installing hardwood not perpendicular to floor joists...what are the implications?

Question

I have just installed hardwood floors and know that they are to be installed perpendicular to the floor joists. On the first level, the installer did it correctly and they were installed perpendicular. I loved the look so much that I also had him install hardwood in our master bedroom upstairs, and when I went to check on him midway through the day, I noticed he was not going perpendicual, but paralel as he said it does not HAVE to be perpendicular, but generally will be installed the longest width of the room. Well, although I appreciated his advice regarding estetics, it stressed me out too much (from everything else I was reading), and I had him rip it all out (he was about 1/2 way in a 13 x 15 room) and re-start again the proper way (perpendicular). Although he was a little upset, I think he knew I was right and the "estetics" is not what is important to me, but the fact to I will not have problems down to road is far more important. However, what I was wondering is what is the actual reason for installing them perpendicular? What would be the long term impact if I had let him continue going paralell with the joists? Of everything I have read, this question really has not been answered (the "why").

Also, what would happen if the hardwood is not given adequate time to aclimatize to the room? The hardwood boxes contain instructions adising 48 hours, which I actually gave 72 hours + ... but what would have happened if we had not let it aclimatize?

Thanks for all your advice!!

Answer 1

Installing wood flooring perpendicular to joists helps avoid squeaks by having a stronger floor as the new flooring is "bridging" the joists rather than settling into the "valleys" between the joists or riding the "crowns" of the joists. Granted, the valleys and crowns are not often a factor in newer homes with adequate sub flooring materials. Wood flooring can also be installed at a diagonal to the joists. As for installing the wood flooring parallel to the longest wall,,, that is generally not true,,, mostly it is installed parallel with either the front or rear exterior wall.



Acclimation is important to help avoid cracks opening where the individual floor boards butt each other. This really becomes important when there is a big humidity difference between where the material was stored and where it will be installed. The temperature between the two locations is something of a factor when you are talking about extreme differences.

Answer 2

Many older homes have hardwood installed directly on the joists beneath. I was in a older home where the home owners had ripped up the carpet, and exposed the hardwood beneath - I could see the basement through the cracks in the floor. Obviously the floorboards were installed perpendicular to the joists, and this illustrates where this rule came from. Todays homes have subfloors PL'd to the floor joists, with additional thin layers of subfloor or fibreboard laid on top of that to make rooms with different flooring types level with each other. You can't install vinyl or tile "perpendicular" to the joists, and neither should that rule apply to hardwood.

The rule I stick to is "what looks the best"? Generally I prefer the floorboards to run from the main windows of the home. ie: front to back, so the eye is led through the house from the front door instead of across the house. If the house has a layout perpendicular to the front door, the floorboards would be laid down across the house, down the length of the hallways. The key is to support the floor with subfloor thick enough to support the wood floor boards - at least 5/8" and up to 3/4", making sure that joints in the plywood are supported by a joist.

Answer 3

The impact of installing the hardwood floor parallel with the joists is that the strength of you floor comes mostly from the sub floor( the tounge and groove of the flooring provides no additional support). If your bedroom was carpeted before, your were relying on the subfloor then (and maybe a little from the underlayment, depending on what it was). Laying the hardwood floor perpendicular to the joists adds strength to the floor between the joists.

If the flooring is not acclimatized, it can warp after installation as the wood's moisture content and temperature change from what it was at installation

Answer 4

The reason for installing perpendicular to the joists is strength. You would have support every 16". If your underlayment is sufficient though, it would not make a difference since the joists would be supporting the underlayment. Your installer is correct that most flooring is installed along the longest wall. Not acclimating the flooring can result in the wood expanding or contracting after installation due to a big difference in the room temperature and the temperature of the flooring. Differences in humidity could also cause this problem.

Answer 5

In older houses I've worked in that had good wood flooring, the sub-floor was installed at a 45degree angle to the floor joist, and the hardwood flooring was installed perpendicular to the joist. The subfloor I'm talking about is slat board though.

Answer 6

I am a structural engineer in California and here is my opinion about laying the hardwood parallel or perpendicular to the joist. If the subfloor and floor framing is sufficient, in my opinion, either direction will be acceptable. Here are my opinion of a sufficient floor: 1) the floor joist framing must be designed stiff enough so that the floor is very stiff. The building code minimum is not stiff enough in my opinion. The building code allows too large a span for floor joist that allows too much deflection and bounciness to the floor. 2) The maximum floor joist spacing should not exceed 16"o.c. This is to ensure stiffness between the joist. 3) Although dimension lumber floor (sawn lumber) floor may work, I recommend using "I" joist framing (such as TJI joist by Weyerhaeuser) because they do not shrink which will minimize floor squeaks. 4) Although 5/8" may floor plywood or OSB sheathing may l work, I prefer at least 3/4" thick floor sheathing over the joists. The floor sheathing should be glued and screwed to and nailed to the joist. 5) This is very important! The floor plywood/OSB must be installed with the face grain perpendicular to the floor joist. The short edge of the plywood/OSB should be staggered by at least 2.0 feet from the adjacent plywood. Always leave at least an 1/8" gap between plywood/OSB edges to allow for expansion.



In my opinion, this above floor framing can also be used for tile flooring.

Answer 7

Hardwood Joists

Answer 8

You were correct in making him rip it up. He was just trying to install it a little quicker. The boards should always be installed perpendicular to the underlying joists to give it the best overall appearance and strength. One of the reasons to do this is they next time you want to sand and refinish the boards that you have down. If run parallel they will 'sag' with load and age and you may end up sanding through the board in worst case. In the perpendicular way there is less 'sag' with normal use and the boards are more likely to take the refinish sanding without any problems. Hope this helps and do not have that installer back.

Answer 9

You were quite correct as the perpendicular configuration would give better strength to the floor.

If you do not let the timber acclimatise but put it straight down it would change in length within a day or so due to the drying out and/or the differences in temperature from where it has been stored. If your house is warmer than the storage area each piece would increase in size according to the coefficient of expansion of timber. If this occurred when the floor was finished then the timber would strain and warp if there was not a point to take up the expansion.

Answer 10

Hi, I was in the floor covering business for 10 years although did not install real hardwood floors. If you subfloor is sound I see no reason why you couldn't install the hardwood any direction you desire. I would image laminate floors would act the same way. I had never heard of having to install a certain direction. As far as letting the floor acclimate unless the flooring was warehoused in a very cold climate odds are you would have been fine.

Answer 11

The hardwood must be perpendicular to the joists for stability. Otherwise, the floor may sag and it could be potentially dangerous over time. You let hardwood acclimate to your home's environment so it shrinks. If you put it down without doing this, once the floor is laid, it could shrink and you will have gaps.

Answer 12

It is not necessary to install that flooring 'perpendicular' provided that

the sub-floor is adequate.

It is better to do so if you feel that the sub-floor might be a bit soft,

but not by much even then.

Answer 13

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