Entry Door Install - Rough Opening Too Short?


The supplier I plan on getting my 36 x 80 door from said the RO should be 38 1/2 x 82 1/2.
I pulled the trim around the existing door and as best I can tell I have 38 1/2 x 81 3/4. That's 3/4 too short.
If you look at this picture, you'll see that the plaster currently comes all the way to the jamb. This is the side of the jamb, but the same situation occurs at the top.
http://i440.photobucket.com/albums/qq121/DerbyDad03/Mobile%20Uploads/1114092135-2.jpg
As you can see from the picture, I chipped out some plaster to see what's behind it. The answer is "nothing", meaning that there is a gap between the jamb and the first 2 x 4. I have a half inch on both sides of the jamb, so I have the full 38 1/2 width. That's good.
However, when I chipped out the plaster at the top of the door and measured from the bottom of the header to the floor, I only have 81 3/4".
Top of door:
http://i440.photobucket.com/albums/qq121/DerbyDad03/Mobile%20Uploads/1114092227.jpg
The current door slab measures 79 3/4" (not 80") and measures 81 1/2" from the top of the jamb to the floor. Add a ~1/4" gap between the top of the jamb and the header and I get ~81 3/4".
I should mention that I've had 2 estimates from local "door stores" who took measurements, basically said "piece of cake" and gave me quotes. They didn't pull any trim so they didn't measure the actual rough opening.
Is 81 3/4" going to be tall enough or do I have header work to do?
Thanks!
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DerbyDad03 wrote:

http://i440.photobucket.com/albums/qq121/DerbyDad03/Mobile%20Uploads/1114092135-2.jpg
http://i440.photobucket.com/albums/qq121/DerbyDad03/Mobile%20Uploads/1114092227.jpg
it gets installed before inside of house is finished out. How thick is the floor in that room? If it is hardwood, tile, or slate, you are probably okay. Your old door threshold is probably sitting on flashing right on the plywood or 1x4 subfloor.
-- aem sends...
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re: "Keep in mind that an exterior door rides BELOW the finish floor"
Thanks for the response.
Here is a picture of the current threshold, inside and out, which might help describe the current installation.
http://i440.photobucket.com/albums/qq121/DerbyDad03/DoorVews.jpg
As noted on the picture, the rough opening I measured is from the header to the linoleum. After the door is installed, I want to replace the linoleum with tile. As far as I can tell, my 81 3/4" is essentially to the subfloor, not a raised finished floor. The surrounding floor is carpet over hardwood and is higher than the linoleum.
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Find out how much top and bottom trim on the door slab is permitted. You will probably have no problems getting things to fit.
Joe
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Joe wrote:

Trimming slab means changing hinges and lockset. He is installing a prehung door, not a blank slab. And a typical steel or glass exterior door slab isn't really trimmable at all.
There is usually a little fine-tuning of reality possible by trimming the jamb ears, or fussing with the sill of the RO.
-- aem sends...
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A rough opening is usually 2"+ on the sides and top. So if your putting in a 36X80 door, the rough opening should be 38X82. I don't think being 1/4" short at the top is going to be an issue.
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I'm 3/4", not 1/4", short of the spec the distributor gave me - 82 1/2".
I'm going to go to a borg today and measure a similar door.
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I went to HD and measured some 80" doors. They measured 81 3/4" from the bottom of the jamb to the top. That is exactly the space I have from the floor to the bottom of the header.
As far as I can tell, my current jamb sits right on the floor, so I will have no room for error without cutting into the header.
Here is a picture of the current threshold, inside and out, which might help describe the current installation.
http://i440.photobucket.com/albums/qq121/DerbyDad03/DoorVews.jpg
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On Sat, 14 Nov 2009 19:57:47 -0800, DerbyDad03 wrote:

Have you got another floor above it, or is this in a porch or something?
Just wondering what load it has to support - when I had this problem with out door, it was in a porch with a flat roof above, so the framing above the door was sufficient that I could cut out what I needed so that the replacement door would fit.
(I suspect taking out 3/4" even with a floor / walls above would be fine, but you might want to do some more digging in the walls up there and see how much material there is currently taking the load)
cheers
Jules
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wrote:

There is a floor above the entryway. This is the main entry into a 2 story colonial built in 56.
I don't know that I would need to take out the full 3/4" to make a 82 1/2" RO, I just need room to get the door in and shimmed if necessary.
The other issue is tiling the entryway afterwards. If I can't raise the door up at all, I may be able to tile.
Since this is my first entry door install, I guess need to go my supplier and take some actual measurements of the jamb height and threshold height.
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An update:
I pulled up the linoleum and some old type of pressed paper underlayment to get down to the subfloor.
I have a RO that is an RCH over 82". The listed size of the Therma-Tru unit I am ordering is 82". It'll be a tight fit, but it'll work.
The interesting thing that I have found while doing my homework is that Therma-Tru doors are about a 1/4" taller than many other doors, which is why they spec an 82 1/2 RO. The units measure 82", not 81 9/16 like Jeld-Wen, etc. Apparently the door slabs are a true 80", not 79 something like many other doors.
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