I am installing prefinished 3/4" solid oak hardwood floors throughout the main level of my house. I have never installed hardwood before.

I have a 3/4" plywood subfloor nailed (and now screwed, during my subfloor prep stage) to the joists (2x10s on 16" centers). The joists run along the length of the house (i.e. horizontally in the diagram). Most sources I have seen indicate that with a 3/4" plywood subfloor on joists, you need to either run perpendicular to the joists OR install an additional 1/2" of plywood on top of the 3/4" subfloor. I do not want to put 1/2" plywood everywhere, so I thus need to install the hardwood perpendicular, as shown by the yellowish lines in the diagram.

House layout, with planned hardwood direction

I am planning on blind nailing into the tongues (2" nails) for most of the floor. I am planning on gluing (PL400) + nailing the transitions into kitchen and bathroom, and the nosed edge on the balconies (overlooking the two staircases to the entrances).

I am planning on using Aquabar-B for the underlayment.

Please ask if there is any other pertinent information I have neglected to supply and I can add it.


I see two potential problem areas in my planned layout. I would appreciate any comments on if they are going to be an issue or not.

  1. Going down the hallway, there will be a run of about 45', from the front of the living room to the back of bedroom 1, which will be one continuous strip (installed parallel to the grain, which is the primary direction that wood moves)
  2. In the dining room there are two balcony areas overlooking the stair cases; I am planning on installing nosings to go over the edge of the balcony, which means that I would not have an expansion gap here that can be covered by baseboards.

Possible Solutions:

For issue #1 I assume that adding a 'washer row' (using washers as spacers) every 10 rows or so may be sufficient?

For #2, the width of the dining room is only 9', so maybe that's small enough that it won't matter (and if I put a couple washer rows in there too, it will just be fine).

Additional information:

I live in Calgary, Canada, so things are reasonably dry most of the time, and in the winter (with forced air heating) it is quite dry.

I don't currently have a whole-house humidifier, but plan on getting one installed before winter this year.

Thanks for any suggestions / pointers!


  • Hello, and welcome to Home Improvement. I'm no pro, but I'm surprised you don't have subflooring between the joists and the 3/4" hardwood. Either way, please take our tour so you'll know how better to contribute here. Jun 11, 2019 at 18:01
  • 1
    Ahh, sorry I neglected to mention that. Yes, I have 3/4" T&G plywood as a subfloor over the joists. The recommendations that I have heard from multiple sources is that even with 3/4" plywood subfloor you should have an additional 1/2" layer if you want to lay hardwood parallel to joists. Updating question to clarify this point.
    – TBO
    Jun 11, 2019 at 18:13
  • What's your joist spacing? 16 or 19.2? Jun 11, 2019 at 20:02
  • 16" centers on 2x10s
    – TBO
    Jun 11, 2019 at 20:45
  • 2
    I have never seen an expansion gap (washer row, if I get the intention) needed with a solid floor like you are using except at the wall perimeter, never at a door or nosing. You need to make sure the material acclimates long enough so everything is compatible moisture content wise....
    – Jack
    Jun 12, 2019 at 2:10

1 Answer 1


Since it appears that the flooring will be going down in the summer months when the humidity is at its highest levels, will be the best time to install since the floor will shrink from there when the heating season starts.

You will need no expansion gaps in the run of the floor. The only gap needed will be at the perimeter of all walls, about a 1/2" will suffice. If your base is a standard base that is close to 1/2", and you wish to eliminate the use of shoe mold, you can cut the drywall up enough for the floor to run under the drywall in case it needs to expand. This way you can create a 3/4" gap at the perimeter if you choose, and the base will still cover the remaining gap.

Since you will be installing floor over such a long run, I would suggest starting the floor along the wall that is at the kitchen, and go into the living room and that portion of the dining room from that starting point. Use a "joining strip" to start the flooring the other direction to finish the dining room and to proceed into the hallway, and the bedrooms beyond.The reason why is when installing a nail down floor, when striking the nailer, it will usually be struck harder on one side of the room than the other. This will cause the floor to "steer" either to the left or right depending which side you favor while nailing. This will really be exacerbated when gong down a narrow hallway, so starting the way I suggest will minimize the steering issue, at least for the living room/dining room. Let me clarify the steering term I use. When nailing, the wood compresses minutely when the nails or staples are driven into the flooring. That compression, albeit the least little bit, will allow one side of the flooring run you are laying down to be shorter on one side of the room compared to the other. It doesn't appear to be a big deal until you get to a wall you are finishing against, then you will be forced to rip tapered pieces of flooring to finish the room.

With all that said, to answer your 2 questions, no "washer row" will be needed if you let your flooring acclimate to the same MC (moisture content) as the subfloor. This is a critical step to adhere too. If the flooring is dry, say about 4-6% MC and the subfloor is higher, say about 11-12% and you lay it down, the subfloor will raise the MC of the flooring rapidly and force the floor start going into the expansion gap you created at the walls. Not terrible, but not good either. There is a potential for squeaky floors though. If it is the other way around, then the flooring will shrink and again squeaky floors possibly. I have seen floors that did not acclimate properly and had 1/16" to 1/8" gaps over most of the flooring which was 2 1/4" plain sawn white oak, not prefinished.

Most professional floor installers usually accept the MC to be with 2% of each other. For what it worth, most interiors are at about 8%+/- with out humidification during the summer. During the winter, it can be as low as 2%, a lot more difficult to get the flooring acclimated in a short time. If your floor is delivered at 6% MC, still let it set for a week, preferably out of the boxes so the air can go freely around it.

  • Great answer! The wood will be stacked (stickered) in the rooms it is to be installed in for about a week prior to install, and has been in the house for 3 weeks (albeit in boxes). I have a moisture meter and will verify the MC again before installation, but the last time I checked the wood and the floor were within 2% of each other. I'll leave this question open for another day or so as per stack exchange recommendations, but this will likely be the selected answer and it addresses all my questions. Thanks!
    – TBO
    Jun 12, 2019 at 13:03

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