How to Fit French Doors: UK Installation Planning Guide
Fitting French doors requires accurate frame alignment because two leaves have to meet cleanly in the centre and lock without being forced. The threshold also has to integrate with internal and external levels, while the perimeter needs correct weather sealing. This guide explains the main stages of how to fit French doors and the checks that help a complete uPVC doorset operate properly.
Always use the installation instructions for the exact product. Our French doors are complete Crystal uPVC systems, so product-specific frame, cill and hardware details take priority over generic installation advice.
Should French Doors Be Professionally Installed?
External glazed doorsets are heavy and precise. An experienced installer is usually the best choice, particularly if the old frame is being removed, the opening is not square or Building Regulations requirements apply. Professional installation also makes it clearer who is responsible for surveying and final fit.
This guide is useful for planning the work and checking quality, even if you are not carrying out the installation yourself.
1. Verify the Doorset Before Removing the Old Frame
Check the delivered size, colour, glazing, handing and cill against the order. Inspect the frame and glass for transport damage. Do this before the existing opening is left exposed.
Compare the product with your final survey dimensions using our French door measuring guide.
2. Prepare the Structural Opening
Remove loose mortar, old sealant and protruding fixings. Repair any unsound substrate. Check the head, base and both jambs with a level and measure diagonals.
The opening can have limited variation, but the new frame itself must be installed square. Do not bend a uPVC frame to follow irregular masonry.
3. Check Structural Support Above
If the opening has been widened or newly created, confirm that the lintel or beam above is appropriate and complete before the doorset is installed. Excessive movement at the head can affect central door alignment.
Where structural alterations are involved, use a competent structural professional rather than treating the frame as support for the wall above.
4. Plan the Cill and Threshold
If the system includes a 150mm cill or another cill configuration, fit it according to the manufacturer’s sequence. Seal joints and end details as specified and keep designed drainage routes clear.
Check internal floor and external paving levels before fixing the frame height. The cill should not later be buried by paving in a way that blocks drainage.
5. Position the Frame
Lift the frame into the opening and support it with appropriate packers. Check the base for level, jambs for plumb, head for level and diagonals for square. Adjust packers before permanent fixing.
Across a pair of doors, even a small frame twist can make the meeting stiles and locks difficult to align.
6. Fix the Frame Correctly
Use fixings suitable for the frame and wall substrate, positioned according to the manufacturer’s instructions. Fix through solid packers so tightening does not pull the frame out of shape.
Recheck the frame after every group of fixings. If the diagonal measurements change, correct the packing before continuing.
7. Install or Rehang the Door Leaves
Depending on delivery format, leaves may already be hung or may need to be refitted. Support their weight properly and use the hinge sequence given by the manufacturer.
Identify the master and secondary leaves. Do not swap them or reverse handing unless the product is specifically designed to allow it.
8. Glaze if Required On Site
Where glazing is supplied separately, install it with the correct setting blocks and bead sequence. Glass packing can affect the squareness of the leaf, so do not improvise the position or thickness of packers.
Large glass units require safe lifting equipment and suitable PPE. Professional glazing is strongly recommended where the product does not arrive fully glazed.
9. Align the Master Leaf
Close the master leaf and check clearance around the frame. Adjust hinges within the manufacturer’s allowed range so the leaf sits square and does not rub the threshold or head.
Then close the secondary leaf and inspect the central meeting line. The leaves should align without needing to be lifted or pushed together.
10. Set the Secondary Leaf
The secondary leaf uses its own retaining or shoot-bolt hardware depending on the system. Confirm that it seats fully into its keeps before testing the master lock.
Do not enlarge holes excessively to make a misaligned secondary leaf appear to work. Correct the frame and hinge geometry first.
11. Test Handles and Locks
Operate the handles and locking mechanism with the doors open first, then closed. If the mechanism is smooth when open but stiff when closed, alignment or keep position is the likely issue.
Never force a multipoint lock. Repeated force can damage the gearbox or keeps and hide the real fitting problem.
12. Weather-Seal the Frame Perimeter
Seal and insulate the gap between frame and building using materials compatible with the installation detail. Internal and external joints may have different functions. Follow the product and building design rather than relying on a single bead of sealant.
Keep frame drainage paths open and ensure external sealant adheres to clean, suitable surfaces.
13. Fit Trims and Make Good
Install internal and external trims after the doors have been fully tested. Trims should cover fitting gaps without interfering with hinges, drainage or leaf movement. Protect the uPVC and glass if plastering or decorating continues nearby.
Remove only the protective film that the manufacturer says can remain during construction; some films should not be left in sunlight for extended periods.
14. Final Water and Operation Checks
Operate both leaves through the full opening range. Check the master leaf alone, then open the secondary leaf and test the complete clear opening. Inspect weather seals and threshold drainage.
After heavy rain, monitor the threshold and perimeter seals. If water appears internally, investigate drainage and frame sealing rather than simply adding sealant over every external gap.
Common French Door Installation Problems
The Leaves Do Not Meet Evenly
Check frame square, hinge adjustment and glazing packers. Do not start by moving the lock keeps.
The Master Leaf Is Hard to Lock
Test the lock while open. If it works smoothly, the problem is usually alignment with the frame or secondary leaf.
The Bottom of a Leaf Rubs
Check hinge position, frame level and leaf adjustment. Do not cut or grind a factory-made uPVC leaf.
Water Collects at the Threshold
Clear drainage routes and check cill, paving and perimeter-seal details. Do not block designed outlets.
French Door Installation Checklist
- Correct size, glazing, colour and handing delivered.
- Opening measured and structurally sound.
- Cill and threshold plan confirmed.
- Frame installed level, plumb and square.
- Fixings packed without distorting profiles.
- Both leaves aligned.
- Master and secondary locks operate smoothly.
- Drainage remains open.
- Perimeter joints are sealed correctly.
- Full swing clearance checked.
Frequently Asked Questions
Can I fit uPVC French doors myself?
A highly competent installer may be able to, but the size, glazing, frame alignment and weather detailing make professional fitting a sensible choice for most homeowners.
Which French door leaf should be fitted first?
Follow the manufacturer’s installation sequence. The master and secondary leaf roles are fixed by the product configuration.
Why will my French doors lock only when I lift the handle and push the door?
The leaves or keeps may be misaligned. Check frame square and hinge adjustment before forcing or altering the lock.
Should the cill be sealed to the frame?
Follow the exact manufacturer detail. Cill joints typically require specified sealing while drainage routes must remain clear.
Can I change a left-hand master set to right-hand on site?
Do not assume so. Factory-made doorsets are configured for a particular handing unless the manufacturer explicitly states otherwise.
Plan the Right French Door Installation
Start with our French doors buying guide, confirm exact dimensions using our size and measuring guides, then browse our current uPVC French door range.