Insulation is commonly used to keep heat in or out of a building. It prevents convection by trapping air in pockets, reducing airflow. Many types of insulation also act as soundproofing by absorbing noise vibrations. With these abilities, insulation can additionally serve as an effective draft stop in some cases.
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What is a draft stop?
A draft stop is a barrier placed in gaps and penetrations in a building’s envelope to prevent air from flowing through. Draft stops reduce energy loss and improve comfort by stopping cold outside air from infiltrating heated interior spaces. They can also stop the spread of fire and smoke.
Common locations where draft stops are used:
– In wall stud cavities and floor joists where plumbing, wiring, ductwork, or other items penetrate walls and floors
– Attic hatches
– Dropped ceilings
– Knee walls
– Rim joists
– Attic knee wall door frames
– Other bypasses in the building envelope
Materials like insulation, caulk, foam, weatherstripping, drywall, and housewrap can act as effective draft stops when installed properly.
Can insulation stop air drafts?
Yes, certain types of insulation can serve as draft stops when placed in gaps, penetrations, and bypasses in walls, floors, ceilings, and attics. The key is using an insulation material that is rigid or semi-rigid to block airflow.
Good options for draft stopping include:
– Rigid foam boards – EPS, XPS, polyiso – rigid foam boards are excellent draft blockers due to their air impermeability, high R-value, and ability to completely fill gaps. Foam boards come in various thicknesses. Use thicker boards for larger gaps. Seal edges with caulk or foam.
– Spray foam insulation – Closed-cell spray foams like polyurethane expand and seal cracks, joints, and penetrations as they cure. This completely blocks drafts. Open-cell spray foam is less rigid when cured so it is not as effective for stopping air leakage.
– Fiberglass batts – When stuffed tightly into gaps, dense fiberglass batt insulation can block drafts. This takes some effort versus just laying batts in place for insulation. Pack tightly and hold in place with caulk, tape or draft stop putty.
– Mineral wool – Like fiberglass, packing dense mineral wool into openings blocks airflows. It is more rigid than fiberglass.
– Cellulose – Dense-pack cellulose that is installed behind outlet boxes and electrical fixtures can stop air from infiltrating through walls. Cellulose blown into stud cavities at 3.5+ lbs per cubic foot density also cuts down on drafts through walls.
Tips for using insulation as a draft stop
For best results, follow these tips when using insulation to block drafts:
– Use rigid insulation – Rigid foam boards, laminated dense-pack cellulose, and rock wool provide the best air sealing. Flexible insulations can work when packed tightly into cracks.
– Cut rigid boards to fit snugly – Precise cuts ensure the insulation fits flush to surrounding surfaces, leaving no gaps. Avoid overstuffing as this can bow the wall.
– Seal edges – Seal all seams and edges with spray foam, caulk or mastic for an airtight seal. For larger gaps, use wider rigid boards and seal the edges rather than trying to fill the gap with a narrow piece.
– Use adhesive – Construction adhesive applied to the back bonds rigid insulation in place. Alternatively, use mechanical fasteners.
– Check for complete coverage – Look for any openings at seams, corners, and around penetrations to ensure full coverage and an airtight seal. Supplement with caulk or spray foam as needed.
– Use tape – Foil, duct or other durable tape can help hold flexible insulations like fiberglass in place and improves air sealing.
– Combine materials – Pairing rigid foam with caulk, spray foam and weatherstripping provides added protection against air leaks.
Where to use insulation as a draft stop
Some common applications for draft stopping with insulation include:
– Attic hatches – Adhere rigid insulation or EPS foam board to the back of the attic hatch. Secure with weatherstripping around the opening to seal.
– Rim joists – Cut rigid foam or fiberglass batts to fit tightly between rim joists. Seal in place with caulk or spray foam.
– Ceiling penetrations – Use fire-rated caulk or putty pads to seal electrical box penetrations. For pipes and wires, wrap with fiberglass and seal with spray foam.
– Floor penetrations – Pack plumbing holes tightly with fiberglass and seal with polyurethane caulk or spray foam.
– Knee walls – Adhere rigid foam boards to knee wall frames and seal with construction adhesive and caulk.
– Wall stud gaps – Install dense-pack cellulose behind outlet boxes or stuff fiberglass into large gaps prior to installing drywall finishing.
– Drywall corners – Apply spray foam to drywall corners and finish with joint compound for increased air sealing.
Does insulation qualify as a fire block?
Insulation materials can only act as a fire block if they meet certain fire resistance ratings. Fire blocks are materials that slow the spread of flames, heat and burning gases past them. They are required by code in concealed wall and ceiling spaces.
Some insulations that meet fire block standards:
– Unfaced fiberglass batts – Fire-rated for use as fire blocks in wall stud cavities.
– Mineral wool – Naturally fire-resistant mineral wool insulations qualify as fire blocks.
– Fire-rated caulk – Special caulks receive fire blocking ratings and can be used around wiring and pipe penetrations.
– Intumescent putty pads – These are molded fire-resistant pads for sealing electrical boxes. They are tested to meet fire block standards.
– Fire-rated spray foam – Special fire-retardant formulations of polyurethane spray foam can achieve a Class II rating for use as fire blocks.
Standard rigid foam insulations like EPS, XPS and polyiso do not meet fire resistance standards, and should not be used alone as fire blocks. However, covering all exposed surfaces with drywall or another approved fire-rated building material allows foam insulations to meet code.
Conclusion
Insulation is very effective at reducing drafts when installed properly in areas where air leakage occurs in a home. Certain rigid and dense-pack insulations can physically block airflow when stuffed into gaps and penetrations. This allows insulation products to perform double duty, saving energy by moderating indoor temperatures and sealing leaks. By combining insulation with caulk, spray foam, weatherstripping and other materials, a complete air sealing system can be created. However, not all insulations meet fire blocking standards, so check codes and the manufacturer specifications before using insulation as a fire block. With the right products and installation method, insulation can improve comfort and energy efficiency by stopping unwanted air infiltration.
References
| Source | Link |
| Department of Energy | https://www.energy.gov/energysaver/weatherize/insulation/draft-stopping |
| This Old House | https://www.thisoldhouse.com/walls/21017135/how-to-seal-air-leaks-with-caulk |
| Family Handyman | https://www.familyhandyman.com/project/sealing-attic-bypasses-to-boost-energy-efficiency/ |
| Insulation Institute | https://insulationinstitute.org/im-consumer/basics/fire-safety/ |