In this article I will give you the inside story on how to nail down a new strip floor so that no future squeaks will occur. I will tell you the hidden truths about OSB (oriented strand board) subfloors. Believe me when I tell you that this article goes well beyond the "industry standard".
Let's start out by defining just what strip floor is. My definition may be different from many contractors, but I call strip floor any random length wood floor strips less than 4" wide. They can however, be any thickness, 3/8", 1/2", but the 3/4" strip is the most common in North America. The 3/4" strip floor is also the most stable and durable. When a strip floor is too thin for it's width it will have a tendency to warp, when great variances in indoor relative humidity occur. For instance a 1/2" thick strip that is 3" wide is a very poor choice, but a 1 1/2" by 1/2" strip should be quite stable. So, as a general rule, try not to exceed a 4 to 1 ratio of the width vs. depth, and 3 to 1 would be ideal. That makes the 2 1/4" by 3/4" strip floor the most stable and longest lasting hardwood floor. It has less of a tendency to warp and when it does shrink in really dry conditions, it forms smaller less noticeable gaps.
The 3/8" and 1/2" strip floors have a much shorter life span, because only the top of the grooved layer can be sanded and refinished repeatedly. The 3/4" thick strip floor has a wearable layer of about 5/16". The 3/8" strip floor only has a little less than 2/16" and the 1/2" floors something in between the two, at about 3/16". Given the fact that labor costs for installation are about the same for each material, the thinner floors make little sense. The 3/4" strip floor has 6-8 sanding and refinishing cycles in its life, giving it at least a life span of 150-300 years. Whereas the 3/8" at best is only cycled thrice, giving it a total life of only 60-75 years. Who knows what costs and availability will be like that far into the future? Installing a long lasting floor now is a wise use of the Standing Tree Nation's venerable bones. Not to mention it gives a boost to your property value too.
Strip floors are easy to install and whether they come in prefinished or unfinished they make for a straightforward do-it-yourself project. But you must realize these wood strips are meant to nailed down to wood, and the fastener and subfloor choice is as important as the floor itself. One of my most common questions in the Ask the Expert section of this web site is what do I do about wood floor squeaks? Why not avoid future squeaking by installing your strip floor correctly now? I'll explain how.
The subfloor is the first thing to take a close look at, even if you are you installing a new strip floor in a modern house with a plywood or OSB subfloor. It should be of no great surprise that the modern building code requirements are there as a minimum safety standard. Subfloor squeaks are not considered to be a safety factor. The writers of most cities building codes just don't want you or a piece of heavy furniture falling through between the joists, that's all.
All the subfloor specs I will mention here are assuming your floor joist are 16" on centers. If they are 20" - 24" apart you must add another layer of plywood to give enough stiffness to the hardwood strip floor. This is best done by using underlay plywood of at least the 1/2" thickness. Id like to see a minimum thickness of 3/4" plywood between 16" joists, but a full one-inch of plywood between 24" joists. This extra thickness is needed in the long spans to prevent the hardwood flooring from deflecting too much and causing squeaks (a loosening of the nails). And it would behoove you to squiggle some urethane construction adhesive between these layers of plywood subfloor to prevent future floor squeaks.
Never, never, never nail a new hardwood strip floor to a old hardwood strip floor. The flooring nails will crack the old hardwood and you will have a double squeaky floor. Remove it and use the softwood subfloor, it makes a much better nailing surface
I have seen nail withdrawal studies of strip floors nailed to various subfloors; pine boards, plywood and OSB. This investigation was done by Virginia Polytech Institute at Blacksburg, Va. The study makes the conclusion that the best sub floors are the thickest and surprisingly the solid wood pine 3/4" held the nails the best. Next down the list was the 3/4" plywood and 3/4" OSB was about the same.
But OSB gets into trouble when it gets wet during the early stages of construction. An unsheathed roof or walls left un-tarped for a rainy weekend, leaves OSB swollen and permanently damaged. It is rarely replaced, just re-nailed and sanded smooth. But the damage inside these panels is set. During the manufacturing process some of the wood chips are folded, and now they have been released during the swelling. Now as the frustrated home owner walks on the dried out floor a popping sound occurs as these double stressed chips finally break. The hardwood floor installer is sometimes blamed for this, as it looks like the finished hardwood floor is popping. But the problem, we know now is deeper.
In cases of minor flooding I have seen a plywood and solid wood subfloors dry out on their own, as long as you take a board of two of the damaged hardwood off to expose them to air. It's funny because in a lot of cases with non-OSB subfloor we just tell the client to wait 4-6 months, or until the heat comes on. The subfloor boards or plywood dry out, and miraculously the hardwood in a lot of cases will settle back into place. But OSB will remain permanently swollen, and both the hardwood and the subfloor will need replacement. At great expense.
The Virginia tech study concludes that once OSB goes through several normal indoor seasonal moisture cycles, the flooring tends to remain out of the original position, so more permanent gaps can be expected. It's not really fair to complain to the osb industry, after we have mistakenly wet their product. But wait there's more. To their credit the OSB industry is improving on the manufacturing method, and have added a water resistant phenolic resins. In an advertisement I just saw in a home building magazine, the caption reads "Why use AdvanTech ® ? (a new water resistant OSB), because I build all my houses outside." You can visit their web site at www.huberwood.com and draw your own conclusions. This new and improved OSB maker admits that the old OSB was having some problems. Now, are all contractors using this new OSB material and why did we all settle for the older OSB? WELL, GOOD OLD PLYWOOD HAS BEEN AVAILABLE ALL THE WHILE.
The use of a water resistant resin is the second major improvement in the osb industry, but the Louisiana Pacific co. is still burdened under tens of millions in class action claims from the osb sheathing products they sold from 1984-1997. This was the first generation of osb. A really checkered past.
Plywood is made of plys of real wood with a waterproof adhesive. I generally get about 15 years use from the plywood sheet I expose to all weather in the back of my pick up. You figure it out. I use always exterior grade plywood for all my subfloor, and underlay uses.
Oh, by the by a typical OSB panel has about 4 times the amount of resins that a plywood panel does, thus has an increase in off gassing due to the greater surface area of resin exposed. But the NEW OSB claims to have ALMOST no urea formaldehyde in the composition. This is a relief, but what was in the old stuff?
If you have an older house and find a 3/4" or thicker softwood plank subfloor by all means nail the new strip floor to this solid softwood. Just be sure to renail the old subfloor back to the joists with spiral standard nails that are at least 3" long (or about 3 times the thickness of the subfloor). The original old nails in these floors have by now come loose, and this is the only chance to get at this subfloor. You can use screws to refasten the subfloor, but not drywall screws, use wood screws (about 2.5 the thickness of the subfloor).
I personally use 3" spiral (ardox) framing nails, and drive at least two nails in every board, in every joist. I use a pneumatic framing nailer when I take this step before installing a new hardwood floor. But I am careful to set the pressure so the nails heads end up slightly proud of the surface. I go back over those rows after the magazine is empty and pound these nails flush with the surface with my 20 oz. decking hammer. This does two things: it assures that the nails will not be over pressured and set deeply into the wood, thus damaging the strength of the subfloor. Also the pounding releases most of the dust and debris that may be caught under the joist. This way my new floors are always squeak free.
Hopefully these old subfloor boards won't be too much wider that 8" otherwise they will have, in time, become warped. It will be difficult to flatten 10-12 " wide subfloor boards, and you may have to sand off the humps to get a decent nailing surface. Don't sand the subfloor any thinner than 3/4". If you find a really bumpy subfloor, renail it anyway and then add 1/2" plywood to even out the surface. This is particularly important with prefinished strip flooring, the smoother the subfloor, the smoother the finished floor will be. In fact, in most old houses with softwood planked subfloors, I don't even think about installing a prefinished strip floor. Prefinished is very unforgiving material and is best laid in newer more level homes on plywood subfloors. That way it will look more like the sample you saw in the show room, not the bumpy floors that you see in some houses.
Read my free article on the Wrong Way Floor in this site. This article also deals with the direction of the new floor. Always install a strip floor in an opposing direction to the subfloor boards. The ideal plank subfloor will be laid on a diagonal to the joists and will allow the hardwood floor to be laid crossing (perpendicular to) the floor joists. You will now have a doubly strong floor. Otherwise if you want to lay the finished floor in the same direction as the planked subfloor, you must lay a buffer layer of at least 1/4" or thicker plywood.
Plywood holds flooring nails about 80% as well as the pine subfloors and as long as you use the 3/4" thickness (T & G is best), it should serve you well. If you are having new home built, be sure they use a good quality urethane based construction adhesive on each joist before they nail it down. When builders try to use thinner plywood, say 5/8" they are really defeating the whole purpose of the flooring nails. The standard flooring nails (for 3/4" hardwood floors) are 2" long and go into the subfloor at a 45-degree angle. They penetrate the subfloor 7/8". It's really dismaying to see flooring nails poking through a thin plywood subfloor by 1/4" just to save the builder a few bucks. If you find you have a 5/8" or thinner plywood subfloor you really should beef it up to a total 7/8" at least. Even with a plywood subfloor you should install the hardwood a right angles to the joists. But when you cannot, add another layer of 1/2" underlay if possible to prevent floor deflection. If you find that you cant raise the level of the floor any more and you still have to lay the hardwood parallel to the joists, try this. Install 2 by 6 blocking under the subfloor between the joists every 16", this will act as a stiffener for the whole floor.
I often encounter modern buildings with plywood subfloors that are nailed with little 2" smooth common nails every foot or so. In these cases I will renail the subfloor with 3" spiral nails every 6-8" before beginning my strip floor installation.
Now that you know what best to nail a strip floor to, what's the best fastener to nail it with? Most flooring contractors and even D.I.Y'ers use some sort of mechanical fastening device to accurately drive and set the 2" nails into the subfloor. For the past 50 years the Power Nail Co., and now Primatech has been making a flat, serrated edged flooring cleats, that imitate the old cut nail that have had centuries of use. You can still buy square cut nails, which by their constant thickness, but tapered width, bend the wood fibers down in the nail channel. The square tip shears the fibers to prevent splitting. The result is a nail that is held strongly by the wood fibers and prevents the nail from easy withdrawal.
Primatech and Power Nail co. have done this one better, in that they have added serrated edges to the nail shaft so the wood fibers will hold the nail even more securely. These flooring nails or cleats (as they are also called) were designed specifically for wood flooring and have a good half-century track record. In the past these flooring cleats were designed to be driven from mechanical (not pneumatic) nailing tools. But as the wood flooring industry grew, the staple making industry saw a opportunity to make some fast money. Staples have been driven pneumatically into lots of light duty factory applications, so why not wood floors? So one enterprising company simply modified it's roofing nailer to shoot these 2" staples on an angle and voila, a pneumatic flooring stapler. Well, sort of. (As a side note, even my roofer refuses to use these staples).
What a change to the hardwood flooring industry! Suddenly, the flooring installer could shoot staples into the floor at twice the rate of the old mechanical flooring nailer. For the piecework floor mechanic, this meant twice the pay and half the backache, and why should he care about the effectiveness of this new staple. After all a well-known company is making them. It wasn't long however, that the piece work rate went down, and if you didn't have a pneumatic stapler you couldn't compete at all at these lower rates. So everybody rushed to the staples, (but not me) leaving companies like Primatech loosing market share even with its superior fastener. So this innovative Quebec, Canadian based company developed a pneumatic nailer for its power cleats. This original nailer had its problems, but six years ago was replaced with a new model, the Primatech P210. I just put this tool through 5,000-sq. ft. of rigorous testing and you can read my glowing review on it free in this site.
Why choose nails instead of staples? Let's go back to the Virginia Tech studies. They have found that staples can actually internally crack a hardwood floor. It will take about 2 years for this to show up and that's beyond the limit on most floor installers warranties. But the owner will experience gaps between the rows, tilting of the boards, and bowing. And of course, the annoying squeaks. The internal cracking happens below the tongue where the staple simply holds the floor too well and doesn't allow the board to shift during normal humidity changes. Even over-pressured pneumatically driven flooring cleats (nails) won't do this.
While on the subject of air driven fasteners, I see a lot of production installers using thin 2" 15-18 ga brads, to fasten the last 2-3 rows of 3/4" strip floor that the big pneumatic nailer can't reach. If you look at these skinny little nails you will realize that they too have no business in these thick floors. I use 2" spiral finishing nails that I spin into the wood with a Vermont American Nail Spinner available through Lee Valley Tools at www.leevalley.com. These nails take a little longer to install but are 12-13 ga. and will hold much better due to their stiffness. But that said, if you find yourself installing the thinner 1/2" or 3/8" strip floors these 15 gauge fully barbed pneumatic finishing nails are OK.
So in conclusion, why use flooring staples when you can use the superior flooring nails, driven also pneumatically? And for flooring contractors that own an older model floor stapler, you can now convert it to drive the more effective flooring nails with the Primatech staple conversion kit. So theres no excuse to be using staples on your hardwood floors. And be sure to nail into a subfloor surface that will hold these nails for the life of the floor. Ignore this advice at your peril!