I need to install a pre-hung 42" door into an 8 foot wide opening. I have never installed a door or window before. I have looked it up on the internet and in a carpentry book I see both talk about "rough openings". My question is why can't I build the frame around the pre-hung door so everything is tight and square? Studs are 2x6 and I have the first one in place, squared up and ready to go. If I square the door frame and screw it in on this stud then I can butt the other stud up flush, square it and screw door frame to it. Top has 1/4 inch play that I can shim. Is there a reason I shouldn't do this? This door is not exterior so will not be affected by weather.
Thanks in advance for your replies!!

 

Doors need space around them so that they can be plumbed and squared. Often, you may think you have the rough opening just the right size and that everything is plumb, but when you try to put the door in, it either won't quite fit, or you wish you could jack it one way or the other. If there is no room around the door and you want to adjust it, you're up a creek. Additionally, if the house moves the slightest bit due to settling, or expansion and contraction, if the door is tight in the rough opening, the door will have no choice but to move with the rough opening, making it hard to open or out of square. If the door has space around it, however, and is shimmed, the shims can be removed and the door readjusted in the rough opening.

Typically, there is roughly 3/8" of space around the jamb of a prehung door, which is where the shims are installed.

Since you've never installed a door before, don't make it hard for yourself. Leave yourself some room around the door and buy some shims. Set the door in the rough opening and plumb the hinges with the shims, then nail that side. next, level the head, and shim the side opposite the hinges, nailing it back. Check the reveal along the top so that it's straight. You should have an even 1/8" gap around all sides of the door. Another trick is just to stick 1/8" shims all around the door (between the slab and the jamb), then shim the entire jamb into the rough opening, and nail it off before removing the shims around the slab. Good luck.

 

From my experience, the pre-hung doors come nailed to the door frame when you buy them. How do you remove the nails after you install the door?

 

I remove the nails before I install the door and wedge 1/8" shims in the top corner instead.

 

can you be a little more specific? if i remove the nails the door is loose in the frame. not sure what you mean by shimming the corner. how about installing a small board across the door connectoin both of the side frames?

 

When you take the nail out, the door wants to open, right? It also wants to sag. If you take some tapered shims 1/8 thick and stick them between the door and the jamb (in the upper right or left hand corner) the door will stay square when you set it in the rough opening, provided you don't open it until you have a few nails into the frame so that it stays put.

As I mentioned in a post above: "Another trick is just to stick 1/8" shims all around the door (between the slab and the jamb), then shim the entire jamb into the rough opening, and nail it off before removing the shims around the slab."

 

Thanks. Should the door frame sit on the flooring or shimmed up off the floor?

 

It depends on what sort of flooring is going down. If the shims will be covered up by flooring or carpeting, it can't hurt to shim them up. If the customer is getting an unusually thick wood floor, shim them up. Otherwise you may be coming back to cut the doors off once the carpet is laid. There's nothing worse than a door that catches on a rug. If the floor gets underlayment and linoleum, I set them right on the subfloor.

 

Good advise, thanks