Egress Window Size, Sill Height & Well Dimension Requirements
This page lays out every dimension in Wisconsin's egress window code in one place, each tied to the exact section of the Uniform Dwelling Code it comes from. If a number appears anywhere else on this site describing an egress window, sill height, or window well, it will match what's written here — and if a figure doesn't have a citation next to it, treat it as general description rather than a code number to build to.
Opening Size
The Wisconsin UDC sets the minimum egress opening at a nominal 20 inches by 24 inches, irrespective of height or width (SPS 321.03(6)(b)1.). That "irrespective of height or width" phrasing matters: Wisconsin's rule is a pair of dimensions, not a net clear opening area calculated from them. That's a meaningful difference from the International Residential Code's commonly cited 5.7-square-foot net clear opening minimum, which several national egress-window articles apply to every state, including Wisconsin, without checking the state's own code. Wisconsin UDC vs. IRC egress window rules covers that distinction — and a handful of others — in full.
Sill Height
The lowest point of the clear opening can sit no more than 60 inches above the floor (SPS 321.03(6)(d)1.). This is another figure where Wisconsin's own number is worth double-checking against outside sources, since a lower maximum (44 inches) shows up widely online as if it were a universal rule — it isn't, under Wisconsin's own code text.
The Platform Rule
If the low point of the opening sits more than 46 inches above the floor, the code requires a permanent platform inside the room to close that gap (SPS 321.03(6)(d)2.–4.). The platform has to be:
- At least 20 inches wide and 9 inches deep
- Built so its top surface sits no more than 24 inches above the floor
- Rated to support at least 200 pounds
In practical terms, this rule exists because a 60-inch sill height without a platform would put the opening out of comfortable reach for using it as an actual exit — the platform closes that gap between the floor and the bottom of a legally allowed opening.
Window Well (Areaway) Sizing
Any egress window installed below grade needs a window well — referred to as an "areaway" in the code text — and the well has a minimum size of its own. It has to be at least as wide as the window and project at least 36 inches out from the wall (SPS 321.03(6)(e)1.). That 36-inch projection is what gives someone climbing out of the window room to actually stand and move, rather than just cracking the window open into a narrow trench.
When a Ladder Is Required
If the bottom of the areaway sits more than 46 inches below grade (or below the top of the well enclosure), a permanent ladder or steps become mandatory (SPS 321.03(6)(e)4.). Where a ladder is required, the code specifies:
- Rungs at least 12 inches wide on the inside
- Rungs projecting at least 3 inches out from the wall
- A load rating of at least 200 pounds
- No more than 12 inches of rise between rungs
- The ladder extending to within 12 inches of grade
Drainage
Separate from the size and access rules, the areaway has to be built so that water drains away from the window rather than collecting and working its way into the house (SPS 321.03(6)(e)6.). This is a functional requirement rather than a fixed dimension — the code doesn't specify a pipe size or a gravel depth, just that the drainage has to actually keep water out of the dwelling.
Under-Deck and Under-Porch Clearance
Where an egress window well sits underneath a deck or porch, there's an additional rule: a clear path to open space at least 36 inches high and 36 inches wide, running no more than 15 feet (SPS 321.03(6)(f)). This one catches homeowners off guard more than the others, since a deck built years after the original foundation can end up sitting directly over where an egress window well needs to go.
Why All of These Have to Be Met Together
None of these rules stands alone. An opening that meets the 20-by-24 size minimum but sits above the 60-inch sill height cap doesn't qualify. A well that's wide enough but shallow on the horizontal projection doesn't qualify. A well deep enough to need a ladder, built without one, doesn't qualify. A code review checks all of the relevant numbers for a given opening, not just the ones that happen to be easiest to hit, which is why a project that looks "basically compliant" on a walk-through can still fail review over one dimension that was overlooked.
Where These Numbers Apply
This full set of dimensions applies to a new egress window opening, an enlarged existing opening being upgraded to egress size, and the window well built around either one. It's also the same set of numbers a building inspector checks a finished project against before signing off on a permit, which is why matching these figures exactly — not approximately — is what determines whether a basement room can be used and represented as a legal bedroom. Egress window installation covers how these requirements fit into an actual project, from the initial opening through the finished well.