Overhead Door Opening Dimensions
I have probably been involved directly with somewhere around 50,000 sectional steel overhead doors in my career. One thing in common about all of these doors, they all require an opening.
In my (and most door installers) ideal dream world, every overhead door opening is perfectly plumb on each side as well as having a perfectly level upper jamb. However, we live in a real life world, where columns on each side of overhead door openings tend to not always be 100% straight. Sometimes these columns were not placed plumb initially, other times they warped, twisted, cupped or did other nasty things (as lumber tends to do), making for potential challenges.
Early in my career, an installer who had placed a plethora of overhead doors in post frame (pole) buildings recommended to me to plan upon finished openings being two (2) inches less in width and one (1) inch less in height than actual call out dimensions of door. This allows for door panels to overlap (again, in our perfect world) an inch on each side, as well as above. With at least five (5) inches of solid wood on each side of any given opening (3-1/2” if a 4×6 plus 1-1/2” of jamb), there is yet plenty of wood available to mount tracks to.
What are advantages of planning for an overlap? If one or both side columns are out of plumb, this allows for as much as an inch of error before reliance upon a vinyl weatherstop to seal up opening. Same goes for top jamb being level.
Columns on each side of door openings do have a 2x jamb attached to them. Done properly (back to my ideal dream world) shims can be placed between an out of plumb, warped or twisted column and jambs to achieve a more close to vertical opening. In most instances (especially those involving ‘professional’ building erectors) this shimming process is ignored entirely and jambs are (for sake of expediency, lack of knowledge, or just not caring) nailed up directly to columns with little or no thought as to future challenges.
Residential overhead door panels are typically exactly door “call out” sized. A 10’ wide x 8’ tall door (as an example) will be exactly ten feet wide and exactly eight feet tall. A perfect finished opening will hence be 9’10” wide by 7’11” tall. Commercial door panels are two inches greater in width and net out an inch greater in height, so ordering a 10 foot wide overhead door, means you will receive 10’2” door panels. Hence, commercial overhead door openings will be equal to call out dimensions of door.
This extra inch of overlap also provides a much tighter seal against wind infiltration and with insulated door panels – less of a heat loss or gain (depending upon the season).
On a semi-related subject, I will encourage readers to always specify wind load rated sectional steel overhead doors. For extended reading, please see: https://www.hansenpolebuildings.com/2014/12/wind-load-rated-garage-doors/.