Understanding insulation gaps within a cavity wall and how to prevent them
Achieving a well-insulated, energy efficient building starts with understanding how insulation gaps occur and how to avoid them.
Insulation Gaps in Drywall Systems
One of the most common causes of energy loss in drywall systems is incorrectly fitted or flimsy insulation. This happens when insulation inside the wall frame does not fit properly between the steel studs, leaving air gaps that reduce thermal efficiency. These gaps often go unnoticed but can significantly impact comfort and energy costs.
What is a Cavity Wall?
A cavity wall consists of two plasterboard walls separated by an air space, creating the cavity between them.
Today, this cavity serves an important thermal and acoustic purpose it’s the ideal space for insulation products like Cavitylite®, Cavitybatt®, or CavityslabTM, installed behind gypsum plasterboard and between non-load-bearing studs. These solutions help reduce heat transfer, maintain comfortable indoor temperatures, and improve energy efficiency without changing the building’s appearance.
In South Africa, Energy Performance Certificates (EPCs) are required for certain building types and sizes under the Regulations for the Mandatory Display and Submission of EPCs, gazetted in December 2020. The requirement applies to public buildings with a net floor area greater than 1,000 m² and private buildings larger than 2,000 m², specifically those classified under SANS 10400 as A1 (entertainment and public assembly), A2 (theatrical and indoor sport), A3 (places of instruction), and G1 (offices). EPCs grade buildings from A (most energy-efficient) to G (least efficient), based on annual energy consumption per square metre, and must be issued by a SANAS-accredited inspection body or a qualified professional in accordance with SANS 1544:2014. Building owners who do not comply may face penalties of up to R5 million or five years’ imprisonment.
How Do Gaps Occur?
Insulation gaps form when:
- Insulation is the wrong size
- Rigid insulation product fail (where insulation products slump in the cavity, creating gaps)[NN2]
- Wall surfaces are uneven
- Installation is incorrect
Even small gaps create convection currents inside the wall, causing heat loss in winter and heat gain in summer. The result? Poor insulation performance and failure to meet SANS 10400-XA energy efficiency standards and increasing the operational costs of a building by adding to the HVAC load
Preventing Insulation Gaps
Even a 5 mm gap can reduce insulation performance, significantly impacting on comfort and energy bills.
To prevent this, use rigid, high-quality Isover glasswool insulation that fits snugly between studs. Products like Cavitylite®, Cavitybatt®, and CavityslabTM are designed for cavity walls in South Africa’s climate[NN3] . Their rigid structure or consider installation methodology, ensures a tight, continuous fit, eliminating gaps and improving thermal and acoustic performance. Proper installation also ensures compliance with SANS standards for energy efficiency and moisture control. Find helpful installation guidance here.
Conclusion
Efficient cavity wall insulation isn’t just about saving energy, it’s about comfort, durability, and long-term performance. By choosing Isover Cavitylite®, Cavitybatt®, or CavityslabTM, and following the correct installation methodologies you ensure a seamless solution that protects your building against energy loss, noise, and moisture for years to come.[NN5]