5 Insulation Mistakes to Avoid

Updated: Oct. 23, 2023

Insulation keeps your home the temperature you want — as long as it's installed correctly. Here are five common insulation mistakes to avoid.

Properly insulating a home is one of the most efficient ways to lower your energy costs. According to an Environmental Protection Agency (EPA) review of the average U.S. household, a knowledgeable homeowner can save up to 20 percent on heating and cooling costs simply by properly sealing and insulating their home.

The trick, of course, is being knowledgeable! Insulation is a full trade in itself, and it takes time and practice to master the skills involved. However, you can get a great start by simply avoiding some of the most common mistakes that can sabotage an insulation project.

Here are five common mistakes to avoid when insulating your home.

Neglecting to Air Seal

Insulation is a barrier that slows the rate at which heat enters or leaves the home. But it’s not necessarily a barrier to air movement. That unchecked air between unconditioned and conditioned spaces can undo all the hard work that goes into installing insulation.

Seal off areas around windows and exterior doors with caulk. In an unfinished attic, look for penetrations from electrical wires, bathroom fans and lights. Use fireproof caulk to block the air flow, and let your insulation do what it does best.

Blocking Air Flow

We just talked about sealing up air flow from inside the house, but another common mistake when insulating an unfinished attic is obstructing the airflow intended for roof ventilation. Many homes have soffit or wall vents designed to allow air to enter the attic and pass out through vents on the roof. This air flow prevents humidity issues in the attic and lengthens the life of the roof.

This is especially common with soffit vents, as they can be easily overlooked when insulating an attic. A great way to avoid this misstep is to use vent baffles — pre-shaped channels designed to allow air to move freely from soffit to roof vent. (One example is this Durovent Rafter Ventilator 70-Pack.)

Spending Time and Money Pulling Out Old Insulation

Many DIYers begin an insulation install by pulling out old insulation. It’s a reasonable assumption, but it makes a huge mess and is often more aggravation than it’s worth.

The first thing to consider is the age of your home. In the 1950s and ’60s asbestos was commonly used in blown-in insulation. Asbestos is safe when left alone but can be extremely hazardous if disturbed and kicked into the air. Similarly, vermiculite was used as insulation in many attics into the 1990s. Although not hazardous on its own, most vermiculite was sourced from a mine contaminated by asbestos.

If you suspect your attic may have these materials, it’s vital to do your research and consult an expert before proceeding. A good starting point are these EPA overviews on asbestos and vermiculite.

Once you’re comfortable that there’s no asbestos risk, asses your existing insulation. Old insulation is a little like a threadbare blanket: It may have holes and tears, but it doesn’t hurt anything and will still help keep you warm when you wrap yourself in a new layer.

That doesn’t mean all old insulation is good. To continue our metaphor, if that old blanket is soaking wet or moldy, it’s not worth keeping. If your standard insulation has gotten wet from a leak or has evidence of rodent activity, then it’s worthwhile to pull out that section and start fresh.


If a little fiberglass insulation is good, then cramming in as much as you can is even better, right ? Unfortunately, it’s not that easy.

Fiberglass insulation functions because the fiber threads create countless tiny air pockets. Those pockets are what slows temperature change, not the fiberglass itself. When you pack in and compress fiberglass insulation, those air pockets are squeezed shut, making the fiberglass insulation less effective.

Stopping Short

Lastly, the most common mistake made by DIYers when insulating is not being thorough enough.

As we mentioned above, insulation is a separate trade all of its own. It may seem simple to throw up a few batts of insulation, but it actually takes a fair amount of precision and thoughtfulness to make sure that the insulation creates a solid barrier.

An insulation job that leaves gaps and holes is better than nothing, but it won’t come close to the energy efficiency increase you can see from a properly done job. So take your time, and check in with resources like Family Handyman to make sure you’re getting the job done right.