Interactive 3D Patio and Sliding Door Designer

A patio door replacement is three jobs stacked on top of each other. There is the unit, which arrives on a truck built to a number somebody wrote down. There is the opening, which is never square, usually rotted at one corner, and sometimes carrying more load than anyone expected. And there is the water management, which is invisible, unglamorous, and the reason most failed installs fail.

So this tool draws the door in a wall rather than floating on white, and it moves, because how a door opens is most of what you are buying. Then it hands you the numbers underneath: the real clear passage rather than the frame width, the design pressure your elevation actually sees, the whole-unit U-factor rather than the flattering centre-of-glass one, and the weight the rollers have to carry for twenty years.

Slider, French or bifold

A slider needs no floor space and gives you the least opening. A French pair gives you the whole opening and takes a leaf width of floor on each side, which in a small room is furniture you cannot place. A bifold gives you almost everything, and asks for a header stiff enough that the track does not deflect, a threshold detail that drains, and a budget that reflects both. The three are not interchangeable and the choice is usually made by the room, not the catalogue.

What the glazing actually buys

Double Low-E with argon is the code baseline and it is genuinely good. The upgrade worth paying for depends on the problem. A laminated inboard lite is the noise answer — it moves a door from around STC 31 to STC 38, which is the difference between hearing traffic and noticing it — and it blocks essentially all UV, so the floor in front of it stops fading. Triple glazing is the thermal answer and it is heavy, which loops straight back to the rollers. Obscure glass buys privacy without giving up daylight, but the etch cannot share a surface with the Low-E coating, so it lands on the room side where it collects fingerprints, or on the outside where it collects everything else.

Why there is no price on this page

Because the door is rarely the variable. Two identical units, one into a clean opening on a first floor with a driveway alongside, one into a rotted sill on a second-floor balcony reached through a finished room, are not the same job and never will be. Add an engineered header and the difference stops being marginal. We would rather hand you an exact specification and quote it after we have seen the opening than publish a number we have to take back.

Four things worth knowing before you order

• Measure the passage, not the door. A six foot slider makes a thirty inch hole. Walk a tape through it before you commit to a type.
• The DP number is a rain number. Water is tested at fifteen per cent of it. That is where cheap units lose, not in a windstorm.
• Buy the rollers. Stainless adjustable tandems cost almost nothing at order and are the difference between a door that still glides in year fifteen and one that drags in year three.
• Decide the sill before the slab. A low threshold has to be planned with the exterior drainage, and retrofitting drainage after the concrete is poured is a different project.