The Difference Between Nominal Insulation And Effective Insulation

For as long as I can remember we have talked about the R value of the walls and ceiling inside residential homes. Decades later we still discuss R value with people because that's what they understand when you are talking about the insulation that goes in the walls and ceilings of homes. Even the building code in Ontario only talked about R value when making the minimum limits for insulation in homes.

Well as the building code is going through an ever changing climb with regard to the rules that govern insulation levels and the air tightness of homes everyone needs to start talking a different way.

Contractors who understand this are now starting to talk to people in a different way, instead of talking about R value of the walls we are now trying to talk to people about effective R value. The old way of talking about R value in walls is considered Nominal R value. Nominal R value refers to the labels or rates that are given to the insulation that you install in the walls or ceilings.

Effective R values are different they take into consideration the thermal bridging that is in the walls, thermal bridging in walls and ceilings are usually the wood framing that creates paths were the air can move through the wall because there is no insulation to stop it.

Now you know the difference but as the homeowner how does this actually affect you and your home? Well if we take the 2016 Ontario building code it stats that your exterior wood framed walls are to have a nominal R value of R-24. That can be achieved by simply installing a r-24 fibreglass batt inside the 2x6 wall cavity. But it you look at that same walls effective R value it is actually down around R-17, that's because of all the thermal bridging that is in the wall cavity from the wood studs.

The 2017 Ontario building code has the same R-value for the exterior walls but they have made one big change and that is that you must have continuous insulation placed on the outside of the wall that is made of polystyrene insulation if you are looking to install the minimum building code. This continuous insulation layer covers all the thermal bridging in the wall effectively insulating the entire wall. You can expect that the R-value of the wall should be what you want it to be, if you are trying to achieve R-24 then with a continuous insulation layer that's what you would end up with an effective R value of R-24.

Effective R values are a more effective way to achieve homes that are sealed against the outside elements, helping reduce the heating and cooling costs and stop wind wash from affecting the inside temperature of the home.

So the next time you talk about R values with your contractor or if you are a contractor then you should be talking about the effective R value and not just the nominal R value. It might take a little educating on your part but it will be worth it in the end.

Rob Abbott
Village Builders Inc.