Install Flooring Underlayment and Moisture Barrier

A. Finished-Project Specification

Quantity: one defined inspection area with a continuous underlayment and/or moisture-barrier system installed to full coverage, every seam butted or overlapped per product instructions and taped or sealed, every penetration sealed, all required movement details preserved, and one completed Underlayment and Moisture-Barrier Installation Record.

B. Installation Schedule

Item	Target Condition	Verification Method
System selection	Underlayment and/or moisture-barrier product matches the flooring manufacturer's written instructions	Written record on Installation Record
Substrate readiness	Repair, flatness, cleanliness, and moisture inspections confirmed passed before placement begins	Review of prior chapter inspection records
Course placement	Each course placed flat, without wrinkles, from the established starting wall and direction	Visual inspection during placement
Seams	Every seam butted or overlapped at the specified distance and taped or sealed with the specified product	Visual inspection and lap-distance measurement
Moisture-barrier coverage	Sheet or liquid membrane installed at the specified coverage, thickness, lap, and cure requirement	Coverage check and product-record comparison
Penetrations and perimeter	Every pipe, column, and perimeter detail sealed or treated per the approved method	Visual inspection at each penetration
Continuous coverage	No open seams, wrinkles, punctures, contamination, or missed edges across the full area	Full-area visual inspection before covering

C. Material Takeoff

• Underlayment or moisture-barrier material: sufficient sheet, roll, or attached-pad product to cover the full inspection area plus the manufacturer's specified waste allowance for seams and cuts.
• Seam tape: the exact manufacturer-specified compatible tape, sufficient length for every seam in the area.
• Liquid or troweled membrane consumables: primer, mixed membrane material, and mixing consumables sufficient for the specified coverage rate and thickness, where a liquid or troweled system is specified.
• Penetration treatment: boots, collars, or sealant sufficient for every identified pipe, column, or fixed-object penetration.
• Documentation: one Underlayment and Moisture-Barrier Installation Record per inspection area, plus photographs of seams, laps, penetration treatment, and coverage before the layer is covered.

D. Acceptance Standards

Check	Standard
Product compatibility	Installed product matches the flooring manufacturer's written instructions for the specific finish flooring; no duplicate or unapproved layer present
Coverage	Continuous coverage across the full inspection area with no open seams, wrinkles, punctures, or missed edges
Seams	Every seam meets the specified minimum lap or butt condition and is fully taped or sealed with the specified compatible product
Penetrations	Every pipe, column, and fixed-object penetration sealed per the approved method, with no gap or unsealed opening
Movement details	Expansion joints, floor drains, vents, and perimeter upturn preserved and not blocked or bridged
Repairs	Every identified tear or hole patched using the approved method before the layer is covered
Documentation	Installation Record complete with product, lot, coverage, seam, repair, and moisture-control entries
Procedure	System selection, substrate confirmation, course placement, seaming, moisture-control installation, penetration sealing, and inspection completed independently and in sequence

E. System Review and Substrate Confirmation

1. Review flooring type, substrate, moisture test results, underlayment requirement, vapor-control strategy, radiant-heat condition, and product compatibility. Confirm the identified underlayment and moisture-barrier products match the flooring manufacturer's written instructions before opening any packaging.
2. Confirm the substrate has passed repair, flatness, cleanliness, and moisture inspections. Review the Chapter 1, Chapter 3, and Chapter 4 records for the inspection area and re-test moisture at a representative location if the prior test is not current.
3. Determine whether the system requires separate underlayment, attached pad, moisture barrier, liquid membrane, sheet membrane, or no additional layer. Record the determination and the controlling manufacturer instruction on the Installation Record.
4. Do not install duplicate underlayment or vapor layers unless the flooring manufacturer permits them. Confirm no existing underlayment or vapor layer remains from a prior installation before proceeding.

F. Course Layout and Placement

1. Establish the direction and starting wall. Mark the starting wall and course direction with chalk or marking tape, matching the manufacturer's layout requirement and the planned finish-flooring layout.
2. Roll or place the first underlayment course without wrinkles. Sweep the substrate immediately before placement and smooth the course from the starting wall outward.
3. Maintain the required wall upturn or perimeter treatment. Turn moisture-barrier sheet up the wall to the specified height where the manufacturer requires a perimeter upturn.

G. Seaming and Sealing

1. Butt or overlap seams according to the exact product instructions. Measure each seam against the specified minimum lap or butt condition before proceeding.
2. Tape or seal seams with the specified compatible tape. Press each seam flat with the seam roller immediately after taping.
3. Keep underlayment flat at transitions and doorways. Trim excess material at transitions without leaving a raised edge or unsupported flap.
4. Avoid puncturing the moisture barrier. Set tools and materials on protective board or scrap material when working on top of the placed barrier.
5. Patch tears and holes using the approved method. Repair any puncture found during placement before continuing to the next course.

H. Course Continuation and Penetrations

1. Place subsequent courses while preserving seam orientation. Continue in the established course direction, checking each seam against the same lap or butt standard.
2. Do not create thick overlaps beneath floating flooring. Trim excess material at overlaps to the specified single-thickness condition where a floating floor will be installed above.
3. Seal pipe and column penetrations where required. Fit a boot, collar, or sealant bead at every identified penetration before the surrounding course is completed.
4. Preserve expansion joints, floor drains, vents, and movement details. Mark and protect each detail so it is not covered or blocked by the underlayment or moisture-barrier material.

I. Moisture-Control Membrane Installation

1. Install sheet or liquid moisture control according to coverage, thickness, lap, and cure requirements. Mix liquid or troweled membrane products using the specified ratio and application rate, and apply at the specified thickness with the specified trowel or roller.
2. Do not cover unresolved moisture or active slab emissions beyond the product limits. Stop work and escalate per the Failure Points section if a moisture reading exceeds the product's stated limit at this stage.

J. Final Inspection and Protection

1. Inspect the full area for open seams, wrinkles, contamination, punctures, and missed edges. Walk the entire inspection area under adequate light and mark any deficiency found.
2. Protect the installed system until flooring begins. Restrict foot traffic, tool storage, and following-trade access to the protected areas only.
3. Document product, lot, coverage, seams, repairs, and moisture-control details. Complete the Installation Record and attach photographs of seams, laps, penetrations, and full coverage before the layer is scheduled to be covered.