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Flat Roof Observatory - Design Help Needed

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#1 midnightlightning

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Posted 03 October 2020 - 05:23 AM

I need an observatory and my only option is to use an existing flat roof single garage. 

 

The garage has a good solid concrete floor so I am thinking:

  • build a platform for the pier on the floor with concrete engineering blocks - it will need to be around 90cm high.
  • Bolt a pier onto the platform
  • Build a raised walkway around the pier platform for access - and probably build some stud walls around (Security, Keep Dust out, stop me falling off the walkway etc)
  • Cut a hole in the roof and have the scope just able to pop out at around 30 degrees. I'm surrounded by houses and don't  image below this anyway. I need to measure accurately but I estimate a 40" square opening should do it.

I'm not worried about vibration because I'll be in the house during imaging :)

 

My main challenge is how to make a weatherproof opener in the roof with it being flat. I need to keep it low profile because we are in a conservation area and the planners will kick off about it if its noticeable. So I'm aiming to keep the profile as flat as possible - 4" max height above the roof plane.

 

Any ideas would be welcome, I think my options are a sliding panel or two hinged panels. 

 

 

 

 

 

 

 



#2 QuietStar

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Posted 03 October 2020 - 06:05 AM

You will need to build a small curb around the opening and bring the roofing material over the curb, that will keep the water out of the opening. Then you can cap the opening with anything that is weatherproof, provided that it covers the curb and preferably extends down around the sides by at least an inch. My guess is that a removable panel would be the simplest method. The cap wouldn’t need to be that heavy if the middle is elevated so it doesn’t collect water and the fasteners could be located on the inside for access.


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#3 TOMDEY

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Posted 03 October 2020 - 06:09 AM

Well... that can be done, provided punching that hole does not compromise the mechanical/structural integrity of the roof itself (do you get snow?!) As you probably know, flat roofs are notorious for (eventually) leaking. That giant hole will turn it into a perfect funnel unless it is thoughtfully and meticulously executed. I've even seen myriad cases where owners have decommissioned skylights because they eventually leak, resulting in severe damage to the house.

 

I know you have decided that this is your one and only alternative. Would at least be worth thinking ~outside the box~ to re-convince yourself of that conditional.    Tom


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#4 QuietStar

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Posted 03 October 2020 - 06:30 AM

Tom makes a good point on the structural integrity of the roof. The roof sheathing and roofing material can be cut without causing a problem, provided the opening gets sealed. The supporting members that are holding up the sheathing is a different story. The roof structure should have been designed and constructed to support the required loads in your location. You can’t just cut a joist out of the way, without adding additional support to the structure to compensate for what is removed.


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#5 jeffreym

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Posted 03 October 2020 - 06:54 AM

I agree with the posts so far, those are important points.  A 40" opening will almost certainly remove critical roof structure support.  The stud walls you refer to in your bullet point 3 will need to be used to support this loss of support structure. Something like this:

 

Attached Thumbnails

  • Revised roof structure.jpg

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#6 midnightlightning

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Posted 03 October 2020 - 06:55 AM

I've been looking for an alternative option for 4 years and there isn't one - the idea of using the garage just came to me yesterday. 

 

Structurally there isn't a problem, I and I have fitted Velux windows in the past so have some experience (btw roof lights shouldn't leak if fitted properly with the correct flashings wink.gif ).

 

Snow worries me more than anything - we haven't had much is any the last few years but every so often we can get up to a foot. I can stop it blowing in but my concerns is what happens when it melts.

 

I need to open the roof from inside so not sure how lift off would work but I'm thinking perhaps put a couple of wheels on one edge (and some channels for them to run in) and then by lifting the other edge to get the lip over the curb I could slide the panel. 

 

Yes, I hate flat roofs, and this one is ready for re-felting. The garage is a horrible building and not worth spending money on a pitch roof but if I could afford it I would knock it down and start again.



#7 midnightlightning

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Posted 03 October 2020 - 07:07 AM

I agree with the posts so far, those are important points.  A 40" opening will almost certainly remove critical roof structure support.  The stud walls you refer to in your bullet point 3 will need to be used to support this loss of support structure. Something like this:

Thanks for the diagram grin.gif

 

No structural problems. It's a felt roof on 1" boards and the joists are oversize (maybe 10x2") and only span around 8' between a wall and a steel beam. Just need to remove 4x4' of board, reinforce the joists at the side, cut out two joists and then box the cut ends back in - as per the diagram :)



#8 kathyastro

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Posted 03 October 2020 - 08:09 AM

How well does the roof drain now?  Every flat roof I have seen has standing water on it after a rain.  If there is anything you can do to improve the drainage, like adding new gutters/downspouts, do it.  The less water you have to keep out, the better.

 

Make sure that you have flashing that extends the full height of the raised portion of the opening, and that drains onto the top of the roof membrane.  The membrane should extend up the sides of the opening under the flashing.  Use plenty of caulking, and pay particular attention to the corners, which WILL leak.


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#9 *skyguy*

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Posted 03 October 2020 - 09:50 AM

I built a ROR observatory over my attached garage 20 years ago. The pier was constructed using 16"x16"x8" chimney blocks and they were placed directly onto the concrete floor ... no isolated foundation was used. I've never had any vibration problems while imaging with a 12"SCT installed on top. I wouldn't hesitate to build another roof-top observatory.

 

Here's some images of the observatory that you might find helpful in building your garage top observatory:

 

https://www.flickr.c...57644177074161/

 

Good Luck with your observatory build ...

 

observatory pier.jpg



#10 midnightlightning

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Posted 03 October 2020 - 05:03 PM

I built a ROR observatory over my attached garage 20 years ago. The pier was constructed using 16"x16"x8" chimney blocks and they were placed directly onto the concrete floor ... no isolated foundation was used. I've never had any vibration problems while imaging with a 12"SCT installed on top. I wouldn't hesitate to build another roof-top observatory.

 

Here's some images of the observatory that you might find helpful in building your garage top observatory:

 

https://www.flickr.c...57644177074161/

 

Good Luck with your observatory build ...

 

attachicon.gifobservatory pier.jpg

Thanks Skyguy, yes I was looking at you post earlier and was impressed with your concrete pillar - nice job all round.




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