My observatory has no roof

[Mr TamiyaCowboy]

yep we have more on the way friday onwards. 

maybe best to redesign the roof, try and take away the pitch

or maybe work in some fixing loops into the floor. 

a couple or four of those web ratchet straps and four hook points 

on the roofs trusses should keep everything tied down if we have more weather like this in the years to come

[JamesF]

That doesn't look good  I hope your kit recovers ok and the roof can be remade without too much pain.

My younger brother was a civil engineer in a previous life.  He has impressed upon me how important it is to make sure the roof of even a small building is properly secured.  Apparently they have to do the figures for the "lift" generated by wind passing over the top of a roof to demonstrate that it is sufficiently secured when putting together building designs.

James

[Stargazer33]

Sorry to hear about your obsy Mark. It's a real shame. I hope you manage to get it sorted before too long. Are you a member of a club with members that could help you get the obsy secured before the next storm hits. If I was closer I would offer my help as I am off work until 2nd Jan. Perhaps SGL members in Kent would help?

As for your equipment, try burying your electronic devices in rice - the dried stuff. Worked wonders for my mobile that went through the washing machine!

If I ever manage to build myself an obsy, I think I'm going to sink a couple of those security bolts into the concrete. The ones that they padlock motorbikes to. I'll then put a couple of webbing straps trough them and attach them to the roof.

I recorded 20.5 mph on our garage roof at 04:38 this morning and the weather vain is quite protected with all the houses and trees around here. The highest I've ever recorded before was 15 mph.

[dmahon]

At least most of the long pieces of timber seem to be intact. It'll need a bit of work putting back together, but you shouldn't need to buy too much more wood.

I like the eye/bolt technique so it locks automatically as the roof is closed, then you just need a single bolt to stop it sliding. I think Gina's thread has some good pictures of it.

[Gina]

Thank you   They certainly seem to work:)  We had exceptionally strong gustsof wind last night and it's fine.   But they do need to roof to be fairly accurately lined up hence my new wheels and track.

[sharkmelley]

I've found some interesting articles online that say it is quite typical for 15 degree pitched roofs to be totally lifted off during hurricanes - so they need to be fastened very securely.  Apparently they act just like the profile of an aircraft wing.  I'm very interested to know the lift generated by a 15 degree pitched roof with an area of 3m  5m in say 60-80mph gusts (or in metric, 30-40m/s).

Mark

[sharkmelley]

Typo - I meant 3m x 5m.

[Peter Drew]

 I think a 747 "lifts off" at less than a 200mph "wind". The positives from this unfortunate event are the ability to discern any weaknesses in the original design and also come up with a satisfactory hold down system to avoid future problems.

[Chris Rowland]

Typical wing loadings for gliders and small aircraft are around 30 to 50 kg/m2 and they take off at around 40 to 50 knots.  Your roof, with an area of 15 m2, could generate lift of 450 to 750 kg.  The lift increases as the square of the speed so doubling the speed will quadruple the lift.

There's easily enough force here to toss a 500 kg roof around, and you need to be serious about tie downs.  Attaching the roof to the building may result in the entire thing taking off.

Chris

[JamesF]

 I think a 747 "lifts off" at less than a 200mph "wind". The positives from this unfortunate event are the ability to discern any weaknesses in the original design and also come up with a satisfactory hold down system to avoid future problems.

180mph according to David Gunson on "What Goes Up Must Come Down".  It's a little dated now, but well worth a listen if you've not heard it before:

http://www.youtube.com/watch?v=7KbUNzi58wM

James

[red dwalf]

What bad luck mark, hope you manage to get it sorted ok, it's certainly got me thinking of doing something to hold my roof down.

checked the inside of my obsy this morning and I was upset a little water had got in so you must be well peeved

[BritAngler]

Sorry to hear about the obsy roof Mark, but it's a good job the rest of the structure held together.

I'm a big fan of over-engineering (you could sit a hippo (or even  my ex-MiL) on my garden bench). I like the idea of those web ratchet straps on hooks anchored into the concrete, but I'd be very tempted to put at least two on each of the cross beams plus another two on each of the outside edges (from your photo's, that would make a total of 18). Obviously, you will not be using them all the time, but for when the next storm comes I'd want to be fully prepared.

I hope all the gear is okay....

[astronymonkey]

Hi,

I was wondering if some sort of vented roof may help prevent the pressure differences above and below the structure that cause the lift. So if the roof had vents then the negative pressure sucks air via the vents and negates the lift.

another idea may be to increase the pitch, this causing a stall effect, or adding something to the roof to create drag such as battons etc.

Im not an expert but just a few ideas which may or maynot be of use.

cheers

[Tinker1947]

Maybe your next roof while being a roll-off should be flat, but higher one side to allow rainwater to run off, if you have got away with out any other damage that will be a nice xmas pressie...

[BritAngler]

Or make it out of concrete

[Macavity]

Having nightmares now! Recalling the installation of an 8' x 10' Alexander's Observatory, Nick and I could relatively easily lift the "naked" roof structure. (With my "dicky ticker", wan't terrible chuffed re. lifting it above head height though!) But say... 100lb tops? Add equivalent of TWO 8' x 4' OSB (3/8"?) sheets - 50lb Each? I reckon my 6m^2 roof would only weigh around 200lb or one TENTH of a ton. No pedantry. I will have to console myself it won't have quite the lift of a high-performance glider?

Since Friday's wind will be from the non-door end, maybe I'll leave it part open, to equalise the pressure. Spend the night swinging Quasimodo-like from the rafters? lol. Certainly the local wind was sufficient to suck the inclined top off an Argos plastic garden store - Simply pulled the plastic lock / hinges apart. Wheelie & recycling bins are a (Non!) standing joke at 200' on the coast these days. But genuinely concerned - Especially since winds of this order are seemingly a fairly regular feature now?

Will (belatedly) add some M12 bolts and turnbuckles to fix the roof to the (heavier) walls. I sense once things *begin* to "fly" there's not a lot one can do. Except possibly keep out of the way... 

[Alien 13]

Hi,

I was wondering if some sort of vented roof may help prevent the pressure differences above and below the structure that cause the lift. So if the roof had vents then the negative pressure sucks air via the vents and negates the lift.

another idea may be to increase the pitch, this causing a stall effect, or adding something to the roof to create drag such as battons etc.

Im not an expert but just a few ideas which may or maynot be of use.

cheers

Im not an aerodynamic engineer but i like these ideas of reducing lift rather than adding mass you could end up having a much more dangerous roof flying around.

[Zakalwe]

Having nightmares now! Recalling the installation of an 8' x 10' Alexander's Observatory, Nick and I could relatively easily lift the "naked" roof structure. (With my "dicky ticker", wan't terrible chuffed re. lifting it above head height though!) But say... 100lb tops? Add equivalent of TWO 8' x 4' OSB (3/8"?) sheets - 50lb Each? I reckon my 6m^2 roof would only weigh around 200lb or one TENTH of a ton. No pedantry. I will have to console myself it won't have quite the lift of a high-performance glider?

Since Friday's wind will be from the non-door end, maybe I'll leave it part open, to equalise the pressure. Spend the night swinging Quasimodo-like from the rafters? lol. Certainly the local wind was sufficient to suck the inclined top off an Argos plastic garden store - Simply pulled the plastic lock / hinges apart. Wheelie & recycling bins are a (Non!) standing joke at 200' on the coast these days. But genuinely concerned - Especially since winds of this order are seemingly a fairly regular feature now?

Will (belatedly) add some M12 bolts and turnbuckles to fix the roof to the (heavier) walls. I sense once things *begin* to "fly" there's not a lot one can do. Except possibly keep out of the way... 

I doubt that leaving the door open will make any difference. The lift comes from the air having to move faster over the pitched roof, thus lowering its pressure (Bernoulli principle). Normal atmospheric pressure below lifts the roof up. opening the door won't change this.

[happy-kat]

There's easily enough force here to toss a 500 kg roof around, and you need to be serious about tie downs. Attaching the roof to the building may result in the entire thing taking off.

Chris

That is interesting, is there a pitch range that is safe from lift off or perhaps a pent roof is best to reduce risk of flying off?

[JamesF]

That is interesting, is there a pitch range that is safe from lift off or perhaps a pent roof is best to reduce risk of flying off?

I'm not sure that a pent roof would make any difference.  It may be that for these purposes a pent roof can just be considered a pitched roof where one of the pitches is vertical  The air still has to travel a greater distance to go over the roof than the width of the building.

I'm not sure when I'm seeing my brother over Christmas, but I shall try to find out some more information when I do.

James

[Macavity]

See figure 12? (Oddly it does mention opening doors - But sadly not "end" doors)

http://www-stud.rbi.informatik.uni-frankfurt.de/~plass/MIS/mis6.html

For the prevailing wind (SW) the leeside is about 3' from a neighbours flat roof garage.

at about the same height. Noticable, even at modest levels of wind, I hardly ever see

rain landing between two. Not sure if this is good or bad. The experiment is tomorrow!

[Tinker1947]

I do hope there are no Obby's out there just sitting on the ground, the roof could be fine if held down, but the whole structure could end up over the fence in a neighbours garden...loads of sand bags in all 4 corners might help.....

[Mr TamiyaCowboy]

looks like we have a double barrel storm lined up. 

we have one heading in over tonight and into tomorrow.

then on monday looks like another chunk of low pressure heading our way.

[Gina]

Nasty   I've decided it's a waste of time repairing our sun lounge while there's still bad storms around.

[Tinker1947]

I removed a broken feather board panel it did hid the filters for the pond, it ended up laying against the filter, roughly 4' 6" high and 5' long, snapped the 3" posts off at the ground, the panel had been there around 10 years, the posts were not in prime condition.