Fitting an Internal Door Frame

Fitting a door frame is a relatively simple DIY project that can be completed in a few hours. Follow these step-by-step instructions for fitting internal doors (and with the right tools and materials) you can easily replace old door frames in any property.

Sometimes you can get away with replacing just the door, but if the actual frame is warped, damaged or worn looking then you may want to replace that too.

Replacing internal door frames is a job that takes some care and attention, but you don’t need to be greatly experienced in DIY to do it.  If you buy the right interior door frame kit and take your time when measuring and installing it, then replacing the door itself should be a breeze.

Instructions for fitting your internal door frame

Step one: getting the measurements

Use a tape measure to measure the gap on the top, middle and bottom of the structural opening. 

Measure the space on the left, middle, right-hand side of the opening. It’s best to use the smallest measurement as your point of reference. You should also mark the measurements on the opening for reference.  

From this, you can then deduct the lining thickness of both sides, and then select the nearest standard size door width for the opening.

Step two: cutting the frame

Cut the new frame correctly so that all the pieces are the right size to suit the selected door size. 

For maximum accuracy, use a table saw and a cutting fence for most of the cuts. If you’re replacing the decorative architrave, you might need to use a mitre saw for some of those cuts.

The legs of the door frame are known as a 'door jamb' or 'side jambs'. Follow the same procedure to make both the jambs of the frame.

The door frame jambs should be cut to allow 3mm clearance above the door. Plus, enough clearance below the door (when considering the floor covering intended) again with a clearance.

Step three: installation

Ensure the frame is assembled correctly and is installed straight, level, and plumb by screwing the jambs, through the head of the frame, with the correct opening width. The door can then be installed easily and will work correctly.

The fixings used depend on the substrate you are connecting to, but the frame should be packed out adjacent to each fixing point, and fixed solid to the structure.

Decide on your hinge side and consider how you want your door frame to open, and then hang the door. Once hung, ‘pin’ in the door stops up the back edge of the door, along the 3 sides of the door lining.

When the door is hung into the frame, install any decorative moulding then finish using decorative wood filler to cover up any exposed joints or nail holes.

Optional step: When the wood filler is dry, sand it gently, prime the surface and paint it.

If you want a visual aid, SkillBuilder on Youtube has an in-depth tutorial on How to Fit Door Frame Lining.