Install a Vapor Retarder Where Required

A. Finished-Project Specification

Deliverable: one continuous vapor-retarder membrane installed at the location specified by the approved assembly design, with seams lapped and sealed by the specified amount, perimeter edges sealed to the adjoining air-control layer, every penetration gasketed, booted, or sealed, and any tears or punctures patched to the required extent, documented with photographs before concealment.

B. Assembly and Membrane Schedule

Assembly Location	Membrane Class/Product	Attachment Method	Lap Requirement
______ (per approved design)	______ (per approved design)	______ (per manufacturer instructions)	______ (per manufacturer instructions)

Do not fill in membrane class, attachment method, or lap requirement from general practice. Use only the values stated in the approved assembly design and the identified manufacturer instructions for the selected product.

C. Penetration and Seam Takeoff

• Seams: record the location and length of every seam requiring lap and seal in the assigned area.
• Perimeter transitions: record every edge where the membrane meets an adjoining air-control layer, window, door, or structural transition.
• Penetrations: record every pipe, wire, duct, box, or structural penetration requiring a gasket, boot, or sealant.
• Existing low-permeance layers: record any sheet foam, foil-faced sheathing, or other low-permeance material already present on the opposite side of the assembly.

D. Acceptance Standards

Check	Standard
Location and class	Membrane class and location match the approved assembly design exactly; no substitution based on general climate assumption
Seam continuity	Every seam is lapped by the specified amount and sealed with compatible tape or adhesive, pressed per manufacturer instructions
Perimeter connection	Every perimeter edge is sealed to the adjoining air-control layer without gaps
Penetration seal	Every penetration is gasketed, booted, or sealed without blocking drainage, electrical access, or required service components
Damage repair	Every tear or puncture is patched with material extending the manufacturer-required distance beyond the damage
Double-barrier check	The completed assembly does not create an unapproved low-permeance double layer

E. Confirmation and Preparation

1. Review the climate, assembly design, drying direction, material permeance, interior humidity, exterior layers, and adopted vapor-control requirements. Record the approved design reference on the installation worksheet before proceeding.
2. Confirm that the vapor retarder is required at the specified location. Verify against the approved assembly design; do not proceed based on general assumption.
3. Do not select membrane class or location based on general climate assumptions when the approved assembly differs. If the field condition does not match the approved design, stop and refer the discrepancy before continuing.
4. Inspect the substrate for moisture, sharp projections, contamination, and incomplete rough work. Correct any sharp projection or contamination that could puncture or contaminate the membrane before staging it.
5. Verify that insulation, air sealing, and concealed inspections are complete where the sequence requires them first. Confirm sign-off from the required prior inspection before installing membrane over concealed work.

F. Layout and Staging

1. Identify seams, corners, perimeter transitions, windows, doors, boxes, pipes, ducts, and structural penetrations. Record each on the penetration and seam takeoff before cutting the first sheet.
2. Stage the membrane flat and protect it from puncture. Keep rolls or sheets away from sharp debris, foot traffic, and protruding fasteners until installation.
3. Establish the installation direction and overlap sequence. Plan the full run across the assigned area so no run ends with an unsupported short piece at a corner or penetration.

G. Attachment

1. Attach the membrane using approved fasteners or adhesive without excessive holes. Follow the manufacturer's fastening schedule; do not add fasteners beyond what the product instructions specify.
2. Maintain required slack or movement allowance. Where the approved design specifies slack for structural movement, install it as specified rather than pulling the membrane taut.

H. Seams and Perimeter

1. Lap seams by the specified amount. Measure and confirm the lap distance against the manufacturer instructions at each seam.
2. Seal seams with compatible tape or adhesive. Use only the product identified as compatible with the installed membrane.
3. Roll or press closures according to the product instructions. Use a seam roller or the specified pressing method to achieve full contact.
4. Seal perimeter edges to the approved adjoining layer. Confirm continuity with the air barrier or structural transition at every edge.

I. Penetrations and Repairs

1. Use gaskets, boots, tapes, or compatible sealants at penetrations. Fit each penetration seal to the specific pipe, wire, duct, or box passing through the membrane.
2. Do not seal drainage openings, electrical access, or service components. Verify that every required opening remains functional after sealing.
3. Repair tears and punctures with patches extending the required distance beyond damage. Use the manufacturer-approved patch material and method for every repair.
4. Coordinate framing or service cavities to reduce future membrane penetrations. Where practical, route new penetrations through existing chases rather than cutting new membrane openings.

J. Inspection and Documentation

1. Inspect continuity, adhesion, punctures, perimeter connection, and compatibility with adjacent layers. Walk the full assembly and check every seam, edge, and penetration against the acceptance standards.
2. Verify that the completed assembly does not create an unintended double vapor barrier. Confirm against the recorded existing low-permeance layers from Section C.
3. Photograph and document the concealed vapor-control layer before finishes. Label each photograph with its location reference and file it with the installation worksheet.