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Saturday 9th Feb: Gusts to 50mph are forecast for this afternoon. So I turned the dome to point the shutters into the wind. Facing them downwind might cause suction which might tend to lift them. Note the emphasis on "might." I have no real data on the subject. The downside with upwind shutters is the short length of rubber skirt under the observation slit which can lift to form a gap in strong winds. Rain tends to drive through such gaps. Which wets the octagon top ring but little else. The rubber strip seems completely uninterested in blowing in to inflate the dome. Spoending more time blowing outwards, directly into the wind. Perhaps it is the updraught from the obs. walls?
The advantage of the short length of rubber is that it can be easily lifted to quickly check outside. Lifting the continuous [heavy] rubber skirt anywhere else is much more difficult. It is stretched around the top ring so resists lifting. The bottom of the dome slit is too high to let me see outside very easily. Opening the doors out to the veranda is rather a chore because of all the security bolts and obstructions. No problem when I do need to go out there but more work than needed for just a quick chat with my wide down on the ground below.
Condensation running off the massive mounting causes far more wetness on the floor. Which, being larch decking boards and intended for outdoor use, can be safely ignored. I do need some sort of "porch roof" to protect me from the constant drips from the veranda. Every time I stand outside, while locking or unlocking the doors in wet weather, I get a free shower.
The rubber flashing on the bottom of the observatory wall cladding is keeping the rain out of the octagon. It was harder work mitering all those veranda boards neatly to follow the sides of the octagon. Any other board arrangement would have drawn rainwater inside at floor level. The only problem is with the parallel floor joists stopping the flashing from sagging freely over their entire length. So rainwater tends to collect around the joists instead of falling straight off. Slitting the plastic flashing either side of the joists might be counterproductive. It might cause more water retention over the joists.
I just went over to check how the dome was coping with the gusty wind. A bit noisy and the rubber skirt was flapping. The dome seemed rock steady with no detectable vibration or shaking to the touch. I hung a weighted cord pendulum from the obs. floor to see if it would swing. Once it had settled it stayed still. So the octagon building is probably stiff enough. The floor has stayed perfectly dry despite all the rain and high winds.
If I could get some aluminium strip say 6" wide it could be fixed to stand up on the outer edge of the top ring to stop draughts. I'm not sure the DPC plastic is quite stiff enough for this purpose. Perhaps I should try it inside the shorter length of skirting to stop rain driving in.
I do need to close the gaps between the lengths of flashing which support the dome's rubber skirt. Trying to cut perfect miters on folded metal is very difficult without practice. So is fixing the resulting meter plus lengths to perfectly close the gaps between them.
The flashing profiles seem to have survived the long term strain of supporting the heavy rubber skirt. I have plenty of off-cuts of the same metal. So can make some 2" wide strips and pop-rivet them onto the undersides of the mitered joints. Putting them on top would just allow the rain to blow under them. Not only would they be more visible but would achieve no more than having them underneath. Since all the metal is sloping downwards and outwards any rain passing through the remaining gaps will just run down and away. The strips would also help to reinforce the flashing against any long term sagging. Because the multi-sided geometry of the flashing becomes even more self-supporting.
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