Should I Insulate Between Floors?

When It Makes Sense

• Good fit: In homes where the floor above is heated (e.g., radiators or underfloor heating) and the space between floors is unconditioned, adding insulation can reduce heat loss and improve comfort on the lower level.
• Good fit: In retrofit projects where a crawl space or unfinished basement lies beneath a living floor, insulating between floors can help prevent cold drafts and lower heating bills.

When You Should Avoid It

• Warning sign: If the building already has a continuous insulation layer in the roof or walls and the floor cavity is too shallow for proper insulation depth, adding material may compress it and reduce effectiveness.
• Warning sign: In historic properties with strict preservation guidelines, altering the floor assembly could violate regulations or damage original materials.

Pros and Cons

Pros

• Reduces heat transfer between levels, which can lower energy consumption and improve comfort on the cooler floor.
• Helps dampen sound transmission, making the space quieter for occupants.

Cons

• Installation can be disruptive, requiring removal of floor coverings and possibly affecting structural components.
• Improper installation may trap moisture, leading to mold growth or rot in timber joists.

Decision Checklist

• Is the floor cavity deep enough to accommodate the recommended insulation thickness without compressing?
• Do you have a clear path for moisture management (e.g., vapour barriers, proper ventilation) in the space between floors?
• Will the installation impact flooring finishes, wiring, or plumbing that would require additional work or expense?

Alternatives to Consider

Instead of insulating directly between floors, you could improve the building envelope by adding insulation to the roof, walls, or exterior basement walls. Installing a floating floor with acoustic underlay can also reduce sound without changing the structural floor assembly. In some cases, sealing air leaks and upgrading windows may provide comparable energy savings with less intrusion.

Final Recommendation

Insulating between floors is worthwhile when the floor cavity offers sufficient depth, moisture control can be ensured, and the expected energy or comfort gains justify the disruption and cost. Homeowners with shallow joist spaces, preservation constraints, or limited DIY experience should consult a qualified builder or energy auditor before proceeding.