Window Fall Prevention: Sill Heights, Stops and Guards

A window screen does not stop a child from falling; a limit on how far the window opens, or a guard across the opening, does. The model building code draws the line at operable windows whose opening sits less than 24 inches above the floor and more than 72 inches above the ground outside. The 2024 existing-building code requires many replacement windows in those positions to come with an opening control device that complies with ASTM F2090.

How often children fall from windows

The U.S. Consumer Product Safety Commission (CPSC) estimates that 5,600 children aged 12 and under were treated in emergency departments in 2024 after falling out of a window. Its April 2026 figures:

About one in three of those cases required hospitalization.
At least 25 children aged 12 and under died in window falls between 2021 and 2023.
80 percent of those deaths happened between May and October, the warmer months of the year.

Screens are not fall protection

Screens do not count as fall protection. CPSC’s advice is direct: never depend on screens to keep children from falling out of windows. New York City’s health department says the same thing in its window guard rules: screens are not a substitute for window guards.

The code’s height rule: 24 inches inside, 72 inches outside

Section R321.2.1 of the 2024 International Residential Code (IRC) applies in dwelling units when both of these are true for an operable window:

the bottom of its clear opening is less than 24 inches above the finished floor, and
it sits more than 72 inches above the finished grade or other surface below it outside.

Such a window has to meet one of two conditions:

Limited opening: even when opened all the way, it does not let a 4-inch-diameter sphere pass through.
Compliant device: it has a window opening control device or fall prevention device that complies with ASTM F2090.

In the 2021 edition this rule was Section R312.2. The 72 inches are measured to whatever surface lies below outside, so the drop can pass the threshold where the ground slopes away from the house or a window sits above a walkout.

When a replacement window must include a device

The 2024 International Existing Building Code (IEBC), Section 505.2, covers replacements in one- and two-family homes and townhouses regulated by the IRC, and in Group R-2 and R-3 buildings with dwelling units, such as apartment buildings. When an existing window is replaced, opening control devices or other fall prevention devices that comply with ASTM F2090 must be installed if all of the following apply to the new window:

it is operable;
the job replaces the sash and frame, or the sash only where the old frame stays;
the bottom of its clear opening is less than 24 inches above the finished floor in a house or townhouse, or less than 36 inches in a Group R-2 or R-3 building;
fully opened, it would let a 4-inch sphere pass through;
the drop from the bottom of the clear opening to the grade or surface below outside is more than 72 inches.

The same wording appears in Section 702.4, which covers Level 1 alterations, the category for replacing existing building elements. The one exception is for windows more than 75 feet above grade that carry devices meeting a separate standard, ASTM F2006, which ASTM describes as covering windows at that height in multifamily buildings.

Guards, stops and control devices

Stops, guards and opening control devices handle the risk in different ways, and the code accepts devices that comply with ASTM F2090:

Window stops limit how far a window opens. CPSC recommends stops that let windows open no more than four inches, which matches the code’s 4-inch sphere.
Window guards are barriers across the opening. CPSC recommends that on the 6th floor and below, guards be the kind that adults and older children can open easily in case of fire.
Opening control devices limit the opening but include a release mechanism, so the window can be opened fully for escape.

The ASTM F2090-21 standard covers opening control devices, fall prevention screens and fall prevention window guards used on operable windows, including windows meant for emergency escape. Its stated purpose is to address falls by children five years old and younger. It also requires a window manufacturer that relies on a device supplier’s test report to verify that the device, installed on its specific window type, complies with the standard.

CPSC’s other household tips: open windows from the top instead of the bottom when possible, and keep furniture away from windows so children cannot climb to them.

Fall protection and fire escape have to work together

A bedroom window may be both a fall risk and the room’s second way out. The code handles the conflict in three places:

R319.1.1: escape windows must open from inside without keys, tools or special knowledge, and devices on them must be mounted no higher than 70 inches above the finished floor.
R321.2.2: once the device is released and the window opens fully, the clear opening cannot fall below the escape minimums.
R319.5.1: on replacement escape windows, the device must be mounted within that 70-inch limit or as low as it can be installed within the existing clear opening.

The U.S. Fire Administration asks households to find 2 ways out of every room and to make sure doors and windows are not blocked. With devices installed, that plan should include showing every adult and older child how to release them.

Local rules can go further

Some cities set stricter rules than the model code. New York City requires window guards in buildings with at least three apartments where a child aged 10 or younger lives. Its health department recommends guards in private homes, though they are not required there. Window falls by children aged 16 or younger are a reportable condition in the city.

Renters elsewhere should ask the building owner or the local health or housing department what applies.

When to bring in a professional, and what to ask

A window replacement is the moment to settle fall protection, because the installer is already measuring every opening and the code may require devices anyway. Questions to ask:

Which of my windows have a clear-opening bottom under 24 inches and a drop of more than 72 inches outside?
Will the new units come with ASTM F2090 devices installed at the factory, or as kits fitted on site, and has the device been verified on this window type?
On bedroom windows that serve as escape openings, what is the clear opening once the device is released?
How does the device release, at what height is it mounted, and can an older child operate it?
Which code edition does the building department enforce, and does the permit inspection check these devices?

Get the answers in writing, window by window, before the order is placed.