In an uninsulated building, the roof is the largest single source of heat loss in winter and heat gain in summer. That makes roof insulation one of the first upgrades worth getting right.
Since the updated SANS 10400-XA energy efficiency regulations came into effect in November 2021, new buildings and qualifying alterations must achieve a minimum total roof insulation (R-value). In most buildings, installing ceiling insulation is the simplest and most cost-effective way to comply.
How roofing R-values work
R-value measures thermal resistance, meaning how well a material resists the flow of heat. The higher the R-value, the better the insulation. It is expressed in m².K/W. Two figures matter for a roof:
- Product R-value: the thermal resistance of the insulation layer on its own.
- Total roofing R-value: the resistance of the full roofing assembly, including the ceiling board, the air space, the insulation and the roof covering.
SANS 10400-XA sets a minimum total roofing R-value. The insulation layer contributes most of that total. The rest comes from the ceiling lining, the enclosed air layers and the roof construction. In typical residential roofs this added contribution is often around 0.3 to 0.5 m². K/W, though the exact value depends on the roof assembly.
Required roof R-value by energy zone
The 2021 update replaced the old six climate zones with seven energy zones. The energy zones are set by how much heating and cooling energy a building needs to reach comfortable indoor temperatures, so they reflect real energy demand rather than location alone. The update also simplified the roof requirement. For a new building or a qualifying alteration, the minimum total roof R-value is now:
- 3.7 m². K/W across energy zones 1 to 7, which covers almost all of South Africa.
- 2.7 m². K/W in Zone 5H, the high-humidity coastal strip (the 85% humidity area) that includes Durban.
Find your location’s energy zone on the official SANS 10400-XA energy zone map. Durban, for example, falls in Zone 5H.
Knauf Insulation glass mineral wool compared to PET
Knauf Insulation Ceiling Roll is a glass mineral wool quilt made with ECOSE Technology, a plant-based binder. The PET products in our range, Fabufill LITE and JUMBO, are polyester quilts spun from recycled plastic bottles. Both insulate, but Knauf glass mineral wool separates itself in three areas: thermal performance per millimetre, fire safety and acoustic absorption.
Comparing a 100 mm layer, Knauf delivers a higher R-value at the same thickness, the best possible Euroclass A1 non-combustible fire rating per SANS 53501-1, and a measurable acoustic absorption rating.
The fire rating is the clearest difference. Knauf Ceiling Roll carries a Euroclass A1 non-combustible classification, the highest available. PET insulation products are combustible and generally achieve a Euroclass B or similar classification, depending on the product tested, so they contribute far less to fire safety than non-combustible glass mineral wool.
Glass mineral wool is also non-hygroscopic and rot-proof, and it will not sustain mould, fungi or vermin. When correctly installed and protected from physical damage and prolonged moisture, it is designed to hold its thermal performance for the service life of the building.
The Knauf Ceiling Roll range
Knauf Ceiling Roll is supplied uncut or combi-cut for joists at 750 mm centres and made with up to 80% recycled glass. The range covers every energy zone:
Installation matters
Glass mineral wool only delivers its rated R-value when it is fitted correctly. Because the quilt works by trapping still air, any gap, compression or cold bridge lowers the real performance of the roof. For best performance:
- Install insulation continuously with no gaps between adjacent rolls.
- Do not compress the insulation, as compression reduces its thermal resistance.
- Fit neatly around trusses, services and penetrations.
- Insulate ceiling access hatches.
- Maintain ventilation where the roof design requires it.
- Where a higher R-value is needed, lay the first layer between the ceiling joists and a second layer across the joists at right angles to cut thermal bridging.
- Keep insulation clear of recessed light fittings and other heat sources unless they are rated to be covered, following the manufacturer’s instructions.
Energy savings
Properly specified ceiling insulation reduces the energy needed to heat a building in winter and cool it in summer. By slowing heat transfer through the roof, it keeps indoor temperatures more stable, eases the load on heating and cooling systems, and lowers running costs over the life of the building.
Because glass mineral wool holds its performance for the life of the roof, those savings continue year after year, while the steadier temperatures and quieter interior add comfort for occupants.
The bottom line
Knauf Insulation glass mineral wool gives you a higher R-value per millimetre, a Euroclass A1 non-combustible fire rating and measurable acoustic absorption. For projects where all three matter at once, that is a combination conventional PET products cannot fully match.
Match the recommended thickness for your energy zone, then speak to the Pelican Systems team for a specification tailored to your project.
New to the range? Read our introductory guide, A Guide to Knauf Insulation High-Performance Glass Mineral Wool.
Ceiling insulation products, brochure and data sheets: https://www.pelican.co.za/product-category/ceilings/ceiling-insulation/