Expert: Bruce E. Johnson - 1/8/2009

Question
I want to replace two doors with one long door. Total length is 19'4". It is a brick home, double garage, with two 9 foot doors and approximately 1 foot center support. It has two headers made of OSB sandwiched with 2x10s. The center support has two supporting 2x4s and one 2x4 kingboard for each door. Can I use a steel plate bolted to the inside only to support the center and if so, How long and how thick should the steel plate be? Thanks.

Answer
Hi Jerry, it's kind of hard to make that call.  First of all, how does your roof system bear on these headers?  Is there a gable end with just one truss sitting on it (preferable).  Or is it a hip configuration where all of your hip rafters bear on it (not so good).

If it is just a gable end truss then the load is fairly well distributed over the entire wall and your headers are holding up the brick more than they are holding up the roof.  

An LVL or laminated beam is a good option.  They are generally 1 3/4" thick and can be purchased through most lumber yards or truss manufacturing plants.  This LVL can be lag bolted to the the existing 2x10's with 3/8" lag bolts in a six inch staggered pattern.

One of the good things about the LVl is that you can attach a garage door opener to it a little easier than a steel plate. Plus it gives the new header some lateral (outward/inward horizontal) stability.

If you really have your heart set on a steel plate I imagine it would have to be at least 3/16" thick and pre drilled (again in a 6" staggered pattern, bolts six inches apart one up one down no closer than 1 1/2" to the top or bottom of your 2x10)

The problem with a steel plate is that you have no lateral support in the middle of the beam unless you have an angle broke onto the bottom of the plate and attach that angle to the underside of the existing header.  This will prevent the center of the new beam from bowing outward at the bottom.

I hope this information helps.  I am not a structural engineer so any suggestions I make are for planning purposes only and should be verified by an engineer prior to implementation.
Sincerely bruce e johnson..bejohnsonconsulting.com