My observatory has no roof

[Tinker1947]

Another way to secure the roof in place......

[laser_jock99]

I now have nine tie down points in total (added another two after Wednesday's gale).

The corner tie downs are 6mm steel cables anchored directly to the 4"x4" corner posts. These are also tensioned to stop any initial jolt turning into a full scale lift.

In the middle of the four sides are roped M10 eye bolt-to-eye bolt (3 x loops of 8mm climbing rope) holding the roof frame to the 4"x4" centre posts.

Having witnessed the full force of the gale from inside last week I added another such rope tie down on the exposed Western side. 

The other thing I witnessed during the gale was that some nailed down parts of the corrugated roof had worked a bit loose and the nailed 'full force front row' were replaced with screws- one for every corrugation on the leading edge!

Call me paranoid but my obsy gets a good battering from storms on a regular basis- being on a very exposed site 1400 feet up a Welsh mountain.

Take the weather risk seriously people.....

[SnakeyJ]

I now have nine tie down points in total (added another two after Wednesday's gale).

The corner tie downs are 6mm steel cables anchored directly to the 4"x4" corner posts. These are also tensioned to stop any initial jolt turning into a full scale lift.

In the middle of the four sides are roped M10 eye bolt-to-eye bolt (3 x loops of 8mm climbing rope) holding the roof frame to the 4"x4" centre posts.

Having witnessed the full force of the gale from inside last week I added another such rope tie down on the exposed Western side. 

The other thing I witnessed during the gale was that some nailed down parts of the corrugated roof had worked a bit loose and the nailed 'full force front row' were replaced with screws- one for every corrugation on the leading edge!

Call me paranoid but my obsy gets a good battering from storms on a regular basis- being on a very exposed site 1400 feet up a Welsh mountain.

Take the weather risk seriously people.....

A stunning site and well worth some sensible precautions.    As well as preventing the roof from blowing down, I would have to invest in a couple of big leisure batteries to make sure I could continue to use this and take full advantage of the dark when the power lines come down

[Paulus17]

Might it be worth covering all the gear up inside  the obsys with some sort of water proofing,even just a bin liner, with all this stormy weather we are having now just in case??

[laser_jock99]

Might it be worth covering all the gear up inside  the obsys with some sort of water proofing,even just a bin liner, with all this stormy weather we are having now just in case??

Always cover the scope with something just to keep off the dust and drips that may arise. If the roof went the wind will take any covers as well! I found a Poundland bike cover fits nicely over a mounted 12" Newt.

[luna 2011]

sorry to hear of your loss,it happend to me too my obsy has mostly broken up now as the winds are still pounding us.lets hope these broken observatories nationwide  rise from the ruins and give us many views of clear skies

[Paulus17]

Obviuosly LJ if i had an obsy and knew of a storm coming in as we have been getting i would make sure the covers were tied on well.

At least it would hopefully keep all the expensive  items dry till i could get em all in the house

[Zakalwe]

These look very useful....after all, no point in securing the roof if the whole shed lifts off....

http://www.groundbolt.co.uk/Sheds.html

[jnb]

These look very useful....after all, no point in securing the roof if the whole shed lifts off....

http://www.groundbolt.co.uk/Sheds.html

They look quite narrow to me. OK they might be long and the might screw into the ground but they still only going into a small area. Unless you fix them into concrete I suspect they would move in a storm. The best option is probably to plant a hedge, that would shelter the walls of the building and add some kind of ridge tile to disrupt airflow over the roof.

[Gina]

In very stormy weather as we have been having lately I would worry about these groung screws working loose.  With a stedy pull they might be alright but with intermittent tugging they could work loose.  Looked a great idea at first but after thinking about it for a minute or two the problem comes to mind

[SnakeyJ]

If you want good ground anchors a good length on angle iron knocked in to the ground is pretty hard to beat for price or resilience.   They will give up eventually, but not without a hell of a fight

[RikM]

Is it necessary to anchor an obsy to the ground? I thought I read in another thread where most shed type buildings are simply plonked on slabs or concrete blocks?

[r3i]

Is it necessary to anchor an obsy to the ground? I thought I read in another thread where most shed type buildings are simply plonked on slabs or concrete blocks?

A lot probably are but they run the risk of being shifted by strong winds.  If you're certain that the observatory is going to be in sheltered spot and won't feel the onslaught of the wind, then anchoring might be unnecessary.

Our garden is rather exposed to the wind so I felt it was prudent to ensure it was anchored to the ground.  I built my observatory on top of decking which is fixed to the ground with 10 anchor posts (aka MetPosts) that are concreted into place.  Hopefully that should be sufficient.

[Gina]

Is it necessary to anchor an obsy to the ground? I thought I read in another thread where most shed type buildings are simply plonked on slabs or concrete blocks?

There are also reports of garden sheds being lifted up or blown over by the wind and most will have plenty of weight inside - observatories tend to have little weight inside.  What there is, is often on a pier not connected to the shell of the "shed".

This is a very exposed position here, particularly from the east round to the south, so I fastened the base beams of the obsy to the 6 poured concrete blocks it stands on.  Hopefully, it's not going very far and has shown no sign of moving yet.

[sharkmelley]

This is something that definitely worries me now.  Once I rebuild my roof and securely clamp it to the shed, all the lifting force will then be transferred to the shed itself.  Add to that the wind loading on the outside walls and there is definitely a possibility that the whole shed could be lifted or tipped up.  My roof lifted off in the early part of the storm when gusts were (probably) only around 60mph.  Gusts of 100mph would give 3x as much lift (lift is proportional to square of wind speed) and would potentially lift the shed wholesale.  It might even happen at a lower wind speed.  I certainly think that in my very exposed location I need to retrofit secure anchoring to prevent this possibility.

Mark

[Paul73]

Difficult balance. Bigger field of view = more exposed.

Might be worth taking a leaf from the beach huts which are essentially garden sheds which take a real battering. They have broad webbing straps with a ratchet to tighten going over the whole thing and secured by ground anchors or to the concrete pad on which it sits. Obviously this would need to be put on when the forecast is bad as it essentially clamps the whole thing to the ground.

Hope that this is a constructive addition to the debate.

Paul

[Zakalwe]

They look quite narrow to me. OK they might be long and the might screw into the ground but they still only going into a small area. Unless you fix them into concrete I suspect they would move in a storm. The best option is probably to plant a hedge, that would shelter the walls of the building and add some kind of ridge tile to disrupt airflow over the roof.

I guess a lot depends on the substrate that they are going into (clay/sandy soil/loam and so on). The website gives the strength for the shortest one as 1800Kg, which I presume is force required to pull them out of the ground?

[Zakalwe]

They look quite narrow to me. OK they might be long and the might screw into the ground but they still only going into a small area. Unless you fix them into concrete I suspect they would move in a storm. The best option is probably to plant a hedge, that would shelter the walls of the building and add some kind of ridge tile to disrupt airflow over the roof.

This video gives an idea of the strength of them:

[astromerlin]

The south side of my obsy is exposed to the wind, I used 4" fence post spikes and 4" fence post on the southern corners and screwed the 'shed' to them.

http://www.wickes.co.uk/metal-post-spike-24in/invt/542500/

[sharkmelley]

Very useful online calculator here:

http://engexp.com/calculators/asce_comparison.cfm

It's American so the figures are in pounds per square foot.   Use the custom settings, put in windspeed, roof type, roof slope etc and it will calculate the forces (lifting forces are negative) that the roof must withstand in various zones of the roof to comply with the American ASCE 7-05 and 7-10 standards. 

To change the figure in a box, click on the box and drag up or down.

When you sum the forces over the whole roof there are some scary numbers there!

Mark

[laser_jock99]

Not taking any chances......my corner posts are concreted to the bed rock.