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Hardwood Flooring and Radiant Heat

Radiant heat is heat energy that is transferred from one surface to another through a space by means of energy waves.  Radiant heat differs from other conventional heat systems which typically rely on rising warm air to heat surrounding air.  Radiant heat is “omni directional.”  When there is a temperature difference between two or more surfaces, the heat energy will travel in multi directions from the warmer surface to the cooler until all surfaces have reached equal temperatures.

Because of radiant heat’s efficiency and benefits (no dust, moderation of temperature), it has become more popular each year.  In fact, manufacturers of tubing used in radiant floor heating systems increased production nearly 25% in 1997 over 1996.

Also, hardwood flooring has increased in demand and design over the last several years.  Today, consumers surrounded by computers, fax machines, cell phones, pagers and synthetics of every kind still prefer natural products, like hardwood flooring, where technology and the forest collide.

Is solid hardwood flooring compatible with radiant heat systems?  It is important to note that hardwood flooring does not impair radiant heat efficiency, however technical difficulties with the flooring may arise when using quarter-inch solid material.  Wood is hydroscopic – it expands and contracts in size with an increase or decrease, respectively, of the environment’s moisture content.  Simply, wood functions like a sponge,  Because of this, the use of humidity controls and acclimating wood products is critical.  When wood experiences drastic shifts in moisture content, such as flooding, or conversely overheating, the wood fibers can become traumatized resulting in problems like cupping, warping, splitting checking and crowning.  Prior to any installation, acclimation of wood products is key.

Radiant heat systems should be operated at least 48 hours prior to delivery of wood flooring.  This allows time to drive existing moisture from the slab or sub floor.  Upon delivery, wood flooring should acclimate to the site for at least 72 hours and all heat sources should remain operable throughout installation and finishing, should the floor need to be jobsite finished.

It should be stressed that cementations products such as concrete and gypcrere should be dried for a period of 50 days to 60 days before the introduction of any wood flooring product.  the radiant hear boiler should not exceed 125 degrees, which should limit the temperature of the sub floor surface to about 85 degrees.  This is important because it not only reduces he likelihood if overstressing the wood fibers, but also is the breakdown temperature for most mastics used with glue down flooring.  In all cases the manufacturers’ instructions and recommendations for the installation of their products should be followed.

Manufacturers of radiant heat systems and hardwood flooring often recommend the use of three thermostats, one to control the temperature of the water in the tubing, one to control room temperature per zone and one for outside the home.  The thermostat outside the home allows the internal system to prepare for the arrival of colder weather.  Many consumers move from the non heating season to the heating season with a bang.  Cranking the hear up on the first cold day of the year can traumatize wood flooring.  It’s best in any case to bring heat on slowly over the course of a few days.  Again, the use of humidity controls us always advantageous.

A variety of wood species are available today, and not all are suitable for installation over radiant heat.  Each species has its own ability to change with moisture conditions, a change measured with the use o dimensional change coefficients.  Such data is detailed in technical manuals and materials from organizations such as the National Wood Flooring Association.  According to the NWFA, Douglas Fir, for example, has a change coefficient of .00267 and is approximately 28% more stable than red oak, which has a change coefficient of .00369.  By multiplying the change in moisture content by the change coefficient, then multiplying the width of the board, the amount the wood will shrink or swell can be calculated.Click here for a graph Example: A three inch Teak board (change coefficient .00186) experiences a 3% change in moisture.  Calculation: 3 * .00186 = .00558 * 3 = .01674 inches.

This is a little technical for wood flooring, but very helpful when planning which products to use with radiant heat.  Aside from the species, wood products that have been quarter sawn rather than plain sawn, offer more dimensional stability as well.  When choosing which species of wood to install over radiant heat, doing your homework is critical.

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Hardwood Flooring and Radiant Heat – Installation Techniques

There are several methods for installing wood flooring products over radiant heat.  In most cases, the use of engineered products is preferable.  Engineered wood flooring products are manufactured by bonding layers of lumber or veneer, similar to plywood.  Each layer is directionally opposed for dimensional stability.  For many years these floors were called “laminated”, but with the introduction and popularity of melamine laminates like Pergo and Wilsonart, wood flooring engineers have chosen the term “engineered” to eliminate confusion between what is wood and what is plastic.  Melamine, or laminate wood flooring, is usually a photograph of wood grain imprinted in a plastic-based material mounted on particle board.  Engineered wood, as described above, has a solid wood surface.  Engineered wood floor products offer the best performance over radiant heat, and can be installed three ways: glue down, staple down or floating.

Glue-down flooring is engineered flooring applied to a sub floor using a notched trowel and a mastic or adhesive.  Though glue-down wood floor installations are popular, problems can arise with the use of radiant heat.  As described earlier in this article, mastics can break down if the heated surface exceeds 85b degrees  Engineered flooring can now be installed with a new system designed to use pneumatic staplers.

Staple-down installations are relatively new.  Specially designed staplers similar to Luan staplers allow the fastening of tongue & groove, engineered flooring over a variety of sub floors, including oriented strand board.  The system uses a small one inch staple that may be blind-nailed.  The problems to avoid with this application are stapling into heating coils and tubes, and under fastening.  If a tight fastening schedule of every 2-3 inches is not followed, the floor can snap and squeak due to excessive movement between board surfaces.  This new method of installation has been moderately successful; many of the minor technical difficulties have corrected over the last few years.

This leaves the last and most efficient application of wood flooring over radiant heat, the floating floor.  Installing a floating floor over radiant heat is the most efficient application.  Though this is my personal and professional opinion it is shared by the vast majority of manufacturers and technicians.  The floating floor is an engineered product, usually 9/16 to 5/8 of an inch thick with a solid wood top layer of about 1/8 of an inch.  Floating floors are installed over an 1/8 of an inch padding of dense foam or radiant heat underlayment.

Offered in a wide variety of wood species, the floating floor usually is comprised of three layers.  The bottom two layers consist of two opposing conifer, or softwood, layers.  The middle is often made of several pieces similar to parquet fingers.  Spaces between each piece allow any expansion that may occur to take place in the area beneath the hardwood surface, this giving the floor more dimensional stability.  The floating floor is installed in seven foot sheets.  The surface typically has three rows of 2.5 inch hardwood that resembles traditional strip flooring, though single strip, plank and other combinations are common.  Installation of floating floors is often very simple.  A wood glue is applied under the upper-inside groove and on the end joints.  The flooring is then banged together with a hammer and a wood block.  Extremely accurate milling allows the floor to square up easily while the glue has time to set.  Once cured, the floating floor does just that — it floats..  No fasteners, no clops, just one big sheet of flooring.  A simple and efficient application of a dimensionally stable wood flooring product over radiant heat, the floating floor may also be sanded and refinished in the future.

Whether choosing an engineered or solid hardwood flooring to install over radiant heat, it is crucial to weigh all technical information to ensure a sound and aesthetically pleasing installation.  The information supplied by the radiant heat supplier and hardwood floor installer should offer answers to any questions regarding the merging of thee two products.  In any case, consider your flooring, hearing and manufacturer’s recommendations with any product installation and enjoy the profits from a satisfied homeowner.

Q: MY FLOOR HAS CRACKS IN IT. IS THIS NORMAL?
A: Because wood is a natural product it will react to changes in its environment. The most common causes of separations are Mother Nature and dryness. The loss of moisture results in  the most frequent reason for shrinkage of individual pieces and cracks. Most cracks are seasonal – they appear in dry months, or the cold season when heating is required, and close during humid periods. This type of separation and close is considered normal. In solid 2 ¼” wide strip oak floors, “dry time” cracks may be the width of a dime’s thickness (1/32nd”). Wider boards will have wider cracks and the reverse is true.
The cure is to minimize humidity changes by adding moisture to the air space during dry periods. A constant Relative Humidity (RH) of 50% with a temperature of 65-75 degrees (Fahrenheit) provide stability to the floor.

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Q: WHY IS MY WOOD FLOOR CUPPING?
A: Cupping, or “washboard”. Across the width of one piece of the flooring material, the edges are high, the center is lower. Generally develops gradually.

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CAUSE:
Moisture imbalance through the thickness is the only cause. The material was manufactured flat and was flat when installed. Job site or occupant provided moisture is greater on the bottom of the piece than on the top. Find the source of moisture and eliminate it. Common moisture sources and their corrections are: Airborne Relative Humidity– dehumidify air space or– humidify air space during the heating season Wet basement – ventilate, dehumidify Crawlspace – total groundcover with black plastic 6 mil; vents; add exhaust fan on timer Rain handling provisions – correct to drain away from house
Reduce excessive lawn & garden moisture, waterproof foundation Repair leaks, i.e. plumbing, roof, doors. Don’t hose patio In kitchen, the dishwasher and icemaker are notorious leakers. Expansion is also the result of site moisture and may have moved the floor tight to vertical surfaces. If so, remove flooring along the wall, or saw cut, to relieve pressure.

CURE:
Allow time. Time for the corrections to take effect – to permit the floor to improve on its own. It may become acceptable.  After stabilized, sand flat and finish.

Hardwood Floors…All that they’re cracked up to be
Well, ’tis the season… the season for cracks in your hardwood flooring.  When the temperature drops, the heat goes on and the humidity goes bye bye, that’s when the phone calls start coming in: “This floor is brand new, why am I getting cracks?”. “Can you send someone from the factory out? I have gaps everywhere.”  The calls will continue until the hear goes off and the humidity returns.

Let me reassure you that not only are gaps common at this time of year, bit they are almost welcome.  If you have a tight floor now, there/s a good chance you have compression this summer, and that’s bigger trouble.  It has been said that there in New England that we have two seasons, July and Winter or in wood terms, heating and non-heating seasons.  There are several other reasons for cracks in floors that have little to do with moisture, here are a few: Foundation settlement, over a drying above forced air hearing ducts, and improper sub floor materials.  The truth of the matter is that conditions vary greatly from site to site, but for certain, the heating months bring about the most significant changes in wood flooring and here’s why as taken from the NWFA technical manual:

“Wood is an hygroscopic material.  When exposed to air, it will dry or pick up moisture until it is in equilibrium with the humidity and temperature of the air in its environment.  Absorption of moisture causes wood to swell.  Loss of moisture causes wood to shrink.  Shrinkage begins at 25-30% moisture content, the fiber saturation point.  Shrinkage continues to 0% moisture content, an oven-dry state.  Swelling occurs as wood gains moisture.  Swelling occurs from 0% to 25-30% moisture content, the wood saturation point.  Wood does not shrink or swell equally in all directions.  Wood changes approximately: 0.1% along the grain and annular rings (radially) quarter sawn, and 5% to 15% across the grain parallel to the annular rings (tangentially) plan sawn.”., Knowing that the majority of flooring used is plain sawn, you can see why we have so much gapping here in New England.

“If a 3/4″ x 2-1/4″ oak strip is exposed to an environment which changes the moisture content by 4% (i.e. from 7% to 11%) the strip may swell as much as 1/32 of an inch.  The opposite is true, if a 2-1/4″ strip begins at 11% moisture content and loses moisture to 7% moisture content, the strip may shrink as much as 1/32”.

Moisture changes such as thos here in New England can range upwards of 9%, a change as drastic as this could cause strip flooring to lose a full 1/16″!  As humid as it was this summer, you can understand why gapping this heating season will be nearly unaviodabl;e without some form of humidification system.  The NWFA Technical Manual offers a more in-depth study of moisture relative to wood flooring including some helpful chart, scales and diagrams and is available through the National Wood Flooring Association.

Field Expansion
The Boston area is known throughout the country as being the exception to the rule in the wood flooring trade.  It seems that for every tip and technique used elsewhere that we always find a way to do things a little different.  This is what makes our region unique from other wood floor markets, and why many of the applications studies for new products involve special attention to the variety of needs here in New England.  We are a valuable, diverse, pioneering and enthusiastic asset to our industry.  However, whether you are a third generation floor man, sand and finish expert, installation genius, hardwood junky, pre-finished powerhouse, designer, architect, retailer, homeowner, mailman, chicken rancher bush pilot, WHATEVER…if you still ‘net-fitting’ wood flooring, you’re not offering a professional wood floor installation.

When a wood floor is scribed to the baseboard, one of two things happen: the floor will shrink, thus leaving a neatly scribed gap everywhere just beg enough to catch dirt, dust-bunnies, kids toys, and other assorted aesthetic distractions.  Or, secondly, compression-set, cupping, squeaks, cracked jams, etc., etc., etc. from the expansion of flooring into areas where THERE IS NO EXPANSION SPACE!
I have heard it all from the ‘I’ve been doing floors since Moby Dick was a minnow’ speech, to the ‘Well, you don’t scribe because you just don’t know how to do it, nah, nah, nu, nah, nah.’ speech.  I have also had the occasions where the speech-givers have called me to say they need to be bailed out of a jam where the customer is complaining of a variety of problems, and in confidence all I can tell thr floor guy is that he should have left proper expansion.

I know that many times, leaving ¾” expansion is impossible, especially when the base is only ½”.  However, make it a point to leave all that you can.  I know floor experts that will clinch jobs because even though the guy before him does good work, he was the only on that promised to leave expansion- a guideline set by all major governing bodies of the flooring industry.  Being ‘in the business for forty years’ isn’t any justification for ‘net fitting’.  If this is one’s gospel, then let them attend the next NWFA convention and they can tell that story to the hundreds of true wood experts that have more experience, knowledge, success and square-footage under their belts than most would hope to have.  .
Here are some guidelines for the application of expansion are and keep in mind that this includes: Unfinished, prefinished, floaters, glue-downs, tracks, clips, and especially products like Natural Reflections and wide planking, which are sensitive to change.Heat and air conditioning should be operating ahead of installation. Products should be acclimated a minimum of 72 hours on the jobsite with boxes open for proper air circulation.

Use a moisture meter to make sure flooring moisture content is equal to moisture content of the jobsite.
Leave maximum amount of expansion possible, even if you have to cut the drywall.
Expansion is more important tangentially, or across the grain of plain sawn lumber which is most commonly used.  Though wood expands only 0.1% along the grain, longitudinally, remember that many floor squeaks come from wood rubbing against drywall and trim. Since moisture content in New England runs an average 6-12%, at an average temperature of 50.5 degrees Fahrenheit, relative humidity at around 55%, a floor that is equal in moisture to the jobsite at close to 9% would be an excellent median point for installation.  With proper expansion, this floor is less likely to gap or compress.

For low humidity jobsites that will eventually become humid, use one of the following methods to avoid problems, or make a note not to install the floor super-tight, leaving natural gaps alone.

  • Use a .020″ sheet metal spacer every 5 to 6 rows to leave small gaps
  • Use a .010″ spacer every 3 rows
  • Use ‘minute’ spacers (.003″) between each row.  With Natural Reflections this can be accomplished by leaving the boards finger tight.

Note: if homeowners go on vacation, the humidity level inside the home will equalize with the outside ambient humidity.  To avoid expansion, temperature should be maintained at approximately 70 degrees Fahrenheit.

Wood changes approximately 5%-15% across the grain and parallel to the annular rings (tangentially) in Plain Sawn wood:  the greatest possible dimensional change.  Because of this, in an area that could change as much as 4% (i.e. from 7% to 11%) wood could shrink or swell as much as 1/32″.  Also, note that finish coatings retard, but don’t prevent moisture.  Being adept to change in any trade is important.  Most floor people don’t use the recommended wood flooring applications, not because their way is better, but because that is their way and they do not want to try anything new.  In actuality, leaving expansion is not only the professionally recommended method, but it will make a job go faster, neater but also reduces the risk of possible problems so as to guarantee repeat business.  Door jams can be undercut which is neater and faster than scribing and no warranties are voided.
In closing, how one chooses to perform their particular trade is their business, but there is an understanding among the best and the majority in the wood flooring industry that expansion is a necessity, not an accessory.  Good luck!

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Wood Floor Care & Maintenance
Today’s wood floor finishes are relatively easy to maintain. Enjoy your wood floor for many years by following the simple steps listed below.
Place walk-off rugs at entrances. This will help trap grit, which can scratch your floor. The rugs should be vacuumed and cleaned on a regular basis. These rugs should occasionally be moved to provide equal oxidation throughout the entire floor, allowing the floor to age at the same rate throughout. Avoid using the rugs until 2 weeks after the finish has been applied to allow the finish to fully cure.
Place mats near high spill areas (refrigerator & sinks). Do not allow soiled rugs to stay on the floor as they can trap moisture in the wood floor. Rugs should be cleaned on a regular basis.
Never apply water on your floor. Never wet-mop your floor. A damp/dry mop is fine as long as the moisture is limited to an amount that will evaporate almost immediately. Any additional water will seep through plank cracks causing the finish to break down and wood fibers to expand. A wet rag may be used for cleaning up spills. However, be sure to dry afterward to avoid leaving any moisture on the floor.

Vacuum your floor regularly to remove grit, dirt and rocks that can scratch your floor finish.
Always use the manufacturers recommended cleaning products on your floor. If you don’t know the manufacturer, use a generic hardwood floor cleaner designed for the type of finish that is on your floor.

A cleaner for surface finishes, such as urethane, is quite common and readily available. This is generally a water-based product similar to Windex. Do not use Windex, as it will leave a film. Do not use a solvent based (petroleum based products) cleaner on urethane-finished floors (surface coated). Solvents/petroleum’s will soften and break down a surface finish.

Solvent type maintenance products were originally created for waxed hardwood floors and are still important products for floors that are finished with penetrating oil or wax finish. Although not as common, there is still a demand for this traditional finish. Using a water-based cleaner as in the urethane finished floor cleaners will ruin a penetrating finish. It will turn it first a white color (like a ring from a glass on a coffee table) and eventually black as it rots the wood.

Put floor protector glides under your furniture legs. This will allow your furniture to move but not scratch the floor.

Shoe Heels can exert a tremendous amount of pressure pounds per square inch. They can dent even the hardest of floors. Baseball cleats or even a dog with unclipped toenails can also damage a floor.
Refrigerators and dishwashers with bottom motors should have appliance trays installed under them to protect the floor from heat. Heat can cause the floor to have varying degrees of dryness. This may cause uneven shrinkage and cracking. These cracks, while not obvious, will collect dirt causing them to become more visible over time.

If the floor is beginning to show significant wear it may be time to recoat the floor. Consult an NWFA flooring professional regarding your options. By recoating the floor at the first signs of wear, you will be able to bring your floor back to new condition with just a recoating. If the floor is allowed to wear into the wood, it will require the floor to be resanded and then coated resulting in a much higher cost.

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Q- What’s the difference between engineered flooring and laminate flooring?
Let’s start with the original term laminate flooring. Before plastic laminate flooring became popular in the mid ’90’s those in the hardwood flooring business called today’s engineered flooring laminate. Engineered flooring is constructed in layers similar to plywood with an actual finished hardwood veneer layer on the surface.

Today’s laminate flooring is a photographed image of finished hardwood and cannot be refinished, whereas manyengineered products can be refinished. How many times will depend on the thickness of the veneer, or top wear layer, and finding someone knowledgeable enough to handle the work.

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Q- Can I have a solid 3/4″ hardwood glued to concrete?
You’ll find some retailers will say yes. However, those that have dealt exclusively in hardwood flooring for some time will say no. In recent times some of the big box stores and adhesive manufacturers have been advocating this procedure. Only time will tell if it’s a viable procedure, but it’s safe to find an alternative.

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Q- What kind of hardwoods can I place on concrete subfloors then?
If moisture conditions are acceptable, two of the most widely used applications would be engineered hardwood floors glued direct with the proper adhesives, and floating engineered flooring types. The latter typically glued by tongue and groove and floated over a foam cushioned underlayment. Floating floors are also available in the click together style that require no gluing.

More traditional 3/4″ solid hardwoods on concrete can be accomplished with the addition of a plywood subfloor, used as a nailing base over the concrete. However, this raises problems with door entries and other items. Overall vertical height of the new floor will increase by 1 1/2 inches. Unfinished engineered hardwood floors eliminate vertical height issues and can be stained or finished to any desires.

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Q- I have a particleboard subfloor. Can I have nail down hardwoods installed?
Many confuse particleboard with OSB(Oriented Stand board). True particleboard commonly used in some manufactured homes does not have the holding power of hardwood flooring fasteners and will loosen over time. There are certain types of OSB that can be used for solid nail down hardwood floors. It is best to consult the manufacturers warranty specs.