11.2 Measuring Above-Grade & Below-Grade Space

Measuring Above-Grade & Below-Grade Space

The Residential Measurement Standard (RMS) provides clear, objective geometric and structural rules for calculating residential property area. Real estate licensees must master the 10 Core Principles of the RMS (effective January 1, 2024) to ensure that published measurements represent lawful, compliant, and accurate property data.

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Overview of the 10 Core Principles of the RMS (Effective January 1, 2024)

The RMS framework is structured around ten core principles:

1. Principle 1 (Mandatory Use of RMS): Real estate professionals must use the RMS when communicating the size of a residential property.
2. Principle 2 (Consistent Units & 2% Tolerance): Identify if the measurement system is metric or imperial and apply it consistently; measurements must be within 2% of the RMS size (tolerance).
3. Principle 3 (Detached Properties): For detached properties, measure the property using the exterior wall at the foundation.
4. Principle 4 (Semi-Detached & Townhouse Properties): For semi-detached (duplex/half-duplex) and townhouse properties, measure each level using the exterior wall at the foundation. If the exact thickness of the demising (party/common) wall(s) cannot be determined, the thickness of an exterior wall is used.
5. Principle 5 (Apartment-Style Condominiums): For apartment-style condominiums, measure the interior perimeter walls (paint-to-paint) at floor level—do not add exterior or demising wall thickness to calculate the RMS area. (An additional representation may be made assuming exterior measurements, clearly explained to consumers.)
6. Principle 6 (Above-Grade vs. Below-Grade Levels): Include floor levels that are entirely above grade; exclude floor levels if any portion is below grade (below-grade areas may be measured under RECA’s Below Grade Measurement Standard and identified separately).
7. Principle 7 (Qualifying Additions & Conversions): Include qualifying above-grade additions and conversions that are weatherproof and suitable for year-round use.
8. Principle 8 (Ceiling Height & Sloped Ceilings): Include areas with a minimum floor-to-ceiling height of 2.13 metres (7 feet). If a ceiling is sloped, include areas with a floor-to-ceiling height of at least 1.52 metres (5 feet) provided there is a ceiling height of at least 2.13 metres (7 feet) somewhere in the room.
9. Principle 9 (Extensions): Include extensions from the main structure (cantilevers, bay/bow windows, dormers) that have floor space and a minimum ceiling height of 1.5 metres (5 feet), measured from the floor.
10. Principle 10 (Exclude Open Areas with No Floor): Exclude open areas that have no floor (e.g., vaulted voids, open-to-below areas, the part of a stair opening beyond the treads and landing).

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Principles 1, 2 & 3: Consistent Units & Detached Exterior Measurements

Principles 1 & 2: Mandatory Standard, Units & Tolerance

Whenever a real estate professional communicates residential property size, Principle 1 requires using the RMS. Under Principle 2, the practitioner must identify whether measurements are in metric (square metres) or imperial (square feet) and apply that system consistently across the calculation, using the appropriate conversion factor on the final result when reporting in both units (1 square metre = 10.7639 square feet). All published measurements must fall within the 2% tolerance of the true RMS size.

Principle 3: Exterior Measurements for Detached Properties

For detached residential properties, Principle 3 requires measuring the property using the exterior wall at the foundation:

┌────────────────────────────────────────────────────────┐
│      Exterior Perimeter of Detached Single-Family      │
│                                                        │
│   ┌────────────────────────────────────────────────┐   │
│   │  Interior Finished Living Space                │   │
│   │                                                │   │
│   │  • Drywall                                     │   │
│   │  • Framing + Insulation + Sheathing            │   │
│   │  • Exterior Wall Assembly                      │   │
│   └────────────────────────────────────────────────┘   │
│   ▲                                                    │
│   └─ Measure Exterior Wall at the Foundation           │
└────────────────────────────────────────────────────────┘

On upper floors or where physical obstacles prevent direct exterior access—such as steep hillside drop-offs or elevated second-storey walls—the measurer may extrapolate the exterior wall boundary from interior perimeter dimensions and exterior wall thickness. Explain how the dimensions were extrapolated.

(Principles 4 and 5, which govern semi-detached, townhouse, and apartment-style condominium properties, are examined in detail in Section 11.3.)

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Principle 6: Above-Grade vs. Below-Grade Floor Levels

Classify each floor level before adding its area to the RMS total.

Defining "Grade"

Under the RMS, "grade" is the level of the ground immediately adjacent to the exterior walls of the building.

• Above-Grade Floor Level: Under Principle 6, include floor levels that are entirely above grade around the entire perimeter of the dwelling.
• Below-Grade Floor Level: Exclude floor levels if any portion is below grade. Use RECA’s Below Grade Measurement Standard if measuring below-grade area, and identify it separately from RMS area.

┌────────────────────────────────────────────────────────────────────────┐
│                     The Above-Grade Perimeter Rule                     │
├───────────────────────────────────┬────────────────────────────────────┤
│ ABOVE-GRADE CLASSIFICATION        │ BELOW-GRADE CLASSIFICATION         │
├───────────────────────────────────┼────────────────────────────────────┤
│ 100% of the floor level sits      │ ANY portion of the floor level     │
│ completely ABOVE the ground level │ sits BELOW adjacent ground level—  │
│ around the entire perimeter.      │ even along a single wall.          │
└───────────────────────────────────┴────────────────────────────────────┘

Walkout Basements, Daylight Basements, Bi-Levels & Split-Levels

This strict perimeter rule directly governs common Alberta architectural designs:

• Walkout Basements: In a walkout basement, three sides of the lower level may be completely exposed with full-sized sliding glass patio doors, oversized windows, and high-end finishes. However, because part of the floor level lies below the adjacent grade, the entire walkout level is below grade.
• Bi-Level Lower Levels: In a raised bi-level home, the lower level may be partly below grade even with large daylight windows. Because a portion of the level is below adjacent grade, the entire lower level is below grade.
• Split-Levels (Three-Levels / Four-Levels): Each floor level must be assessed independently. Levels entirely above grade are included in the above-grade RMS area, while any level partially or wholly below grade is excluded from above-grade RMS and reported separately.

Communicating above-grade and below-grade area

For a detached bungalow with a 1,500 sq ft above-grade main floor and a 1,300 sq ft developed walkout level partly below grade, the RMS is 1,500 sq ft. If communicating the walkout area, measure it using RECA’s below-grade guidance and label it separately. A combined above- and below-grade total may be useful in remarks if the two components are stated clearly and the total is identified as combined area.

Some listing systems require a size-field entry even when a property is wholly below grade. RECA's guide describes entering the level closest to grade and stating that the property is below grade. For a partly below-grade apartment or stacked townhouse with identical units elsewhere in the building fully above grade, RECA's current FAQ describes a listing-field exception. Identify the below-grade area in public remarks and explain the grade situation.

Principle 7: Qualifying additions and conversions

Include above-grade additions to the main structure and conversions within it when they are weatherproof and suitable for year-round use. RECA's guide checks for a permanent structure with a foundation or footings, a permanent connection to the main electrical service and a permanent heat source reasonably able to maintain 22°C in winter. The space can be heated from the main system or by its own permanent system. An interior entrance from the residence or garage can qualify. A room accessible only by an exterior door is excluded. Apply the relevant ceiling-height rules.

For example, an above-grade former garage accessed through an interior door can qualify after conversion to a weatherproof room with permanent power and a suitable permanently installed heating system. An extension cord and portable heater would leave the year-round requirements unmet.

Principle 8: Ceiling Height Requirements & Sloped Ceilings

Floor area can only be counted toward the RMS measurement if it provides adequate vertical clearance.

Standard Minimum Ceiling Height

Under Principle 8, include areas with a minimum floor-to-ceiling height of 2.13 metres (7 feet).

• Ductwork, Beams, and Bulkheads: If a room generally meets the 2.13-metre (7-foot) ceiling height, RECA’s guide includes space beneath localized beams, ducts and similar obstructions when the clearance to the obstruction exceeds 1.52 m (5 ft).

Sloped Ceilings (1.5-Storey Homes, Attics & Lofts)

In rooms with sloped ceilings—such as 1.5-storey character homes, attic bedrooms, and top-floor lofts—Principle 8 applies a straightforward two-part rule:

                         ▲ (Peak: >= 2.13 m / 7 ft somewhere in room)
                        / \
                       /   \
                      /     \
                     /       \
 -------------------┌─────────┐------------------- 2.13 m (7 ft) Threshold
                   /│         │\
                  / │         │ \
                 /  │         │  \
 ----------------┌──┴─────────┴──┐---------------- 1.52 m (5 ft) Cutoff Line
                /│               │\
               / │               │ \
 ═════════════╧══╧═══════════════╧══╧═════════════ Floor Line
   EXCLUDED   │    INCLUDED      │   EXCLUDED
  (< 1.52 m)  │ (>= 1.52 m / 5ft)│  (< 1.52 m)

1. Presence of 2.13 m (7 ft) Somewhere in the Room: There must be a floor-to-ceiling height of at least 2.13 metres (7 feet) somewhere in the room. If no part of the room reaches 2.13 metres (7 feet), the entire room is excluded.
2. The 1.52-Metre (5-Foot) Minimum: Provided at least 2.13 metres (7 feet) exists somewhere in the room, include all floor areas with a floor-to-ceiling height of at least 1.52 metres (5 feet), and exclude any areas below 1.52 metres (5 feet).

(Note: Unlike some U.S. standards such as ANSI Z765, RECA's RMS Principle 8 does not require 50% of the room's floor area to reach 2.13 metres—it only requires that a height of at least 2.13 metres exist somewhere in the room.)

Sloped Ceiling Calculation Walkthrough

An attic loft bedroom in a 1.5-storey home has total floor dimensions of 6.0 metres by 5.0 metres (total footprint = 30.0 square metres):

• Floor area where ceiling height is under 1.52 m (5 ft): 6.0 square metres
• Floor area where ceiling height is between 1.52 m (5 ft) and 2.13 m (7 ft): 12.0 square metres
• Floor area where ceiling height is 2.13 m (7 ft) or greater: 12.0 square metres

Step 1: Verify the 2.13 m (7 ft) Room Requirement: Because 12.0 square metres of the room reaches a height of at least 2.13 metres (7 feet), a ceiling height of at least 2.13 metres exists in the room, so the sloped-ceiling area qualifies for inclusion.

Step 2: Calculate Compliant RMS Area (Exclude area < 1.52 m): RMS Room Area = 12.0 + 12.0 = 24.0 square metres The 6.0 square metres with floor-to-ceiling height below 1.52 m (5 ft) is excluded.

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Principles 9 & 10: Extensions, Open Areas & Staircases

Principle 9: Extensions from the Main Structure

Under Principle 9, include extensions from the main structure—such as cantilevers, bay/bow windows, and dormers—if they meet both requirements:

1. Floor Space: The extension has actual floor space (the finished floor extends out into the projection); and
2. Minimum Ceiling Height: Apply RECA’s five-foot minimum from floor level. The current principles page gives the metric figure as 1.5 metres.

If a bay window features a raised interior bench or window seat built above floor level (meaning the floor does not extend into the bump-out), or falls below the applicable five-foot height threshold, the projection must be excluded from the RMS area.

Principle 10: Exclude Open Areas with No Floor

Modern homes frequently feature two-storey great rooms, vaulted foyers, and upper landings looking down onto lower floors. Under Principle 10, exclude open areas that have no floor, including:

• Vaulted ceiling voids;
• Open-to-below areas; and
• Parts of stair openings without treads or landings.

A measurer calculating an upper-floor level must deduct the exact dimensions of any open-to-below floor void.

Stair treads, landings and extra openings

Count the area of stair treads and landings on the above-grade level the stairs lead to, even when all or part of the stair run starts below grade. If the stair opening is larger than the treads and landings, deduct the extra open area. For example, if an upper-floor stair opening spans 44 sq ft and its treads and landing occupy 32 sq ft, keep 32 sq ft and deduct the extra 12 sq ft from the upper floor’s exterior envelope. A separate 150 sq ft open-to-below void over a great room is also deducted from that upper level.

Comprehensive Calculation & Measurement Guide

Official sources

• RECA Residential Measurement Standard principles and FAQs
• RECA comprehensive RMS guide, principles 2–10 and below-grade measurement