Retrofitting fiber cement boards onto existing buildings is rarely straightforward. Unlike new-build projects, refurbishment works must adapt to unknown, inconsistent, and often non-compliant substructures that were never designed to receive modern cladding systems.
Many façade failures in retrofit projects do not stem from the fiber cement boards themselves, but from the assumption that existing substrates behave like new, flat, regulated framing. They do not.
This article examines the practical, technical, and regulatory constraints of using fiber cement boards on non-standard existing substructures—and how to design around them without compromising long-term performance.
Why Retrofit Substructures Are Fundamentally Different
Existing buildings introduce variables that cannot be eliminated, only managed.
Typical retrofit substructure conditions include:
- Out-of-plumb walls exceeding modern tolerance limits
- Mixed substrates within the same elevation
- Unknown fixing capacity due to age or degradation
- Previous interventions with undocumented materials
- Irregular load paths not aligned with current façade systems
Fiber cement boards can perform well in retrofit scenarios, but only if these conditions are acknowledged early in the design phase.
Common Non-Standard Substructures Encountered in Retrofit Projects
Aged Timber Framing
Timber may be twisted, split, undersized, or weakened by moisture and biological attack. Fixing pull-out values are often inconsistent and unreliable.
Legacy Masonry and Blockwork
Older masonry frequently shows variable density, voids, or deteriorated mortar joints, making anchor performance unpredictable.
Mixed Steel and Timber Hybrids
Partial refurbishments often leave fragmented substructures where load paths change across the façade.
Irregular Concrete Surfaces
Concrete from earlier construction periods may be uneven, cracked, or carbonated, limiting anchor performance and edge distances.
Each of these conditions affects how fiber cement boards must be fixed, spaced, and allowed to move.
Tolerance Reality: When “Flat Enough” Is Not Flat
Modern fiber cement façade systems assume relatively tight tolerances. Existing buildings rarely meet them.
Key issues include:
- Accumulated deviation across storeys
- Localised bowing or stepping of substrates
- Inconsistent fixing planes
Attempting to force boards flat against uneven substrates introduces permanent internal stress, accelerating cracking and fixing fatigue over time.
In retrofit applications, secondary substructures or adjustable fixing systems are often required to re-establish a controlled plane before boards are installed.
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Authored by Smartcon Int’l. Trade & Marketing Ltd. on 28.01.2026. All rights reserved.