How To Insulate a Vaulted Ceiling

Insulating a vaulted ceiling can bring many benefits. Achieving proper insulation is important for both comfort and energy efficiency. A well-insulated ceiling can help regulate temperature, reduce energy costs, and improve noise control.

If you’re planning to insulate your vaulted ceiling, here are some key steps to consider.

First, assess the existing insulation. Determine if there is any insulation present and if it needs to be replaced or upgraded. This is an important step to ensure you’re starting with a proper foundation.

Next, choose the right insulation material for your vaulted ceiling. There are various options to consider, such as fiberglass batts, spray foam, or rigid foam boards. Each type has its own advantages and considerations, so do your research before making a decision.

Once you have chosen the insulation material, it’s time to prepare the ceiling for installation. Remove any existing drywall or finishes to access the cavity. Clean the area thoroughly and make sure there are no obstructions or damages that could affect the installation process.

Before installing the insulation, ensure that all air leaks and gaps are sealed. Use a combination of caulk, weatherstripping, or spray foam to seal any gaps around windows, doors, or electrical fixtures. This step is crucial to prevent air infiltration and maximize the insulation’s effectiveness.

Now it’s time to install the insulation. If you’re using fiberglass batts, roll them out between the ceiling joists, making sure they fit snugly and completely cover the cavity. For spray foam or rigid foam boards, follow the manufacturer’s instructions for proper installation techniques.

After the insulation is in place, it’s important to reinstall the finishes. Replace the drywall or other finishes that were removed earlier, ensuring that they are properly secured and sealed. This will provide a finished look and protect the insulation from damage.

Lastly, remember to inspect your work and make any necessary adjustments. Check for any gaps or areas that were overlooked during the installation process. A thorough inspection will ensure that your vaulted ceiling is properly insulated and ready to provide the desired benefits.

In conclusion, insulating a vaulted ceiling is a worthwhile investment. It provides comfort, energy efficiency, and noise control benefits. By following these steps, you can achieve a well-insulated vaulted ceiling that will enhance your living space.

Insulating a vaulted ceiling requires careful consideration of insulation materials, gravity, and ventilation. Vaulted and cathedral ceilings, although often used to describe non-flat ceilings, are architecturally different.

Vaulted Ceilings:

Vaulted ceilings differ from the roofline, utilizing scissor trusses for construction. The highest part of the ceiling is at least 10 feet from the floor. Lower slope scissor-trussed vaults can be insulated with fiberglass blanket or blown-in loose-fill insulation on the attic floor.

Loose-fill insulation is not suitable for steeper slope vaulted ceilings.

Properly insulating the underside of a scissor truss-built roof is difficult due to the web design of the truss, making gap-free attachment nearly impossible. Trusses are typically made of 2 x 4 material, providing shallow cavities for insulation.

Cathedral Ceilings

Cathedral ceilings start at the wall and follow the roofline to a peak, which is at least 13 feet from the floor. Insulation is installed between the roof rafters or attached to the underside, or both. They can be ventilated or unventilated, which affects the insulation process.

Insulating a rafter sloped roof is done from the inside using the rafters and roof deck.

There are various types of insulation commonly used for vaulted ceilings, each with its own advantages and disadvantages. Most of them can be done as a do-it-yourself project, although some are better left to professionals.

Regardless of the insulation type and R-value, installing a ceiling fan can help circulate air in living areas. Warm air tends to collect near the ceiling, so moving it around keeps the room comfortable and reduces heating and cooling costs. For a vaulted ceiling, use fiberglass batts or rolls, mineral wool insulation, or denim insulation. Fiberglass is the most popular option, available in batts or rolls, faced or unfaced.

Faced rolls can be easily stapled onto the rafters to stay in place and provide a vapor barrier, reducing the need for cutting and fitting.

Mineral wool and denim batts are unfaced and rely on friction to stay in place when installed in wall cavities where gravity is not a problem. Install 1 x 2 strapping across the rafters to prevent insulation from falling out. (Unfaced fiberglass also requires strapping.)

Rigid Foam Board Insulation can be applied in two ways. It can be installed between the rafters directly onto the undersides of the roof deck or across the bottoms of the rafters. Use acoustic caulking or small cans of spray foam insulation to seal the foam to the rafters and fill all cracks and gaps.

The most popular insulation options are expanded polystyrene (EPS), extruded polystyrene (XPS), and polyisocyanurate (ISO). XPS and ISO provide a vapor barrier when two inches thick or more and all gaps and cracks are sealed.

Cellulose insulation can be applied wet or dry. Wet applications should be done by professionals with the proper equipment. It is sprayed directly onto the underside of the roof deck and sticks in place once it dries.

This is a common method for insulating flat-roofed commercial buildings.

Dry cellulose installations require attaching a net to the undersides of the rafters. The net holds the cellulose in place during and after it’s blown in dry. You can rent a blowing machine, buy the material, and do it yourself, or hire an insulation contractor.

Cellulose insulation, both wet and dry, fills all voids when applied correctly. Dry cellulose can also be installed with the drywall already on the ceiling by using a dense-pack application. Small holes are cut into the drywall to allow hose access, then patched.

Contractor installation is usually recommended.

Spray foam insulation provides the best R-value for a vaulted ceiling. It seals cracks and gaps and fills voids around wires, pipes, and electrical fixtures. It is also the most expensive insulation.

Spray your vaulted ceiling with closed-cell foam instead of open-cell foam. Open cell absorbs water, has a lower R-value per inch, and does not qualify as a vapor barrier.

Most people hire contractors to foam vaulted ceilings. However, DIY kits are available from home improvement outlets or online. The kits are ideal for smaller areas (under 1000 square feet) or houses located in remote areas.

When insulating larger areas, contractor costs are usually less than buying multiple kits.

Reflective Insulation

Reflective or radiant barrier insulation has no R-value. Staple it across the bottom of the rafters to reflect heat away from the building. It can reflect up to 97% of the sun’s heat.

Reflective insulation is only effective in hot climates. It provides little value in cold climates and can be counter-productive in winter–preventing any solar gain from adding warmth to the house.

Ventilation in Vaulted Ceilings

Spray foam insulation and rigid foam board insulation installed against the roof deck–sealed properly–do not require ventilation. They make the ceiling cavity between rafters airtight–preventing moisture build-up on the underside of the roof deck. Rigid foam installed on the bottom of the rafters should allow ventilation.

Reflective insulation can have ventilation between it and the roof deck because it does not absorb moisture. The foil works best when kept clean. Airflow brings dust that adheres to the foil face, reducing its effectiveness.

If possible, make the rafter cavities ventilation-free.

Fiberglass and cellulose absorb moisture and do not dry easily. The wetter they get, the less insulation value they have. Soaked fiberglass has no insulation value. In colder climates, a vapor barrier should be installed on the warm side to prevent moisture absorption from inside the house.

Most building codes in northern states and Canada require at least a 6 mil poly vapor barrier.

Vented soffit and a ridge vent pull cooler air in at the bottom and expel warm air through the ridge. Install fiberglass insulation, leaving a 1.5” – 2” gap between the batt and the roof deck for airflow. If insulation may block the soffit vents, install baffles in the lower 4’ of the cavities.

Purpose-made foam baffles are inexpensive and available from your insulation supplier.

Some shingle manufacturers void warranties if there is no ventilation. Know your roofing status before insulating your ceiling.

Vaulted Ceiling Insulation Safety

Never install insulation close to heat sources. Pot lights, especially, produce a lot of heat. Wear appropriate clothing, a respirator, and eye protection.

Some products, like cellulose, are relatively safe but can be dusty. Others, like spray foam, can be toxic. Follow all manufacturer’s safety guidelines.

Exterior Roof Insulation

One effective method of insulating a vaulted ceiling is from the outside. This is only practical for new construction or when replacing the shingles due to the cost. Installing rigid foam board insulation directly onto the roof deck solves ventilation issues.

Extruded polystyrene or polyisocyanurate insulation boards are the best choices. They provide a high R-value per inch and do not absorb water. Apply them directly onto the roof deck, install sleepers, cover with a minimum 7/16’ thick OSB sheathing, and install the roofing material of your choice.

How Much Insulation to Use

Ninety percent of US homes do not have enough insulation. The map and tables below show the recommended amount of attic insulation areas in the United States. The R-values for attics should be used for vaulted ceilings.

Alaska climate zones:

– 7 – Aleutians East

– 7 – Aleutians West

– 7 – Anchorage

– 7 – Bethel

– 7 – Bristol Bay

– 8 – Denali

– 7 – Dillingham

– 8 – Fairbanks North Star

– 6 – Haines

– 6 – Juneau

7 – Kenai Peninsula

5 – Ketchikan Gateway

6 – Kodiak Island

7 – Lake and Peninsula

7 – Matanuska-Susitna

8 – Nome

8 – North Slope

8 – Northwest Arctic

5 – Prince of Wales-Outer Ketchikan

5 – Sitka

6 – Skagway-Hoonah-Angoon

8 – Southeast Fairbanks

7 – Valdez-Cordova

8 – Wade Hampton

6 – Wrangell-Petersburg

7 – Yakutat

8 – Yukon-Koyukuk

Zone 1 includes Hawaii, Guam, Puerto Rico, and the Virgin Islands.

CLIMATE ZONE UNINSULATED ATTIC 3-4 INCHES OF EXISTING ATTIC INSULATION UNINSULATED FLOOR UNINSULATED WOOD-FRAME WALL

1 R30–R49 R19–R38 R13 R13 or R0 + R10 CI*

2 R49–R60 R38–R49 R13 R13 or R0 + R10 CI

3 R49–R60 R38–R49 R19 R20 or R13 + R5 CI or R0 + R15 CI

4 EXCEPT MARINE R60 R49 R19 R20 + R5 CI or R13 + R10 CI or R0 + R15 CI

4 MARINE AND 5 R60 R49 R30 R20 + R5 CI or R13 + R10 CI or R0 + R15 CI

6 R60 R49 R30 R20 + R5 CI or R13 + R10 CI or R0 + R20 CI

7 AND 8 R60 R49 R38 R20 + R5 CI or R13 + R10 CI or R0 + R20 CI

Terry Schutz is a freelance writer with expertise in home renovations, DIY advice, and construction. With over 30 years of experience in the industry, Terry has gained knowledge as an installer, manager, salesperson, and business owner.