Window height requirements and safety glass

Here’s a question our inspectors have fielded a couple of times in the last few months: how high off the floor do windows have to be?

It’s a really good question, but the answer – well, in typical fashion, Code makes things a bit complicated.

Before we delve into the Code, let’s look at the core thought behind the “how high should windows be” question contractors are asking us: they’re quite correctly intuiting that if you have a window that’s too low to the floor, someone might accidentally fall out the window to the ground below. Most times, the contractors think, “hey, if it’s low to the floor, and there's along drop to the ground, I probably need safety glass, or something.”

That’s a pretty good thought, and it’s pretty close to what Code wants… mostly.

In fact, Clause 9.8.8.1 of the National Building Code speaks to just that matter by stating that openable windows that present a risk of having someone plunge to their doom should have either a guard, or ways to limit window opening to 4” (10 cm) if the window is sufficiently large enough (38 cm or 15”).

However, these protections are not required if any one of the following is true:

• The window serves a dwelling unit that is not located above another suite (think apartment),
• The window serves a house with a secondary suite, (Note that this does NOT include a single-family dwelling.)
• The only opening greater than 10 cm by 38 cm is a horizontal opening at the top of the window,
• The window sill is located more than 45 cm (17 ¾”) above the finished floor on one side of the window,
• The window is located in a room or space with the finished floor …. located less than 1.8 m above the floor or ground on the other side of the window.

In other words, in many situations there is no restriction on window height from the floor. That said, the general best practice is to have the sill of windows in a single-family home - and elsewhere - at 18” height just to avoid problems. It's such a common practice that many contractors think it's a Code requirement in its own right - even though in many situations, it's not actually required.

With that solved, there some situations where safety glass is required. Usually, this is in a situation where a pane of glass might be confused with a door – sidelights next to a door, or large panes of glass next to a patio door, for example. Clause 9.6.1.4 speaks to this, by requiring safety glass for glass sidelights greater than 50 cm (18 ¾”) wide that could be mistaken for doors; glass in storm doors and glass in sliding doors within dwelling units (ie: houses).  Glass in doors, for the most part, must be safety glass if it’s area exceeds 0.5m2 (about 5.5 square feet) and extends to less than 90 cm (35 ½”) from the bottom of the door.