When building a new home, investing in insulation is one of the best ways to decrease your energy consumption and save money far into the future. Talking about insulation may not be an especially exciting topic in residential construction, but is one of the most important subjects to understand because choosing the correct amount and placement of insulation will directly affect the physical and financial comfort of you and your family.
Insulation has one of the fastest payback times of all investments you’ll make in your new home. The savings can be so great that you can often recover your initial investment in just a few years. So if you can afford it, add the maximum amount of insulation recommended for your home design and region. We’ll talk about some general recommendations for insulation in just a minute. And over the next few weeks, we’ll learn about some specific types of insulation that are commonly used in residential construction, including spray foam insulation, rigid foam board insulation, batt and blanket insulation and blown-in cellulose.
Before we delve into a basic overview of how and where to insulate, let’s talk about
R-value and U-value, our Pro Terms for this week. I’ve mentioned R value in previous episodes, but today I want to define it in more detail.
R-value is the measure of a material's resistance to heat flow. R-value is one the main characteristics that distinguishes different types of insulation. The higher the R-value, the more resistant a material is to heat flow, meaning it’s resistant to heat gain and heat loss. So the higher the R-value, the better.
The R-value is determined by the type of insulation, its thickness, or how many inches you install, and its density, meaning how compact or solid the material is. When calculating the R-value of an area with multiple layers, such as a home’s wall, the first step is to add the R-values of the individual layers together. For example, the R-values of the exterior siding and sheathing, the wall insulation and the drywall. This is the first step in determining overall R-value. But getting to the overall R-value of a wall or ceiling is more complicated than simply adding together the R-values of all the layers of insulation.
As you know, insulation is added along side wall studs, joists and other structural building materials. Those building materials are thermal bridges, which allow for unwanted, increased heat loss or gain. Because of those thermal bridges, the R-value of a wall system is usually less than that of the R-value of the insulation itself.
While R-value is used to express the energy efficiency of walls and ceilings, U-value is usually used to express the energy efficiency of doors and windows. U-value is the measure of heat flow through a material. And remember, heat flow through a home’s structure a bad thing and we don’t want a lot of a bad thing. So, the lower the U-value, the better.
The U in U-value is the symbol for internal energy. But that doesn’t help me remember what U-value is. So I think of U value like this: the U-value is the measure of unwanted, unobstructed heat flow. It’s kind of the opposite of R-value.
So, our pro terms this week are R-value and U-value. R-value is a material’s resistance to heat flow. The higher the R-value the better. U-value is unwanted, unobstructed heat flow and lower the U-value the better.
Up next is this week’s mini lesson— an overview of how and where you should insulate. This information will help you understand what you should be asking for from your insulation subcontractors. But remember that building codes will vary from region to region, so double check information with your building inspector or home energy rater. Let’s start the lesson by talking about the main reasons insulation is needed in the first place— heat loss and heat gain.
Heat is always on the move. Heat flows from warmer to cooler until there is no longer a temperature difference. So in the summer, heat likes to move from outside, to the cool, air-conditioned inside. This is called heat gain. And the opposite is true in the winter. Heat generated by your heating system wants go from the inside to the outdoors. This is called heat loss.
Heat can move through the walls, windows, the foundation and the roof. Heat can also flow from heated spaces inside the home to adjacent unheated attics, garages, and basements.
To maintain a comfortable indoor environment, the heat lost in the winter must be replaced by your heating system and the heat gained in the summer must be removed by your air conditioning system. The goal of insulation is to stop, or greatly decrease heat gain and heat loss. Insulation can significantly slow the rate of heat flow — which influences the comfort of your family and the amount of your utility bills.
The savings that you can see in your utility bills depend not only on the type and amount of insulation chosen, but how well it’s installed. The home’s building envelope should be insulated continuously, without gaps. But keeping the insulation continuous is challenging since there are numerous openings in the building envelope, including windows, doors, electrical outlets, and pipes. To make the insulation continuous, all gaps or openings need to be sealed. The effectiveness of whatever insulation you choose will be significantly decreased if heat is able to escape around openings.
To keep heat from escaping, you need to properly air seal your home. There are two simple, cost effective ways to air-seal your home: caulking and weatherstripping. Caulking is usually done for cracks and openings between stationary house components, such as around door frames and window frames. Weatherstripping is used to seal house components that move, such as doors and windows that open and close.
Not only should you caulk and seal windows and doors, we should also caulk and seal gaps where plumbing, ducting, or electrical wiring come through walls, floors, and ceilings. Gaps around fireplace chimneys, furnaces, and water heater vents should be sealed with fire-resistant materials such as sheet metal and furnace cement caulk.
For optimal energy efficiency, you should air seal your home, plus you insulate it from the foundation to the roof. State and local building codes typically include minimum insulation requirements, but if you want a really energy-efficient home, you’ll most likely want to exceed the minimum requirements. The US Department of Energy has specific guidelines for different regions of the United States. I’ve attached a link below that will detail their recommendations.
You may even what to exceed the recommendations of the Dept. of Energy if your goal is to build an exceptionally energy efficient home. For example, the Dept. of Energy recommends attic insulation with an R-value between R-30 to R-60, but those who want to shoot for the Passive House standard will need attic insulation between R-60 and R-90.
Pop Quiz: Do you remember what the Passive House standard is? We talked about Passive House in episode 10, when I interviewed Ben-Adam Smith about Energy Efficient Building Practices… Well, Passive house is a strict, voluntary building standard of energy efficient construction that results in homes that require very little energy for heating or cooling. So, if you want to build to Passive House standards, you need to exceed the R-value recommendations of the US Dept. of Energy. Keep in mind, though, it may be many years before you recoup your investment in such high levels of insulation. Make sure that investing in that amount insulation makes sense in light of how long you plan to live in your house.
One of the most important parts of the house to insulate is the attic. Whether you are in a hot or cold climate, the US Dept. of Energy recommends that the attic get more insulation than any other part of the house.
In unfinished attic spaces, insulate and air seal any knee walls, which are short, vertical walls in the attic that help support the roof.
In addition, make sure that attic flooring is raised high enough above the ceiling joists to leave room for adequate insulation. Insulate your roof, especially if you have to locate your air distribution system or any HVAC components in the attic. If you live in a hot or warm climate, consider installing a radiant heat barrier in your attic to reduce summer heat gain. Finally, don’t forget to insulate and seal your attic access door.
In finished attics, additional insulation should be added between the wall studs and roof rafters, plus the attic ceiling should be insulated.
Now what if you have cathedral ceilings?
If your home has cathedral ceilings instead of a flat ceiling with an attic space, you’ll have different R-value recommendations than for an attic space. Properly insulating cathedral ceilings helps ceiling temperatures remain closer to room temperatures, instead of being a hot spot.
There must be enough space between the roof deck sheathing and home’s ceiling so adequate insulation can be installed. This can be achieved through the use of roof trusses, or sufficiently large rafters. For example, cathedral ceilings built with 2x12 rafters have enough space for standard 10-inch batts (R-30) and ventilation.
So ducts need to be insulated? No, not if they are placed in insulated, conditioned spaces. Putting ducts in conditioned spaces helps decrease the energy losses associated with most duct systems. You can get ducts in conditioned spaces by making your attic a conditioned (insulated) space and putting ducts there. Option 2 is the lower your ceiling some and putting ducts right below the attic, and option 3 is to put ducts between floors in a 2 or 3 story house.
Moving on to exterior walls. All exterior walls should be insulated, including walls next to unheated garages, above ground foundation walls, and foundation walls in heated basements.
If you are still designing your home, you might want to consider wall systems that combine insulation with the homes structural elements. These include structural insulated panels (SIPs), insulating concrete forms (ICFs), and insulated concrete blocks. These materials are extremely energy efficient, but also expensive. We’ll talk more about these options in the future.
If you’re building a traditional stick framed house, the Dept. of Energy suggests that you consider using advanced framing techniques. Advance framing improves the R-value of the whole wall by decreasing thermal bridges and increasing the space available for installing insulation. You can hear more about advanced framing in episode 16.
For the exterior of your house, you might also consider using insulating wall sheathing, instead of wood sheathing products. So, instead of using OSB for your wall sheathing, look into rigid insulating foam sheathing. The foam sheathing will provide a higher R-value than OSB and the thicker foam board you use, the higher the R-value you can achieve.
When should floors be insulated?
Insulate floors above unconditioned spaces, such as floors over a garage or cantilevered floors. If you have a room above your garage, you’ll also want to seal all possible sources of air leakage, not only to help with energy efficiency, but to keep dangerous garage fumes from getting into the home.
Moving on to foundations. A properly insulated foundation will keep basement rooms, and the home in general, more comfortable. Plus, it helps prevent moisture problems.
During the construction process, many builders think that backfilling the outside of foundation walls is adequate insulation. Pop Quiz: Do you remember the term Backfill? It was our Pro term is episode 13, called “How long does it take to build a house? What happens and when?” Backfill means to return soil and other materials to a hole— in the case of a foundation, it’s returning soil back around the foundation wall. Backfilling alone is not the most energy efficient strategy for insulating a basement.
With basement foundations, adding insulation on the exterior of the basement walls will: decrease thermal bridging and associated heat loss, protect its damp-proof coating, and reduce the potential for condensation on surfaces in the basement.
Optimal foundation insulation materials and placement vary by climate, so consult a local insulation professionals or home energy rater when designing your new home.
If your plan calls for an unventilated crawlspace, you should consider sealing and insulating foundation walls rather than the floor between the crawlspace and the house. The advantage of this is it keeps pipes and ductwork within the conditioned space of the house. Then those building components won't require insulation for energy efficiency or protection against freezing. The downside of this strategy is that rodents, pests, or water can damage the insulation and the crawlspace must be built airtight.
For a ventilated crawlspaces, add insulation between the crawl space and the floor above.
Concrete slabs can be a huge source of discomfort in a home, especially in cold climates. An insulated slab is easier to heat.
Slab insulation, typically foam board, is installed either directly against the exterior of the slab and footing before backfilling or under the slab and along the inside of the stem wall of the foundation.
Some foundation insulation may be prohibited in termite prone regions. Termites can tunnel undetected through exterior slab insulation to gain access to the home's wood framing. As a result, some insurance companies won't guarantee homes with slab insulation against termites. Because of potential termite damage, building codes in several southern U.S. states prohibit installing foam insulation in contact with the ground.
Well, that’s the basic overview how and where to install insulation. In the next several weeks, we’ll cover the specific types of insulation you’ll have to choose from.
Ok, let’s do a couple of quiz questions.
1. True or False. The R-value is a measure of unobstructed heat flow.
The answer is false. R-value is the measure of resistance to heat flow and usually relates to the energy efficiency of walls and ceilings. The U-value is the measure of unobstructed heat flow and usually relates to the energy efficiency of windows and doors. The higher the R-value the better and the lower the U-value the better.
2. What are 2 cost effective methods that you can use to air seal your home?
The answer is chalking and weatherstripping. Caulking is used on stationary components such as door frames and weatherstripping is used on movable components, such as doors.
3. What part of a house does the US Dept. of Energy recommend get the highest R-value insulation?
A. the foundation
B. the walls
C. the attic
D. the floors
The answer is C, the attic. The US Dept of Energy recommends that insulation with the highest R-value be installed in the attic. Depending on what part of the country you’re in, they recommend R-values between R-30 and R-60.
How you’d do? Well, I hope you learn as much as I did.
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Please remember that the purpose of this podcast is simply to educate and inform. It is not a substitute for professional advice. The information that you hear is based the only on the opinions, research and experiences of my guests and myself. That information might be incomplete and it’s subject to change, so it may not apply to your project. In addition, Building codes and requirements vary from region to region, so always consult a professional about specific recommendations for your home.
Thanks for spending some time with me today. Come back next week for another episode of Build Your House Yourself University (BYHYU). Enjoy the rest of your day.
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