Dispelling the Myths About Insulation
Adding insulation to a cavity wall is a relatively new concept , driven by the SANS-10400-XA regulation . In the first of two features , Suria Ramnarain , Sales Development Manager at Knauf Insulation sets the record straight about some misconceptions surrounding cavity wall insulation and insulation in general .
MYTH : You only need a cavity ;
adding insulation makes properties unbearable in hot weather TRUTH Many people believe insulation should not be installed in warmer climates because properties will overheat , but actually , insulation will help keep them cool .
Heat always flows from warm to cool areas . Mineral Wool insulation has a low level of conductivity , so in cold weather , it prevents heat from escaping through a building ’ s walls and roof . But equally , in hot weather , insulation keeps an airconditioned home cool and slows down heat gain in homes without AC , making the internal temperature more pleasant . Remember , if insulation didn ’ t stop heat gain , your refrigerator wouldn ’ t stay cold !
And because it helps maintain a stable indoor air temperature , less energy is needed to cool or heat a property , leading to lower energy bills .
MYTH You can only partially fill a cavity with insulation TRUTH In fact , fully filling a cavity with Mineral Wool insulation can give better real world thermal performance than partially filling it with products with higher declared performance values .
This is because Mineral Wool has been manufactured to fit between standard centres for brick ties and brick force . It compresses slightly during installation then springs back to create a tight fit inside the cavity . Mineral Wool adapts to any imperfections in the substrate , such as mortar snots or protruding brick force , and insulation knits together filling gaps and preventing thermal bridging .
By contrast , rigid insulation boards are harder to install correctly . Substrate imperfections cause boards to pivot , breaking contact between the insulation and substrate or between boards . This creates air gaps , reducing thermal and acoustic performance .
When using Mineral Wool in a cavity wall , look for products developed specifically for external applications , such as our DriTherm Cavity Slab . It contains water repellent additives , so if any water enters the cavity it will not transmit across to the inner leaf or affect the slab ’ s performance . Remember , not every product with ‘ cavity ’ in its name is appropriate for the application .
Fully filling a cavity with unfaced Mineral Wool also improves fire safety . It is non-combustible with the highest possible Euroclass A1 Reaction to Fire Classification rating , so will not contribute to the development or spread of fire should it occur .
Insulation prevents heat loss in cold weather and heat gain in hot weather
MYTH All thermal measurements are the same TRUTH In South Africa , the thermal conductivity , known as the R-value , of an insulation product is determined using Standard Thermal Measurement , which calculates the median ( middle ) value from tested product samples . This means 50 % of the products purchased could have a performance value under the declared lambda and 50 % could be over . So , half the time , customers don ’ t get what they pay for .
By contrast , the European Lambda 90 / 90 Value guarantees 90 % of a manufacturer ’ s insulation will meet or exceed the declared lambda value 90 % of the time . Knauf Insulation only uses Lambda 90 / 90 Value , so customers can be confident our products will perform as required .
MYTH Insulation can be specified by density or thickness TRUTH Density refers to how much insulant there is in a cubic metre of a product . The more material there is , the higher the density , but density doesn ’ t actually reflect thermal , fire or acoustic performance so you could easily be under or over-specifying .
Similarly , thickness is not a good measure , because you won ’ t be comparing like-for-like . Different insulants are made from different materials so even if they are the same thickness , they won ’ t provide the same level of performance . But even products manufactured from the same material will perform differently depending on the applications they are designed to insulate . For example , both Ceiling Roll and Cavity Roll are manufactured from Glass Mineral Wool , but 100mm of Ceiling Roll has an R-value of 2.4 while 100mm of Rafter Roll has an R-value of 2.63 .
Therefore , insulation must only be specified by performance measures such as R-value , fire safety or acoustic performance , or a combination of all three . This ensures you ’ re choosing insulation for the performance it delivers , not any other arbitrary measure that may lead to underperformance or unnecessary extra cost .
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