Install Hardwood Floor

using these

General Guidelines

Install hardwood floor materials subsequent to any masonry, plaster, tile, marble, terrazzo, or mechanical work that may adversely raise the relative humidity of working conditions.

Job site conditions, at the time of delivery, should approximate what the prevailing conditions will be when the building is occupied.

The Wood Floor Conservancy recommends a stable atmospheric humidity level between 35% and 50% and a moderate temperature of 65 degrees or more.

Install hardwood floor materials only after acclimated to building conditions on the job site

and at a moisture content not to exceed 8%, except in areas of constant high humidity where the moisture content of the flooring shall not exceed 10%.

Subflooring moisture content needs to be within +/- 3% of flooring. A minimum expansion gap of ¼” will be maintained at your floor’s perimeter, as needed.

With only a few exceptions, sub flooring for a nail down installation should be sound and level ¾” thick plywood.

According to The National Wood Flooring Association, all substrates for any kind of wood floor installation must be level to within 1/8” per 10’.

Nail Down Installation

Nail down flooring must be installed perpendicular to joists. The only time this cardinal rule can be broken is MAYBE when the subfloor thickness exceeds 1 inch.

It must be proven with a straight edge that there's no flex between the joists.

A minimum expansion gap of ¼” will be maintained at your floor’s perimeter, as needed.

Again, subflooring for a nail down installation must be sound and level ¾” thick plywood.

NEVER particle board.

OCCASIONALLY oriented strand board is permissable,


-the OSB is 3/4" tongue and groove

-the house is at least 5 years old

-and is stable, (no wet basement, for example.)

Both plywood and concrete substrates must be level to within 1/8” per 10’. Does this sound like the real world? Of course not. It is simply what we shoot for because most wood flooring is joined and each joint in a natural product like a wood floor will have its tolerance.

Guaranteed, over time, your wood floor will tell you if you short-cut the leveling process.


Underlayment paper lies between the subfloor and the floor for several reasons:

First, it provides a slippery surface which speeds the racking out of flooring prior to nailing, which has nothing to do with squeaks, BUT

it also eliminates friction between the flooring and the subfloor, and thus, does eliminate a potential squeak.

Finally, it allows seasonal movement in the floor which relieves stress on the thousands of joints and fasteneres within a floor, and again, the potential for squeaks.

Underlayment paper must also be rolled out evenly between subflooring levels, in the event you are shoring up your nailing surface with an additional layer of plywood.


The Director recommends PowerNails. A singular, L-shaped, heavy guaged wire with serrated edges.

The size and shape seems the most versatile from species to species.

Thick enough to penetrate exotics, and to do so without splitting the tongue.

Also, PowerNails allow the floor to breathe seasonally from side to side while still holding down the floor boards.

When I started, they were the only flooring fasteners. Then again, there was pretty much only one kind of nail down flooring and it was 3/4" thick.

Every flooring fastener company now has to have their answer to whatever product is being installed. Solid or engineered. 3/4" thicknesses down to 3/8".

At The Wood Floor Conservancy's School of Lower Learning, apprentice Floorwrights learn the benefits of learning and understanding the oldest line of fasteners

for the most repeatable and predictable results.

If you intend to hire a professional, ask them if they are a Floorwright accredited by The Wood Floor Conservancy. It's your insurance that these guidelines will be followed


and for


Request a Floorwright

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