How to Install Airtightness Tape Around Windows and Doors
A window can be well fitted and still leak air at the connection between the frame and the wall. Airtightness tape closes that connection by joining the frame to the building's specified air barrier. Getting the corners, preparation and final inspection right matters as much as laying a straight strip along the reveal.
This guide follows the preparation and application principles published for IM Fleece Airtight Tape. Use it alongside the current technical data sheet, installation guide and your project's window detail. If you are still choosing a tape, read our guide to selecting window tape for retrofit and Passivhaus work.
1. Identify the connection before starting
Confirm which surface on the wall forms the air barrier and where the tape must meet the frame. Trace that connection around the head, sill and both jambs. Include fixing brackets, corners and changes of material; a break at one of these points can leave a leakage path behind the finished reveal.
Agree the relationship between the internal airtight connection and the external weathering detail. Protect window drainage openings, moving hardware and other designed functions. If a sill, threshold or bracket prevents a continuous bond, resolve that detail with the designer or technical team before covering it.
2. Prepare sound, dry bonding surfaces
Remove dust, grease, loose material and residues that could interfere with adhesion. Inspect existing paint and plaster on retrofit reveals: tape bonded to a loose surface can detach with that surface. Repair weak areas before taping and ensure the bond is made to stable material.
Highly porous backgrounds may need an appropriate primer. Confirm the primer for the actual substrate and adhesive, then follow its drying requirements. Do not apply the tape to a wet or damp reveal. A quick adhesion trial on the prepared frame and wall helps identify a problem before a whole opening is completed.
3. Check temperature and prepare the tools
The IM technical data sheet gives an application range of +5°C to +40°C; the installation guide also states that the substrate must not be below +5°C. Check the surface, especially on cold masonry, rather than relying only on the room temperature.
Have a measuring tape, suitable cutting tool, cleaning equipment and a roller or pressing tool ready. Keep the adhesive clean while handling it. A foil applicator gun is for dispensing compatible sealant; it is not the tool used to press this tape onto the frame.
4. Measure the width and cut lengths
Select a width that provides the bonding areas and movement allowance in the approved connection detail. IM Fleece Tape comes in 75, 100, 150 and 200 mm widths, with 25 m on each roll. Check the widest and most awkward parts of the reveal before assuming one size suits every opening.
Measure and cut manageable lengths, including the required joins and corner treatment. Do not stretch a narrow strip to cover a wider gap. Large unsupported gaps need an agreed supporting or sealing detail, not simply the widest available tape.
5. Apply without tension and close the corners
Position the tape carefully and work progressively so that its adhesive makes full contact with both bonding surfaces. Leave the movement allowance specified for the connection. Pulling the tape tight can put a continuous load on its edges when the frame and wall move differently.
At corners, use the agreed fold, cut or patch detail to avoid open channels and raised edges. The technical data sheet requires at least 50 mm where two tape pieces overlap. That overlap is a tape-to-tape joining requirement; it should not be confused with a universal minimum frame bond or permitted gap width.
6. Press every bonded area firmly
Use the roller or pressing tool across the bonded sections and overlaps, paying particular attention to edges and corner pieces. Laying tape onto a surface is not the same as achieving continuous adhesive contact. Check from more than one angle for wrinkles, lifted edges and areas that bridge over depressions.
If an edge lifts, stop and establish why. Dust, moisture, an unsuitable surface, poor pressure or tension may be responsible. Deal with the cause and remake the affected connection on a suitable substrate before continuing.
7. Connect the adjoining membrane and inspect
Where the design combines tape with Passive Purple liquid membranes, complete the transition using the specified system sequence and coverage. Keep the inspection stage before plaster, lining or trim conceals the work. Photograph corners and other complicated connections, and check the perimeter as one continuous line.
A planned pressure test while the connection remains accessible can reveal remaining leakage. Tape improves a connection; the measured result depends on the whole building envelope.
8. Finish and record the detail
The fleece face is intended for plastering or painting with the appropriate finish. Follow the specified finishing sequence and cover exposed tape within the documented exposure period; IM's guide gives a maximum of 12 months. Protect completed work from damage by subsequent trades.
For the wider system, read the airtightness tape guide. View tape sizes and download the current installation documents, or ask our technical team to review an unusual window or threshold connection.