Installing hardwood floors FAQ

Q: Do I have to install the new wood perpendicular to the joists?

Oh, my, yes. Unless your subfloor is thicker than 1-1/2″ AND made of solid wood or plywood, hardwood strip must be laid at right angles to the joists. (Exception: Over diagonal, solid subfloor boards, install perpendicular to joists OR subfloor direction.)

Q: What tools will I need to install a hardwood strip floor?

Most, but not all installation tasks can be accomplished with hand tools. Here is a list of what you might need, noting where it is worth upgrading to a power tool to save time and aggravation.

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  • POWER TOOL: Pneumatic stapler, compressor and mallet
    • HAND TOOL EQUIVALENT: Manual nailer and mallet (not recommended; it is very difficult to snug boards tight together without pneumatic assistance)
  • POWER TOOL: Finish nailer and compressor (makes top-nailing your starter course much easier)
    • HAND TOOL EQUIVALENT: Drill, hammer and nail set (slower, but less expensive than buying a finish nailer)
  • POWER TOOL: Power jamb saw (for undercutting doorway trim)
    • HAND TOOL EQUIVALENT: Flexible blade pull saw and a chisel
  • POWER TOOL: Table saw or jig saw (for cutting right-angled notches for fitting flooring around corners)
    • HAND TOOL EQUIVALENT: No hand tool equivalent
  • POWER TOOL: No power equivalent
    • HAND TOOL EQUIVALENT: PowerJack (for snugging tight final boards that cannot be nailed with pneumatic stapler)

Q: Are you sure I need a pneumatic-assisted stapler?

Yes. Getting boards to snug tight together, especially long boards that are slightly out of true, is much harder without that pneumatic boost. Your rotator cuff will thank you.

Q: What is the deal with underlayment paper—do I really need it?

According to the National Wood Flooring Association, if you have a wooden subfloor, you do. The job of this paper is to act as a vapor retarder. A vapor retarder will slow down the movement of wet air to your floor.

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Your hardwood flooring needs to be in the room where it will be installed long enough that a moisture meter reading of the new wood is within 2 percentage points of the moisture meter reading of existing wood (primarily the subfloor) in the house.

This means that you must not have wood delivered to a jobsite before it is fully enclosed or before temperature and humidity conditions have reached the level they will be kept at when the space is lived in.

If you rush this step, and your installed floor either dries or absorbs moisture faster than the wood it is nailed to, it will exert force against its fasteners causing extreme gapping, lifted boards and squeaking.

“How will I know when my wood moisture is in equilibrium with its surroundings?” I hear you ask. You measure it with a moisture meter. We rent them. They are very easy to use and they will tell you exactly when that wood is ready.

Q: How long should the wood sit and acclimate in my house before I install it? Do I really have to do this?

Yes, you really have to do this! Acclimation is the act of allowing wood moisture content to achieve equilibrium with the environment in which it will perform. So, acclimation is not measured in time, but in moisture.

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Floors are designed to handle changes in humidity, but when it happens too fast, the boards can swell underneath, which leads to crowning on top.

Red rosin paper has long been the traditional underlayment, but it is no longer considered acceptable!

Acceptable vapor retarders over wood subfloors include:

  1. An asphalt laminated paper meeting UU-B-790a, Grade B, Type I, Style 1a.
  2. Asphalt-saturated kraft paper or #15 or #30 felt that meets ASTM Standard D-4869 or UU-B-790, Grade D.

Unfortunately, both alternatives are twice as expensive as red rosin paper. You never want to use plastic sheeting as an underlayment because that will cause moisture vapor to condense on its underside, which will lead to mold and rot in your subfloor and joists.

Q: What kind of nails should I use for top nailing?

2 to 2-1/2″ 7-penny finish nails.

Q: How do I know where to start?

In general, it’s best to choose a starting wall according to the most aesthetically or architecturally important elements in the room, taking into consideration fireplaces, doors, cabinets, transitions, and stairs.

If you are only worried about keeping things true, start on an exterior wall because it is more likely than other walls to be square.

The starting wall will often be the longest unbroken wall in the room. It is worth bringing your floor plan into our storefront to discuss the pros and cons of the various starting point possibilities of your space—we love doing this.

Q: Why do I need to leave an expansion gap? It would be so much easier to start right up against my drywall.

As a general rule, when installing solid 3/4″ hardwood, a 3/4″ expansion space must be left around the perimeter and all vertical obstructions.

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Yes, it’s a pain. Because of that gap, your starting course of boards must be artificially braced with screwed-down backer board or spacers.

But the consequences of eliminating that expansion gap can be dire. Remember, wood is hyrgoscopic; it wants to absorb moisture from the air.

When wood absorbs moisture, it swells, and the swelling produces enormous force. If your flooring is laid tight up against your studs or drywall and the indoor humidity increases, the floor has no place to expand and so the pressure will force the flooring up off the floor.

The moisture caused by a wet basement is enough to significantly swell and buckle the hardwood floor above it, so ignore the expansion gap rule at your own peril.

Q: How do I snug the last few rows together when I can’t use the nailer?

The accessory pictured above is a fabulous tool called a PowerJack. It is a simple, ratcheted jack that is braced against a stationary object while the lip end is hooked over the groove side of your flooring.

Just work the lever and those last crooked boards are drawn tight together. Our store in Minnesota rents a PowerJack to DIY homeowners.

Q: Is one species of wood better than another? Is there a difference between different grades of wood?

Different species of wood have properties that make them better suited to certain conditions (or customers!) but there is no ‘best’ wood. Many people equate hardness with high quality, but harder woods are simply harder to dent.

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If you are planning to routinely drop canned goods on your floor, or dance in stiletto heels, hardness is an important quality. But when it comes to the damage caused by wet, gritty boots or unprotected chair legs, a really hard floor is only as hard as its finish.

Coniferous woods (fir or pine) are significantly softer than most hardwoods and deep dents and dings will appear quickly in floors made of those materials. Still, even those dents do not seriously affect the performance of the floor, and some people consider such marks a form of character or patina.

Cherry is one of the softest American Hardwoods, but it is much sought-after for its beautiful color. Oak is an inexpensive wood that some consider common, but it is particularly easy to cut and sand and it takes stain more readily than most species.

Other qualities to take into consideration are the dimensional stability of the species (how much it swells when it’s humid), cost, availability, and appearance. Despite the popularity and apparent green qualities of many imported, exotic species like bamboo or Brazilian Cherry, flooring tends to behave best when the tree it came from grew in a climate similar to that of the final floor location.

The grading of hardwood follows national standards that are monitored by the National Oak Manufacturer’s Association.

They explain it like this: “Appearance alone determines the grades of hardwood flooring since all grades are equally strong and serviceable in any application.” The higher the grade, the higher the cost, the more uniform the appearance of the boards and the higher the proportion of long boards in any given set of flooring.

The one grading category that can make a difference to the performance of your floor is “quarter-sawn” or “quartered.” Wood of any species that is quarter-sawn is much more dimensionally stable through changes in humidity and is much less prone to gapping and cracking over time.

Minnesota has one of the country’s largest annual ranges of humidity change so dimensionally stable lumber makes an especially good investment in this state.

Q: Is my subfloor the right composition and thickness to hold strip flooring? What if it isn’t??

The ideal substrate for regular 3/4″ strip flooring is a minimum of 3/4″ of plywood or solid dimensional lumber (most homes built prior to 1965 will have an adequate subfloor because they were built with the assumption that solid strip hardwood would be installed).

The next best subfloor option is is 3/4″ of OSB (Oriented Strand Board).

If you have OSB that is thinner than 3/4″ or if you have MDF or particle board of any thickness, then you have a problem. Those substrates are apt to crumble over time – it would be like nailing your hardwood floor to big piece of shortbread.

Inadequate subfloors can be torn out and replaced or, a new subfloor can be installed directly over the existing one.

Q: I just finished installing hardwood in my kitchen, but I don’t want to finish it until after the cabinets have been installed. Can I just put some red rosin paper down to protect the floor?

Don’t do it! Yes, protect the floor, but don’t used red rosin. It is too thin to protect the wood from wet feet and dropped hammers but, even worse, if something heavy is dragged across the paper and rips it, the red pigment from the paper gets driven into the wood.

We’ve even had instances where the red from the paper has been driven into the top layer of a new finish. The safest combo would be sheets or dropcloths, covered with thin fiberboard, or at least cardboard.

Pete’s Bonus Tips

More subfloor knowledge

Subfloors are not created equally and some will hold your new hardwood better than others:

BEST:

3/4" plywood is the gold standard of subfloors, but you should still resecure it to the joists with screws before you proceed with installation - squeaks are easier to prevent than they are to fix.

JUST BELOW BEST:

Homes built in the 1940s or earlier usually have 1x6s laid diagonally across the joists for subfloor. This gives you plenty of thickness to hold a 3/4" solid hardwood, but those 1x6s can often be cupped and distorted and so you’ll want to grind down any uneven spots (edgers are great for this).

Those older subfloors were usually nailed to the joists and will have loosened over time so take the time to resecure them with screws, especially if any butt joins are "piano-keyed".

GOOD:

Oriented Strand Board or OSB is technically a type of particle board, but it is considered an adequate subfloor if it is thick enough. If your subfloor is 3/4" OSB, your hardwood floor is more likely to move and develop squeaks over time because the the fibers in the OSB are somewhat friable and fasteners will tend to crush and stretch their openings over time.

As always, resecure with screws before you attach your hardwood floor to it.

Three installation definitions

End-matched

When even the short ends of hardwood flooring are tongued-and-grooved. This creates a superior holding on all four sides of every board. This is important because seasonal change can cause hardwood to change in both width and in thickness.

Board width change just creates gapping, but even a slight lift at the end of a board can create enough lippage for you to catch a toe! It also exposes that board end to chipping.

End matching keeps those short ends tight and level. Conventional milling puts a tongue on the north and east side of every board and a groove on the south and west edges.

Blind-nailed

When tongue and groove flooring is nailed at the tongue of each board, allowing the adjacent board to cover up the fastener, which means the floor is secured almost invisibly to the subfloor.

Even more important, the nails are at least a 1/4" from the surface of the boards, which makes for a much less risky sanding experience.

Top-nailed floors are a beast to sand because all your fasteners must be counter-sunk by hand or they might catch the sanding drum.

Relief groove

There is endless debate about the purpose of these grooves that are milled into the back side of hardwood flooring. The best explanation we've heard is that the grooves prevent the board from becoming "case-hardened" during the drying process.

This keeps the board from developing shinkage-induced interior stresses that would cause cells in its core to buckle and collapse. For the rest of us, the relief grooves tell us which is the face side of the board.

Spline (slip-tongue)

A narrow strip of wood that can slip into the groove of a piece of hardwood flooring and turn it into a tongue.

Because tongue and groove floors are always installed tongue-forward, spline allows you to change your installation direction in irregularly-shaped rooms.

We have everything you need, online or in our St. Paul, MN store.

Visit our online store from the comfort of your sofa or visit our cute store at 186 Fairview Ave N in St. Paul, MN. We've got everything you need for your project, and friendly people to answer your questions.