How To Finish A Garage Door Opening? (What You Need To Know!) is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to . The website is also an affiliate of a few other brands.

What Should be the Rough Opening for the Garage Door?

Do you wish to replace the old garage door with a new one? Or are you planning to build a new garage? You need to know the garage door opening size or how to finish a garage door opening. Without this information you will not be able to order the correct size of the new garage door.

The garage door opening size should be the same size as the garage door, after the trim boards have been put in place. Without the trim boards and the threshold seal, the garage door rough opening should be 3” wider and 1 ½” taller.

Standard off-the-shelf Garage Doors come in standard sizes. Custom designed garage doors in a size of your choice can of course be made. 

Non standard sized garage doors take a lot more time and cost a lot more too!

It is best to settle for one of the standard garage door sizes. Which in turn means that you have to be very sure of how to finish a garage door opening.

In this post I shall be explaining about the important measurements that you need to take for garage door opening, how to take them, how you frame the garage door header, and how you frame and trim a garage door opening.

Which Measurements Should you Take before Ordering a New Garage Door?

Of course you need to measure the width and the height of the garage door opening to arrive at the correct size of the new garage door that you should be ordering.

How To Finish A Garage Door Opening?


Measure the width, using a tape measure, both at the bottom and at the top end of the garage door opening. If the two width measurements are exactly the same, then that is just perfect. 

However, if there is a slight difference, then you have to let your door dealer know. He will likely have a corrective solution to your problem.


When it comes to measuring the height, you must measure it at three points. Measure the height at the left and right ends and also at the center of the garage door opening. 

A two car garage door will be at least 16 feet wide. There is always the risk of the header sagging a bit at the center. Once again, let your garage door dealer know. He will suggest a solution.


You also need to measure the height of the headroom. Headroom is the space between the top of the garage door opening and the garage ceiling or the lowest point of any obstruction such as a beam or a duct. 

Headroom is important and must be a minimum of 12” to accommodate the horizontal garage tracks and the sectional garage door in the open position. Add another 6” if you are planning to install an overhead garage door opener

If you do not have this space available you may have to settle for a wall mount garage door opener. On the other hand if you have a much larger headspace, you can consider installing a high track. A high track helps you maximize overhead storage space. 


Finally you need to measure the sideroom, that is the space between the garage wall and the side of the garage door opening. This is required for the vertical tracks. Further, if this is too narrow, the door installer will not have enough workspace during garage door installation.

A typical two car garage should be 24’ wide and 24’ – 30’ deep. This is pretty good for a 16’ wide garage door (a standard size). It gives the door installer 4’ of workspace on each side.

In any case the sideroom has to be a minimum of 12”. Considering that the absolute minimum dimensions of a two car garage door are 20’ X 20’. You will have that sideroom. But this will be a really compact two car garage with practically no wiggle room.


This may become critical if you have a particularly short garage or have some obstruction at ceiling level. The minimum backroom requirement (from the door header to the nearest obstruction) is garage door height + 4’.

Usually this will be the least of your concerns.

How do you Frame a Garage Door Header?

The garage door header is a very important part of the garage door frame. The Garage Door Header is typically a micro laminated beam that is at least 12” wide. It is common to use two 2X12 nailed together for strength.

Two Car Garage

Of course the length of the garage door header has to be more than the width of the garage door it needs to span. For a 16’ garage door the garage door header should be 16’ 9”.

The height of the garage door header should be 1 ½” more than the garage door height when measured from the garage floor.

Single Car Garage

A standard single car garage door is 8’X7’. The garage door header should therefore be 8’ 9”. If the header is not load bearing then a 2X12 should be OK.

Installation certainly requires some help. You may also need to use one or two step ladders in the middle for temporary support.

How do you Frame a Garage Door Opening?

Before you can hang your new garage door, the rough garage door opening needs to be finished. So how to finish a garage door opening? 

Finishing the garage door opening really means installing all the lumber frames on which the garage door tracks, jambs, springs etc. can be anchored.

The Side Boards

Some folks will use 2X4 for the side board, but I think it is a lot better to use a 2X6 for the side board. Nailing and setting up the side board is also called setting up the goal posts by some.

It is a good idea to paint the 2X6 side boards while they are still down. It is certainly a lot easier. You can always touch up the bits that get scratched, later.

The Center Board

Another important piece is the center board. This goes right at the center and just above the garage door header. The torsion spring ends will be attached to this center board. 

The centerboard should go all the way from the garage door header to the garage ceiling (or at least 24)” tall and around 12” wide.

Though not necessary, finish off the top of the garage door header with 2X6, just like the side boards to give a nice aesthetic look.

How do you Trim the Inside of a Garage Door?

You can use wood or PVC trims for the inside of your wood, steel or aluminum garage door. To start off, you have to determine the width of the trim that you need.

So first you measure the thickness of the garage opening. Let us say it is made out of 2X6 then the depth would be 5 ½”. But if there is a ½” sheathing on the exterior then the thickness becomes 6”.

Now there is going to be another 2X6 board on the interior. In order to keep it flush, you need to add another 1 ½” to the 6”. In other words you need a trim material that is 7 ½” wide.

You start off by nailing the trim to the top end of the garage door opening. The process is the same when you are doing the sides, except that the garage floor is not perpendicular to the side.

Garage floors always pitch towards the garage door (as per the International Building Code and to allow for easy drainage). So you have to take the slope angle when cutting the side trim.

TIP: Space nails around 16” apart along the length of the trim board.

Finish off the edges by using a brick mold.

Bottom Line

How to Finish a Garage Door Opening? To be honest it is not an easy job. Unless you are a serious and very experienced DIYer, leave it to the pro. But if you think you can do it I would still recommend

  • Watching quite a few YouTube Videos
  • Talking to pros who have actually done this kind of work
  • Talking to advisory staff at Home Depot, Lowes or a Garage Door Dealer
  • Ensuring you have the right tools
  • Absolutely making sure that you are using all the recommended Personal Protective Equipment (PPE) for the job

Thank you very much for reading the post. I do hope you found it informative and useful.

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