Indoor Moisture Content Fluxuation in NC ?

[02blues]

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I am sure this has been covered but could someone help me out. Sadly for the first time I am actually trying to calculate the expected amount of wood movement over the year based on wood species and fluctuation in moisture content here in NC. I have read and reviewed the Wood Movement reference giude by Lee Valley and will look up a FWW article I saved a while back.

1. Practically speaking what range of moisture content fluxuation should we expect "indoor" here in NC.The piece will be indoors so the fluctuation in indoor moisture content is what I need to know. We have forced air / AC and a built in humidifier which is set for 30% I think. Is it safe to assume 6%? :eusa_doh:Temp in house ranges from 68-75 F.

2. Why dont more joints fail secondary to wood movement? ie all those dovetails etc.??
I am making this calculation for a loose mortice and tenon on a bed ie not glued. When we glue up a snug mortice and tenon why dont they fail? Guess it depends on all the factors: thin widths, grain direction etc :icon_scra

This may be over kill however I do not want the tenon to bust my bed post mortice during the summer!

 

[Trent Mason]

John,

I don't have any specific answers to your questions, but if you have a humidifier in your house, I seriously doubt you'll have any issues. When I built my bed frame, I used mortise and tenon joints for the headboard and footboard, as well as the rails (?). I've had much larger changes in moisture content and humidity than you have and have only had one issue. And that was that one of the legs on the footboard twisted. I think that had more to do with that individual piece of wood though and not changes in the mc and humidity in the house.

 

[02blues]

Thanks. That is helpful to know.
Beautiful bed too!:icon_thum

 

[02blues]

Much ado about nothing?

After running the numbers with 6% moisture change for both Tangential and radial movement the actual wood movement or change in size of the mahogany tenon (1x2") is an enormous 1/32" (actually a little less).

OK...so it was a good exercise and I feel a lot better now.:icon_scra

just trying to avoid this exercise later:BangHead::slap:

 

[Trent Mason]

Thanks for the compliments John. :embaresse I assure you that it is not nearly as nice as yours is going to be and no where near as much work went into it. :gar-La;

 

[scsmith42]

For homes that do not have dedicated humidification / dehumidification, here in NC a swing between 6% - 12% or thereabouts would be expected.

Air conditioning alone is not necessarily enough to control RH inside your home. I've seen RH%'s of 60% or greater inside of air conditioned buildings that had the doors opened frequently on high humidity days, which equates to an EMC of around 11% at 70 degrees.

 

[AAAndrew]

Whenever I start to worry about wood movement from moisture or temperature, I remember the cherry upright piano that sat in my great grandmother's abandoned house for about 25 years before we plucked it out. It had gone through the broiling, humid summers and frigid winters of Indiana without climate control except for a sound roof and windows. Yet today it's as sound as ever. It probably helps that most of it is 4/4 black cherry from the 19th century with a cast iron, full-grand-piano-sized soundboard and the bracing to support said soundboard. The only thing we had to do was replace the ivory keys (which had been eaten by bugs) and have it tuned. It still had the original strings for the next 20 years. It has since been restored by a professional, but he didn't have to touch the woodwork, just the piano part.

You'll be fine.