There’s a big difference between a system and a product R value. A product R value is a measure of the thermal resistance of the product itself whereas the system (or total) R value is a calculation of the performance of the entire system when the product is installed and takes into account all the building products in the system.
The important thing to note here is that simply adding a product to a system doesn’t add that product’s R value to the total R rating.
For example, adding R6 batts to a ceiling does not increase the system R value by R6. There are a number of factors come into play, especially the type, size and spacing of the timbers in the system as these contribute to the reduction of the total R value through Thermal Bridging. When working out what insulation to add to a ceiling, wall or floor, we focus on the impact on the system R rating rather than focusing on the R value of the product itself.
Our installation guide goes in to more detail about R values and how to achieve the best system R value in your home. If you haven’t done so already, download a copy below.
Need to find out more? Get all the information in our installation guide