I have a 35 1/2" New steel door that I was given by a friend and want to install in my basement. The existing opening in the cinderblock wall is 35 5/8" if I gut the existing (rotten wood frame.) How do I make this new door work? Do I widen the opening of the opening enough to build a frame or is there another option? The cinderblock doorway was built with the house and I wonder how I would widen the opening so minimally without weakening the structure. I can't see a lental as the previous owner smeared wood putty all over the top of the door frame. (I'm guessing he thought he was patching a leak) What would the skill level be for a project like this? This would be the first time I tackled a load baring project.

Thank you for any advice that you can provide.
Sincerely,
April

I assume the steel door has no frame, so you need several more inches taken out of the cinderblock.
Building your own door frame is not easy. Lining up the hinges and routing the frame for insetting the hinges, just for starters, and the keyset is a killer. I'm not even sure a steel door would fare well in a wood frame.
Then there's cutting out some cinderblock, also not easy.
There could be a steel lintel but who knows how wide it is?

Give the steel door back and go buy a door set up (with frame) that fits 35 5/8 PLUS shim room on each side, probably a 30" door. Buy one with the lockset and knob too, or you will be working on that forever too.

What was the size of the previous door? A 32" door is still too narrow to fill the space.