How to insulate and air seal your home

Whether you’re trying to save money on your utility bill or control your house’s temperature, you can insulate and air seal your home with these three tips. You’ll need to air seal the “envelope” of the home, seal the ductwork and add attic insulation.  

These are the most common air leakage issues in American homes that can make a big difference with little investment. Here’s how to do all three. 

Air sealing the ‘envelope’ of the home 

First, you’ll want to start with air sealing the home. This will get you the most improvement with the least investment. And it’s crucial that you air seal the home before doing any insulation. Otherwise, you’re wasting your time. Fibrous insulation needs an air barrier to work as it was intended, which is why it’s recommended last. 

When talking about air sealing the “envelope” of the home, it’s important to note the way air behaves naturally in a building. The pattern of air in and out of your home is known as the “stack effect.” It essentially means warm air rises and cold air dives. So warm air leaves your home through the attic and cold air comes in through a crawl space, unfinished basement or other unconditioned lower part of your house.  

That’s why air sealing the higher and lower levels of your home, in combination with insulation, is one of the best ways to fight air leakage.  

When a window is drafty, it’s obvious to a homeowner immediately, but leaks in attics or crawl spaces are typically worse, but usually hidden from view. And these areas are going to be the most beneficial in working against the “stack effect.”  

You’ll want to air seal window trims, doors, vents, fireplace and furnace flues, and other things like pipes and wires that penetrate the “envelope” of the home.  

Windows will often have gaps around the trim and under the sill. To seal these, you can use a caulk gun. Cut the top of the tube of caulk at a 45-degree angle. Use the pin underneath the gun to break the seal and place the tube into the caulk gun. Position the caulk gun and press the trigger as you go along the frame. The 45-degree angle allows the tip to shape the bead of caulk into a neat line as it’s applied, but it still might need some touching up. You can do this easily with your finger. And don’t worry, the caulk rinses off easily with water. 

You can also use the caulk gun for areas like a bathroom exhaust fan, floor supply vents and any other crevices. But as far as air sealing a flue, you want to make sure to use a fire rated caulk instead for areas that are more combustible to ensure fire safety. And before you air seal a flue, make sure the furnace is off and there isn’t a fire going/you’ve let it cool off enough.  

Now, to air seal the front or back door frame, you can add a weather strip. These doors can have a little gap between the door and the outside that’s letting not only light to shine through, but air to come in. You can pick up a weather strip kit that comes with everything you’ll need.  

First, you’ll need to remove any old existing weather strip from your door frame. Then you can install the new weather strip. It’s easier to start with the left and right side of the frame first and then pressure fit the top. You’ll need to measure the side of your door frame and cut the weather strip to fit. And when you cut it, make sure to cut it from the metal side — you’ll get a cleaner cut. 

Close the door and make sure it’s locked before you install the weather strip. If it’s not locked and you install the weather strip too close, you could put a lot of tension on the lock and it could break or come out of the wood. 

Line up the weather strip tightly on the side of the frame, but don’t press too hard against the door. Using a drill, put the first screw in the middle, then do the top and bottom next. Now do the same steps for the other side — and again for the top. 

Now, for awkward areas where there’s a bigger gap or wires in the way, you can air seal these areas with can foam. It’s easier to just spray the foam in these openings and let it expand.  

To use the can foam, attach the nozzle to the top and handle with care. This will not come out of your clothes or carpet. 

Again, leaks in your attic or crawlspace are the most important areas to address. So you can spray the can foam on the openings around pipes and vents and the crevices in a crawlspace and on the tops of the interior walls in the attic. If you have an unfinished basement instead of a crawl space, you can use caulk or can foam to air seal the rim joist and sill plates. 

Sealing the ductwork 

Moving on to the ductwork. If your ducts are leaky and in a space without air conditioning (like a crawl space, unfinished basement, cellar, attic and so on) you’ll literally be heating or cooling the outdoors. So when you seal it, more of the heat/air conditioning that was intended for your home will make it inside.  

Not only that but sealing your ducts will also improve your indoor air quality. If the duct is leaky, it could be pulling in dirt, dust, mold and possibly radon from outside. Sealing the ductwork allows the duct to only suck from air that’s already in the house.  

To seal the ductwork in a lower space without air conditioning, you can use a mastic sealant. Mastic is good for sealing the joints of the ductwork because it’s fluid and can get into hard-to-reach areas. It’s also flexible in that it will withstand expansion and contraction due to temperature changes. 

This part is easy. With a rubber glove, you can literally dip your hand in the bucket of mastic and spread it along the seams, joints and holes of the metal ductwork. Just be careful, as metal ductwork can have sharp edges. 

Adding attic insulation 

And last but not least, you’ll want to insulate your attic space. As previously mentioned, if you insulate your attic before air sealing the attic floor, it will have a minimal benefit.  

When talking about insulating the attic space, it’s important to note that the insulation and air barrier should be continuous and contiguous (meaning they touch). The continuous part is that it’s more effective to have 6 inches of insulation everywhere rather than 10 inches of insulation in a concentrated spot. The contiguous part is wherever drywall is, insulation should be touching it. If it’s not touching (for example, if the insulation is on top of wires and not underneath them), the insulation will do nothing.  

Another thing to note is that you want to make sure there’s no air gap between the layers of “batts”, which are the strips of insulation.  

In other words, you want the insulation to be the same depth as the joists, if you’re using batts and not loose-fill (or blown) insulation, because otherwise there will be an air gap when you add the second perpendicular layer of insulation.  

If the depth is lower than the joist, there will be an air gap from the second layer; if the depth is higher than the joist, there will still be an air gap from the joist to the second layer. Only the first layer needs to be the same depth, though, the second perpendicular layer can be thicker. 

And the first layer needs to be as thick as necessary depending on the Energy Star recommended R value for your geographical location. The R-value is a measurement of how effective a material is in preventing heat loss. The higher the R-value, the better. 

Keep in mind, when insulating your attic, you want to make sure you’re wearing protective equipment and cover your skin to avoid breathing in dust and fiberglass or getting it on your skin. 

First, you’ll need to clean out the joist bay so the insulation can sit completely flat. Then put a batt of insulation in the bay and cut the length so it fits snugly. Try to cut the batt as perfectly as you can, but it’s okay if you mess up — as long as you fill the bay’s depth evenly with insulation.  

Then add the second batt layer perpendicular over the joists, so that the wood is also insulated and not just the bay. 

Energy audit and the Weatherization Assistance Program 

These tips can help minimize the air leakage and cold spots in your home. But if you do want a more in-depth professional opinion before attempting some of these methods, you can get an energy audit done to your home to see what specific areas your house is lacking in terms of energy efficiency.  

Also, the US Department of Energy has a Weatherization Assistance Program at the state and local level if you qualify as low income, over the age of 60 or are part of a family with disabilities. You can check with your local utility company for more details.