he had in hand.
This time, the inspector took only a cursory look at the completed shed. He noted that the internal bracing had been incorrectly positioned (something I remedied when I added the extra bracing described last issue), and that the stormwater absorption trench had been placed on a slope whereas it should have been level (actually, I dug the trench to largely negate this slope, that is, it was deeper at the ‘uphill’ end).
But neither observation was a deal-breaker: overall, he was happy.
The approval certificate arrived in the mail about a week later.
Next issue: the electricals