Motion
- Bi-fold
- Two leaves fold out and up
- Hydraulic one-piece
- One leaf swings out and up
- Sliding
- Leaves slide sideways
Comparison guide
Hangar Doors
A hangar door is not a large garage door. It is a structural decision that changes the building's frame, its clear height and its cost, and it has to be made at the start rather than at the end.
Once an opening spans most of an end wall, the door stops being an accessory. The frame around it is designed for it, the door's own weight and operation feed back into that frame, and the mechanism you choose determines how much of the opening you actually get to use.
There are three common answers — bi-fold, hydraulic one-piece, and sliding — and they differ in ways that matter long before price.
Written by Gary Thompson · Steel Building Research EditorSteel Building Research EditorReviewed by Find Steel Buildings Editorial Team
Why hangar doors are their own category
Three things separate them from ordinary vehicle doors. The opening is wide enough that it dominates the end wall's structure. The door assembly is heavy enough that its weight and the forces from operating it are part of the building's design. And the usable clear height is affected by the mechanism itself, sometimes substantially.
That last point catches people out. An opening measured on a drawing is not the height available for a tail once the door and its hardware are in place. Always ask for clear opening, in the open position, with the door fitted.
Three ways to open a hangar-scale opening
- 01Bi-fold — two leaves fold out and up; needs space in front, folded leaves sit at the head
- 02Hydraulic one-piece — one leaf swings out and up; needs more space in front, generally leaves more head height
- 03Sliding — leaves stack sideways; needs no space in front but consumes wall length beside the opening
Bi-fold doors
A bi-fold door is made in two horizontal leaves hinged together. Cables or straps lift the lower leaf, folding the door up and outward against the upper part of the opening, where it sits as a canopy.
The practical characteristics: the door remains attached across the top of the opening when open, it projects outward as it lifts so it needs clear space in front, and the folded assembly sits within the head of the opening, which reduces clear height at the top compared with the framed dimension.
- Motion
- Two leaves fold outward and up.
- Needs
- Clear space in front of the building through the swing arc.
- Side effect
- Folded leaves occupy the head of the opening.
- Bonus
- Provides a canopy over the opening when open.
Hydraulic one-piece doors
A hydraulic door is a single rigid leaf hinged at the head, pushed outward and upward by hydraulic cylinders until it sits roughly horizontal above the opening.
Because the leaf is one piece and finishes above the opening rather than folded into it, this arrangement generally preserves more of the framed height as usable clear opening. In exchange it projects further from the building when open, and it introduces a hydraulic system with its own maintenance and power requirements.
- Motion
- One rigid leaf swings out and up on cylinders.
- Needs
- Substantial clear space in front; hydraulic power supply.
- Side effect
- Deep canopy projection when open.
- Maintenance
- A hydraulic system to service, unlike a purely mechanical door.
Sliding doors
Sliding hangar doors run horizontally on tracks, stacking to one or both sides of the opening. Nothing lifts and nothing projects forward, which makes them the choice where there is no room in front or where wind exposure makes a raised canopy undesirable.
The trade is lateral space: the leaves have to go somewhere, so wall length beside the opening is consumed, and on a wide opening you rarely get the full span clear at once. Bottom tracks also need to stay clear of debris, snow and ice, which is a real maintenance item in some climates.
- Motion
- Leaves slide sideways along tracks.
- Needs
- Wall length beside the opening for the leaves to stack.
- Side effect
- Full span may not be clear at once.
- Maintenance
- Tracks must stay clear; ground-level tracks collect debris and ice.
The three mechanisms compared
Characteristics of the mechanism, not of any manufacturer's product.
Space needed in front
- Bi-fold
- Yes, through the swing arc
- Hydraulic one-piece
- Yes, more than bi-fold
- Sliding
- None
Space needed beside
- Bi-fold
- None
- Hydraulic one-piece
- None
- Sliding
- Wall length for stacking
Effect on clear height
- Bi-fold
- Folded leaves occupy the head
- Hydraulic one-piece
- Generally preserves more head height
- Sliding
- No head reduction
Canopy when open
- Bi-fold
- Yes
- Hydraulic one-piece
- Yes, deeper
- Sliding
- No
Power
- Bi-fold
- Motor and lift system
- Hydraulic one-piece
- Hydraulic system
- Sliding
- Manual or motorised
Main maintenance item
- Bi-fold
- Cables or straps and lift hardware
- Hydraulic one-piece
- Hydraulic system
- Sliding
- Tracks kept clear of debris and ice
General mechanism characteristics. Actual clearances, weights and requirements come from the door manufacturer for the specific product.
Settle these before engineering
Which mechanism?
- Consequence if left late
- The end frame is designed around it; changing later is a structural change.
What is the clear opening with the door fitted and open?
- Consequence if left late
- The framed dimension is not the usable dimension.
Is there space in front for a lifting door?
- Consequence if left late
- Rules out bi-fold and hydraulic on constrained sites.
Who supplies and who installs?
- Consequence if left late
- Building manufacturer and door specialist are usually two contracts.
What power is required, and who provides it?
- Consequence if left late
- Electrical and hydraulic supply is rarely in either quote.
Who owns the seals and weathering around the door?
- Consequence if left late
- The most common interface gap between the two contracts.
The sequence that keeps this cheap
The door type has to be settled before the building is engineered, because the end frame is designed around it. Changing from sliding to hydraulic after the drawings are sealed is a structural change, not a substitution.
The door is also frequently a specialist's supply rather than the building manufacturer's, so there are two contracts and one interface. Make sure someone owns that interface explicitly — the framing, the door, the seals around it, the power supply and the commissioning.
Sizes and structure are elsewhere
Clear opening dimensions for aircraft are covered in our hangar dimensions reference. The framing, loads and connections that carry a door of this scale are engineered for your building. Final spacing and sizing are determined by the engineered building system.
Terms used on this page
- Bi-fold
- A door in two horizontal leaves that folds outward and up.
- Hydraulic one-piece
- A single rigid leaf lifted outward and up by hydraulic cylinders.
- Clear opening
- The usable width and height with the door fitted and fully open — not the framed dimension.
- Stacking
- Where the leaves of a sliding door sit when the opening is clear.
Confirm before engineering
Mechanism decided pre-engineering
Before the frame drawings are produced.
Clear opening with door fitted
In writing, from the door manufacturer.
Site clearances
In front for lifting doors, beside for sliding.
Contract boundary
Who supplies, installs, powers and commissions.
Weathering interface
Seals around the opening explicitly owned by one party.
Frequently asked questions
They solve the same problem differently. A hydraulic one-piece door generally preserves more usable head height because the leaf finishes above the opening rather than folded into it, but it projects further from the building and adds a hydraulic system to maintain. A bi-fold is a mechanical lift with no hydraulics. Site clearance in front and how much clear height you need usually decide it.
Yes, and it is the right answer where there is no clear space in front of the building or where wind exposure makes a raised canopy unwelcome. The trade is that the leaves have to stack somewhere, so you need wall length beside the opening, and on a wide opening you may not get the full span clear at once. Ground-level tracks also need to be kept clear of debris, snow and ice.
Substantially. An opening at this scale dominates the end wall, and the door's weight and operating forces are part of what the frame is designed for. That is why the mechanism has to be chosen before engineering — swapping types after the drawings are sealed is a structural change rather than a substitution.
That follows from the aircraft, including wingspan, tail height and how you intend to manoeuvre in and out, and it is a dimensions question rather than a mechanism question. Our aircraft hangar dimensions reference covers it. The one thing to carry over from this page is that the framed opening and the clear opening with the door fitted are not the same number.
Often not. Hangar doors are commonly supplied by a specialist manufacturer while the building comes from a metal building supplier, which means two contracts and one interface between them. Make sure someone explicitly owns the framing, the door, the seals around the opening, the power supply and the commissioning, or those items fall between the two.
Verification and sources
Every material statement on this page maps to a published source, and each record states what that source does not cover. Where something was not verified it is recorded as not verified rather than estimated.
Bi-fold door mechanism · Tier 2
Bi-fold hangar doors are manufactured as two hinged horizontal leaves lifted by cables or straps so the door folds outward and upward.
Supports the mechanism description only. No dimension, weight, clearance or performance figure is taken from the source, and no relationship with the manufacturer is implied.
Schweiss Doors — bifold door productsHydraulic one-piece mechanism · Tier 2
Hydraulic hangar doors are manufactured as a single rigid leaf hinged at the head and lifted outward and upward by hydraulic cylinders.
Supports the mechanism description only. No product claim, dimension or performance figure is used, and no relationship is implied.
Hydroswing — hydraulic door productsLarge openings are engineered · Tier 1
Framing around large wall openings in a metal building system is designed as part of the engineered structure.
Establishes the engineering boundary. No member, load or connection is specified here.
Metal Building Manufacturers AssociationNot verified · Tier 4
No opening dimension, door weight, clearance figure, cost or operating time is published on this page.
Records a deliberate absence. Dimensions are covered in the hangar dimensions reference; product figures come from the door manufacturer.
Find Steel Buildings editorial policyWhere to go next
Next step
Aircraft hangar dimensions
Once the mechanism is chosen, the size question is the next one, and it lives in the reference silo.
Also useful
Compare building quotes
Door type must be in the specification before hangar quotes mean anything.
Planning a building?
Compare steel building quotes
The door decides the end frame. Choose the mechanism before anyone engineers the building, not after.
Requests go to Find Steel Buildings so we can compare whole-building options. Find Steel Buildings does not sell individual components, no component manufacturer or named company receives your request, and we are not affiliated with the companies referenced on this page.