Best Attic Knee Wall Insulation Options

The best insulation for attic walls depends on various factors, including budget, climate, and installation preferences.

Fiberglass Batts: Common, cost-effective, but requires correct installation to avoid gaps.
Rigid Foam Board: High R-value, creates vapor barrier, but more expensive.
Spray Foam Insulation: Highest R-value, excellent sealing, but pricier and needs professional installation.
Blown-In Insulation: Good for hard-to-reach spaces, needs professional installation.

Regardless of the type of insulation you choose, remember to properly seal any air gaps in the knee wall before insulating. Always check local building codes or consult a professional.

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About Knee Walls

• Knee walls have different names in different cultures and are used to close off space in the attic where the height is too short to use as room floor space (due to the slanting roof). Here are the ways to use the knee wall. Storage, ductwork, furnace, vented, or unvented.
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• The attic floor of a knee wall is the horizontal ( flat ) portions. The horizontal (slopped ) portions are insulated similar to cathedral ceilings ( enclosed framing assembly vented or unvented).

• The knee wall includes the sloped ceiling vented or sealed roof space. The Attic usually stays vented using cross gable vents and a power fan to draw cool air from the soffits across the roof deck to cool sunlight-heated shingles in summer and move out warm air in winter to prevent condensation/mold in the rafters. Vented rafters prevent insulation from blocking airflow, and fresh outside air in all seasons will also move through the rafters.

Unlocking the Power of Knee Wall Insulation

Our knee wall insulation services offer cutting-edge solutions to optimize the performance of your home. With our cathedralization technique, we cater to both conditioned storage areas and spaces with ductwork in the attic floor. By air sealing knee walls, insulating rafters or framing, and utilizing advanced materials like cellulose and rigid foam board, we ensure superior insulation, improved energy efficiency, and a more comfortable living environment.

Insulate Knee Wall Slopes

Cathedralize the knee wall space if the storage area is conditioned. The cathedral option: air seal knee walls along the roofline and insulate the rafters with cellulose.

This innovative approach to knee wall insulation ensures that conditioned air remains within the storage area, creating a more stable and comfortable environment.

Insulating Knee Walls

Insulate the knee wall space if a storage area is not used. The cathedral option: air seal knee walls along the framing and insulate the vertical knee wall.

The cathedral option offers an effective solution by air sealing the knee walls along the framing and insulating the vertical knee wall, ensuring enhanced thermal performance and reduced energy consumption.

Cathedralize the knee wallspace if ductwork is on the attic floor

Option to cathedralize the knee wall space if there is no passive ventilation for the space. Continue the insulation from the attic down to the floor through the rafter.

Add rigid foam board and seal seams for additional insulation ( R-value ) and a vapor barrier or install drywall for a lower R-value with vapor and fire barrier ( intumescent barrier).

Hot in the summer
Cold in the winter

Knee walls are often found in Cape Cod-style homes or Bungalow ( Chicago ) style homes. They are vertical surfaces that typically use drywall or paneling to create a finished look inside a room. These rooms are often used as bedrooms around Chicago, and sometimes as home office playroom or workout space. The knee wall is sometimes load-bearing to support the horizontal sloped rafters. The purlin is a horizontal beam along the length or a roof, resting on main rafter and supporting the common rafter boards such as a knee wall.

This assembly makes it hard to cool in summer and hard to keep from wasting heat and creating mold and condensation in the rafters from heat escape in winter. This also creates a drafty colder first floor in winter due to heat escape at a faster rate than traditional attics. In either method of insulation, it is essential to air seal the seams of the interior/exterior framing (see photo) to prevent drafts and air movement between the interior conditioned air and exterior weatherized air.

Knee Wall Ventilation

If there are no soffits, the knee wall area may breathe, and ventilation is provided through cross gable vents ( passive or active with fan motor). Ventilation can prevent a space from being dry. A healthy clean storage space can be destroyed by introducing humidity and moisture to the organic building materials such as wood with ventilation. Sometimes the knee wall area of a second floor will not be a vented, however, ventilation through baffles ( air chutes ) may be placed under the roof deck insulation to feed fresh air intake to the top of the roof / attic area power vents and passive vents.

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3. Schedule the work process

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4. Live happy in your new cozy house

After all the steps are done the single thing you can do is to wonder how could you live without a heat pump before. Enjoy