Why does water leak under my sliding patio door?

The most common causes are a failed threshold seal, clogged weep holes in the track, worn bottom weatherstripping on the door panel, or improper flashing at the rough opening. Cleaning the track and weep holes is the first step. If the threshold seal or weatherstripping is damaged, they can often be replaced without replacing the full door unit.

How do I know if my patio door needs replacing versus repair?

Repair is usually sufficient for isolated issues like worn weatherstripping, a broken lock, or a fogged glass unit. Replacement is warranted when the frame is warped or rotted, when the door no longer seals properly after weatherstripping replacement, when the threshold is corroded or structurally compromised, or when you want to upgrade to better energy performance.

Is a permit required to replace a patio door?

In most jurisdictions, replacing a patio door within the existing rough opening is a like-for-like replacement that does not require a permit, though some localities require a permit for any exterior door or window replacement. Enlarging the rough opening or changing the door configuration typically does require a permit. Check with your local building department before starting.

Can sliding patio door tracks be repaired?

Often yes. Bent, corroded, or clogged tracks can sometimes be cleaned, straightened, or replaced as components. Replacement rollers are available for most door brands and can dramatically improve a sticky or hard-to-slide panel. If the frame itself is damaged, full unit replacement may be more cost-effective than piecemeal track repair.

What is the standard size for a residential patio door?

Sliding patio doors are most commonly 6 feet wide and 6 feet 8 inches tall (a 6-0 x 6-8 unit), though widths of 8 and 12 feet are also standard. French doors vary widely. Height options of 8 feet are increasingly common in newer construction. Custom sizes are available for replacement situations where the rough opening does not match standard dimensions.

Patio Door — Sliding, French, and Folding Types Explained

A patio door is a large exterior door unit that provides direct access to an outdoor living area, typically consisting of glass panels in a frame that slides, swings, or folds.

Patio Door diagram — labeled parts and installation context

What It Is

A patio door is a glazed exterior door designed to connect interior living spaces to patios, decks, balconies, and yards. Unlike a standard entry door, a patio door is primarily composed of glass panels to maximize light and outdoor views. The door unit is framed in wood, aluminum, vinyl, or fiberglass and includes a threshold, weatherstripping, a locking mechanism, and a screen option. Standard residential units range from 5 feet to 12 feet wide and stand either 6 feet 8 inches or 8 feet tall.

Patio doors must meet the same energy code requirements as windows — U-factor, solar heat gain coefficient, and air infiltration ratings all apply. The IRC and IECC specify maximum U-factor values by climate zone, typically 0.30 to 0.32 for northern zones. The door frame and threshold are also critical to weather resistance; improperly flashed or poorly maintained thresholds are a common source of water intrusion into the floor system below.

Because patio doors contain large areas of glass, safety glazing is required by code. Tempered or laminated glass meeting ANSI Z97.1 and CPSC 16 CFR 1201 standards is mandatory for all glass panels in the door unit. Insulated glass units with argon or krypton gas fill between the panes improve thermal performance and reduce condensation on the interior face in cold climates.

Types

Sliding patio doors (gliding doors) consist of one fixed panel and one or more panels that slide horizontally along a track. They are the most common residential type because they require no swing clearance. Standard two-panel units fit a 6-foot-wide opening, while three-panel and four-panel configurations handle wider spans up to 16 feet.

Hinged French doors are double-door units where both panels or one panel swings inward or outward on hinges. They offer a more traditional aesthetic and, when outswing, better weather resistance than inswing configurations. Outswing French doors compress the weatherstripping against the frame under wind load, creating a tighter seal.

Multi-fold (bifold) patio doors stack accordion-style when opened, allowing full-width access to the opening. Individual panels are typically 24 to 36 inches wide, and systems of four to eight panels span openings up to 24 feet. They are popular in high-end renovation and new construction where a seamless indoor-outdoor transition is desired.

Lift-and-slide doors use a mechanism that lifts the panel off its seal to slide and then lowers it back onto a compression seal when closed, providing superior air and water tightness at large widths. These units can handle individual panel weights exceeding 400 pounds.

Where It Is Used

Patio doors are installed in exterior walls adjacent to decks, patios, balconies, sunrooms, and yards. In multi-family buildings they are common on balcony-facing walls. They are also used in sunroom additions and as interior dividers between formal rooms and enclosed porches. In coastal construction, impact-rated patio doors with laminated glass meet high-velocity hurricane zone requirements under the Florida Building Code and similar regional standards.

How to Identify One

A patio door is a full-height exterior door with a predominantly glass panel, a low threshold designed for egress, and weatherstripping around the full perimeter. Sliding doors have a visible track at the bottom and a top rail at the head. French doors have visible hinges on the frame or sash. The threshold profile is wider and flatter than a standard entry door threshold, and the sill track on a slider is recessed into the subfloor to minimize the step-over height, which must not exceed 3/4 inch at accessible locations per ADA guidelines.

Replacement

Patio doors are replaced when the frame is warped, the weatherstripping has failed, the threshold leaks, the glass unit is broken or fogged, the locking mechanism is non-functional, or the unit no longer meets current energy codes during renovation. Full unit replacement — frame and all — is more common than sash-only replacement for patio doors. Rough opening modification may be required if upgrading to a larger or differently configured unit.

Proper installation includes a pan flashing beneath the threshold, flexible flashing tape integrated with the wall water-resistive barrier at the jambs and head, and shimming every 12 inches around the frame. Failure to install pan flashing is the single most common installation defect leading to water damage in the floor structure below the door.