Ceiling Insulation done right: Learn more about required roofing R-Values. In an uninsulated building, the roof is one of the largest pathways for unwanted heat gain in summer and heat loss in winter, making roof insulation one of the most effective energy-efficiency upgrades.
Since the adoption of the updated SANS 10400-XA energy efficiency regulations in November 2021, new buildings and qualifying alterations must achieve minimum total roof insulation (R-value) requirements. In most buildings, installing ceiling insulation is the simplest and most cost-effective way of complying.
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 m²K/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 the total roof R-value. The remaining thermal resistance comes from the ceiling lining, enclosed air layers and roof construction. In typical residential roofs, this additional contribution is often around 0.3 to 0.5 m²K/W, although the exact value depends on the roof assembly.
Recommended R-value by South African climate zone
South Africa is divided into six climate zones. Each zone has its own minimum total roofing R-value. The table below maps each zone to typical areas and the Knauf Ceiling Roll thickness we recommend achieving it.
The example towns below are indicative only. Refer to SANS 10400-XA for official climatic zone maps
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.
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. It is designed to hold its thermal performance for the service life of the building when correctly installed and protected from physical damage and prolonged moisture.
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 climate 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.
- Ensure ceiling access hatches are insulated.
- Maintain ventilation where required by the roof design.
- 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 thermal performance, fire safety and acoustic comfort are all priorities, it offers a combination of properties that conventional PET insulation products cannot fully replicate.
Match the recommended thickness for your 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.
Link to website Ceiling Insulation products, brochure, and data sheets
https://www.pelican.co.za/product-category/ceilings/ceiling-insulation/
Keep insulation clear of recessed light fittings and other heat sources unless they are rated to be covered, following the manufacturer’s instructions.