Remove the interior trim and measure the width and height of the frame. It is important that you use a waterproof membrane to shield the top sill. Untitled Document Replace Exterior Door Exterior Doors Exterior Door Threshold Insert the assembled frame into the opening. How to fit an external door frame . Use a spirit level to get the sill perfectly horizontal. Also measure the jamb depth. Remove the old threshold and screw the new threshold down onto a work table to keep it from moving. Theyre usually made of heavy materials designed to hold up to extreme weather conditions. Step 3 - Install frame. External doors should open inwards. The door and the frame must be completely snug. How to fit install upvc door and frame. Part 1DisclaimerDue to factors beyond the control of backstreetmechanic It cannot guarantee against improper use or. Lay the frame on a clean dry floor or appropriate workbench where there is enough space. Replacing the shims with thinner...