Multi-Slide, Pocket and Folding Glass Doors: Planning an Indoor-Outdoor Wall

Large opening glass doors come in three main forms, and manufacturers use overlapping names for them: moving glass walls, multi-slide doors, panoramic doors, stacking doors, bi-fold or folding doors. This guide, part of our California window guide, sorts out the types and then spends most of its time on the parts of the project that are not the door.

The three types

Multi-slide, stacking

Three or more panels on parallel tracks. Opened, they slide and stack in front of one fixed panel or against each other at one end. Milgard describes stacking doors as very large multi-slide doors whose panels stack on top of each other when open. Andersen describes its MultiGlide door as available in straight stacking configurations for limited wall space. Because the stack stays in the opening, the clear opening is always less than the full width.

Multi-slide, pocket

The same sliding panels, but they travel past the end of the opening into a cavity built into the wall and disappear. Milgard notes that when its pocket doors are fully open the panels slide into the wall pocket and completely disappear from view. The opening is clear from jamb to jamb. The cost is the pocket, which needs wall length, careful waterproofing and access for cleaning.

Folding, or bi-fold

Hinged panels that fold against each other and park perpendicular to the opening. Milgard explains that bi-fold doors fold completely to one side and that its design is top-hung. LaCantina describes its folding doors as top hung as well, with the weight of the doors carried above. A bi-fold clears nearly the entire opening without a pocket. The folded stack sits on the inside or outside of the opening and needs room there.

What manufacturers offer

These are the product facts as each manufacturer states them on its own site. Options vary by region and configuration.

• Milgard groups these products as Moving Glass Walls. The AX650 is an aluminum system available in bi-fold, pocket and stacking styles. The AX450 is an aluminum stacking system and the VX350 is a vinyl one. Milgard lists two-, three- and four-panel configurations for its stacking and pocket doors and describes its aluminum pocket doors as thermally broken. Our Milgard page covers the brand's window lines.
• Andersen states that its MultiGlide door can be straight stacking or pocketing and can be sized for openings up to 50 feet wide and 10 feet tall, with sliding panels up to 60 inches wide. Its limited warranty for liftslide, pivot, bifold and swing door systems covers glass for twenty years and non-glass components for ten; ask for the warranty document that applies to the MultiGlide.
• LaCantina lists folding doors in aluminum, thermally controlled aluminum, aluminum wood, contemporary clad, wood and vinyl. It states that folding panels can be 39 inches wide and 120 inches tall without horizontal mullions, and that dual-glazed low-e tempered glass is standard. Its sill options are a standard weather-resistant sill, a flush guide sill and an ADA-compliant sill.
• Western Window Systems offers its Series 7600 Multi-Slide Door in pocketing, non-pocketing, bi-parting and 90-degree configurations, with a stated design pressure rating of up to 50 and a listed thermal value of 0.27. The company says the series was designed with California's Title 24 requirements in mind.

A design pressure or performance grade number tells you how much wind and water the tested unit withstood. For a large door on an exposed wall it is one of the most useful figures to compare, and it changes with the sill you choose.

The header: the structural question

Replacing a six-foot slider with a sixteen-foot glass wall means removing ten more feet of the wall that holds up the roof. Everything that wall carried now has to span the opening on a beam and come down on posts at each end, through the floor, to the foundation.

Three things make this a real engineering problem in California:

• Span. The California Residential Code provides header span tables for ordinary openings. Openings of this size are typically beyond what those tables cover and need an engineered beam, often engineered lumber or steel.
• Deflection. A beam can be strong enough and still sag too much for a door. Sliding and folding panels need a head that stays straight. For top-hung bi-folds the header carries the full weight of the panels as well as the house, so ask the door manufacturer for its header deflection limit and give it to the engineer.
• Earthquake bracing. In a wood-frame house the solid sections of exterior wall resist earthquake and wind forces. Remove most of a wall and that resistance has to be replaced, usually with narrow engineered shear panels or a steel frame at the ends of the opening. This is often the largest hidden cost. Our article on earthquake resistance in Northern California exteriors gives background.

Expect the building department to require a permit with structural drawings and calculations for a new or widened opening. Snow load pushes beam sizes up further; see our Tahoe mountain homes page.

The simpler case is replacing an existing large door with a new one of the same size. No structure changes, and the job resembles any sliding patio door replacement on a larger scale.

The sill: where water and convenience conflict

Everyone wants the floor to run uninterrupted from the living room to the patio. Water wants the same thing. The sill is where you choose.

Manufacturers are candid about the tradeoff. Western Window Systems, for example, offers four sills on its Series 7600:

LaCantina draws the same line between its standard weather-resistant sill and its flush sill. The pattern across brands is consistent: the taller the interior leg of the sill, the higher the water rating; the flatter the sill, the more the rest of the design has to keep water away.

What makes a low sill work:

• A roof overhang or covered patio deep enough that rain rarely reaches the track.
• Exterior paving that slopes away and sits below the interior floor, or a trench drain directly outside the track.
• A sill pan under the whole assembly that drains to the exterior, since some water will get into a multi-track sill.
• Orientation. A flush sill facing the prevailing winter storms is asking for trouble. See our coastal windows guide for exposed sites.

Read the warranty on this point. Milgard's 2026 warranty, for instance, excludes water intrusion caused by wind-driven rain in high wind events. A leak at a flush sill in a storm is likely to be treated as a design choice, not a product defect.

The Residential Code adds one constraint: exterior doors need a landing or floor on each side, and for doors other than the required egress door that landing can be no more than 7 3/4 inches below the top of the threshold.

Title 24: the part that surprises people

These doors are fenestration. The Energy Code defines a glazed door as an exterior door with 25 percent or more glazed area and requires it to meet fenestration product requirements. How the code applies depends on whether you are replacing glass or adding it.

Replacing an existing door of the same area

This is replacement fenestration under Section 150.2(b)1B. The new door has to meet the U-factor and SHGC for your climate zone: U-factor 0.27 in Zones 1 to 5, 11 to 14 and 16, and SHGC 0.23 in Zones 2, 4 and 6 to 15. The 75-square-foot exception with its looser values rarely helps, because these doors are usually larger than that. A twelve-foot door at standard height is already about 80 square feet.

Making an opening bigger or adding one

The compliance manual treats any new fenestration area that increases the total in an existing wall as new. Added fenestration falls under Section 150.2(b)1A, and it has to meet more than the U-factor and SHGC:

• Total fenestration area for the house may not exceed 20 percent of conditioned floor area.
• West-facing fenestration may not exceed 5 percent of conditioned floor area in Climate Zones 2, 4 and 6 to 15, which includes Sacramento.

The code exempts additions of up to 16 square feet from those area limits, which does not help with a glass wall. Consider a 2,000-square-foot Sacramento house: 5 percent is 100 square feet of west-facing glass for the entire house, and a sixteen-foot door at eight feet tall is 128 square feet. On a west wall the prescriptive path fails on that door alone.

The answer is the performance approach, where an energy consultant models the whole house and shows that it uses no more energy than a prescriptive design would. It has to happen before you order the door, because it may dictate the glass.

Product limits

Large aluminum systems are the hardest fenestration products to get to a 0.27 U-factor. Frame area is a bigger share of a multi-panel door, and aluminum conducts heat. Thermally broken frames are the baseline, and you should ask for the NFRC-certified whole-product values for the configuration you are buying. Our pages on Title 24 for replacement windows and reading an NFRC label explain the numbers.

Heat and glare

A glass wall changes the room year-round, not only when it is open. West glass takes the hottest sun of the day at an angle no overhang blocks, so a covered patio or exterior shade does more than any coating and protects a low sill as well. Low solar gain glass is required in most inland zones; see the best windows for cooling.

Safety glazing and wildfire

All glass in these doors is in a hazardous location under Section R324.4.1 of the 2025 California Residential Code, which names swinging, sliding and bifold doors, so it must be safety glazing. Manufacturers supply tempered glass as standard. Laminated glass is an option for security and noise.

In designated fire hazard severity zones, exterior doors and glazing must also meet California's Wildland-Urban Interface Code. Large doors are a significant part of a wall's exposure, so raise it with your designer early. See wildfire-resistant exteriors.

Maintenance

Big doors have more track, more rollers and more seals than a standard slider, and they are less forgiving of neglect.

• Tracks. Vacuum them. Grit in the track flattens rollers and scores the rail. A multi-slide has one track per panel, and a pocket has track you cannot easily see.
• Weeps and drains. Clear them before the rainy season. A trench drain full of leaves is a dam.
• Pockets. Open the door fully a few times a year and clean inside as far as you can reach.
• Hardware. Folding doors have hinges, carriers and flush bolts at every panel; keep them clean and lubricated as the manufacturer directs. Near salt water, rinse with fresh water on a schedule; Andersen's warranty for its bifold and liftslide doors requires cleaning at least every three months within two miles of the coast.
• Alignment. If panels start to bind, have the door adjusted promptly, and operate every panel regularly. Milgard's warranty asks for monthly operation.

Planning sequence

1. Check the wall: what is above it, what is inside it, and whether there is room for a pocket.
2. Bring in a structural engineer and an energy consultant before choosing a product.
3. Choose the sill with the patio design, overhang and drainage in front of you.
4. Select the door, confirm NFRC values and performance grade for your configuration, and settle screens.
5. Permit, then order.

These are among the most expensive openings in a house once structure and finishes are included. For general budgeting see our cost hub, and if a simpler door would do the job, compare French and sliding patio doors.

Sources

• 2025 Building Energy Efficiency Standards: definition of glazed door, Sections 150.2(b)1A and 150.2(b)1B, Section 150.1(c)3 and Table 150.1-A
• 2025 Single-Family Residential Compliance Manual, Chapters 3 and 9
• 2025 California Residential Code, Chapter 3 (Sections R318.3 and R324.4) and Chapter 6 (Section R602.7 headers, Section R609)
• Milgard: stacking doors, pocket doors, bi-fold doors, AX650 Moving Glass Walls and warranty
• Andersen MultiGlide door and the Andersen warranty page
• LaCantina folding doors
• Western Window Systems Series 7600 Multi-Slide Door

Working with Heritage Exteriors

Large door systems involve structure and energy calculations as well as the door, and we will be straightforward about which parts are ours and which need a structural engineer or energy consultant first. If your wall, exposure or budget points to a simpler door, we will say so before you order. Licensed in California, CSLB #1055919. Call (916) 546-2991.