16' wide x 8' tall garage door (x 2 doors - 4 car garage)
Load = 280 lbs/lineal foot
Ridge beam in garage which cuts the roof load in half
Steel SIP roof dead load

Will a 12" lintel work or will it require a 18" lintel above the garage doors?

The 12" lintel puts the ICF wall at 9 feet, which is ideal. The 18" lintel puts the garage wall at 9' 6", less than ideal

This is off the charts for lintel span. I recently did an eighteen foot span but it had to be designed by an engineer. It was two #8 under two #6 effectively forming a tie beam with stirrups. Special order rebar of twenty five feet. To get the heighth that you are wanting, I think you should look at a steel beam.

Posted By scicf on 15 Jun 2012 11:21 PM
This is off the charts for lintel span. I recently did an eighteen foot span but it had to be designed by an engineer. It was two #8 under two #6 effectively forming a tie beam with stirrups. Special order rebar of twenty five feet. To get the heighth that you are wanting, I think you should look at a steel beam.

Just to clarify, the garage doors are 16 feet in width but they are separated by a 4 foot wide wall in the middle of the doors and then a 6 foot wall on each end of the garage door.