Rolling roof - Wind speed

[Starlight 1]

Not sure this is the right place for this post but ever since I have had a rolling roof on my shed and have seen roofs disappearing in  the wind, my question is

when the roof is open do you strap it down just in case the wind gets under it and what wind speed would you say is suitable to have the roof open without

worrying about it?  I know it would depend a lot if  is in an open or sheltered area, but some idea would be appreciated.

[perfrej]

You really need to use a roll-off system that includes upward movement restriction. Our wheels roll on a flat surface, and there is another flat surface a few mm above the wheels.

I intend to use the same design in my next one, which is for a single pier and no humans present:

/per

[Merlin66]

I always use a couple of turnbuckle hooks to rigidly clamp the roof when closed....

If it's windy enough to be of concern, when the roof is open, it's too windy to observe.

I think Per's idea is a good one.....

[NickK]

If you think about it there's three ways the wind causes issues:

1. wind over an angled roof, like a wing, causes low pressure that sucks the roof up

2. wind flow gets under the roof, perhaps pushed up from the side of the obsy

3. the pressure isn't linear, so rotation and shear are in there

Per's design is good, as it stops the air getting under.

It's possible to get electric clamps - so once closed the clamps could be engaged by remote operation, alternatively a hoop and electromagnetic bolt actuator to lock the roof down.

[laser_jock99]

If it's windy enough to be of concern, when the roof is open, it's too windy to observe.

Good advice- if it's windy leave the roof firmly closed. I often end up just using my outside pier and a wide angle camera rig if it too windy for the main scope. A 200mm lens solidly mounted on an EQ6 can take a lot of buffetting and still be okay!

[ollypenrice]

Obviously I know Per's design because it lives here (!) and it works well. However, you can have other self-captive designs of various sorts. But one way or another you do need to be sure your roof cannot lift off just because it wants to. One day it will, without doubt, want to do so.

Olly

[Merlin66]

The turnbuckle I used on the TSO

A 6m x 3m roll of roof (under construction) when hit by a mini tornado.....

[saac]

Give your local planning office a call, they may be able to offer you advice or at least point you in the direction of wind loading and structural requirement data.  But as most have said I would go with the common sense approach, if it is windy at ground level then keep the roof shut.  Having said that, I guess it would be relatively straightforward to put an anchor bolt in the ground to tether the roof while in the open position - that would give some protection against gusting. I may consider doing just that with my own.

Jim

[r3i]

I added a captive mechanism into my build for a bit of peace of mind but I'd echo Merlin's comment that I would not be opening the roof if the wind was really whipping up as observing/imaging in those conditions is going to be less than ideal.  

[teleskopjo]

Very interesting topic, I think it's imperative not to let wind get below the roof through the gaps

[Starlight 1]

Very interesting topic, I think it's imperative not to let wind get below the roof through the gaps

Some very interesting ideas as the post was more to do with when the roof is open just sitting on its frame, so some of these ideas will become very useful

as the attachments can go all the way through from shed to frame.

[astronymonkey]

I read up on wind loads on a roof a while back and also into the design of wind breaks. One of the options seemed to be to design a roof to minimise lift rather than building a wing shaped roof and then trying to stop it from taking off.

As has been mentioned the roof can act like a wing which causes lift and elements can be introduced into the design to slow the wind over the roof which basically causes the wing shape to "stall" for want of a better phrase.

The introduction of a small pallisade fence type of arrangement along the edge, the sort of thing you see on a pidgeon loft , can introduce turbulent air over the roof which prevents lift from developing.

So Per's design is good but may benefit from on upright pallisade arranagement protruding up along the captive edge .. on the right and left eaves in order to stall the air.

Apparently a solid upright edge wont work as this adds vacuum in the leeward side and creates lift but breaking up the airflow rather than blocking it seemed to be the idea.

Im no aeronautical engineer but the principle seemed reasonable but it was ages ago so I may have forgotton a lot of the detail !

Cheers

[jnb]

I was looking at this recently while building a studio in the garden and one interesting suggestion was decorative ridge tiles. A lot of the damage can arise not from the load of the wind against a surface but from the roof acting like an aerofoil, if you do the calculations then even on a small roof such as 3m x 3m then a 50mph gust can suddenly generate a lifting force that is a significant fraction of a tonne. The principle is to use decorative ridge tiles which introduce turbulence over the building roof and so disrupt the aerofoil effect. They are obviously prone to damage themselves but better to replace them than a roof.

[Gina]

First really severe storm of the winter here and I have had problems - the storm resistant fittings need some improvement as I found the obsy roof half off     Fortunately, some of them held and the roof didn't come off completely!!!  See my own post in this forum.

I certainly recommend paying considerable attention to fittings to hold your roof firmly closed and well held down.  Don't worry about over-engineering it!

[Starlight 1]

Just about all the wood I used is only 5/10mm  over-engineering its not.

[teleskopjo]

When putting on turnbuckles they are best set at 45 degrees and against each other otherwise if vertical the roof will still rock to-fro