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Can You Lay Insulation Over Electrical Wires in an Attic?

Laying insulation over the electrical wire is a subject that is often debated. When it comes to an attic, it is even more important to get it right. For instance, the wrong type of insulation or improper installation might cause a fire. So, can you lay insulation over electrical wires in an attic safely?

Yes, you can lay insulation over electrical wires located in the attic. You can also lay insulation around junction boxes. However, guarantee that the insulations are made of fiberglass and should be fireproof. These insulations shouldn’t reduce airflow from the home to the attic.

I’ll cover more of this matter in the following article.

Things You Should Know about Insulation Over Wire in an Attic

Depending on the type of insulation, you can decide whether you can or cannot lay insulation over wires.

For instance, the insulation you plan to lay on the attic should be non-flammable. That is why the insulation made from fiberglass is most suitable for this kind of job. Apart from that, the chosen insulation shouldn’t reduce the airflow from the home to the attic.

Cellulose fiber is one of the most popular insulations people use for attic insulation. However, they are made from recycled paper, which can be flammable in suitable conditions.

Modern fiberglass insulation comes with a vapor barrier.

You can find this barrier on one side of the insulation, which is made of paper. The vapor barriers always go to the warm side of the attic. Check out the above image.

However, the vapor barriers should point in the other direction (up) if you use air conditioning at your house.

You can also use polyethylene vapor barriers.

What is a Vapor Barrier?

A vapor barrier is a layer that prevents moisture from damaging the building structure. Polythene sheeting and foil sheeting are the most common vapor barriers. You can install them on the wall, ceiling, or attic.

Insulation Around Junction Boxes?

Also, most people think they cannot install insulation around junction boxes. But when you use fiberglass insulation, you can lay it around the junction box without any worries.

Quick Tip: However, you cannot put insulation if the junction box is a heat source. Remember, you don’t want an electrical fire in your attic, So avoid such things.

R-Value for Insulations

When talking about insulation, I cannot leave out the R-value of the insulation. You probably heard about that. But do you know what the meaning of it is?

In construction, the R-value represents the capability of resisting heat flow. It could be insulation, a wall, a window, or a ceiling; the r value can affect their lifespan.

Regarding the R-value of insulation, the following bullet points might help you.

  • Use R-13 to R-23 insulation for exterior walls.
  • Use R-30, R-38, and R-49 for ceilings and attics.

What Type of Electrical Wiring Should I Use for an Attic?

wiring inside a box
Video | Southwire

You’ll be surprised to hear that insulation type is not the only factor that affects attic insulation. The wire type plays a significant role, too.

The best choice for attic electrical wiring is non-metallic cable (NM cable). This wire type is allowed in most US areas. So, remember to discuss this matter with your contractor (if you are building a new house). Or contact a professional electrician if you want to check your old house for attic wiring.

Quick Tip: Some wire types won’t be a good option for a place like an attic. So, remember to double-check this.


Some Tips to Install Insulation in the Attic

When laying insulation in an attic, there are a few things that you should follow carefully. Here, I’ll explain them to you one by one.

First and foremost, remember to seal around the wires with any spray foam or caulk.

Then, lay polyethylene vapor barriers before placing the insulation. If you use fiberglass insulation with a vapor barrier, there is no need to lay polyethylene. Instead, lay the insulation’s vapor barrier on the attic’s warm side.

Quick Tip: Remember to create a slit for electrical wires on the insulation. You can use a sharp knife for this.

You can lay insulation over the top of other insulation.

If you use insulation that doesn’t have a vapor barrier, you can lay the second insulation without any issue. However, when laying insulation that has a vapor barrier, remember not to lay the vapor barrier side on the previous insulation. It will trap moisture between the two insulations. So, remove the second insulation’s vapor barrier. Then, place it on top of the old insulation.

Quick Tip: Moisture between the two insulations is never a good thing, and it is the perfect environment for mold and mildew to grow.

Another thing you should look out for is the attic ventilation system. Without a proper ventilation system, the attic won’t be able to maintain the warm or cool temperatures needed for different periods of the year. So, make sure the ventilation system is working properly.

If you can, get a thermal imaging inspection. It will give you a clear idea about the temperature of the attic. Also, it will indicate pests, leaks, and electrical issues in the attic.

Important: Always wear a face mask and gloves while installing fiberglass insulation.


Most Common Problems That Come with Attic Insulation

Whether you like it or not, attic insulation has a few problems. One of the most common issues is the attic wiring.

For instance, most homes built in the 1960s-70s have aluminum wiring. Aluminum wiring is good for many things but not for attic wiring, and it will significantly increase the chances of an electrical fire in your attic. So, checking the attic wiring before laying the insulation is recommended.

Some homes built in the 1970s-80s have cloth wiring in the attic. Like aluminum, this is also a fire hazard. So, remember to get rid of such wiring.


Is it Okay for Insulation to Touch Electrical Wires?

It is okay, given that the electrical wires are properly insulated.

Otherwise, the wires might heat up and start an electrical fire on the insulation. This is a significant concern while you are laying insulation in an attic. It doesn’t matter if you use the best insulation on the market. If the electrical wires aren’t insulated properly, it could cause lots of trouble for you.

One uninsulated live wire can be dangerous for your attic. So, make sure to avoid such situations.


Cost of Adding Insulation

Adding insulation will cost you around $1300 to $2500. Here are some of the factors that affect the cost of attic insulation.

  • Size of the attic
  • Type of the insulation
  • Labor cost

Is Spray Foam Insulation Good for Attic Insulation?

Yes, they are indeed a good choice. Spray foam insulation has a higher R-value, which is perfect for attic insulation. However, installing spray foam insulation is not a DIY project; a professional should handle it.

On the other hand, fiberglass insulation is much easier to install and can be completed by you without professional assistance. Therefore, the labor cost will be at a minimum.


References

Website Resources:

Video References:

This Old House

Southwire

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About Sam Orlovsky

AvatarCertifications: B.E.E.
Education: University Of Denver - Electric Engineering
Lives In: Denver Colorado

Electrical engineering is my passion, and I’ve been in the industry for over 20 years. This gives me a unique ability to give you expert home improvement and DIY recommendations. I’m not only an electrician, but I also like machinery and anything to do with carpentry. One of my career paths started as a general handyman, so I also have a lot of experience with home improvement I love to share.

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