Timbers and anchors.

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Having completed the gravel movement from the gate to the site it was time to think more seriously about construction. I had decided on an octagonal building which would be supported at the eight 'corners' with 100x100mm [4x4"] posts. These would rest on and be bolted to precast concrete, carport anchors or footings via height adjustable galvanized brackets. No leaning tower of Pisa for me.

The raising of the ground with gravel has reduced the required height of the building to the observatory floor. I had planned on 3m or 10' on stilts but can now aim for 2.5m with a solidly made building. 2.44m is only slightly above the height of a 2.44m [8'] plywood cladding sheet. The observatory floor is intended to extend  beyond the dome walls to become an octagonal veranda. The joists are intended to radiate from an octagonal 'ring' around the isolated pier.

I needed 4m lengths of timber for the overall height, with no waste. As they had only 6m in stock I went with twelve of those. Eight for the octagon uprights and four more for the pier. The off-cuts can be used for cross bracing the framework. Cutting the 22.5° angles should be good fun.

I had help loading the trailer at the timber yard but had to take it all off myself when I arrived back at home. You would not believe the moment arm on an 18' length of timber as it is rotated 90° for stacking. Now do it twelve times.

It was a good job I had warmed up over last few days with all the gravel shifting. Or it would have been quite a struggle handling these heavy items alone. I tried loading three blocks at a time on the sack truck. It was too difficult to tilt it over safely on such uneven ground. They are rather shorter than my original choice but still tapered.  Of course it rained as I was unloading the trailer.

The concrete foundation blocks must weigh well over 30kgs each. I shall weigh them and the timbers later with luggage scales. Just out of  curiosity and being a lifelong pedant. The information might be of use to someone. [The concrete footings weigh 34kg or 75lbs each with adjustable bracketry.] The 6m lengths of 4x4" timber weigh 60lbs each. Or 10lbs per meter.

Cladding of the observatory building is under serious discussion. I used machine grooved plywood cladding for the shed next to the planned observatory. As can be seen just behind the stacks of blocks the plywood surface has weathered to a low impact grey-brown with grainy figuring. These nicely uniform, but varied, plywood sheets would be cheaper and far easier to use than other cladding alternatives with which I am familiar.

It is no coincidence that the sheet width perfectly matches the eight sides of my planned 3m, 10' diameter octagon. The 8'x4' sheets [1220x2440mm] would also have the distinct advantage of acting like a stressed skin to the building once firmly fixed with lots of screws along all the edges. It lasts well out of doors without any treatment and stays flat in my own experience of the shed cladding on 60cm [2'] stud centers. I prefer this cladding option for quite a number of good reasons. The appearance is largely a matter of taste. I like it and it is my building after all.

The adjustable height bracket as supplied. The large, square washer is removed and placed on top of the concrete, anchor block before use. The washer is only placed between the two nuts to stop it from being lost before use. The L-shaped brackets are slotted on their base legs to allow a perfect clamping match with the timber size. The large, flat head of the adjusting screw resists downward pressure from the bottom end of the wooden post. The lower nut, of the two supplied, makes the up and down, level adjustments. While the second nut is used to support and then lock the brackets to the underside of the round screw head.

The alternative cladding would be vertical planks of [say] 1"x 6" [25x150mm.] This is available in opposed planed and sawn surfaces for those who like a choice between simply rustic or downright rustic. I think one-on-two planking would be a bit "heavy" in appearance for a tall, octagonal building. Though thinner wooden strips could be laid over the 1x6s.

Managing the eight 'corners' would be much more difficult with planks. The other most obvious downside is shrinkage, cracking and warpage of natural timber. I would obviously use building paper behind the boards, for waterproofing and draught proofing. There would still be long term upkeep issues if not properly coated and maintained.

A third alternative might be a faux half-timbered look. Plain outdoor plywood with an overlay of boards to suggest oak framing. Half timbered houses are still very commonplace in Denmark. Such a cladding would require painting and regular maintenance and might not even work visually.

The grooved plywood just works for me in an understated sort of way in our natural, rural situation of mixed trees, shrubs and high hedges.

The 'naked' grooved plywood clad shed has taken care of itself for 14 years without the least attention. Though I should really have put downward extended "skirting boards" all around it. Just to ensure no wildlife got in under the wooden floor. We just used heaped gravel chippings around the edges instead and have never noticed any signs of wildlife inside. Any digging would have been fairly obvious at a glance. 

Click on any image for enlargement.

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