In most modern builds, you do NOT need an air gap between insulation and plasterboard—as long as the correct insulation type, vapor barrier placement, and wall prep are done properly.

However, some systems do require a small controlled air space for moisture management or performance.

This guide explains when an air gap is essential, when it’s unnecessary, and how to get the best results for energy efficiency and moisture control inside a basement or interior wall.

Why Air Gaps Were Traditionally Used

Older construction commonly included an air space behind plasterboard because:

• Walls were built with solid masonry or cavity walls that allowed moisture to migrate inward.
• Insulation materials (like mineral wool or fiberglass rolls) needed room to “breathe.”
• Vapour control layers were inconsistent or missing.

But modern insulation materials—like rigid PIR boards, insulated plasterboard, and spray foam—are designed to fit tightly to the substrate without leaving a gap.

When You DO Need an Air Gap

You may need some air space behind your insulation/plasterboard in the following situations:

1. If You Are Using Certain Types of Mineral Wool

Mineral wool or quilt insulation often performs better with:

• A small ventilated air space on the cold side
• A proper vapour check on the warm side

This reduces the risk of moisture buildup and thermal bridging.

2. On Damp or Cold Basement Walls

If the wall has any moisture issues:

• An air cavity (usually 10–25 mm)
• A vapor barrier
• A thermal break (foam board)

may be required to avoid trapping moisture directly against the insulation.

3. When Using Timber Stud Walls

A slight gap naturally exists when:

• Timber studs are spaced away from the wall
• Insulation boards or rolls are placed between studs

This air space isn’t “designed,” but it still functions as a thermal barrier.

4. With Insulation Systems Designed for Air Movement

Some proprietary wall insulation systems use:

• Furring channels
• Dab method installation
• MM PIR boards with foil facings

These often require an intentional air space to achieve rated performance.

When You Do NOT Need an Air Gap

Most modern interior insulation systems are designed to be installed flush.

1. Insulated Plasterboard

Rigid insulated plasterboard systems are meant to:

• Sit directly against the wall
• Be mechanically fixed or dot-and-dabbed
• Provide both insulation and a built-in vapour barrier

An air gap is not recommended, because it can:

• Reduce thermal efficiency
• Create condensation zones
• Prevent the board from bonding correctly

2. PIR / Foam Board Insulation

Boards like PIR, XPS, or EPS are designed for a tight, continuous thermal envelope.

Adding a gap:

• Reduces the insulation value
• Creates cold spots
• Can trap moist air behind the boards

3. Spray Foam Systems

Spray foam adheres directly to:

• Masonry
• Concrete
• Existing plaster
• Timber

Foam must not have an air gap—its performance relies on being fully bonded.

The Role of Vapour Barriers

The vapour barrier is more important than the air gap.

You typically need a vapour barrier when:

• Warm indoor air could migrate into colder insulation
• The wall is below grade (basements)
• Mineral wool or fiberglass is used
• You live in a cold climate

You typically do not need one when:

• Using insulated plasterboard with a foil layer
• Using closed-cell foam boards
• Using spray foam

Correct vapour barrier placement prevents:

• Condensation
• Mold
• Heat loss
• Damp patches on the finished wall

Best Way to Build a Modern Insulated Plasterboard System

For most homes—including basements—the best practice is:

1. Inspect the Existing Wall

Check for:

• Moisture
• Cracks
• Structural problems
• Flaking paint

Fix these BEFORE insulating.

2. Choose the Right Insulation Material

Best options:

• Foil-backed PIR boards
• Insulated plasterboard
• Rigid foam systems

Avoid using quilt insulation directly on concrete or basement walls.

3. Install the Vapour Barrier (If Needed)

This depends on the insulation type:

• Mineral wool → yes
• PIR / plasterboard → usually already built in
• Spray foam → not needed

4. Fit the Boards Tight, With No Intended Air Gap

Boards should be:

• Butt-jointed
• Fully supported
• Taped or sealed

5. Finish With Plasterboard or Direct Finish

A smooth finish layer completes the interior.

If you need additional information on DIY Basement Insulation look to our guide.

Pros and Cons of Adding an Air Gap

✔ Pros (in the right situations)

• Helps manage moisture
• Reduces mold risk on damp walls
• Adds slight acoustic performance
• Works well with stud walls

✘ Cons (if used incorrectly)

• Can reduce insulation performance
• Creates thermal bridging
• May cause condensation in the gap
• Can trap moisture if not ventilated
• Reduces interior floor space

So… Do You Need an Air Gap Between Insulation and Plasterboard?

Most homeowners do NOT need an air gap, especially when using:

• Insulated plasterboard
• PIR foam insulation
• Spray foam
• Modern rigid insulation boards

You may need one when:

• Using mineral wool
• Working with damp basement walls
• Reinsulating older solid masonry homes
• Using systems designed to include an air space

The key is to match your insulation type with the correct moisture control strategy. If you need more tips on DIY Basement Fixes or Basement Waterproofing look to us.

Related posts:

Finished Basement Ideas: Creative DIY Designs for Every Space DIY Basement Insulation: How to Insulate Your Unfinished Basement DIY Basement Finishing: Step-by-Step Guide for Homeowners Average Cost to Finish a Basement DIY (Homeowner’s Guide 2026)