A window safety restrictor is a mechanical device fitted between a window sash and its frame that limits how far the window can open, normally to a clear gap of no more than 100 mm, so the window still ventilates a room without creating a fall hazard. In Canada, the device is usually called a window opening control device, or WOCD, and the term you will see on a building permit or an inspection note is the Canadian one rather than the British one that dominates most online guidance on this subject.
The 100 mm limit is not arbitrary. A gap that size is small enough to stop a young child’s head from passing through, which is the physical threshold fall-prevention research settled on. Since the National Building Code of Canada 2020, the code has included that threshold. The change came from a code change request submitted by the City of Calgary together with Alberta Health Services, prompted by more than 400 children a year arriving in emergency departments across the country after falling from a window in a house. Alberta adopted the provisions in the National Building Code 2023 Alberta Edition, so the rule that now shapes how windows for Calgary homes are specified on upper floors applies across the country, and it started as a Calgary problem.
This article explains what the Alberta requirement actually says, when it applies, how the three compliance paths differ, how a control device interacts with the bedroom escape rule that pulls in the opposite direction, and what to check on an existing window before ordering hardware.
Key Takeaways
- A control device limits opening, not airflow. It stops the sash at a set gap, normally 100 mm, so the window still ventilates a room without creating a fall hazard. In Canadian code language, the device is a window opening control device, or WOCD.
- The Alberta trigger is a combination, not a single measurement. Sentences 9.8.8.1. (4) and (5) of the National Building Code 2023 Alberta Edition apply when the bottom edge of the openable portion sits less than 900 mm above the finished floor, and the drop on the other side is more than 1800 mm. Both conditions have to be true.
- There are three ways to comply, and hardware is only one of them. Raise the openable portion to at least 900 mm above the floor, fit a guard, or fit a device that limits the opening to 100 mm and releases only with tools or special knowledge. On a new build, the first option is often the cheapest, because it is a design decision rather than a purchase.
- A bedroom escape window needs a device with an escape release. Sentence 9.9.10.1 requires the window to open from inside without keys, tools or special knowledge, which directly contradicts the fall prevention rule. ASTM F2090 devices resolve the contradiction, and Alberta accepts them as an alternative solution.
- The requirement is not retroactive. Existing windows do not have to meet the new standard. Fitting a control device to an older upper-floor window is a voluntary safety upgrade, and a sensible one in a house with young children.
- Insect screens are not safety devices. They are built to keep insects out, not to hold a child in, and they detach under very little load. Any fall prevention plan that relies on a screen is not a plan.
- The device is only as reliable as the frame it fixes to. The screws have to land in material that carries load. On a warped sash or a deteriorating frame, a control device looks like protection without providing it, which is worse than having none.
How a Window Opening Control Device Works
A control device creates a physical stop between the sash (the moving part of the window) and the frame (the fixed surround). When the sash reaches the set gap, the device engages, and the window cannot open further under normal force. To open it beyond that point, the user has to deliberately operate a release.
The stop must engage early in the opening arc, not at the end of the window’s travel. A window that swings freely to 200 mm before anything catches it has already passed the threshold the device exists to protect. That is why the accepted device types all act on the sash’s initial movement.
The Three Main Mechanical Designs
Canadian code language names the accepted types directly. Alberta guidance on Clause 9.8.8.1. (4)(b) lists a fixed stop lever, a fixed length cable and a fixed position stop block as devices that satisfy the requirement.
- Fixed length cable. A short steel cable anchored to both the sash and the frame. As the sash moves outward, the cable goes taut at the design length and stops further travel. The release is a catch or clip an adult can operate and a small child cannot.
- Fixed stop lever. A hinged arm or lever fixed to both frame and sash that locks at the design position as the window opens. Some versions use friction, others a positive catch. Two fixing points resist lateral force better than one, which is why hardware guidance generally calls for a pair rather than a single unit on larger sashes.
- Fixed position stop block. A compact block that engages at the set gap and limits the swing arc or the linear travel depending on the window type. Common on hinged units where the sash swings outward.
What matters in that list is the word fixed. A spring-loaded button, a removable pin, or anything a child can defeat by pressing and pulling at the same time is not an accepted device, because the hardware must hold under deliberate force rather than casual force.
Window style affects which design fits. A slider or a hung window moves on a linear track, so a cable or a stop block interrupts that travel cleanly. A casement or awning swings on a hinge and is driven by a rotary operator, so the limit has to act on the swing arc or the arm rather than the crank, and removing the handle does not count as a control device. If you are figuring out which hardware suits your openings, it helps to understand how casement hardware operates first, because the mechanism is the constraint rather than the frame.
Tamper Resistance and Release
A control device sits between two failure modes. If a child can defeat it by pulling harder, it is not performing its function. If an adult cannot release it quickly in an emergency, it has created a different hazard. Every specification decision on this subject balances those two.
The code language handles the first by requiring release with tools or special knowledge, which rules out anything a toddler can operate by accident or by persistence. The second is handled by the escape release built into ASTM F2090 devices, covered in detail below. The two requirements don’t conflict once you specify the right device type, but they do conflict if you fit a generic restrictor to a bedroom window.
What the Alberta Requirement Actually Says
The Trigger: Two Conditions, Not One
Sentences 9.8.8.1. (4) and (5) of the National Building Code of Canada 2020, adopted in the province as the National Building Code 2023 Alberta Edition, apply to an openable window in a residential occupancy where two things are true at once. The bottom edge of the operable portion sits less than 900 mm above the finished floor, and the drop on the other side of the window is more than 1800 mm measured from that bottom edge to the floor or ground below.
Both conditions matter. A window with a low openable edge on a main floor, where the ground outside is close, does not trigger the requirement. A high sill window on a second storey does not trigger it either, because the openable portion is already above the 900 mm line. The provision targets the specific combination that produces child falls: an opening a small child can reach and climb into, with a significant drop behind it.
The 900 mm figure is not a coincidence. It matches the minimum height required for guards as a means of fall protection in residential occupancies, so the code is treating a high enough sill as functionally equivalent to a guard.
The Three Compliance Paths
Where the trigger applies, the code offers three ways to satisfy it, and they are genuinely alternatives rather than a hierarchy.
- Position the openable portion at least 900 mm above the finished floor. This removes the trigger rather than mitigating it, and on a new build it usually costs nothing beyond an early design decision.
- Fit a guard. A barrier across the opening, subject to the height and load provisions that apply to guards elsewhere in the code.
- Fit a mechanism that limits the opening to not more than 100 mm in either the horizontal or the vertical direction, releasable only with tools or special knowledge.
Appendix Note A-9.8.8.1.(4) points to ASTM F2090, the North American specification for window fall prevention devices with an emergency escape release, as the reference standard for the third path. The standard is not cited in the body of the code, so it functions as guidance on what an acceptable device looks like rather than a hard requirement.
The Bedroom Escape Conflict, and How Canada Resolves It
This is where the subject gets genuinely awkward, and where guidance written for other jurisdictions stops being useful.
Sentence 9.9.10.1 requires that, except where the suite is sprinklered, each bedroom has at least one outside window or exterior door openable from the inside without keys, tools, or special knowledge, and without removing sashes or hardware. That window must provide an unobstructed opening of at least 0.35 square metres, with no dimension smaller than 380 mm, and it must hold that opening during an emergency without additional support.
Read the two rules side by side, and the contradiction is plain. Sentence 9.8.8.1. (4) wants a device that releases only with tools or special knowledge. Sentence 9.9.10.1 wants a window that opens without them. Applied literally, a second-storey bedroom window cannot satisfy both.
ASTM F2090 is the standard that resolves it. It specifies fall prevention devices with an emergency escape release: the device holds the sash at 100 mm under normal use, and an adult can release it to full opening from inside the room in a single deliberate action, without a key or tool. Alberta issued a standard variance accepting an ASTM F2090-compliant device as an alternative solution for meeting Sentences 9.8.8.1 (4) and (5), which is the mechanism that makes both rules satisfiable on the same window.
The practical consequence for a homeowner is a single specification question. If the window is a bedroom escape window, the device has to be ASTM F2090 compliant rather than a generic restrictor. Because the escape opening is measured between the sash, jamb, sill, and operating hardware rather than across the rough opening, measuring the clear opening correctly tells you whether the window still qualifies as an escape window once the device is fitted.
Existing Homes: Not Retroactive, Still Worth Doing
The requirement applies to new construction. It does not reach back into the existing housing stock, and nobody is obliged to retrofit hardware to a house built before the provisions came into force. The City of Calgary made that point explicitly when it announced the change, noting that guards and control device hardware are readily available and straightforward to add to an existing second-storey window.
That distinction is worth holding onto, because it changes the nature of the decision. On a new build, the question is compliance. On an existing home the question is risk, and the answer depends on who lives there. A house with no young children and no vulnerable adults has a very different exposure from one with a toddler and a bed pushed against a bedroom wall.
“What I see on site is that people fit a device to the bedroom window and think the job is done. Then I check where the screws landed. On a lot of older units, the hardware went into the outer wall of the profile with nothing behind it, so it holds against a breeze and fails against a child. We fix into the reinforced chamber, and on a bedroom window I want to see the escape release work before I leave, not just the stop.” – Chris Perry, Project Manager, Weather Pro Windows and Doors
What a Control Device Delivers
Reduced Risk of Falls from Height
The primary purpose is fall prevention. An upper floor window left open for ventilation is a hazard for any child who climbs toward it, and the hazard rises sharply when furniture sits under the sill. A control device removes that hazard without requiring the window to stay shut through the summer. In a typical two-storey house in Calgary or Edmonton, bedrooms are on the upper floor, and windows are the main source of overnight ventilation, so keeping them closed isn’t realistic. For Edmonton homeowners and anyone else with second-storey bedrooms, a device that allows controlled opening is the only option that addresses the risk without removing ventilation.
Ventilation Without Compromise
A 100 mm gap moves a meaningful volume of air. In a bedroom with limited mechanical ventilation, that gap is often enough to keep air quality acceptable overnight without opening the window fully. This is the reason control devices are generally preferred over fixed barriers in housing: the window stays functional as a ventilation opening, just within a controlled range.
Protection for Occupants Who Cannot Assess the Risk
The 100 mm threshold comes from child anthropometric research. A gap that size prevents a young child’s head from passing through, which determines whether a fall is possible. The same logic extends to adults who may be disoriented or physically impaired, which is why managed care settings apply the requirement more strictly than a private home does.
Secondary Security Benefit
A control device offers some resistance to forced entry through a window left open for ventilation. This is a secondary effect rather than a purpose. A control device is not a security product in the sense that a multi-point locking system is, and it should never be specified as a substitute for proper window locks.
Where Control Devices Get Used
Residential Housing
In housing, control devices are most often fitted to upper floor windows in homes with young children. They can be added to many existing windows as a retrofit, provided the frame and sash are sound, and the profile can carry the fixing. On a new build or a full window replacement, the more reliable route is to settle the question at order stage, because the frame can be selected to accept the hardware rather than adapted to it afterwards.
Managed Buildings and Care Settings
Care facilities, supported living properties and multi-unit residential buildings apply the requirement more strictly than a private home. Occupants may not be able to assess the risk themselves, and keys and tools can be controlled centrally in ways that are impractical in a family home.
In those settings, the obligation often comes from occupational health and safety duty of care as well as from the building code, which matters because that duty is not limited to new construction. It can apply to an existing building where the occupancy changes or where a risk assessment identifies a hazard that was not previously present.
New Construction and Renovation Design
For a builder or designer, the most efficient response to Sentences 9.8.8.1.(4) and (5) is usually to design the trigger away. Placing the openable portion of upper floor windows at or above 900 mm removes the requirement entirely and costs nothing at the drawing stage. Where a lower opening is wanted for daylight or for the view, a fixed light below an openable upper sash achieves the same visual result while keeping the openable portion above the line.
Where a bedroom is involved, the escape window provision still has to be met somewhere in the room, so the design must meet both requirements at once. This is the point where a control device becomes the practical answer rather than a fallback.
Control Devices Compared With Window Guards
The two devices address the same risk differently, and the code treats them as alternatives under the same sentence. A control device limits how far the window moves. A guard blocks the opening. The table below sets out how they differ in practice and in the code.
| Dimension | Window opening control device | Window guard |
|---|---|---|
| Primary function | Limits how far the window opens, to no more than 100 mm | Creates a barrier across the opening so a person cannot pass through it |
| Physical form | A fixed stop lever, fixed length cable or fixed position stop block fitted between sash and frame | A grille, bar set or mesh panel installed across or over the opening |
| Opening limit | 100 mm maximum in either the horizontal or the vertical direction | Barrier spacing narrow enough that a child cannot pass through, with the guard meeting the height and load provisions for guards |
| Ventilation | The window opens to the set limit. Controlled airflow is the design intent | Airflow passes through the barrier, and the window can open fully behind it |
| Release for escape | An ASTM F2090 device carries an emergency escape release an adult can operate from inside without a key or tool | The guard itself must open or release, and it must not reduce the required escape opening |
| Canadian code basis | National Building Code Sentences 9.8.8.1. (4) and (5), adopted in Alberta as the 2023 Alberta Edition. Device standard ASTM F2090 via Appendix Note A-9.8.8.1.(4) | Treated as the guard option under Clause 9.8.8.1.(4)(a), subject to the guard provisions in Article 9.8.8.3 |
| Egress interaction | On a bedroom escape window, the device must carry the escape release, because Sentence 9.9.10.1 requires the window to open from inside without keys, tools or special knowledge | Must not reduce the required 0.35 square metre escape opening or prevent the window opening from inside without tools |
| Typical setting | Second storey bedrooms and upper floor rooms where the window has to open for ventilation | Low sill openings and settings where the window is likely to be left fully open |
| Installation | Fits to the sash and frame hardware channel. Retrofit is possible where the profile can carry the fixing | Fits to the window surround or the wall, independent of the window operating hardware |
The two are not mutually exclusive. In higher-risk settings, a guard is sometimes fitted outside the window while a control device limits sash movement inside, because two independent measures are harder to defeat than one. In housing, that combination is uncommon, because it costs more and complicates the escape route.
How to Specify One
Step 1: Work Out Whether the Opening Triggers the Requirement
Measure two things at each upper floor window. First, measure the height from the finished floor to the bottom edge of the openable portion; this is not the same as the height to the sill if the window has a fixed panel below the operating sash. Second, the drop from that bottom edge to the floor or ground on the outside.
If the first is 900 mm or more, or the second is 1800 mm or less, the code requirement does not apply to that opening. It may still be worth fitting a device if young children use the room, but it is a choice, not an obligation.
Step 2: Assess the Existing Window’s Condition
A control device fixes to the sash and the frame. If either is structurally compromised, the fixing points will not hold when load is applied. Before ordering hardware, check:
- That the sash opens and closes smoothly without binding
- That the frame is square, and the sash sits correctly within it
- That the existing hinges, operators and locks work as intended
- That the profile has solid material, normally a reinforcement chamber, at the positions where the device screws will land
A control device is only as strong as the material holding its screws. If the frame is deteriorating, the sash has moved out of square, or the reinforcement chamber is compromised, the fixing points will not carry load when a child leans on the sash. That is worse than no device at all, because it looks like protection. Working through the signs that a window is past repair before ordering hardware is the cheaper sequence, because it tells you whether you are buying a piece of hardware or planning a replacement.
Step 3: Choose the Device Type and the Release
The device type follows the window style. Linear travel on sliders and hung units suits a cable or a stop block. Hinged units driven by a rotary operator need a device that acts on the arc or the arm.
The release follows the room. In a bedroom that serves as the escape window, the device must be ASTM F2090 compliant so an adult can release it from inside without a key or tool. In a room that is not an escape window, a device requiring a tool or a key is acceptable and offers higher tamper resistance. In a managed building, key control is usually appropriate because staff can hold the keys. In a family home, a key stored elsewhere in the house is a liability rather than a safeguard.
Step 4: Confirm Frame Compatibility Before Ordering
Not all control device hardware fits all window profiles. Vinyl, aluminum and wood frames use different hardware channels and different screw fixing depths, and within vinyl the position of the reinforcement chamber varies between profiles. A device that seats correctly in one profile may have nothing but hollow wall to bite into in another.
This is the strongest argument for settling the question at the point of manufacture rather than afterwards. Weather Pro Windows and Doors builds its own vinyl units factory direct, so the profile, reinforcement layout, and hardware channel are known quantities before the order goes into production. Specifying an ASTM F2090 device for a window style engineered to accept it removes the most common retrofit failure: discovering on installation day that the frame cannot carry the fixing.
If you are retrofitting rather than replacing, confirm the profile with the hardware supplier before ordering. A non-standard profile may need an adapter plate or a different device design, and in some cases the hardware will not seat correctly at all.
Five Questions to Ask Before You Fit One
- Is the bottom edge of the openable portion less than 900 mm above the finished floor, and is the drop outside more than 1800 mm?
- Is this window the escape window for the bedroom it serves?
- If it is, does the device carry an ASTM F2090 emergency escape release?
- Will the screws land in reinforced material, or in the hollow outer wall of the profile?
- With the device fitted, does the window still deliver 0.35 square metres of clear opening with no dimension under 380 mm when released?
Where a Control Device Stops Working
A window opening control device is a narrow tool. It stops a sash at a set gap. Three things fall outside what it can do, and all three cause real failures.
The frame it is fixed to. A device is only as reliable as the material holding its screws. On a sound frame with an intact reinforcement chamber, it is a straightforward upgrade. On a warped sash or a deteriorating frame, it is hardware attached to an unsolved problem, and the fact that it looks like protection makes it worse than nothing.
The rest of the room. A device on the window does not address a dresser pushed under the sill, a bed against the wall, or a screen that a parent believes is holding. The City of Calgary and Alberta Health Services put furniture placement and screen misconceptions alongside hardware in their guidance for a reason: the hardware is one layer, not the whole plan.
The windows it is not fitted to. The Alberta requirement applies to new construction. It does not reach back into an existing house, so the decision about which windows get a device is yours to make, and the answer is usually every upper floor opening a child can reach rather than only the one in the bedroom.
The Question Is the Window, Not the Device
The specification itself is not complicated. Work out whether the opening triggers Sentences 9.8.8.1. (4) and (5), pick one of the three compliance paths, and if you pick hardware on a bedroom window, make it ASTM F2090 compliant so the escape release still works. That is the whole decision, and you can settle most of it with a tape measure.
What takes judgement is the window underneath it. If the sash operates cleanly, the frame is square, and the profile can carry the fixing, a control device is an afternoon of work and no reason to touch the window itself. If the frame has moved or the reinforcement is gone, replacement meets the safety and structural requirements in the same visit. Age tells you nothing useful here. The inspection does.
Frequently Asked Questions
What is the standard opening limit for a window control device in Canada?
100 mm, or approximately 4 inches, measured horizontally or vertically. The figure appears in Sentence 9.8.8.1 (4) of the National Building Code 2023 Alberta Edition, and in the device standard the code references, ASTM F2090. North American child safety guidance uses the same threshold, expressed as 4 inches. The limit is based on child anthropometric research showing that a gap of that size prevents a young child’s head from passing through.
Are window opening control devices required by building code in Alberta?
Yes, in defined circumstances. Sentences 9.8.8.1.(4) and (5) of the National Building Code 2023 Alberta Edition apply to an openable window in a residential occupancy where the bottom edge of the openable portion is less than 900 mm above the finished floor and the drop on the other side is more than 1800 mm. Where that applies, the window must have the openable portion raised to at least 900 mm, be protected by a guard, or be fitted with a device limiting the opening to 100 mm. The requirement applies to new construction and is not retroactive.
Does a control device affect bedroom fire escape?
It can, if the wrong type is fitted. Sentence 9.9.10.1 requires a bedroom escape window to open from the inside without keys, tools or special knowledge, and to provide an unobstructed opening of at least 0.35 square metres with no dimension under 380 mm. A device that requires a tool to release does not meet that. The answer is an ASTM F2090-compliant device that holds the sash at 100 mm under normal use but releases to full opening from inside in a single deliberate action. Alberta accepts such devices as an alternative solution precisely because they satisfy both rules.
Can a control device be fitted to any window type?
Most openable types can accept one, including casement, awning, hung and slider units. Compatibility depends on the frame profile and the operating mechanism rather than on the style alone. Linear travel on sliders and hung windows suits a cable or a stop block. Hinged units driven by a rotary operator need a device acting on the swing arc or the arm, and removing the crank handle does not count as a control device. A warped sash or a profile with no reinforcement at the fixing positions can make a retrofit impractical.
What is the difference between a control device and a window lock?
A lock secures the window in the closed position and prevents it from opening at all without a key. A control device allows the window to open for ventilation but limits how far. They serve different purposes: a lock is a security product, and a control device is a fall-prevention product. A window can have both, and often should. A lock secures it when nobody is home, and the control device governs how far it opens when the room needs air.
Do I have to add control devices to my existing windows?
No. The provisions apply to new construction and are not retroactive, so an existing house is not required to meet the current standard. Whether it is worth doing depends on the occupants. In a home with young children and upper-floor bedrooms, adding devices to the windows a child can reach is a low-cost measure that addresses a documented risk. A screen is not a substitute, since screens are built to keep insects out and detach under very little load.
Can a control device be specified when a window is being replaced?
Yes, and this is usually the more reliable route. When a window is replaced, the profile, reinforcement layout, and hardware channel are known before the unit is built, so the device can be specified against a frame engineered to accept it. That removes the most common retrofit problem: finding on installation day that the fixing has nothing solid to land in. If fall prevention is a concern and a replacement is already planned, raise it with the installer before the order goes in, not afterwards.
