[Cob] corn storage bins, roofing systems

[drub]

Very interesting conversation.  Great links too.  Thanks.

I am not a roofing expert.  But ... a roof always needs to breathe.  
There should be at least 4" between the ceiling insulation and the roof 
membrane.  The membrane may be plywood and asphalt shingles, or skip 
sheeting and shakes, or metal roofing, or a grain bin roof, or 
whatever.  Doesn't matter.  Without ventilation there is moisture 
accumulation, and rot.  So, Charles, your questions are spot on.

The photos on the first link don't show the roofing details, but I 
didn't see provision for ventilation.  The hexagonal ledger at the 
center top appears to block the possibility of venting at the highest 
point, or at least severely restricts ventilation.  See the second to 
last photo and last photo.  I don't see provisions for venting this roof.

The general method of building a roof is to have vents at the lowest 
point, around the soffets or eaves, and at the highest point.  The roof 
heats and creates a thermal convection, drawing drying air through the 
minimum 4" space.  This draws the moisture out of the materials, and the 
building, which inhibits rot.  The vents should be installed at the 
absolute top of the system.  Any point lower for the vent creates a 
"dead air" space above the vent, which causes rot, etc.  Keep in mind 
"dead air" = rot and other bad stuff.

To correct what I see in the photos ...
- Install that hex ledger 4" lower.  Space the ledger and the ceiling 
joists below the roof metal..  Have the ceiling parallel the roof all 
the way to the walls.  Keep that 4" open between the top of the ceiling 
joists and the steel roofing.
- Install the ceiling insulation in the joist space to maintain at least 
4" of open space.
- Cut exterior vents in each of the ceiling joist spaces.  This is where 
the air will be drawn in.
- Install an air vent at the highest point. Maybe the center cap *is* 
the vent.  Not certain from the photos.  This is where the air will exit.

Hope this is helpful. Also hope a *real* roofer is on the list to 
correct and further embelish.

All the best!
David


Leslie Moyer wrote:
> Charles,
>
> Try these:
>
> http://www.dancingrabbit.org/building/GrainBin.php
> http://www.csmonitor.com/2005/0817/p16s01-lihc.html
> http://sicarius.typepad.com/althouse/home_conversions/index.html
>     (other links on that page, too)
>
> --Leslie
>
>
> charles medic wrote:
>   
>>    does anyone one this list have any knowledge of building inside of
>>    corrugated corn/grain storage bins?
>>   
>>     
>
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