How To Insulate A Sloped Ceiling [A Complete Guide]

Since heat rises, ceilings are particularly susceptible to heat loss. Specifically, you are wondering how to insulate a sloped ceiling. Well, you have found yourself in just the right place. This post combines industry professional knowledge and up-to-date research to provide a thorough and useful answer.

Slopped ceilings come in many different configurations and constructions that can be insulated using different techniques and best practices. Primary techniques for insulating sloped ceilings include:

  • Fiberglass batts
  • Attic blow
  • Gable end blow
  • Roof blow
  • Ceiling blow
  • Roof foam board

Keep reading the rest of this post for the details on each of the above bullet points. This guide will first teach you how to assess the type of sloped ceiling you have and how to insulate that space. To conclude, we answer a few questions related to the topic of this post.

A man installing thermal insulation layer, How To Insulate A Sloped Ceiling [A Complete Guide]

Assessing Your Sloped Ceilings

Looking up and seeing a sloped ceiling is only part of the story. The next step is determining if you can get access to the uninsulated space. This determination will define the type of insulation most appropriate for your slopped ceiling.

Sloped ceiling types include scissored trusses, dropped ceilings, and standard sloped ceilings. Sloped ceilings are also known as vaulted ceilings and cathedral ceilings.

Scissored Trusses

Scissored truss construction involves roof rafters that angle to the roof peak and ceiling rafters that angle less strongly to a lower ceiling peak. This creates a 'V 'on both sides of the ceiling peak, which is shaped like partially open scissors.

You can determine if you have scissored trusses by measuring from the top of a window to your ceiling inside and then from the top of the same window to the roof outside. If the measurements are significantly different (8" or more), you likely have scissored trusses.

Dropped Ceilings

Sometimes there are areas of a home with a small sloped ceiling, such as above stairs. These are often dropped ceilings from inside a larger attic. To determine if you have a dropped sloped ceiling, you will probably need to head into your attic.

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Wearing the proper personal protective equipment and making sure the space is safe to enter and exit, carefully explore until you can see if there is a dropped portion above your sloped ceiling. Recommended equipment includes breathing protection, eye protection, gloves, and Tyvek suits.

Alternatively, you can hire an insulation professional to go do the attic digging for you. This is usually part of a standard bid write-up procedure.

Standard Sloped Ceilings

These ceiling types are the most common type of sloped ceiling and have no attic space. The ceiling cladding and roof cladding are affixed to opposite sides of the same rafter for standard sloped ceilings. This means there is no horizontal access to the uninsulated space in your sloped ceiling.

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If you do not have scissored trusses and are sure the ceiling is not dropped, then you have a standard sloped ceiling with no attic. Unfortunately, these are the most difficult types of sloped ceilings to insulate as a remodel.

What is the best way to insulate a vaulted ceiling?

In the following subsections, we discuss the many ways to insulate sloped ceilings.

Fiberglass Batts

Fiberglass batts are premade fluffy fiberglass that fit perfectly between framing elements such as roof rafters. Fiberglass batts are an option if you can access the rafters, such as during construction or from the attic.

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However, using blown-in insulation provides a better R-value because of fiberglass insulation's limited thickness and inevitable gaps. That being said, fiberglass batts are the easiest to install as a DIY project.

Fiberglass batts work on scissored trusses if there is enough space to access all the rafter bays, on dropped ceilings, and new construction. They do not work on standard sloped ceilings.

Blown-In/Loose Fill Insulation

Blowing insulation is a common way to improve home energy efficiency. Using a specialized blower and insulation, a big hose is used to shoot insulation evenly into uninsulated spaces.

While these tools are possible to rent, most homeowners opt for hiring a professional to blow insulation.

Technician spraying blown fiberglass insulation between attic trusses

Usually, cellulose blown-in insulation, which is just paper, is the most affordable and energy-efficient option.

For mobile homes, it is common to blow fiberglass because of the increased likelihood of water leaks; fiberglass is much more resistant to getting wet. Some people choose the more expensive but more insulative blown-in foam insulation.

For easy to access attics, it is possible to buy blow insulation and simply dump it in place out of the bag for a cheaper loose fill option. Read the following subsections for details on the many ways to blow your slopped ceiling.

Attic Blow

An attic blow is possible if you can access the attic and/or get a hose or piece of PVC into the space above the sloped ceiling.

Thus, attic blows are great for some scissor trusses and dropped ceilings.  Since an attic blow uses an already existing attic access, they are the cheapest type of blow.

In some cases, it is possible to do an attic blow of standard sloped ceilings. This is possible if you can access the end of each rafter bay from an adjoining attic space. This is very common for older homes with knee wall construction.

Gable End Blow

Gable end of an aged cottage with horizontal wooden siding and windows

Sometimes, there is no way to access your scissored trusses or dropped ceiling spaces. In that case, you can cut a hole in the gable end to access the attic space. Often, the hole is replaced with a vent after the work is completed.

Roof Blow

Roof blows are appropriate for all types of sloped ceilings. However, roof blows do require cutting holes in the roof cladding and/or roofing material.

This means that roof blows are only possible in tandem with reroofing or for mobile homes which have a shed roof over the main roof.

To perform a roof blow on standard sloped ceilings, round holes will need to be cut in the roof.

For standard ceilings, a hole will be drilled for every rafter bay. For scissored and dropped ceilings, fewer holes may need to be drilled.

Then, the insulation is pumped into the ceiling space. Afterward, the holes are patched, and then the new roof can be installed, which covers up all the marks of the new insulation addition!

Ceiling Blow

If you cannot perform an attic blow, a roof blow, or a gable end blow, then consider a ceiling blow.

Ceiling blows require cutting holes in the finished ceiling cladding inside your home. They generally are used for standard sloped ceilings and scissor truss ceilings that are very tight.

Worker puttied wall using a paint spatula

After the blow is completed, all the holes need to be patched and painted to match.

However, even the most meticulous technician will have trouble removing all signs of the insulation work. It is common for visible rounds to remain in the ceiling afterward.

Roof Foam Board

The final way of insulating sloped ceilings involves putting foam board on the roof but under the roofing. Extruded foam board has some of the highest R-value per inch of any insulation installed in residential construction today.

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For maximum energy conservation, sloped ceilings will often be insulated with fiberglass or cellulose inside the attic, and foam board is put on the roof.

However, if you are interested in insulating as a remodel, you can add foam board at the same time you perform a re-roofing project.

How much does it cost to insulate a vaulted ceiling?

The cost of insulating a vaulted ceiling varies based on the technique and type of insulation used. Generally, fiberglass batts cost the least, followed by blown insulation and then foam board insulation.

Exact prices vary from area to area based on material and labor costs. To get a good price for your project, either contact a professional for a bid or determine the cost of buying the required materials on your own.

Generally, fiberglass batts cost anywhere from $1 to $3 per square foot. Blown insulation costs between $1.50 to $9 per square foot. Foam board costs $1.60 to $4 per square foot.

What is the cheapest way to insulate your attic?

The cheapest way to insulate your attic is to perform the work yourself during the construction.

If this is not possible, the next cheapest way is to buy loose-fill blow insulation and simply dump it into place. This technique is not possible for many types of sloped ceilings.

The next cheapest way is to use fiberglass batts to fill the rafter bays. This also requires access to the space. Unfortunately, blowing in insulation is the most expensive method because of the additional work and tools required.

How to Tell if Your Sloped Ceiling is Uninsulated?

Before going to all the effort of figuring out how to insulate your sloped ceiling - you first need to determine if it is uninsulated.

For the sloped ceiling that you can inspect from the attic, it is easy to see if there is insulation between the rafters or not.

However, for standards sloped insulation with no visual access, the answer is more difficult to determine. Techniques include the poke test, drilling a hole, and infrared cameras.

Poke Test

To use the poke test, find a ceiling penetration such as a light. Then use a thin metal tool like an awl or screwdriver and carefully poke it into the cavity. Often, you can hear and feel the tool going through the paper backing of fiberglass batts.

Drilling a Hole

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Usually, contractors prefer to use a 1" or 2" hole saw. It is best to find a place that is out of the way, such as in a closet.

Then, drill the hole and check for insulation. You can reinsert the drywall plug and patch or put in a premade wall patch as part of the cleanup.

Infrared Camera

Using infrared radiation and during the winter, specialists can determine if there is insulation in your walls without the need for any invasiveness.

The cost of this is usually only worth it if you fear your home insulation is uneven throughout the entire home.

How do you insulate an attic with a vaulted ceiling?

As mentioned above, vaulted is another way to refer to sloped ceilings.

As such, reading the body of this post on how to insulate sloped ceilings provides all you need to know when deciding how to insulate your attic with vaulted ceilings. The sections on attic blows and gable end blows are most applicable to this question.

Should you insulate between rafters?

Only insulate between rafters if those rafters are in contact with the heated space of the home.

Sometimes, rafters run along the top of the attic and support the roof. Other times, rafters are in direct contact with a sloped or flat ceiling and the internal heated space.

In Closing

In this post, we answered the question of how to insulate sloped ceilings. We include how to determine the type of sloped ceiling, a guide on the many ways to insulate sloped ceilings, a quick intro to the cost for this project, and a few tips for determining if there is existing insulation.

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