How Much Insulation Should You Use?
Last Updated: Feb 11, 2025Research by the North American Insulation Manufacturers Association (NAIMA) estimates that roughly 90 percent of existing US homes are under-insulated. Improved energy-efficient construction techniques are increasingly available to builders and contractors. But, it is, unfortunately, safe to assume that many new builds continue to be under-insulated. Air leaks around window and door frames and older, single-pane windows can amount to about 25 percent of all heat loss in homes. The remaining 75 percent of unwanted heat loss and heat gains driving up your energy bills are mostly attributed to insufficient insulation in your home's walls, attic, roof, and foundation.
So how much insulation should you ideally use in your new home or renovation? This short article will start by looking at the minimum amount required by local building codes - depending on your house's location and climate. We will then turn our attention to the insulation used by high-performance homes that meet the highest sustainable building standards.
Table of Contents
- Important Insulation Terminology
- What is R-Value?
- What is U-Factor?
- What is RSI?
- Effective R-Value vs. Nominal R-Value
- What is Nominal R-Value
- What is Effective R-Value?
- How Much Insulation Do I Need at a Minimum?
- How Much Insulation Does A High-Performance House Need?
- How Much Insulation Does a High-Performance House in a Moderate Climate (Zone 5) Need?
- How Much Insulation Does a High-Performance House in a Cold Climate (Zone 6) Need?
- How Much Insulation Does a High-Performance House in a Hot Climate (Zone 8) Need?
Important Insulation Terminology
Before we look at the exact amount of insulation required for specific climate zones, understanding the basic terminology related to insulation will help us better understand what we are looking at.
What is R-Value?
The R-value of different insulation materials is a rating of an insulation product's effectiveness as determined by its thermal resistance or insulation value. The higher the R-value, the more insulated the home will be. R-value is measured by Imperial units and is the most common rating of insulation used in the United States and even some 'metric' countries like Canada. You can find a helpful chart showing the estimated R-value per inch of a wide range of common insulation materials here.
What is U-Factor?
The U-factor, also known as the U-value, is a rating you'll more often see on windows or doors, and it's essentially the opposite of an R-value. It is a measure of how fast heat will transfer through the product. For U-factor, lower is better. Check out this Rise energy-efficient windows buying guide for a more in-depth analysis of the U-factor for windows.
What is RSI?
RSI is the same concept as R-value but in metric units. To convert an RSI value to an R-value, multiply by 5.678. Again, the higher, the better. You can expect to find RSI units for products made in the United Kingdom, Australia, or New Zealand. Knowing how to convert this measurement can help make sure you are purchasing insulation products that will maximize your home's energy efficiency and thermal performance.
Effective R-Value vs. Nominal R-Value
There is an essential difference between effective R-value and nominal R-values to make things even a bit more confusing.
What is Nominal R-Value
The nominal R-value is the insulation value (R-value) of the insulation layer only. For example, a 6-inch layer of mineral wool insulation batt has a nominal R-value of R-24.
What is Effective R-Value?
The effective R-value is the insulation value of that part of the building when it's fully assembled.
This measurement considers the R-value of all the different materials that go into the total wall construction, including wood, concrete, drywall, siding, etc.
For walls with framing extending from the exterior to the interior, the effective R-value is lower than the nominal R-value because heat is lost through the uninsulated frame, a process called thermal bridging.
Consider the example above. A 6-inch wood stud wall with mineral wool insulation in the cavities has an effective R-value of R-20 instead of the R-24 of the insulation itself. It is essential to discuss the difference between effective R-value and nominal R-value with the contractor you hire. This way, you will make sure that they minimize thermal bridging during the construction or renovation process.
When talking about a material's insulation value, people usually mean the nominal R-value, but that is not always the case. It makes the most difference when you consider walls with a 'thermal break,' a continuous layer with no thermal bridges. These walls have a higher effective R-value than walls without a thermal break. To optimize your home's energy efficiency, you should also consider all the insulation and other structural components' interactions. This method is known as the whole-house systems design approach. According to the US Department of Energy, "this approach considers the house as an energy system with interdependent parts, each of which affects the performance of the entire system. It also takes the occupants, site, and local climate into consideration."
Here are three examples from different climate zones to illustrate how much insulation is used in super-efficient homes.
For every part of the home, Claire has insulated to levels more than double the minimum required by code. By doing this, she has a dwelling that practically heats itself and only needed a minimal and low-cost back-up heater.
How Much Insulation Does a High-Performance House in a Cold Climate (Zone 6) Need?
This home is named the Naugler House and is located near Fredericton, New Brunswick, Canada, and is considered the most energy-efficient home in that province. It's in a cold winter climate zone (zone 6) and was built to the Passive House standard. Here's how the insulation stacks up against the energy code for the area.
Once again, all the home's surfaces are insulated to more than double the minimum R-value required by code. The floor slab is exceptionally well insulated, keeping it the same temperature as the rest of the house, making it pleasant to walk on. The attic was designed with lots of space for insulation, so it was easy and affordable to pile it up to R-100. This entire home is heated with a single electric heater, the size of a large toaster, installed in the air supply duct. Avoiding paying for a regular furnace made up for a lot of the cost of the extra insulation.
Tobias Roberts
Tobias runs an agroecology farm and a natural building collective in the mountains of El Salvador. He specializes in earthen construction methods and uses permaculture design methods to integrate structures into the sustainability of the landscape.
