I intend to replace my old front door. It is currently a steel left-hand inswing door. The slab itself is 36"x77.5". The ceiling is very short and this door opens within an inch of the ceiling. I estimate the actual rough opening height is about 80.75". The house is cinderblock and below he threshold is concrete. The threshold, from the inside perspective, sits barely above some composite flooring.

Looking at the usual sites like Home Depot and Lowe's, I don't see any options for these dimensions. Lowe's has a single option for 78" height but it is too pricey and not the style I would like.

I'm hoping for answers to two related questions:

  • Are there options others would consider besides shopping around as I've tried including possibly ordering something custom which I feel as though I should try to avoid if not only for cost reasons but also less room for error.

  • Can I cut the frame and slab of a prehung door likely fiberglass to fit?

Thank you

  • 1
    I would measure the height as buying a door on an "estimated" "rough opening height" reminds one of the builder of a certain nationality wanting a window about "so big".. When challenging it turned out that the hole did not exist...
    – Solar Mike
    Sep 29, 2023 at 21:55
  • the doors are hollow, but have a wooden frame all around. If you cut, you might have to insert a wood as frame to close the opening
    – Traveler
    Sep 29, 2023 at 22:08
  • @asinine I assumed so just like interior doors. Any other pitfalls? I think I could manage replacing the bottom part of the frame. Top or bottom better?
    – CircArgs
    Sep 29, 2023 at 22:13
  • @SolarMike the reason I mentioned the proximity to the ceiling is because the rough opening height is definitely close enough that more accuracy is pointless since I'm ultimately limited by the ceiling which guarantees it is a only nonstandard door that could open. Edit: and I mean I will ultimately need precise measurements at some point of course, I just know right now I have to make a decision where standard doors are not an option right now
    – CircArgs
    Sep 29, 2023 at 22:14
  • 1
    Have you called a real door supplier? Sep 29, 2023 at 22:37

1 Answer 1


Most importantly, call a real door supplier. They might surprise you in a good way with a door that’ll fit your opening. And if the price is surprising in a bad way, think about how the price amortizes over the life of the door.

As to your opening, pull the casing off all 3 sides of the interior. This will show you the actual framing. (You need to pull the casing eventually, so you might as well do it now.) Check for plumb and level and measure the smallest dimension. This is your rough opening. Don’t waste time and increase risk by playing with a stud finder.

Personally, I’d never cut down a fiberglass door. And I particularly wouldn’t cut the top. A solid wood door is a much better candidate for a cut, though clearly fiberglass has some advantages.

  • No questions until you finish the demo, +1.
    – Mazura
    Sep 30, 2023 at 12:29

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