Concrete Roof Question
Last Post 19 Aug 2008 01:29 AM by Chicano. 7 Replies.
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pjfUser is Offline
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18 May 2008 07:08 PM
I am looking for a poured concrete roof system that is structural and can span a maximum of 40ft. It must be able to sit on top of the exterior ICF walls and overhang so there is a soffit/fascia. I does not need to be a icf roof. As long as i can pour concrete and there will be no thermal bridging. There will be very little slope to the roof, almost flat Any recommendations would be appreciated
AltonUser is Offline
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18 May 2008 10:05 PM

PJF,

Since concrete is very strong in compression and your span is so large, have you considered a thin shell dome roof?  Search the internet for dome roofs.

Residential Designer & Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu, 334 826-3979
pjfUser is Offline
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18 May 2008 11:16 PM
Sorry I am not interested in a dome roof
insuldeckfloridaUser is Offline
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19 May 2008 09:21 AM

i live in one of those after frances, jeanne and wilma.....

email me for more info and cd...

peter

insuldeckflorida@aol.com

icicle earth homeUser is Offline
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08 Aug 2008 11:16 PM
we are doing an ICF roof by LOGIX. it will span your distance. and be earth covered.

http://icicleearthhome.blogspot.com/

steve
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09 Aug 2008 08:07 AM

pjf,

Not sure about the cantilever over hangs for soffit but a bar joist like Hambro sells could be just the ticket. We are going with a 3' parapet wall. This will make the roof top patio safe to be on. Our stiar case goes to the roof for easy acces.

The thermal bridging is a topic I have addressed here without much help. In the end, I think I will be using AAC/Y-Tong as a top 2" of my wall for my flat roof thermal break. My roof spans are 30' max and I have 16" deep joists with a 4" slab.

Where are you building? Here in S. IN, we need 100lb sq-ft load rating for snow. How will your roof be used? Green, patio or just a roof?

Patrick T

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09 Aug 2008 11:20 AM

PJF,

A suspended slab will do the trick for you, and there are many ways to accomplish this type of roof. 

You can use prestressed precast concrete panels although 40 feet may be at their outer limits.  I haven't used them in awhile and would have to check.  We did do a 36 foot clear span garage with them though.  Depending on where you are located and the loads on the roof this can be a fast no fuss no muss way to go.

Cast in place is a viable option also and here you would have many options to choose from.  ICF system, conventional wood forming, a commercially available forming system used in high rise construction, and or post tensioned concrete to name a few.  For some one who has never done suspended slabs the ICF systems offer a simple and proven route to accomplish your goal.  The commercial systems are set up for speed and efficiency but you usually have to have big equipment to move them around.  Post tensioning is great but you have to have the contractors available and the access to the building site for the post tensioning process.

Having the right engineer is key to the success of your endevour.  You need to find an engineer that has a good amount of experience with suspended slabs.  Don't go to the first name you come to in the phonebook a say great I found my engineering firm, AAA Engineering We engineer all kinds of stuff call 555-1212.  This would be certain path to disaster.

Find someone who will listen to your wants and desires for your roof then let them come up with your needs and requirements of a system.  This will ensure a smooth building process.

ICF Contractor

ChicanoUser is Offline
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19 Aug 2008 01:29 AM
I recommend you take a quick trip to basically anywhere in Mexico and talk to a local "Maestro". I grew up in Mexico in a large 2 story, concrete block with poured concrete floors (1st and 2nd) and a vaulted poured concrete roof (not ICF) covered with traditional red clay tiles. I don't know why it seems like rocket science to American buildders when the 3rd world has been doing this for years! Anyway, I can't answer your exact question, but I do remember about 25 foot spans with no beems for our roof at home. Any more than that and we had a concrete column beem constructed horizontally from wall to wall (6-8" thick) to support larger sections of roof. I believe the roof was 5" thick poured concrete. This was built in the 70s and is still solid today with no cracking. Not sure about thermal bridging and all that. That was not a consideration back then. My mother-in-law (Mexican) builds houses down there out of concrete today. Some of her roofs span probably pretty close to 40ft. I would still put a concrete beam in. (Easy--just build a box out of ply wood with the top open, put in some rebar, brace it in place with some 2x4s, bend the wall rebar into the form, pour the concrete and wait for it to set.)
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