Sliding patio doors are big, heavy pieces of glass that have to run smoothly for years, so most of what makes a good installation happens before the glass goes in: a level base, a square opening and a frame fixed so it cannot flex.
This guide explains the process so you know what to expect, what you may need to do beforehand, and what questions to ask if a builder is involved.
Replacing existing doors or forming a new opening?
Swapping an old set of patio doors for new ones in the same opening is the more straightforward job. The opening already exists and has been carrying the wall above it for years; the work is mostly removal, preparation and fitting.
Forming a new opening, for example knocking a window down to floor level or opening up a rear wall onto an extension, is building work first and glazing work second. A structural lintel is needed, the opening has to be finished, and only then can it be measured for doors. In that case the builder and the door fitter need to be talking to each other early.
Step by step
Survey and measuring
The structural opening is measured, not the old frame, and checked for level and square. We measure every opening ourselves and the person measuring is the person fitting.
Manufacture
Doors are made to measure for the opening. Larger sliding doors and coloured frames often take longer to make than a standard window, so allow for that in any wider project plan.
Removing the old doors
Sliding panels are lifted out, the outer frame is cut free, and the opening is cleaned back. This is when any hidden problems with the sill, the floor or the lintel appear.
Preparing the base
The track a sliding panel runs on has to be dead level along its whole length. If the base is out, the door will drift open or closed and wear its rollers. Packing and levelling the base properly is the single most important step.
Fixing the frame
The outer frame is set level, plumb and square and fixed into the surrounding structure so it cannot bow under the weight of the glass.
Glazing and adjusting
Panels are lifted into the track, rollers adjusted so they slide with light pressure, and the locks set so they engage without forcing.
Sealing and finishing
The frame is sealed outside, finished inside, and the area cleaned up. The old doors are taken away.
Sliding, bifold or French?
If you have not decided on sliding doors yet, the main differences are how much of the opening becomes clear, how much space the open doors take up, and how the frames look. We compare them properly in our bifold vs sliding vs French doors guide. In short, sliding doors never swing into the room or garden, which makes them the usual choice where space in front of or behind the doors is tight.
| Sliding patio | Bifold | French | |
|---|---|---|---|
| Space needed to open | None in front | Room for folded stack | Swing clearance |
| Critical install point | Level track | Level track and square frame | Hinge side plumb |
| Opening fully clear | No, one panel overlaps | Nearly | Yes, across both doors |
What you can do before fitting day
- Clear furniture back from the opening inside
- Move pots, benches and barbecues back from the outside
- Take down curtains, poles and blinds
- Tell us about any underfloor heating pipes or cables near the opening
- If a builder is forming the opening, confirm the finished floor level first
Floor levels and thresholds
The floor level inside and the patio level outside decide what sort of threshold is possible. A step-free finish needs the outside ground to be set up for drainage, otherwise water can sit against the bottom of the frame. If you are laying a new patio or floor at the same time, get the levels agreed before either the paving or the doors are ordered.
Getting it done
We fit patio sliding doors as well as bifolds and French doors across Central Scotland. The survey is free and the quote is provided in writing.
Common questions
Replacing like for like usually does not, but new openings, listed buildings and conservation areas can. Our Scottish window rules guide covers the basics.
Usually dirty tracks or worn rollers. See our patio door not sliding guide.
Often, but it is building work: the opening has to be lowered and properly supported before doors can be measured.
Want a straight answer on your own windows or doors?
DM Installations fits and repairs windows and doors across Central Scotland — Cumbernauld, Glasgow, Falkirk, Stirling and the surrounding towns. Free survey, written quote, and an honest answer on whether you need a repair or a replacement.
Related guides
Bifold vs Sliding vs French Doors
The three ways to open the back of a house onto the garden, and which one suits your opening, budget and habits.
When to call a proPatio Door Not Sliding Properly
Sticking, grinding and jumping sliders — the usual causes, the DIY fixes, and the repairs that need a professional.
Cost guidesBifold and Patio Door Cost
Fitted prices for bifolds, sliders and French doors by width, plus the structural and finishing costs people forget to budget for.
How-toFrench Doors Buying Guide
The decisions that matter when choosing French doors, from which way they open to the locks and threshold.