Building the Octagon Pt.20 Obs. floor joists and ladders.

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Today I climbed all over the structure measuring up for the observatory level floor joists. The outside dimension of the octagon across opposing posts is 296cm. Allowing a 60cm width of veranda front and back that makes 4.16 m overall joist length. Joist spacing is 41cm [16"]  and metric 2x6 should be adequate.

I wanted slightly more space around the pier for isolation in case I needed to increase the size of the pier later. The very tall pier is still an unknown quantity and may prove too flexible or too prone to swaying in use. Splaying the four timbers of the tapered pier will require more room for clearance at obs. floor level.

I have also moved the access trapdoor nearer the pier. This provides more horizontal clearance at ground level to reduce the steepness of the stair. The amateur astronomer user is very like to be carrying something whether ascending or descending. The steeper the stair, or ladder, the more difficult the climb. The user is very likely to be tired and/or cold and certainly elderly. Lighting may not be ideal if the user is trying to preserve their dark adaptation.

Anything which make the stair less like a ladder is a very good thing. Proper treads are also very desirable. If a ladder provides access, then a stepladder provides relaxed working platforms at each tread. There is world of difference between a ladder rung and a tread with depth. Forum advisers have suggested a commercial stepladder be modified for the task. While certainly a clever idea this may well set a practical limit on the minimum slope angle of the stairs.

So off I went to check the octagon: As can be seen from the image the ladder is set at exactly 60 degrees. This provides a 50x50cm clear "landing" at ground floor level. The difference in floor height is 245cm.

It should be remembered that the "upstairs" also needs a safe landing space. Climbing onto a flat [floor] surface from a ladder which simply stops [or starts] at that level is very hard work! Usually involving a careful balancing act or crawling away on all flours! Loft ladders should provide an extension of the handrails beyond loft floor level.

I have no need of a retracting ladder and automatic trapdoor but I do need real safety. So a banister rail [or two] is going to be vital to provide a safe continuation of the sloping ladder or stair to allow the climber to balance in that vital moment when they arrive at the obs.floor.  The large "hole" in the floor cannot be left open. A sturdy, hinged trapdoor is vital for safety. So that the trapdoor itself becomes a natural extension of the obs. floor when closed. A shelf near the landing site might be desirable to improve the transition from climbing to arrival at obs. floor level. Care must also be taken to avoid rising directly under the mounting's counterweights!

I have been looking at the ladder manufacturer's offerings which have "proper" treads. They are certainly expensive! The odd thing is that they don't give specifics on lean angle in use. How, on earth, is one supposed to guess this vital information? If the lean angle is wrong then the flat treads will be at the wrong angle too! Many websites use exactly the same image of only one example while a whole range of different sizes is offered. Taller stepladders usually taper. This tapering isn't shown most of the time.

It has just occurred to me that I could use a normal, double, sliding ladder. When arranged properly the pairs of offset rungs are essentially deep treads. The downside is the relatively narrow width of most ladders. Noise in use is also an issue. Wood is quiet but aluminium noisy unless well fixed to kill the natural clang. Clanging an observatory, metal ladder in the middle of the night is certainly not on!

If you haven't discovered the benefits of useful tread depth then you really ought to. One can easily balance without hands on a stepladder because the treads offer excellent and natural feedback through one's soles. On a normal ladder you need knees or hands to maintain balance because your feet rock freely on the narrow rungs.

Interestingly[?] Denmark's ladder manufacture seems never to have caught up with UK ladders. The latter have their slightly triangular rungs "rotated" to provide a flatter, wider and much more comfortable surface for the feet. Danish ladders force the user to rest their feet on the sharp shoulder of the square rung when the ladder is tilted as normal. Historically, Danish manual workers wore wooden soled clogs. So perhaps nobody bothered to update the ladders when construction workers moved on to flexible soled, work boots?

One manufacturer [Alulock] have a deeper tread on a straight, single ladder. They are rather costly, probably because the rungs are a much more expensive profile than a normal ladder rung. These ladders are sold for stores requiring access to high shelves.

Click on any image for an enlargement. 

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