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Old 10-28-2011, 09:22 AM   #1
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Flat Roof: Joist Layout, Slope, & Membrane Help Needed!


We are renovating a building that used to be a church built in 1930. We totally redesigned the old "tower". We ripped off the old flat roof (wow did this really need to happen), added a third level, and are now getting ready to build the roof to it (see attached images). The tower is 36' tall and will stretch to 40' when the roof is added with its "battlements".

My thought is to use 2x12s and create a flat structure that overhangs the main tower. These 2x12s would be completely level and would have a layer of OSB covering them. On top of this I thought I would use "firrings" that would create a 4" drop (2.5 Degrees) from the north side of the tower roof to the south side over a 12' distance. I would then add a layer of OSB to the firings.

I thought I would then use 45mil EPDM Membrane for the slope. As this is designed to look like a castle turret with battlements, I thought I would use "Liquid Rubber" (manufactured by Meridian) on the Merlons and Crenels that would be built on all sides of the "turret". These would then have stone veneer installed over them.

Does anyone see any issues with this design? Is Liquid Rubber an effective material? We are already planning on moving the roof access from the Southeast corner of the roof to the Northeast corner of the roof (North is up) so as to prevent pooling of water next to the roof access. Your thoughts on our joist layout and the materials we are considering to use are greatly appreciated!

Note: This is located in Central Iowa where we experience all four seasons.
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Flat Roof: Joist Layout, Slope, & Membrane Help Needed!-towerdesign01.jpg   Flat Roof: Joist Layout, Slope, & Membrane Help Needed!-roofjoists01.jpg  

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Old 10-28-2011, 09:48 AM   #2
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Flat Roof: Joist Layout, Slope, & Membrane Help Needed!


No clue what liquid rubber is. When you 'set' the roof height, go up 16" to 24", run 20oz. copper all the way through the walls before adding any more height to it. You want 6" to 10" of copper on the roof side, and I'd figure 6" more on the outside than the finished product is to be thick. It can be trimmed back for the appearance you decide you like best when all else is done.

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Old 10-28-2011, 09:49 AM   #3
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Flat Roof: Joist Layout, Slope, & Membrane Help Needed!


If it was me, I'd use commercial .090 EPDM over 2" of ISO for the roof for longevity.
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Old 10-28-2011, 10:14 AM   #4
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Flat Roof: Joist Layout, Slope, & Membrane Help Needed!


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Originally Posted by tinner666 View Post
No clue what liquid rubber is. When you 'set' the roof height, go up 16" to 24", run 20oz. copper all the way through the walls before adding any more height to it. You want 6" to 10" of copper on the roof side, and I'd figure 6" more on the outside than the finished product is to be thick. It can be trimmed back for the appearance you decide you like best when all else is done.
The "liquid rubber" I am talking about is located here: http://www.amazon.com/Liquid-Rubber-.../dp/B003KA00VQ

I am not sure what you are talking about when it comes to the "roof height". The 2x12 joists (installed level) would have a top height of 36'-3". I thought I would then cut 2x6s from 5.5" on the North side down to 1.5" on the south side, providing me with a 4" drop for rain water run-off.

My apologies if I sound ignorant, but I have no idea what you are talking about when you are discussing copper. Can you provide an image or link that gives me a visual as to what you are describing?
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Old 10-28-2011, 10:16 AM   #5
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Flat Roof: Joist Layout, Slope, & Membrane Help Needed!


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Originally Posted by tinner666 View Post
If it was me, I'd use commercial .090 EPDM over 2" of ISO for the roof for longevity.
Can you provide a link as to where this may be purchased? I thought the 45mil was the thickest membrane availalbe. Then again, I have not been researching roofing materials for very long. Thanks again for your suggestions!
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Old 10-28-2011, 10:50 AM   #6
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Flat Roof: Joist Layout, Slope, & Membrane Help Needed!


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If it was me, I'd use commercial .090 EPDM over 2" of ISO for the roof for longevity.
In what order would everything be installed?

1. OSB flat on level 2x12s?
2. Firrings providing slope over the flat OSB?
3. OSB over the sloped firrings?
4. 2" Extruded Polystyrene Board over sloped OSB?
5. .090 EPDM Membrane over the Extruded Polystyrene Board?

Thanks again for all of your help!

Are you talking about this stuff? -

http://www.lowes.com/pd_96554-46086-...rene&facetInfo=

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Old 10-28-2011, 01:27 PM   #7
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Flat Roof: Joist Layout, Slope, & Membrane Help Needed!


"I am not sure what you are talking about when it comes to the "roof height". How high do the parapet walls extend above the roof?

The 2x12 joists (installed level) would have a top height of 36'-3". I thought I would then cut 2x6s from 5.5" on the North side down to 1.5" on the south side, providing me with a 4" drop for rain water run-off."

Last edited by tinner666; 10-28-2011 at 01:33 PM.
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Old 10-28-2011, 01:32 PM   #8
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Flat Roof: Joist Layout, Slope, & Membrane Help Needed!


n what order would everything be installed?

1. OSB flat on level 2x12s? No
2. Firrings providing slope over the flat OSB? No
3. OSB over the sloped firrings? The tapered 2x6's are fine
4. 2" Extruded Polystyrene Board over sloped OSB? No, ISO http://www.firestonebpco.com/roofing/insulation/ and this link
http://www.gaf.com/Roofing/Commercia...nsulation.aspx
5. .090 EPDM Membrane over the Extruded Polystyrene Board? No, over the ISO.

ABC supply, Bradco, or other roofing supply house can fill you in.

Thanks again for all of your help!
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Old 10-28-2011, 01:38 PM   #9
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Flat Roof: Joist Layout, Slope, & Membrane Help Needed!


Quote:
Originally Posted by dutchswan0311 View Post
I thought the 45mil was the thickest membrane availalbe. Then again, I have not been researching roofing materials for very long. Thanks again for your suggestions!
.045 is a short term material in my opinion. Use it if you like to redo things every so often. As light as it is, I find it harder to roll it into the glue without bubbles, wrinkles, bulges, etc, than it's stiffer cousins.
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Old 10-28-2011, 01:43 PM   #10
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http://www.reverecopper.com/index.html
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Old 10-28-2011, 01:44 PM   #11
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Flat Roof: Joist Layout, Slope, & Membrane Help Needed!


I'm a slow typer and have been booted and lost my posts about 4 times now. Give me a call and I'll answer your questions.

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