I am going to be building a small insulated shop building on a finished concrete slab with 14″ of stem wall above the slab. For a typical 2/8 door I usually assume a 2′-10 1/2″ r.o., but when it comes to forming up the conrete to the appropriate width, is allowing an additional 3″ for a r.o. of 3′-1 1/2″ correct”?
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I honestly don't know what is routinely done, but I think I'd like to have about 3 1/2" on BOTH sides. This would allow room for two PT studs on each side to allow space for some kind of casing.
Al Mollitor, Sharon MA
What, your Ramset dealer doesn't have trim nails? :)
Good catch. I forgot all about casing.
Around here, the outside width dimension of the brick mold of a 2-8 exterior door is about 36". If you make it much larger than that, you will have an ugly gap to try to fill. You can size your opening width at about 35 1/2 - 36" (both the stem wall and the 2by framing) and then in-fill with PT 1by material on either side to give a standard RO width of 2'10" - 2-10 1/2", and you have something to nail your door to for the full height. The PT 1bys will be about 82 1/2"" tall. That is they way pre-hung doors are sized in my part of the country anyway. A bit of a tangent, but I like to pre-paint exterior door frames prior to installation, especially if they are going to be in close proximity to cementous material.
Here's something else to consider: I've seen PT nailing blocks imbedded in the concrete. These must have been tacked to the inside of the forms before the pour. They come in handy when installing the door.
Al Mollitor, Sharon MA
Mojo,
IMHO, pour your stem wall with a 4'7" opening. 4' + 2x3" + 2x1/2".
You can frame the RO for the door you buy now any width you want. If you decide to put in a bigger door later, you got the room.
SamT