No other compliance issues require more back-and-forth discussion with the reviewer than spatial separation. Make a small mistake regarding either the limiting distance or the area of the exposed building face, and you may be forced to redesign the windows and walls after you have designed them properly. The spatial separation calculator removes all the hassle of going through the tables manually, but understanding how the calculations work behind it is important if you want the outcome to be accepted by your AHJ.

What Spatial Separation Is Actually Protecting Against

Fire protection through spatial separation is intended to prevent the spread of fires between buildings through the transfer of energy by radiation and not as a measure to protect people who occupy the building. Spatial separation is achieved in accordance with guidelines stated in the Canadian National Building Code, which includes the Ontario Building Code, British Columbia Building Code, and Alberta Building Code, which provide tables stating the maximum percentage of unprotected openings, such as windows, doors, and other openings without fire resistance ratings, on the exposed building face.

The Three Numbers That Drive Every Calculation

Each spatial separation computation is based on three factors input into the code table:

• Limiting distance: the distance from the face of the exposing building to the property line, centerline of a street or lane, or an imaginary line joining two buildings on the same site
• Exposing building face area: the area of the face = width x height, sometimes computed per fire compartment, not overall building area.
• Occupancy classification: The allowable percentage of unprotected openings depends on whether the building falls under residential, mercantile, industrial, or some other category

Having obtained the three values, you refer to the correct table – e.g., Table 3.2.3.1 of NBC and read off the maximum percentage of unprotected openings allowed.

Why Interpolation Trips People Up

The code table contains discrete values, but it’s rare that a particular building will fall perfectly on one of those rows or columns. You’ll need to interpolate between the numbers if your limiting distance is 3.5 meters, but your table has 3 meters and 4 meters. The same goes for the exposed area of a building. It is precisely here where manual calculations can go wrong – rounding down when interpolation is needed, choosing a closer number rather than the interpolated result. Having a special calculator of spatial separation eliminates any possibility of doing so, a technique well accepted by the authorities having jurisdiction.

Common Mistakes That Show Up in Plan Review

Some mistakes cause the majority of resubmissions in terms of spatial separation:

• Calculating the limiting distance from the point nearest to the adjacent structure rather than from the property line, while the requirement is the latter;
• Ignoring the fact that unprotected openings include all the unglazed openings like overhead garage doors;
• Taking the entire building as a single exposed face rather than considering fire compartments.

All of them can be easily avoided by reading the proper subsection, but at the same time, they are typical examples of things experienced fire risk consultants notice before submitting the project.

Getting It Right the First Time

The accuracy of the results of the calculator depends on the data that you enter into it; therefore, certain practices will be beneficial for you:

• Ensure that you know which version of the code is used in your location, as there are differences in tables between NBC and its provincial editions
• Make sure that your project is eligible for reduction before taking the table results as final ones, for example, in the case of sprinklers
• Perform calculations by fire compartments whenever possible, since this way the number of unprotected openings will increase

Conclusion

Calculations for spatial separation are right on the line between measuring accurately and interpreting the code, and a minor mistake in the limiting distance or face exposure could lead to an entire redesign of the façade. A good spatial separation calculator eliminates any need for estimating, but those judgment calls with regard to the measurements, reduction factors, and occupancy classifications are all the better for having a second opinion. Fire risk consultants, experts early on in your design process, will give you peace of mind about your inputs before someone else flags them.

FAQs

1. What is limiting distance in a spatial separation calculation?

The limiting distance is defined as the distance from an exposed building face to the property line, centreline of the street or alley, or imaginary line drawn between two buildings at the same site. It is one of the main inputs into the formula.

2. Does spatial separation apply to interior walls or only exterior walls?

It pertains to exposing building faces, which means those building faces that expose themselves to the property line, street, or another building, because we are talking about limiting the spread of fire between buildings or sites.

3. Can I reduce the required spatial separation if my building is sprinklered?

Yes, typically. The NBC, for example, allows reductions for certain circumstances, like sprinklers, but there are specific criteria that must be met. They must be checked by a fire risk consultant.

4. Why would a manual calculation give a different result from a spatial separation calculator?

This is because of erroneous interpolation between the values in the table, or the improper measurement of the limiting distance or the exposed building face. The calculator interpolates correctly, but the inputs must be correct.