Underlayment Do’s & Don’ts for Engineer Hardwood

Choosing the right underlayment is a critical decision when installing engineered hardwood flooring in your home. The underlayment sits between the subfloor and the hardwood planks, serving several important functions:

Cushioning: It absorbs impacts and makes the floor more comfortable to walk on.

Moisture protection: It safeguards against moisture damage and mold growth.

Thermal insulation: It reduces heat loss through the floor and makes rooms feel warmer.

Sound insulation: It dampens noise transmission from foot traffic and improves quietness.

With all these benefits, it’s vital to pick an underlayment tailored to your specific flooring and subfloor type. The right choice depends on factors like climate, room use, and whether the installation is over concrete or wood. The wrong underlayment can lead to premature floor damage, mold, squeaking, and more problems down the road.

This comprehensive guide takes the guesswork out of choosing underlayment for engineered hardwood installations. It covers:

  • Key types of underlayments and their best uses
  • Recommendations for concrete and wood subfloor applications
  • Proper underlayment installation techniques
  • Cost considerations and product options
  • Common underlayment mistakes to avoid

Follow these engineered hardwood underlayment dos and don’ts to protect your investment and enjoy a warm, quiet, durable floor for decades to come.

Types of Underlayment for Engineered Hardwood

Underlayment falls into four main categories, each with advantages and ideal applications:

1. Foam Underlayment

Foam underlayment provides cushioning for engineered hardwood floors. It absorbs impacts from walking and furniture shifting, protecting planks from denting while making the floor more comfortable.

It offers thermal insulation against heat loss, helping rooms feel warmer. Most foam underlayments have moisture barriers to safeguard from spills and high humidity. They moderate sound transmission as well, cutting down on creaking and ambient noise transfer.

The two types of foam underlayments are:

  • Polyethylene foam: Made from plastic polymers, polyethylene foam comes in lightweight rolls. It’s one of the most affordable and common foam underlayment options.
  • Polyurethane foam: Polyurethane foams have higher density and rigidity than polyethylene. They offer firmer support, better moisture resistance, and longevity. But they also have a higher price tag.

Foam underlayment works well over wood and concrete subfloors in above-grade installations. The thickness can range from 2 to 3 mm up to 10 mm for maximum cushioning. Go with a thicker foam underlayment for concrete subfloors, which offer less natural give.

2. Cork Underlayment

Cork underlayment is fabricated from recycled cork oak tree bark. It boasts natural moisture-wicking properties and resists mold and mildew growth. Cork holds up well under heavy furniture without flattening.

As a natural material, cork provides warmth and insulation against both hot and cold. It dampens vibrations and sounds for serene interiors as well. Cork underlayment works with radiant heating systems too.

Cork comes in dense sheets sized to fit floors with little waste. It lasts for decades with proper installation and care. And it’s a sustainable green product made from recycled organic materials.

On the downside, cork is one of the more expensive underlayment options. The cost is justified by exceptional durability and performance.

Cork underlayment suits concrete and wood subfloors in above and below grade rooms. Go with a thickness between 2 and 5 mm based on flooring type and traffic levels.

3. Felt Underlayment

Felt underlayment is an economical choice made from recycled fibers. It goes down quickly in wide rolls spanning large floor spaces.

Felt underlay’s moisture barrier protects against spills, humidity, and subfloor moisture. It insulates from heat loss and cold transfer for better energy efficiency. Felt also blocks noise for serene spaces.

However, felt underlay does not cushion floors from impacts. It compresses and flattens readily under heavy furniture loads. Felt also lacks longevity compared to foam and cork, requiring replacement sooner.

Felt underlayment suits floating engineered hardwood floors over wood or concrete subfloors. Use thicker 10+ mm felt for basement and concrete floor installations. Otherwise, 2 to 3 mm felt should suffice in ground level rooms.

4. Rubber Underlayment

Rubber underlayment boasts unmatched durability and resilience. Made from recycled rubber, it bounces back from compression without flattening or taking a set.

Rubber underlayment blocks moisture, insulates from temperature swings, and prevents noise transmission better than most alternatives. It works on any subfloor type, above or below grade.

Thanks to its stiffness and vibration damping, rubber excels at reducing floor squeaks and creaks. This makes it a top choice for multistory homes and floors with existing noise issues.

Like cork, rubber does cost more than foam and felt underlayments. But it lasts for decades, outperforming other cushioning materials over a lifetime of use.

For engineered hardwood, choose rubber underlay thickness based on the subfloor type:

  • 2 to 3 mm for plywood/OSB subfloors
  • 5 mm for concrete subfloors

Underlayment Recommendations by Subfloor

Underlayment selection depends greatly on the subfloor the engineered flooring gets installed over. The two most common subfloors are concrete and plywood/OSB. Each has important considerations when picking underlayment:

Underlayment for Concrete Subfloors

Concrete lies at ground level or below, making moisture migration a pressing issue. Without protection, moisture seeping through concrete can warp hardwood planks.

Thus proper moisture barrier performance is the top priority for underlayment over concrete subfloors.

The underlayment also needs enough compression resistance and thickness to cushion engineered hardwood over rigid concrete:

Recommended products for concrete subfloor:

  • 5+ mm polyurethane foam
  • 5 mm rubber
  • 5 mm cork

Cork rates as the best concrete subfloor underlayment for sound insulation and warmth. Polyurethane foam offers the next highest performance for the price. Rubber costs more but lasts longer.

Install these underlays loose laid over concrete subfloors. Tape seams with moisture barrier tape to protect from moisture migration at joints.

Underlayment for Wood Subfloors

Plywood and oriented strand board (OSB) subfloors have more give than concrete naturally. Here moisture migration is less of an issue.

The priorities become cushioning the floor, insulating from heat loss, and reducing ambient noise transfer.

Recommended products for wood subfloors:

  • 2-3 mm polyurethane foam
  • 2-3 mm rubber
  • 2-3 mm cork

Polyethylene foam can also work for floating floors over OSB/plywood. But polyurethane foam offers better compression resistance and insulation.

For wood subfloors, attach the underlayment with staples so it stays fixed to the subfloor. The stapled seams don’t require moisture barrier tape.

Proper Installation Techniques

Installing underlayment takes precision and care to realize the benefits. Follow manufacturer instructions for best practices. Here are general guidelines for engineered hardwood underlayment installation:

1. Subfloor Prep

The subfloor must be level, clean, and structurally sound before underlayment goes down. Scrape up old adhesives or debris and vacuum thoroughly.

Check for loose boards, protruding fasteners, and gaps to address first. Moisture test concrete subfloors to ensure dryness. Let new concrete cure 60+ days before underlayment installation.

2. Layout

Map out the underlayment layout to minimize seams and waste material. Underlayment seams should offset from subfloor seams by at least 6 inches.Run the underlay lengthwise down the room parallel with the flooring planks. Face the moisture barrier film up to the hardwood flooring backer.

3. Attachment

For concrete subfloors, loose lay underlayment over the surface without attaching it.For wood/OSB subfloors, roll out the underlayment and staple it every 4 to 6 inches along seams and throughout the floor. This prevents slippage during flooring installation.

4. Seam Taping

Seal underlayment seams with moisture barrier tape for concrete subfloors. Use acrylic or pressure-sensitive tape for best adhesion. This prevents moisture sneaking under the flooring along seams.Do NOT tape seams for wood subfloor installations. Stapling the underlayment is sufficient here.

5. Overlaps

When joining rolls end-to-end, overlap underlayment seams by 4 inches minimum. For concrete subfloors, seal the overlap seam entirely with moisture barrier tape.

6. Upturns

Extend the underlayment 2 to 3 inches up walls around the perimeter. This acts as a termite barrier and minimizes drafts from outside walls. Note that upturns are often not required for floating engineered hardwood installations.

With the underlayment installed properly, you can proceed with acclimating and fitting engineered flooring planks. Take care not to tear or puncture the underlayment moisture barrier when fastening boards.

Underlayment Cost Considerations

Here’s how the four main underlayment categories compare by typical price range:

  • Felt: $0.15 – $0.40 per sq.ft.
  • Foam: $0.20 – $1.00 per sq.ft.
  • Cork: $1.00 – $2.00 per sq.ft.
  • Rubber: $1.00 – $2.00+ per sq.ft.

Cork and rubber cost more upfront. But their durability offsets that over years of use before needing replacement. Polyethylene foam offers the most bang for the buck, while polyurethane foam balances cost and performance.

Also account for labor savings during installation. Rolls of felt and foam underlayment go down quicker than rigid sheets of cork. Excess cutting and seam taping can add hidden costs too.

Consider the engineered hardwood flooring cost per square foot too. Higher-end engineered wood merits splurging on better underlayment materials to protect your investment.

Common Mistakes to Avoid

Pitfalls like these trip up homeowners and flooring contractors alike. Avoid these underlayment blunders on your next engineered hardwood installation:

1. Wrong Thickness

Too thin, and the underlayment fails to cushion floors properly. Too thick interferes with locking engineered planks together tightly.Stick to manufacturer guidelines for underlay thickness. Generally aim for 2 to 5 mm padding.

2. Forgetting About Moisture Protection

All underlayments provide some moisture resistance. But polyethylene foams and felt lack enough protection for concrete subfloors. Spring for polyurethane foam or cork instead.

Don’t forget to tape seams between underlayment sheets and upturns. Moisture ingress through gaps causes the most problems.

3. Uneeded Upturns

Upturning underlayment along perimeter walls wastes material on floating floors. It can also block floor movement, causing buckling issues.

Reserve upturns only for nail-down installations. For floating engineered hardwood, trim flush with walls.

4. Stapling Underlay Over Concrete

While stapling underlayment makes sense for wood subfloors, it’s wrong for concrete. Possible punctures compromise the moisture barrier. The staples also lack grip in concrete and fail to hold.

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