Having moved the hardcore into the base it was time to cover with the carrstone sub-base. After using up the remainder of the original tonnage, about 5 tons, I needed to bring in another load of which about 6 tons was added to raise the level to what is seen in this picture.
Over the sub-base was installed the DPC. The reason the DPC is folded back is to protect the wall plates from the now constant rain. Things were getting very wet and very muddy. The weather had caused a delay of eight days, that being the time between the top image taken on the 14th March and the one above taken on the 23rd.
On the 24th I built the six main frames on the ground, then it started raining again so they got covered over and work stopped until the next dry day, the 29th March. Although I had arranged for some help to raise the frames, I became impatient after watching a program called Building Alaska in which it took five or six people to lift a single frame and fix it into place. And they were even then complaining about the weight. These are slightly smaller but were lifted into place and secured without help.
The support timbers seen in the picture held the frames upright while the second was lifted and cable ties were used to hold the frames together while they were screwed together.
On the 30th March the first order of timbers for the roof were delivered and by 8pm on the 31st I had part of the roof built and had run out of timber. Work stopped until my timber suppliers could deliver again, unfortunately the Easter break intervened so the delivery was delayed until Wednesday the 4th April with a second delivery of timber on the 5th. It so happened that the plastics for the walls also arrived that day so it was busy.
Today is the 7th April and the roof is up and watertight, the back walls have started to go up so I am back on track for the projected build time if not the cost.
Actually, I could have saved myself two weeks and 18 tons of sub-base, neither of which is now needed due to a change of design. The change was not planned and not even necessary except for one thing … cost.
The original plan was to have the floor as a concrete screed, cost was £75 per cubic meter of which the floor area needed 6, costing £450 plus VAT, total cost £540. Timber joists £288 plus VAT total cost £345.60, no contest.
A note on the roof construction, The unsupported span is a fraction under 5m so I am using 150mm x 47mm timbers for the main joists at 6m long on 400mm centers. The top joists are 100mm x 47mm also at 6m long. The top joists are posted to the main joists at each end with stud timber in the center. The sloping front also supports the roof by deflecting the weight loading.
On top of the joists I have used 25 of 12mm plywood sheets 2.4 x 1.2. This may seem thin by many, but the decision was taken on a number of levels based on past experience. The first was the weight that I would have to carry up the ladder and place on the roof. The second was cost. The third was calculated on the manner of the construction for the building.
The test for the strength of any roof I build is whether it will support my weight, well this roof does that and more.
The plywood was then painted with bitumen paint to seal it against water ingress before being covered with 7m x 6m sheets of pond liner. two positioned side by side with a third positioned centrally over the join. The last two were positioned over the first and sealed down with double sided bitumen pond repair tape. Once the front panels are in place the whole roof will be covered with a heavy duty bitumen cap sheet.
So now we are up to date with progress.