Firstly decide if the replacement is just the door leaf or door leaf and frame. Once this has been determined then the following procedures should be followed step by step.

Door leaf Replacement

1. Take three measurements across the width of the frame, top, middle and bottom, measure in millimetres and take the measurements from where the door closes onto the frame. Take the largest of these measurements and this will become the width.

2. Secondly do the same again for the height in millimetres and take three measurements right hand height, middles and left hand height. Take the largest of these three. The measurement should be taken from the finished floor level.

3. Next check the thickness of the fire door to be replaced usually 44mm is a 30 minutes fire door and 54mm is a 60 minute fire door. 

4. Once these two measurements are known the next step is to subtract 6mm from the total width and 10mm from the height measurements. This will allow for the door to fit into the rebates and allow for a combined heat and cold smoke seal which will either be in the frame or alternatively you can have the door edges, top and two long sides to be milled out for the seals.

5. If the door is to be compliant with smoke control seals (FD30s or FD60s) the two long edges and the top should have these fitted. the bottom of the door may have either a 3mm gap only if the floor levels allows, but if the floor level doesn't allow for this either a drop down smoke seal should be fitted to the bottom of the door, a threshold strip should be fitted or a calculation made which would only allow a maximum of 3 cubic metre of smoke to penetrate under the door in a maximum of 60 minutes.

For further technical information you should consult the fire door manufacturer to obtain a copy of the fire certification to confirm the requirements above.

Door and frame replacement

If the frame/lining is to be replaced with the door leaf the following measurements should be taken.

1. Remove the architrave from around the door frame.

2. Now measure from the outside of the frame width at the top middle and bottom and take the largest measurement as you frames width. 

3. Do the same for the height