I've built a timber inner skeleton to a building and made a frame for a door. Which matches the dimensions of the opening in the internal wall.

See photo here:

enter image description here

The door measurements are 94cm x 204cm

Do I buy a door at those dimensions, or does the frame need more things added to it and then I measure again for a door?

Online it seems unclear, some site suggests taking 50mm off to factor in a "jamb"?

Would be helpful to get instructions on what I need to do to get a door on ASAP.

Does plasterboard have in factor in the door depth?

  • You're missing jack studs.
    – MonkeyZeus
    Jun 24, 2022 at 13:56
  • Sorry I think this is an American concept, I can't seem to find any references in UK building specs. Do you mean bits of CLS timber above the door frame? Jun 27, 2022 at 8:44
  • Sorry, didn't notice the UK tag. hometips.com/wp-content/uploads/2012/09/…
    – MonkeyZeus
    Jun 27, 2022 at 11:50
  • Hmm looks like I will need to cut out my insulation board to make it less wide. Do I really need this if my stud frame is solid? Or is this to compensate when a door bangs? Jun 27, 2022 at 12:36
  • Your insulation seems fine but I'm confused, you said that UK building specs don't require a jack stud? Your current opening is 37" wide which is perfect for a 36" door. If you add jack studs then you'll only fit a 32" door. Is that a load-bearing wall? If so then you definitely need jack studs and a proper header board so that your framing doesn't start bowing due to the load above.
    – MonkeyZeus
    Jun 27, 2022 at 12:48

2 Answers 2


TL;DR advice: find a door with a frame that's smaller than your opening by about 12mm.

When you buy a door, you're typically purchasing the door with the jamb/frame and sometimes the threshold is included (exterior doors, typically). There are several standard sizes but they're sold based on the frame dimensions, which is more or less the size of the opening in the wall that they will fit into. Jack suggested clearance from the opening to the door jamb for shims - this is also typical, in NA construction anyway.

The following diagrams may help, though they don't show the shims.

door frame diagrams, exterior and interior doors

The shims are to fill space between the 'rough opening' (larger) and the 'net frame dimension' (slightly smaller) and help square the door frame in the opening so it fits the door without gaps or pinching. As shown in the diagrams, the gap left after shimming the jamb is usually covered with molding or casing.


Unless you want to wait, maybe a long time, for a custom door, you need to see what door sizes are available at your lumber or home store. Then you add to your frame so the door will fit. You'll want to have 6 to 12 mm clearance from the frame to the door jamb so you can shim the door plumb.

  • I just checked there are plenty of doors in this size. I think the original opening is a standard UK size. Does the door jamb go ontop of the plasterboard? So an extra 12mm take away from the door measurement? Jun 22, 2022 at 15:12
  • The jamb usually extends past the framing member and the drywall would butt up against it. Then the casing goes on top of that. + or - 12 mm, it all depends of the accuracy of the framing.
    – JACK
    Jun 22, 2022 at 17:10

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