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I have a garage with an odd size entry (not bay) door. The old door, which recently broke, was only 24" x 70".

Time to put in a new door. My intent is to enlarge the opening for a more standard size. I expect this will be cheaper while also improving the structure. In fact, I can see the space where there was once a wider opening... it measures at 36" rough, which would have fit a 34" door. It should be very easy to restore this old opening, and I can get a 34" x 80" prehung door at a reasonable price.

No word yet on why a previous owner put in such a weird door ¯\_(ツ)_/¯

The problem is the height. My understanding is a 34" x 80" door needs a 36" x 82" rough opening. The entire height of the garage wall from the concrete to the bottom of the beam is only 81 3/4".

Will I be able to make the standard door fit, or will I need to do something custom? If it will fit, will I need to do anything extra to make it work?

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  • Is this an Exterior or Interior door? Apr 8, 2020 at 16:19
  • Exterior, but the project is done now Apr 8, 2020 at 16:20

4 Answers 4

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Checking online there are the actual unit dimensions for these doors on the "Big Box" websites. I am finding the actual sizes are 81 5/8" in many cases. Tight for your opening but a little off the header will get it in. As a note, this is for an exterior door. Typically interior doors are perhaps a 1/2 shorter. If the header needs a 1/4" taken out of the bottom, and you have a 2x6 header for a 36" rough opening, there will be no issue. The sheathing on the wall outside aids in supporting the surrounding framing.

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I would not cut the header, as this is far more work than cutting an 1" off the bottom of the pre-Hung door frame.

Edited to clarify:
The above is based on standard residential wood frame door, not a steel security or commercial door. Link to HD exterial door, which comes in 34x80 size, to the installation manual, which in Step 17, figure 11, states to cut the bottom of the sides to fit into the opening. Per the HD installation manual, "Measure the hinge rail, starting at the top and then marking the bottom with the measurement that you took of the door opening (Figure 11). Using the hacksaw, cut the hinge rail to its proper length". This is an easy cut, which I have done, replacing my garage side door. If the door is too long at the bottom, just trim the bottom a little.

Link to HD Door installation here: Installation manual for prehung door

Check the HD online, there are several doors that can be order with width of 34". After looking at the door in person, you can order and pick up at the store later. Yes, another trip, but you have more choices than what's in stock.

If Lowes is available, they have a door that cost a little more than the HD door, but the sides are expandable/retractable. The storm door is also adjustable to accommodate threshold, uneven floor, etc. What's strange is that a 36" door cost $109, but the 34" cost $158.

My assumption was that this was for an exterior door. Interior doors are cheaper, all wood, etc.

This is the door off the Lowes website.

enter image description here

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  • Cutting off an inch at the bottom could be a TON of work depending on the type of door. Let's assume it has to look good too.
    – DMoore
    Apr 6, 2020 at 16:35
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I installed the same size door in a hallway to isolate a second bedroom and bathroom. The actual frame needed 82 inches but the door is 1 inch shorter than the frame. I guess it's to allow for carpet, threshold, etc. You can easily saw off 1/4"+- from the bottom of the frame to get your 81 3/4" height. You'll still have room for a threshold. Good luck.

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  • Go to your local big-box home-improvement store.
  • Head to the tool section an pick up a nice tape measure.
  • Wander back to the doors & windows department.
  • Find a nice 34x80 door
  • Use the tape measure, still in its factory packaging, to measure the outside dimensions of the door you've picked.
  • Return the door to the rack*
  • Return the tape measure to the tool section*

Odds are it will fit just fine.

I have to admit, I've heard of 32" & 36" as standard door sizes. 34" is a bit unusual to me.

*Unless, of course, you need a tape measure and you happen to really like the door you pulled off the shelf.

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  • I live in rural Nebraska. The nearest big box is 53 miles. I like to know what I'm doing before I make the trip. Nov 8, 2019 at 14:35
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    Fair enough @JoelCoehoorn... :) I'm a mere 20 miles from mine. If you don't have a definitive answer by then, I'll measure mine when I get home - the garage door isn't trimmed on the inside, so I can easily measure the outside jam dimensions.
    – FreeMan
    Nov 8, 2019 at 14:49

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