Window perimeter airtightness tape before cover

The required airtightness route comes from national energy performance rules, the approved design, project specification, and any whole-building test target. EPBD supports energy performance improvement, but it does not prescribe one EU window perimeter tape detail.

Find the designed airtightness line at the window: frame edge, wall substrate, reveal return, membrane, plaster layer, or internal lining. Confirm which product creates the air seal and what evidence is needed before cover-up.

- Window foam treated as the airtightness line without a tape, membrane, sealant, or approved system

- Airtightness line not shown on the detail drawing

- National or project airtightness target not known by the installer

- Internal lining or render planned to hide an unresolved perimeter gap

Where applicable, CE marking, Declaration of Performance, ETA/EAD documents, product labels, and manufacturer instructions must match the installed window perimeter product and its intended use. National rules and the project specification still decide whether the declared performance is acceptable.

Compare the label, batch, DoP or ETA route where supplied, and current instructions with the actual frame material, masonry, concrete, timber, metal, insulation board, render carrier, or vapour control layer. Check that primers, adhesives, tapes, membranes, and sealants are from a compatible system or have written compatibility evidence.

- Tape specified for one substrate used on another without primer or confirmation

- Similar product name but different variant, width, adhesive, or exposure rating installed

- DoP or ETA kept in the office but not linked to the installed batch

- Installer follows a marketing sheet instead of the current installation instructions

Airtightness tapes, membranes, and sealants rely on substrate condition. Manufacturer instructions and the project quality plan control cleanliness, dryness, primer use, curing, temperature, and minimum bonding surface.

Inspect the frame edge and reveal substrate before cover-up. Look for dust, laitance, standing moisture, frost, loose render, sharp projections, release agents, wet timber, and unfilled voids behind the bonding line. Confirm primer or surface preparation where the instructions require it.

- Tape bonded to dusty blockwork or damp concrete

- Primer omitted on porous or friable substrates

- Membrane stretched over cavities with no backing support

- Sealant applied over wet foam or uncured surrounding work

The designed airtightness layer should be continuous around the head, jambs, sill, and corners before it is hidden. Acceptance depends on the national project requirements and the product system, not on a generic EU detail.

Trace the seal around the full window perimeter. Check for gaps, pinholes, unbonded edges, missed corners, short tape lengths, wrinkles, cuts, and junctions where the window seal must connect to plaster, membrane, vapour control layer, or sheathing.

- Good tape on the jambs but open gaps at the sill corners

- Tape stops short of the plaster or membrane airtightness layer

- Wrinkles or fishmouths create air paths behind the tape

- Temporary packers, brackets, or shims interrupt the seal without treatment

Corner pieces, overlaps, folds, movement allowance, and termination methods should follow the product instructions or approved project detail. Do not invent overlap values where the manufacturer or project has already specified them.

Inspect each inside and outside corner, especially at sill-to-jamb transitions and head corners. Check that overlaps are pressed down, changes of plane are not stretched tight, and tape ends are terminated where later plaster, lining, or render will not peel them back.

- Tape pulled tight across a corner and lifting before cover-up

- Overlap hidden behind reveal board with no photo record

- Membrane folded so water, dust, or air can track behind it

- Corner patched with a small offcut instead of the system detail

Where sealant is part of the airtightness system, joint width, depth, backing, primer, curing condition, and adhesion surfaces should follow the manufacturer instructions and approved detail.

Check representative sealant joints for correct backing, two-sided adhesion where required, continuous contact, no skinning over voids, and no contamination at the bond faces. Confirm that expanding foam, packing, or insulation is not being relied on as the only air seal unless the approved system allows it.

- Surface bead applied over a deep unbacked gap

- Sealant bonded to three sides and likely to tear with movement

- Joint too narrow or too wide for the specified product

- Fresh sealant covered before curing or before the defect can be photographed

Many window details separate internal airtightness from external rain, wind, or weather protection. The approved national design and manufacturer system decide the vapour, drainage, and exposure arrangement.

Confirm which layer is the internal air seal and which layer handles external weather protection. Check that external tapes, membranes, sill pieces, drainage paths, and weep routes are not blocked by the airtightness product or later render and reveal work.

- External weather tape treated as the only airtightness measure without an internal seal

- Internal tape blocks sill drainage or weep paths

- Render bead, lining track, or insulation return planned to cut through the seal

- Vapour-control intent changed by substituting a different membrane without review

Before reveals, linings, plaster, insulation returns, or render hide the junction, the project quality plan and national inspection practice may require a hold point, photo record, or correction sign-off.

Photograph the full perimeter, close-ups of corners and overlaps, product labels, batch data, primer or sealant where relevant, and any corrected defects. Mark the window location on a plan or photo log and confirm who has accepted cover-up.

- Junction covered before defects are rechecked

- Photos too close to identify which window was inspected

- Batch labels discarded before record capture

- Correction made after inspection but no second photo before closure