By Michael Merlino
Learning how to fit bifold doors correctly ensures smooth operation, long-term durability and a professional finish. Whether you're a skilled DIYer or an experienced installer, fitting bifold doors requires precision, careful preparation and an understanding of how each component works together.
In this guide, we explain exactly how to install bifold doors step by step, highlight common installation mistakes, and share practical insights from the NOW Aluminium team.
What To Consider Before Fitting Bifold Doors
Before starting installation, preparation is everything.
Measurements Must Be Precise
Measure the structural opening in at least three places for both height and width, and check the diagonals to confirm the opening is square. Always use the smallest measurement when determining frame size.
The structural opening should typically allow a 10–15mm tolerance around the frame to enable packing and adjustment. If you are still in the measuring phase, refer to our detailed Bifold door measuring guide before ordering.
The Opening Must Be Level, Plumb and Structurally Sound
The aperture should be flat, straight and capable of supporting the door system without transferring load onto the frame. Establish a datum line using a laser or long spirit level, commonly set 1000mm above finished floor level, and measure consistently to both threshold and lintel positions.
If the threshold or head is not level, this must be corrected before installation. Attempting to compensate later through adjustment will lead to operational problems.
Fixings and Tools Matter
Bifold doors are heavy, particularly aluminium systems with double or triple glazing. Fixings must suit the structural substrate, whether that is brick, block or timber.
Typical tools required include a drill, appropriate drill bits, frame and glazing packers, Allen keys, a spirit or laser level, silicone and glass lifting equipment. Having the right equipment from the outset prevents damage and misalignment.
Step By Step Guide to Fitting Bifold Doors
Below is a clear installation sequence based on our NW1 aluminium system.
Step 1: Install the Sub-Sill (If Required)
If your design includes a sub-sill, begin here. Check that drainage slots are clear and seal the ends of the sill using low modulus silicone. Install the end caps and position the sill onto the prepared aperture.
Use packers to achieve a perfectly level finish before securing through the thermal break at appropriate centres. Fill fixing holes with silicone prior to inserting fixings to maintain weather resistance. Re-check the level once secured.
Step 2: Assemble the Outer Frame
Apply low modulus silicone at all connecting joints before assembling the frame. Secure the corners using the specified cleats and machine screws, ensuring the frame is square before tightening fully.
For low threshold systems, particular care should be taken to prevent water escape past the jambs. Clean away any excess silicone before proceeding.
Step 3: Install the Frame Into the Opening
Position the assembled frame into the structural opening and pack at fixing points to maintain plumb, level and square alignment. Fix approximately 150mm from each corner and then at regular centres along the frame.
The frame must remain square across its full width and height. Once secure, seal internally and externally around the perimeter to prevent water ingress. Clear debris from the track area before panel installation.
Step 4: Install the Adjustable Jamb
Remove any temporary seals and ensure grub screws are set flush before inserting the adjustable jamb profile. Secure using the designated fixings and pilot holes.
The adjustable jamb allows fine width adjustments later, which is essential for achieving correct panel gaps and smooth locking.
Step 5: Install the Door Panels in Sequence
Panels are factory numbered and must be installed in order. Begin with the panel hinged to the adjustable jamb, securing hinges with the correct machine screws.
Subsequent panels should be slightly angled to allow bottom rollers to engage into the track and top guides into their channel. Lock previously installed panels together before fitting the next one to maintain alignment.
Take care not to substitute incorrect screw types during hinge installation, as this can compromise performance.
Step 6: Glazing and Toe-and-Heeling
Before glazing, lock all panels fully. Remove glazing beads carefully and insert the glass using appropriate setting blocks. Both inner and outer panes must be properly supported.
Toe and heel each panel to maintain equal, parallel gaps. Correct glazing prevents panel drop, which is one of the most common problems with bifold doors.
Once glazed, replace beads and wedge gaskets securely.
Step 7: Final Adjustments and Operational Checks
At this stage, check horizontal and vertical gaps between panels and the outer frame. The master door should maintain the correct locking gap to avoid interference.
Adjust the width using the adjustable jamb if necessary. After final alignment, secure hinges with their final fixing screws and ensure weather seals are correctly positioned.
Operate the doors repeatedly to confirm smooth sliding and locking action.
Summary
Understanding how to fit bifold doors properly ensures smooth operation, precise alignment and long-term reliability. From preparing a square structural opening to glazing and final adjustment, every stage plays a critical role.
Take your time, prioritise levelling and sealing, and follow a structured installation sequence.
If you require guidance or technical advice, get in touch with NOW Aluminium and our team will be happy to help.
