By following our check list you can avoid problems like this
I thought I'd write a check list to help general contractors, builders or DIY home owners address some of the basic issues regarding hardwood flooring installation.

1. Plywood sub-floor
  • For nail down installations (engineered or solid wood) use STD Douglas Fir plywood     
  • Minimum plywood thickness should be 5/8”
  • We don't recommend OSB (oriented strand board) for nail-down installations because we don't believe it provides the same holding power as plywood.

2. Sub-floor 'flatness'
  • Should be 3mm + or – over 10’ (concrete or plywood)
        For plywood sub-floors
                - Level the plywood sub-floor by sanding off high spots and building up low spots with layers
                  of 1/8" or 3/8" thick plywood as necessary. Glue and nail, or staple the extra layers of plywood
                  into place.

        For concrete sub-floors
               - Grind down high spots and use cement leveling compound to fill in low areas.  Use best quality
                 cementitious leveling compounds with an acrylic additive for flooring that is to be glued down.
                 Less expensive self leveling products can be used for floating floors.

3. Sub-floor moisture
  • The maximum moisture content in the plywood sub-floor should be 12%. The difference in                           moisture content between the plywood and the hardwood should be no more than 4%.
  • Concrete moisture content should be no more than 3lbs of vapor emissions per 1000sqft.                               Use a Calcium Chloride test (ASTM F1869) or RH test (ASTM F2170) to confirm this.
  • Installing solid wood flooring over a crawl space or car port or garage risks excessive                                     shrinkage and expansion.
  • Always use a moisture barrier when installing wood flooring on concrete which is at or below                         ground level.

4. Site Conditions
  • Never acclimate the wood flooring on site without confirming the sub-floor is dry, the space is heated to 20c, and the relative humidity is between 40% and 60%.
  • Ensure the space to receive the hardwood flooring is at lock-up stage (protected from the outside elements) and has the main heat on before delivering the flooring to site.                      

5. Hardwood flooring moisture content
  • Should be approximately 8%.

6. For nail down installation
  • Nail or staple the hardwood every 6” to 8” when installing over plywood.

7. Reducing squeaks/tighten the sub-floor
  • Re-screw old sub-floors with 2” or 3” decking screws before installing the hardwood flooring.

8. Relative humidity in the house
  • Should be between 40 and 60% before the wood flooring is delivered.

9. House temperature

  • Should be at 20c before wood flooring is delivered.

10. Trades using water in their product (i.e. tile and drywall)
  • Work must be completed before the hardwood flooring can be shipped to site.

All of this information and more can be found in the National Floor Covering Association's 'Floor Covering Reference Manual' -  a fantastic source of information for floor covering installations. You can buy this manual on line at http://www.mfcsi.com/reference-manual.html

Note: ALWAYS read the installation guidelines or instructions that come with the product you have purchased.  Those instructions should supersede any instructions given above.  Avoid purchasing your flooring from an auction because of potential milling, moisture content and warranty issues.  Hardwood flooring problems are expensive to fix (if they can be corrected at all), choose a product and installation firm that has a good reputation and offers a real warranty.

acoustical sound underlay, hardwood flooring sound barrier
Noisy neighbors and hard surface flooring don't mix. 

You can, however, reduce noise transference by using 'sound absorbing underlay' for floating hardwood or laminate floors.

Here are some general points about sound-absorbing underlays that may help you with your purchase decision:

Make sure that the underlay you choose has been tested using ASTM International (formerly American Society for Testing and Materials) standards .  Ask for paperwork that substantiates the underlay manufacturer's claims of the product's sound absorbing qualities. The product should have been tested in accordance with ASTM E-492.

The test results should show a couple of things....

1. An IIC (impact insulation class) rating
This is the number used to rate the sound absorbing characteristics of the underlay when noise produced from a test impact is measured.  The higher the rating the better the product is at absorbing sound.  Most products on the market have an IIC of between 60 and 75.

2. An STC (sound transmission class) rating
This measures a building material's (in this case underlay) ability to absorb audible noise such as voices or TV sound.  Most products on the market have an STC in the high 60's.

I tell my customers that 90% of the noise problems in condos exist because of lifestyle.  If you have a noisy lifestyle, then your neighbors will hear you. There is not a sound absorbing underlay on the market that is going to stop clacks and bangs, or noise from loud TV's from transferring through walls or wood flooring to neighboring suites.  Yes, a high density foam underlay with a good IIC rating will reduce the noise transference but it will not eliminate it. 

With this in mind, strata councils or building managers put rules in place (by-laws) that require a high IIC rated underlay be used for any new wood or laminate floor installations.  By doing this, they can say they made a reasonable effort to keep noise transmissions to a minimum should there be a complaint.

In some cases, just to keep the peace between neighbors, by-laws go further and demand that for example, 60% of the new hardwood or laminate flooring be covered with area rugs.  If you've ever lived beneath noisy people who have hardwood flooring you will understand why.

My advice....keep it simple.

1. Check your building's by-laws regarding sound barrier and IIC / STC requirements for hard surface flooring before installing your new floor.  In this case, it's better to ask permission than beg forgiveness!

2. Set expectations - living creates noise!  If you have a couple of active kids, play the piano, wear shoes that clack on the floor as you walk around the apartment, walk with heavy foot falls, you drop things, you like your stereo or TV sound turned up louder than most - then you are going to be heard by your neighbors.

3. Use area rugs to help reduce noise.

4. Do not nail wood flooring to an acoustical underlay.  This allows for too much movement in the wood floor pieces and will likely lead to squeaks and gaps.  Also, nails or staples facilitate sound transference similar to that of a tuning fork.  If you are nailing the flooring to a wooden sub-floor and want to insulate against sound transmission, then you will need an altogether different kind of sound barrier system - it's time to consult an architect or experienced builder.

If you live in a wood frame building with no acoustical concrete topping between floors, a sound absorbing underlay with the highest IIC rating, will not prevent sound transference.  Most underlays achieve their IIC and STC ratings from testing over concrete sub-floors. Wood frame construction and plywood substrates are notoriously bad at muffling sound and none of the products that I know of on the market are going to change that.

Hi-rise concrete buildings are best for natural noise containment because concrete is a great sound barrier.  Most hi-rise construction consists of 6" to 8" of concrete sub-floor between you and your neighbors below.

With all this said, a few underlay recommendations that are readily available and that I consider to be good value sound barriers for a floating floor installation are:

1. Dura-son
2. Sound Blocker
3. Floor muffler
4. Cork

There are many more on the market to choose from.  Check that the IIC and the STC ratings comply with your bylaws, and make sure that the IIC rating given to the product was gained using ASTM E-492.

Radiant heat and hardwood flooring diagram
It happens more often than you would think.

I was called out to measure a hardwood flooring project for a new custom-built home being constructed by a local builder. The builder wanted over 3000 square feet of solid, unfinished, quarter sawn nail-down, oak flooring installed, sanded and finished.
I reviewed the job site with the builder. He described the sub-floor as being 3/4" standard douglas fir plywood that he had glued and screwed to sleepers. The heating system was hot water radiant heating set in concrete (as shown in the cross section picture). 

I measured the square footage and took my moisture tests.  It showed the plywood was dry at 11 - 12% moisture content. This is exactly what is recommended.  I went back to the office, wrote up my quotation and faxed it to the builder.  Two weeks later, I was awarded the job and asked to go back to the job site to measure an additional room.

It turned out to be a stroke of luck that I had to return to the site.  While I was there, I did another moisture test. The reading was now 18% in the plywood.  I went into the other areas of the house that I had tested two weeks prior, and all were reading 18% plus moisture content. 

What was going on?

The builder had poured the concrete over his radiant heat piping and up to the top of the sleepers in the correct way, but had not allowed the concrete enough time to dry before he installed the plywood. The newly installed plywood was now absorbing the moisture from the concrete raising it to 18 - 20%. Way above the recommended 12%. 

Even with the heat turned on, this situation would take a really long time to correct itself.

The result?  All the plywood had to be removed....an expensive mistake.
Now, with the concrete exposed the heat was turned on and the concrete allowed to dry.  The new 3/4" plywood was then installed. 

At least a bigger disaster was averted...had the hardwood flooring been delivered to the site and allowed to acclimate on the 18% sub-floor, it would have absorbed the excess moisture and been installed in an expanded state. Later, once the heat was turned on, the flooring would have shrunk leaving behind unsightly gaps between the boards.

Simple advice:
  • Just because the concrete is hard and looks dry does not mean that it is dry enough for a hardwood floor installation. Check the concrete moisture content and the moisture content of the 2 x 4 sleepers before you overlay with plywood.
  • Ensure that the home's heating system is operational, the temperature in the home is approximately 20 celsius and humidity levels are between 40% and 60%.
  • If the heating system is not yet hooked up, do not deliver the hardwood floor to site until it is.
  • Under good drying conditions, concrete dries at about 1" per month in a 3" thick pour.  Radiant heated slabs will dry much faster. The thicker the slab the slower it dries (i.e. 4" might take 5 months to dry and so on).