Last updated: October 30, 2026
Spatial separation is not a wall problem. It is an opening problem that arrives disguised as a wall problem.
The code starts with two measurements and ends with a percentage. That percentage dictates three things about the exterior wall: its fire-resistance rating, whether its construction has to be noncombustible, and whether its cladding has to be noncombustible. A precast wall panel answers two of those three in every band of the table. The one that moves is the rating. The one that constrains the design is the glass.
Get the percentage wrong at tender and the elevation gets re-glazed after award. On a precast job that is a drawing-release problem, not a site problem.
The short answer
Limiting distance and the area of the exposing building face set the maximum area of unprotected openings permitted in that face. Convert that area to a percentage of the face, and Table 3.2.3.7 of the National Building Code – 2023 Alberta Edition returns three requirements: a fire-resistance rating, a permitted type of construction, and a permitted type of cladding. Precast satisfies the construction and cladding columns in every row. Specify the rating per elevation, fix the opening percentage before panel drawings release, and the panel order does not change.
Two inputs decide everything
Limiting distance. The horizontal distance from the exposing building face to a property line, measured per the code. Confirm the measurement rule and the reference line with the authority having jurisdiction before anyone sizes a window. Some configurations are set by variance, not by the prescriptive path.
Exposing building face. The exterior wall of a building or fire compartment facing the property line in question. The code works it as a rectangle: L is its length, H its height. The ratio matters, because the opening-limit tables are entered by ratio as well as by distance.
Two table notes are worth carrying into a design meeting. Where two ratios could apply, the code says to use whichever ratio is greater. And the Group C entry in that table is flagged as applying to Part 9 residential buildings, not Part 3 buildings. That distinction quietly disqualifies a lot of borrowed spreadsheets.
We are not printing opening-area values from that table. In the comparison document we worked from, those rows were not legible, and a spatial separation number you cannot read is a number you do not use.
What the code limits is the opening, not the panel
Nothing in these provisions says “do not use concrete.” They constrain how much unglazed wall you must keep, then describe the minimum quality of the wall surrounding the glass. The panel is never the thing being rationed. The opening is.
The sequence on a precast elevation runs: limiting distance, then face area and ratio, then permitted opening area, then opening percentage, then the row of Table 3.2.3.7 you are in, then the rating you specify. The chain terminates one step before it reaches the product.
Table 3.2.3.7: what each opening band costs you
Required fire-resistance rating, type of construction and type of cladding for an exposing building face, by percentage of unprotected openings.
| Unprotected openings | Groups A, B, C, D, F-3 | Groups E, F-1, F-2 | Construction | Cladding |
|---|---|---|---|---|
| 0 to 10% | 1 h | 2 h | Noncombustible | Noncombustible |
| Over 10 to 25% | 1 h | 2 h | Combustible or noncombustible | Noncombustible |
| Over 25 to 50% | 45 min | 1 h | Combustible or noncombustible | Noncombustible |
| Over 50 to under 100% | 45 min | 1 h | Combustible or noncombustible | Combustible or noncombustible, with conditions |
Group A is assembly. Group B is care, treatment or detention. Group C is residential. Group D is business and personal services. Group E is mercantile. Groups F-1, F-2 and F-3 are high-, medium- and low-hazard industrial.
Two readings fall out immediately. The rating requirement falls as the opening percentage rises, because the rated wall exists to limit radiant transfer to the neighbour and once half the face is glass the wall has stopped being the control. And the mercantile and higher-hazard industrial family carries double the rating of the other family in the two tightest bands.
Read the table backwards
The useful insight is the top row, not the bottom.
The band that allows the least glass, zero to ten percent, is the only band that requires noncombustible construction. Above ten percent, combustible construction becomes permissible. In the 2023 edition, encapsulated mass timber is added as a permitted construction type in several rows, which widens the field further.
So a precast wall panel is not merely allowed at a tight limiting distance. It is in the narrow set of assemblies usable there at all. As the setback grows and the permitted opening percentage climbs, that exclusivity disappears, and the case for precast then rests on span, erection speed, finish or the frame itself – the ground covered in our comparison of precast concrete versus steel framing in Alberta.
Where a precast panel sits in every row
Run the two columns that are not the rating.
- Construction. A structural precast concrete wall panel is noncombustible construction. It satisfies the one row that demands it and every row that permits a choice.
- Cladding. An architectural precast face, an exposed structural face, and a precast panel with an integral or applied mineral finish are all noncombustible cladding. Noncombustible cladding is required in three of the four bands. The panel clears all three.
That is why the limiting distance conversation on a precast job is short on the wall and long on the window. It is also why the elevations facing the tightest property line usually carry the simplest panel schedule: fewer and smaller cast openings, more solid panel. This shows up most on the building types in our solutions index, on tight urban parcels.
The waivers in Article 3.2.3.7, and what they are worth
The article carries relief from the noncombustible cladding requirement. On a precast elevation these waivers are usually irrelevant, and knowing that saves a meeting.
- Where unprotected openings exceed 10%, the noncombustible cladding requirement is permitted to be waived for exterior wall assemblies complying with Article 3.1.5.5. or 3.1.5.6.
- Where unprotected openings exceed 25% but do not exceed 50%, a waiver is available under conditions that include a limiting distance greater than 5 m and the building or fire compartment, together with all combustible attic and roof spaces, being sprinklered throughout.
- In the 2023 edition, a note on the highest band requires cladding on Group C and Group D buildings to be noncombustible, or to consist of a wall satisfying Article 3.1.4.8.
The 5 m and sprinklered-throughout conditions in the second waiver are the ones most often assumed rather than checked. The NRC Canadian Codes Centre’s presentation on spatial separations describes the same pair of conditions attaching to cladding relief in that band, which independently confirms the relief is conditional rather than general. It addresses an earlier code cycle, so treat it as background on intent, not as clause text.
What changed between the 2019 and 2023 editions
Encapsulated mass timber is added as a permitted construction type in several rows of Table 3.2.3.7. A new note is attached to the cladding entry in the highest opening band. And the Group C and Group D cladding condition is now expressed through Article 3.1.4.8.
None of these change what a precast panel is permitted to do. All of them change who else is permitted to be in the row beside it. If your office is still working from a 2019-era spatial separation spreadsheet, the construction column is where it is now wrong.
One further provision in the same subsection catches teams late: a walkway connected to a building required to be of noncombustible construction has to be noncombustible itself, and is capped at not more than 9 m in width.
The number that has to be final before panel drawings release
Openings in a precast wall panel are formed at the plant. That makes the opening percentage a drawing-release milestone, not a design-development nicety.
- Confirm limiting distance per elevation with the authority having jurisdiction, including the measurement reference.
- Establish the exposing building face area and ratio per elevation.
- Establish the permitted unprotected opening area from the official code tables.
- Convert to a percentage and record the Table 3.2.3.7 row for that elevation.
- Issue the rating requirement on the contract drawing, per elevation, before the panel package goes out.
Step five is the one that slips. A rating that appears only in the specification, or only in a code consultant’s report, does not reach the panel drawings. Put it on the elevation. The erection side of a panel and link connection is covered in our note on installing a precast concrete panel.
Ordering: what the plant needs
For each elevation governed by a limiting distance, send:
- Elevation mark, plus the property line or reference line the limiting distance is measured to.
- Limiting distance, and whether it was established prescriptively or by variance.
- Exposing building face dimensions, L and H.
- Occupancy group or groups for the compartment behind the face.
- Unprotected opening area permitted, and the percentage it represents.
- Required fire-resistance rating for the face, taken from the code table and stated on the contract drawing.
- Opening schedule for the face: size and location of every cast opening.
- Whether the building or fire compartment is sprinklered throughout, and whether combustible attic and roof spaces are included.
- Finish requirement for the face, and whether any applied cladding is proposed over the panel.
- Erection window and crane access date.
Panels carrying load as well as enclosure should come with the framing information set out in our guide to precast concrete beams and columns.
Where this article stops
This article covers what limiting distance and the unprotected opening percentage require of an exterior wall, and what that means for a precast panel order. It does not cover:
- How a precast unit earns a fire-resistance rating. That is a separate question, answered by section geometry and by the depth of the steel, and it is handled in our material on precast fire-resistance ratings rather than here.
- Interior fire separations, firewalls, or the protection of service penetrations through an assembly.
- The forming of openings in precast floor elements, field-cut versus cast-in decisions, or the effect of an opening on prestress. Those belong to the hollow core discussion.
- Part 9 housing. The City of Calgary’s zero lot line variance advisory, Revision 4 dated 17 June 2024, shows how different that path looks at a zero limiting distance: no glazed openings below 1.2 m, a prescribed cladding and sheathing stack, and a registered right of way. It is a house variance for one permit address, not a Part 3 route.
Clause numbers and table values move between editions. Confirm every number above against the official National Building Code – 2023 Alberta Edition before you release drawings. The current building STANDATA are where to check whether an interpretation or variance has modified a provision.
FAQ
Does a precast wall panel count as noncombustible construction? Yes. A structural precast concrete wall panel is noncombustible construction, and an exposed or architecturally finished precast face is noncombustible cladding. That satisfies the construction and cladding columns in every opening band.
Does a small limiting distance mean no windows at all? No. It means a small permitted unprotected opening area. The area is calculated from the limiting distance together with the size and ratio of the exposing building face, so two elevations with the same setback can carry different opening budgets.
Which occupancies carry the heaviest rating? Groups E, F-1 and F-2 carry 2 h in the two tightest bands and 1 h above 25%. Groups A, B, C, D and F-3 carry 1 h, then 45 minutes above 25%.
Can sprinklers buy more glass? Sprinkler protection appears as a condition attached to specific relief, including the cladding waiver in the band above 25% and up to 50%, which also requires a limiting distance greater than 5 m. Confirm it with the authority having jurisdiction rather than assuming it.
When does the opening percentage have to be final? Before the precast panel drawings release. Openings are formed at the plant, so a late change to the opening schedule is a remake, not a revision.