The thing about true-scale shed modelling, is that it is addictive, so when Suzanne took over her new allotment, we inherited a 6 x 6ft galvanised zinc and polycarbonate box. In case this sounds a bit modern, trust me it isn’t. The existing shed came with an almost flat roof, a 1000 litre water cube and a massive galvanised water cistern from the 1940s or 50s. It looked like this last November:
The big piles of dark brown earth are all horse poo!
And like this after we had managed to get onto the plot and grow stuff post lockdown.
The plot is windy and has no piped water (hence the cube), so the first priority was to build a rain collector from corrugated polycarbonate, recycled from our pergola at home circa 2004.
Then a roof for the original shed , but this time with enough slope not to leak, and enough height for me to stand up in (one of the very few disadvantages of being tall.)
After that it seemed pointless not to roof the space between the rain collector and the shed. The problem with big roofs and shallow foundations is WIND SUCTION. A good online primer to start with can be found here: (https://www.mcrma.co.uk/pdf/Wind_guidance_document_final.pdf) . Our immediate neighbour’s shed felting blew off in the last windy spell that we had, so I’m not being cocky about the very real possibility of having just built a 18 sq metre wooden kite. I anchored the roof down to the water cube until everything is completed. That’s only 700kg at the moment until it fills up, but we normally get rain in October, so that will be a ton of dead weight that The Kite has to lift. Oh, and a neighbour was throwing two French doors away; well it would have been rude not to …
Various names were floated about .. The Cowshed, Shed Ordinaire, Bonnydoon, but in the end, it had a water tank in it, so it was the Tank Shed. Suzanne didn’t think that The Kite was funny.
A proper Engineer would have done his calculations before throwing up such a ramshackle structure, and as the full calcs are complex, I did my usual engineering approximation to see if my roof would fly. As luck would have it, The Den is about the same roof area as The Kite, so that gave me a negative pressure of about 1kN/sq m. ( A Kn is 101.97 kg) The rough calculations gave me just shy of 1000kg to pull a fence post out (found by rooting about on university websites for student design projects for fence pullers), that gives me 4 tonnes of downforce on the upwind side resisting a likely up force of 1kn/sq m acting on 18 square metres of roof or 1.8 tonnes. That’s without any dead weight from the structure itself. I should be OK by a factor of two, and need to rethink my sail area if I want to be an aviator, but I’m still keeping the tiedowns, just in case ……………………………..