Hardwood Floor Expansion

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  #1  
Old 11-30-04, 07:25 PM
Don Zorn
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Hardwood Floor Expansion

Hello,

I have read that I need to allow 3/4" of expansion around the perimeter of my room when installing hardwood flooring.

The thing that I don't get is that the hardwood is nailed to the plywood subfloor and the plywood subfloor goes right underneath the walls. So if there is expansion in the hardwood, don't the nails try to transmit this motion to the plywood which can't move because it is stuck under the walls - thus restraining the hardwood from moving?

If the hardwood did indeed move 3/4", and the plywood stayed fixed, wouldn't the nails get ripped out of the plywood?

I am confused - something doesn't add up. Can anyone explain this?

Don
 
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  #2  
Old 12-01-04, 02:43 AM
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Plywood is laminated so is does not expand/contract as much as a "solid" product would. Both subflooring and underlayments should be installed with about an 1/8" gap to allow for some movement. Just because the subfloor runs under a wall does not keep it from expanding. I have to sand down proud edges at the joints whenever I run into this.

I think most flooring manufactures will recommend an expansion gap that is equal to the thickness of the material. Having said that you do not need 3/4" gap if you are installing 3/4" solid hardwood.

The solid products will expand across the grain or width. You will get little or no movement on the length. I allow a 1/2" expansion so the quarter round will barely cover it. You can also just remove or undercut the base and use the recommended 3/4" expansion if you are really worried about that.

The most common mistake I see is that not enough expansion was allowed when going under door jambs. Just a little bit of a "lock in" there will cause some major problems down the road.
 
  #3  
Old 12-01-04, 05:09 AM
killerk70
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But Jerry, going back to Don's original question:

How can the "solid" hardwood expand/contract by 1" (I'm adding the expansion gaps at the both ends) when it is nailed to the subfloor???

And when the "solid" hardwood does expance, shouldn't the subfloor move with it as much??? Thx.
 
  #4  
Old 12-01-04, 09:22 AM
Don Zorn
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Hi Jerry,

Thank you for your response. I kind of figured that the plywood subfloor would not expand or contract as much as the hardwood due to the laminated construction of the plywood. Also, I have read that across the grain expansion is more than with the grain. Some references recommend 1/4" expansion allowance at the end of the strips and 3/4" at the sides. Thank you also for the tip around door jambs - I will be careful to leave adequate clearance in this area.

What still puzzles me, however, is that if the hardwood expands by 1/2" MORE than the plywood - wouldn't the nails around the perimeter of the room get pulled right out of the plywood?

Anyone have any ideas on this?

Don
 
  #5  
Old 12-02-04, 09:55 PM
Join Date: Nov 2000
Location: Austin, TX
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With any hardwood interior climate control is a must, or expect movement(shrink & swell)

Moisture content of the wood determines the boards width.

A change of just a couple of % of moisture content, will cause each board to swell or shrink in the width. Say each board grew 1/64 of an inch. How far would the floor grow in 64 boards? The floor would buckle, and pull fasteners as it expands that much!

If your calling a locked board under a doorjamb in a fastened or glue down installation, the cause of the failure, I'm calling lack of controlled enviroment.
 
  #6  
Old 12-04-04, 04:39 AM
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We don't live in a perfect world Perry. We all experience power failures from time to time.

If you lose power during a tropical storm for 1 day to a week a floor will survive that if the proper expansion has been left. Any board that is locked in from the "get go" is going to cause a buckle or even tenting. A properly spaced floor will survive that easily, but not if you have a lock somewhere.

Don, are you an engineer?

Heres the way I look at it. People hire me to install their solid hardwood floors. I make sure that the subfloor is adequate and within specs. or I correct it. I always acclimate the wood throughly and if its within 4% of the subfloor I'm good to go. I then install it to the best of my abilities leaving a 1/2" gap for expansion.

I never said that the floor would expand that much, I simply allow for it.
I'm paid and my job is done.

After I am gone my clients job is to keep the environment within a certain humidity and temperature "range". I think it is between 45% and 55% humidity but don't quote me on that. I don't have a "Hardwood Ranger" that is going to stop by my clients house on a weekly basis to see if this is being done.

I would never tell anyone not to follow the mfg. instructions but if I leave a 1/2" your floor will survive most anything but a flood. This is assuming we are not talking about a ballroom dance floor or a basketball court. Those situations require spacing in the field also.
 
  #7  
Old 12-04-04, 07:21 PM
Don Zorn
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Jerry, Thanks for your candid response.

How did you guess? I am a mechanical engineer and a perfectionist to boot - bad combination eh?

I am installing 740 sf of 3/4" birch (entire upper floor) in about two weeks. The hardwood is currently on back order. I am a pretty serious DIYer. Have set ceramic tile and installed laminate, but this is the first time for hardwood. I would rather spend a bit more money and take a bit more time to do it right than rush into the project and sacrifice quality on the install. I am in the research phase of the project right now - hence all of the questions. I bought a book on Hardwood Floor installation (by Don Bollinger) and read it conver to cover.

The book confirms your recommendation of a maximum of 4% differential in moisture content between the hardwood and the subfloor before installation. The book also insists on the clearance around the perimeter of the room as you recommend. I know that behind every good rule of thumb there is a practical reason - I was only trying to gain a better understanding of what exactly happens.

Having said that I plan use 1/2" clearance, but do not like the 1/4 round shoe molding, so am planning to undercut the 1/2" thick drywall about 1" off of the subfloor. My baseboards are 5/16" thick - so if I install the hardwood flush with the drywall, that will leave 1/2" for expansion and 5/16" for contraction. What do you think?

As far as the maximum 4% differential moisture content between the hardwood and the subfloor is concerned, I am seriously considering purchasing a moisture meter. They are pretty expensive though - about $240 for a Wagner moisture meter. Curious to know what model you use and can you set the species up for measuring a plywood subfloor?

I have also read conflicting information on the time reqired to acclimate the hardwood - anywhere from 48 hours to 6 weeks. What is your experience? Also, is it necessary to open up the packaging during this time?

Thanks in advance for your response. Anyone with other thoughts or opinions, please feel free to jump in.

Don
 
  #8  
Old 12-04-04, 07:27 PM
Don Zorn
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Perry,

Thanks for your response.

Regarding climate control - if you click on the link below, they state that you can go about a month without climate control before there are any serious problems.

http://www.nofma.org/installation1.htm

My feeling is that the whole climate control thing is a bit overblown. Hardwood floors have been around long before air conditioning and humidifiers/dehumifiers. My theory is that the hardwood flooring manufacturers hide behind the humidity argument as a means of limiting their liability. This is my own personal theory - I can't prove it or disprove it.

Having said this, we commonly have the windows open in the summer time if the weather is nice. Only close the windows and turn on the air conditioner if there is a heat wave. If a hardwood floor can't handle this, I would be surprised.

Don
 
  #9  
Old 12-05-04, 12:08 PM
floorman
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The norm here in St.Louis is to acclimate the product for 3 days prior to installation after permanant heat /air is turned on(i work on alot of new consruction).When i do work on my own i have people open the ends of the boxes to aid in the acclimation process.
The cutting of the drywall is a good idea i'm not very fond of the shoe mold either but if you have say6" base it is the way to go to hide those dark lines in the floor,wear a dust mask though.
As far as the reast goes sounds like these guys have you covered good luck!
 
  #10  
Old 12-05-04, 05:06 PM
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Location: Austin, TX
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Acclimation is not a time thing, it is a moisture thing.

The temperature and humidity of the area the flooring is to be installed in, determines what the MC of the flooring should be before it ever hits the subfloor, to be installed.

If your installing hardwood without a probe type moisture meter, you taking a gamble.



No, we don't live in a perfect world, and in the old days they dealt with cupping in the summers and gaps in the winters. If your floor was installed in the winter, gaps were left in the field of the flooring so it didn't buckle come summer time. Same as in the summers, no gaps were left in the installation, but developed in the winter and the drying heat of the stoves and fireplaces, going constantly, all day.
 
  #11  
Old 12-05-04, 06:47 PM
Don Zorn
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Hi Perry,

Thanks for your response.

What you said makes a lot of sense. Acclimation based on time alone is risky. The moisture meter minimizes the risk by taking actual readings. Also what you said about the installers methods in the "old" days makes a sense too. Leave a little bit of a gap during the winter installs for expansion during the summer. Perhaps in the "old" days, home owner's weren't quite as fussy as they are now?

Note that I have been researching moisture meters on the internet and know that most of the more sophisticated ones allow you to program a correction factor to take into account the species of species of wood. I am looking at the Wagner Proline Model 210 which allows this. It uses an electromagentic wave technology.

However, In the Wagner website under FAQ's, they have the following question listed:

Q: Can you check moisture content of plywood, particle board or wafer board with hand-held meters?

A: Because of the glues and mixed species nature of these materials, it is very difficult to take reliable moisture readings with pin-type or Wagner Hand-Held Moisture Meters.

Note: However, If you would like to work up your own calibrations for materials you use repetitively, you can contact Wagner for guidelines and suggestions.

If it is difficult to get reliable measurements for plywood underlayments using a moisture meter, then how do you installers actually do this?

Don
 
  #12  
Old 12-06-04, 05:42 AM
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If it is difficult to get reliable measurements for plywood underlayments using a moisture meter, then how do you installers actually do this?


poke it in several places in a one foot square.


I use a Tramex Professional, as it is industry standard, in which all specs use to refer too. Now more manufacturers make pin type meters and that has been removed from the literature. But everything is still compared to the Tramex meter / meters.
 
  #13  
Old 12-06-04, 03:21 PM
Don Zorn
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Hi Perry,

Thank you for your response.

I did a little investigation today and took a look at the Tramex pin type Professional Moisture Meter on their website. It retails for $298 US.

http://www.tramexltd.com/page/moistwd.html

The unit is made in Ireland, however, they do have a distributor in Littleton Colorado, phone: 303-972-7926.

I called the distributor today and discussed the above meter with their customer service representative. They indicated that the meter is calibrated for Douglas Fir. Therefore, if you use the meter to measure the moisture in any other type of wood, the reading that the meter gives is not the true moisture reading of the wood. You must use the tables that they supply or go onto the internet to find the density of the wood that you are measuring. With this information in hand, you have to take the meter reading and perform a calculaton to adjust the reading which takes into acoount the density of the actual wood being measured.

I also discussed measuring the moisture content of plywood with the Tramex customer service representative. They indicted the while the meter will give you a reading, it is not the true moisture content of the plywood. The problem is that plywood is a laminated product with glues holding it together - so it is impossible to predict and correct for the density of the plywood.

The reading that you get may be used to compare one piece of plywood to the next to determine if one piece of plywood has relatively more moisture than another, however, it cannot be used to determine the exact moisture content of the plywood.

Tramex indicated that the only way to accurately determine the moisture content of plywood would be to weigh it, put it in a kiln and dry it out completely and weigh it again and use the difference in weight to calculate the moisture percentage.

So, when you poke your Tramex pin type Professional Moisture Meter into the subfloor, in several places over a square foot, you will get a reading, but there is no guarantee that it is an accurate reading of the actual moisture content of the sub-floor.

I too have read in several places the 4% rule - but I am beginning to think that this is impossible to practically measure. It would appear that installers who use a moisture meter to measure plywood or OSB subfloor moisture content are just fooling themselves.

Don
 
  #14  
Old 12-07-04, 03:09 AM
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I new you were an engineer Don!

I'm just pulling you leg and I have a dry sense of humor too.

I have done a lot of work for engineers and they seem to appreciate that I do read and understand directions. In your situation you don't need a moisture meter. Bring the flooring in and let it set for about 5-7 days.

The cartons are usually perforated on the top lid and have 2 or 3 straps around the carton. I tear of the top lid while leaving the straps on so i can carry the cartons around better. try to scatter the flooring out some so it is not stacked too high.

My delmhorst meter is also calibrated to doug fir. In all honesty the only time I worry about moisture in a remodel like yours would be the rare situation the sub flooring got wet from a water leak or a washing machine hose busted, etc.

I am limiting my post just to your situation.

I am confident that you are going to do an excellent job and that should make you very proud. Remember, everybody had to do their first one.
 
  #15  
Old 12-07-04, 05:15 AM
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Don, you are correct. Are you sure they were not talking about a density meter, and not a pin type meter that you stick into the wood. Those density meters are junk, and only good for sand and finish crews to see if there finish is dry enough for a second or third coat.

I do have tables and charts on wood species density. They are in my NWFA manuals, that go everywhere I go. I have one copy for the office and one rides in the truck.

Only the true professionals, will use these, and even have a moisture meter. You would be surprised how many wood installers out there, that don't own or use wood moisture meters at all.

Plywood although laminated, will give a reading. The same as engineered hardwood does.

With a pin type meter we are not measuring density, like the non-distructive meters do. We are measuring along the vessels of the wood, not across them.



What is moisture content of wood? What effects moisture content of wood? What is equilibrium moisture content?
 
  #16  
Old 12-07-04, 02:31 PM
Don Zorn
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Hi Guys,

This is an educational forum. I appreciate your responses and the fact that you don't get defensive when I challenge you on points. It is not the case on all forums.

Perry - to answer your question, Tramex specifically told me that the pin meters suffer from the same problem as the non-destructive type meters. The pin meter passes a small current through the wood and measures the resistance between the pins - but it still relies on a wood density correction factor. So in theory, you can't use the pin meter for accurately measuring plywood or OSB subfloor moisture content. I did ask Tramex how far out it might be - they refused to speculate. So I really don't know how far off the readings would be - it could be quite close - it could be off by a country mile - I have no idea.

Jerry - I am laying hardwood in three existing bedrooms (17 year old house) and in our new addition (enclosed and heated/ac now for a little over a year). No leaks, no spills - so I am quite confident that the subfloor has reached the equilibrium moisture content. Note that this is all second floor construction with heated rooms below, except one bedroom which is over an insulated, enclosed garage. Currently we don't humidify the air - so I assume that we are stitting around 20% RH. It is pretty dry in our house. Today, I purchased a hygrometer to measure relative humidity and will install it tonight to see what kind of reading I get over the next few days. I will let you know.

Coincidentally, my wife has always wanted a humidifier, but I have always resisted due to the condensation on the windows and calcium build up which needs to be cleaned out at the end of the season. But, I am now re-considering this. A WAIT 6000 furnace mounted unit is only $168 the local HD - a good investment in my mind if it will help keep the hardwood floor from shrinking and also keep the wife happy!

As a point of interest, I found a neat table on the NOFMA website yesterday - it shows the moisture content of wood in equilibrium with a given dry bulb temperature and a given relative humidity. Click on the link below and scroll down to Table 2.

http://www.nofma.org/tips1.htm

Once I know the relative humidity in my house (I will measure it over the next few days using my new hygrometer), I am pretty sure I can enter this table with the drybulb temperature of our house (70F) to estimate the equilibrium moisture content of the plywood subfloor. Then I would only need to measure the hardwood when it arrives and ensure that it is within 4% - or I could just do as Jerry stated and leave the hardwood to acclimate for a week before installing.

Food for thought - the moisture saga continues!

Don
 
  #17  
Old 12-07-04, 05:26 PM
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Originally Posted by Don Zorn

As a point of interest, I found a neat table on the NOFMA website yesterday - it shows the moisture content of wood in equilibrium with a given dry bulb temperature and a given relative humidity. Click on the link below and scroll down to Table 2.

http://www.nofma.org/tips1.htm

Once I know the relative humidity in my house (I will measure it over the next few days using my new hygrometer), I am pretty sure I can enter this table with the drybulb temperature of our house (70F) to estimate the equilibrium moisture content of the plywood subfloor. Then I would only need to measure the hardwood when it arrives and ensure that it is within 4%


Don



Bingo!

You have found the holy grail.

This is what I have been trying to explain. Temp & Humidity, determine moisture content.
 
  #18  
Old 12-09-04, 05:54 PM
Don Zorn
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Perry - when you have measured the moisture content of hardwood flooring in the past, what is your experience.............Is the moisture content usually 6-9% like it is supposed be? I am curious to know roughly what percentage of the time, the hardwood is too wet to lay down or are the mills pretty good with moisture content? Any brand names that have been more problematic with moisture than others?

Don
 
  #19  
Old 12-10-04, 06:48 PM
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I install it around 9%. Depends what the temp & humidity is inside the installation area, also taking into consideration equilibrium MC.

Now that might not be what it is when it is delivered to the home for acclimation to begin. The mills do pretty good, kiln drying and milling there wood.

It is the shipping and warehousing through distributors, where moisture content increases.

I have stuck wood from china, that read 16% when it was delivered for acclimation. Took it a month to come down to 10%, with dehumidifiers running, and the A/C pumping.
 
  #20  
Old 12-11-04, 09:19 AM
floorman
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Never claimed i acclimated on time alone the question was how long does it usually take to acclimate i gave the answer based on prime conditions not just taking wood in and throwing it in the house of course you take a meter to it and check the moisture of both ,but a good time to chech is after it has been in the house for 3 days after the initial stick
 
  #21  
Old 12-11-04, 09:44 AM
Don Zorn
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Guys,

Thank you for your response.

Perry - I have read that nine percent a good rule of thumb for the hardwood prior to laying - so this confirms what you have stated. A month to go from 16% down to 10% - that is good to know.

Floorman - What model of moisture meter do you use? Based on your past experience in your area, what type of moisture readings do you get on the initial "stick"?

I assume that you stick the pins into the ends of the hardwood. Is this hard on the meter - do you ever break the pins - how far do you normally stick them in?

Don
 
  #22  
Old 12-12-04, 08:28 AM
floorman
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I have a lignomat mini ligno dx/c meter a plunge type meter.New construction will give you a variety of different %'s mostly high sometimes off the meters range depnding on the circumstances.Is there standing water in the basement?Did the subfloor get wet at some point?Is the heat on or is it temp. heat ?It goes on and on.
Now i don't live in perfect but there are some that do and they can pick and chhose their work appearantly and dictate the job site conditions on their jobs but we can only do that to a certain point and then the pen comes out and they sign off on it and assume the risk.
Usually the way it works is when the differintial in moisture from subfloor to hardwood is no more than 4% then it is a go as long as there is no standing water and the siding is complete and the heat/air is on,its brutal here with some of these builders i tell ya!
So if everyone can afford to pick and choose and keep walikng away from the job cause everything is'nt perfect then more power to ya but that does'nt work very well where i am from
 
  #23  
Old 12-14-04, 06:22 PM
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Originally Posted by floorman
So if everyone can afford to pick and choose and keep walikng away from the job cause everything is'nt perfect then more power to ya but that does'nt work very well where i am from


To stay in context with the above comment, it is OK to throw the installation specs out the window. What's it going to do? Fall up Slap it in, it should last a long time.
 
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