R-Value — Contignum

When people talk about sustainability in renovation projects they will often say “I increased the R-Value of my house”. But what does this really mean? What does an R-Value really indicate? Why is it important? How do we get a wall assembly to be highly insulative? And how do we ensure the effective R-Value of the wall assembly is not compromised during construction or the life of the house?

What is an R-Value?

The R-Value of a material indicates that material’s resistance to conducting heat. Thus, the higher the R-Value, the more insulating the material. Since the R-Value is in fact calculated by dividing the thickness of the material by the conductivity of the material, the thickness of the material is a very important factor. Your drywall (gypsum board) for example has some insulative properties. If the drywall used is 9.5mm then the R-Value is 0.06 m2⋅K/W. However, if the drywall is 12.5mm, then it will conduct less heat and have a higher R-Value of 0.08. Now, this of course does not compare to the R-Value of insulation, which is more in the neighbourhood of 1.90 to 8.0 per inch.

Getting the Required R-Value

If drywall and insulation have varying R-Values that are much lower than the building code requirements, then how do we get the required R-Value? We get it through the wall assembly. Your project consultant will be able to design a wall assembly that looks similar to the one you see here. They will then look at the R-Values for all of the materials and add them up together to get the effective R-Value. A good consultant will use their Building Science knowledge to combine the right materials and design the best wall assembly with a high R-Value. In fact, they might even be able to specify materials that will get you to an R-Value greater than what is required by the building code.

Risk factors: Thermal bridging

The challenge with wall assemblies is to watch for thermal bridging. Thermal bridging occurs when there is a part of the wall assembly that makes contact with the exterior and interior of the assembly, conducting heat away from the house. The most common source of thermal bridging in a wall assembly is the wooden studs used to hold the drywall and fiberglass insulation in place. If there are any thermal bridges in the wall assembly, the insulating properties of the wall are greatly reduced, regardless of the effective R-Value calculated.

Good design and construction are key

Thermal bridging must be prevented by using thermal breaks. In the scenario of the fiberglass insulation and studs, the studs could be covered with continuous insulation. The good news is: with all the advancements in construction technology, there are now many solutions to assist in achieving high R-values, with effective thermal breaks or low conductance materials to prevent thermal bridging.

The challenge, now that you’ve gone through all the effort of creating a good design, is to ensure the construction workmanship. High-quality workmanship is crucial in order to guarantee that thermal bridges aren’t present, the wall assembly is built as required, and that there are no gaps that may lead to a decrease in the effective R-Value of the wall.

Ready to start your project?

Let's chat!