← Back to Insights Facades

Elevation vs Wall Face Approach: How to Assess Complex Buildings Under F3V1a

When applying the weatherproofing risk matrix in NCC 2022 Volume One, Table F3V1a, one of the first decisions a facade engineer or building certifier must make is how to divide the building for assessment. The code does not prescribe a single method. In practice, two approaches have emerged: the elevation approach and the wall face approach. Each has distinct advantages, and choosing the right one can significantly affect the risk score, the cladding specification, and ultimately the project cost.

This guide explains both methods, compares them side by side, and provides a worked example showing how the choice of approach can change the outcome for a complex building.

The Elevation Approach

The elevation approach treats each building elevation as a single assessment unit. You complete the Table F3V1a risk matrix once per elevation — typically four times for a rectangular building (north, east, south, and west).

For each of the six risk factors, you take the highest-scoring condition found anywhere on that elevation. If even a small section of the north elevation has a parapet while the rest has a hip roof with generous eaves, the entire north elevation is assessed using the parapet score.

When it works well

• Simple buildings where features are consistent across each elevation — a standard rectangular dwelling with the same roof form, eaves width, and wall height on each face
• Quick documentation — four assessments cover the entire building, making it straightforward to present in a report
• Simpler construction — one cladding specification per elevation means fewer transitions for trades to manage on site
• Conservative by nature — the elevation approach never underestimates risk because it always adopts the worst-case condition

The downside

On complex buildings, the elevation approach can impose unnecessarily high scores on low-risk portions of an elevation. A single parapet section or a localised balcony can drag the entire elevation into a higher risk band, requiring cavity cladding across the full face — even where a simpler direct-fix system would have been perfectly adequate. This leads to over-design and increased construction cost without a proportional improvement in weatherproofing performance.

The Wall Face Approach

The wall face approach breaks each elevation into individual wall faces and assesses each one separately through the Table F3V1a matrix. A “wall face” is a distinct section of wall defined by changes in geometry: a change in wall height, a setback, a different roof form above, or a transition between building wings.

Each wall face receives its own risk score based on the conditions that actually apply to that specific section. A single-storey wing with a hip roof and 600mm eaves is assessed on its own merits, independently of a two-storey parapet section on the same elevation.

When it works well

• Complex buildings with varied features within a single elevation — mixed wall heights, different roof types, localised balconies, or stepped floor plans
• More accurate risk scores for each wall section, reflecting the actual exposure conditions
• Potential cost savings by avoiding over-specification — low-risk wall faces can use direct-fix cladding while high-risk faces use cavity systems
• Mixed cladding strategies become justifiable, allowing different systems on different wall faces where the risk scores support it

The downside

• More documentation — a complex building might have 12 to 20 individual wall face assessments instead of four
• More complex construction supervision — trades must track which cladding system applies to which wall face and manage the transitions between them
• Risk of underestimation — assessing small, isolated wall faces can miss the broader risk created by junctions and interactions between adjacent faces

When to Use Which Approach

The decision is not arbitrary. It should be driven by the building’s geometry and the practical implications for the project:

• Simple rectangular dwelling with consistent features on each face → elevation approach. It is faster, and the result will be the same as assessing individual wall faces because the conditions are uniform.
• Complex multi-level building with varied wall heights, mixed roof types, different deck conditions, or stepped plan forms → wall face approach. The additional documentation effort is justified by more accurate scores and potential cost savings.
• Borderline cases: If the elevation approach pushes a building into a higher risk band unnecessarily (e.g. scoring 14 instead of 8 on a largely simple elevation because of one localised feature), the wall face approach may save considerable cost. However, you must account for the junctions between faces.

Worked Comparison: L-Shaped Two-Storey Dwelling

Consider a two-storey L-shaped dwelling with a single-storey wing. The north elevation comprises two distinct sections:

• Section A — Two-storey parapet wall (the main body of the house), flat roof behind the parapet, no eaves, fibre cement cladding
• Section B — Single-storey hip roof wing (the garage/living area), 450mm eaves, brick veneer

Both sections are in Wind Region A2 (most of coastal NSW per AS/NZS 1170.2) and have no decks or balconies on this elevation. The building has a simple rectangular shape overall.

Elevation approach (north elevation assessed as one unit)

Factor	Condition (worst on elevation)	Score
Wind region	A2	0
Number of storeys	Two storey (worst case)	2
Roof/wall junction	Parapet (worst case)	3
Eaves width	0 mm — parapet, no eaves (worst case)	5
Envelope complexity	Two cladding types (fibre cement + brick)	3
Decks/balconies	None	0
Total risk score		13

A score of 13 falls in the medium risk band (7–14), requiring a drained cavity behind the cladding for the entire north elevation — including the single-storey brick veneer wing that, on its own, presents very low risk.

Wall face approach (two faces assessed separately)

Section A — Two-storey parapet wall:

Factor	Condition	Score
Wind region	A2	0
Number of storeys	Two storey	2
Roof/wall junction	Parapet	3
Eaves width	0 mm (parapet)	5
Envelope complexity	Single cladding (fibre cement)	0
Decks/balconies	None	0
Total risk score		10

Section B — Single-storey hip roof wing:

Factor	Condition	Score
Wind region	A2	0
Number of storeys	Single storey	0
Roof/wall junction	Hip roof	0
Eaves width	450 mm	1
Envelope complexity	Single cladding (brick veneer)	0
Decks/balconies	None	0
Total risk score		1

Under the wall face approach, Section A scores 10 (medium risk — drained cavity required) while Section B scores just 1 (low risk — direct-fix cladding is acceptable). The single-storey wing can use standard brick veneer construction without a cavity, saving cost and complexity on that portion of the building.

Important Cautions on the Wall Face Approach

The wall face approach is more precise, but it carries risks that must be managed carefully:

• Junction vulnerability — The transition between adjacent wall faces (corners, height changes, cladding transitions) creates additional weatherproofing vulnerability. These junctions are often the most failure-prone locations on a building envelope, and the wall face approach does not inherently account for them.
• Isolated face underestimation — Assessing a very small wall face in isolation can produce an artificially low score. A narrow two-metre section of wall between windows may score low on its own, but it exists within the context of a larger, more complex elevation.
• Overall building shape ignored — The wall face approach does not capture the cumulative risk created by the overall building form. A deeply recessed courtyard, for example, creates complex wind and water patterns that may not be reflected in any individual wall face score.
• Boundary scores — If a wall face scores near a band boundary (e.g. 6 or 7, or 14 or 15), use the more conservative interpretation. The precision implied by assigning exact scores to individual wall faces can create a false sense of certainty.

Practical Recommendations

For most projects, we recommend the following approach:

1. Start with the elevation approach. It is faster and provides a conservative baseline.
2. If the elevation approach produces a score that seems disproportionate to the actual risk (typically because one localised feature is driving the score up), consider switching to the wall face approach for that elevation.
3. When using the wall face approach, always detail the junctions between adjacent wall faces. The junction details should be designed to the higher of the two adjacent risk levels.
4. Document your rationale for choosing one approach over the other. A building certifier assessing your design will want to understand why each wall face was delineated as it was.

The NCC Table F3V1a risk matrix is a tool for informed decision-making, not a checkbox exercise. The approach you choose should reflect the actual complexity of the building and produce a result that is both technically defensible and practically buildable.