Relative Humidity

[Coop]

How important is RH? My shop like many others on here, is my garage. I have a window a/c-heater but is rarely used. If I take kiln dried lumber and build a piece in the Gulf Coast area and move it into my climate controlled house, should I expect problems? Is the rh more of a concern on how and if it is dried than where it is processed and end destination?

[Mark J]

It takes time for the wood to come to equilibrium, but relative humidity determines the moisture content of wood.  So even wood that has been kiln dried will respond to long term changes in relative humidity.  

[BillyJack]

We did nothing special on the cabinet, commercial or furniture shops other than grab a board and go to work. No acclimation…

We use nothing but kiln dried lumber from a reputable source 

[wtnhighlander]

@Coop, I think the best way to determine how much you need to account for wood movement is to experiment, when possible. Make panel glue-up of solid boards, and put breadboards across the ends. Take it into the house and wait to see how much the panel expands or contracts relative to the breadboard ends.

I have a coffee table made this way, and the 36" panel shrank a total of about 3/8" as compared to the breadboards, over 6 months or so.

[Chestnut]

Do you know what the RH is in your shop vs your house? I ask because RH varies almost 10% from our top floor to the bottom floor within our house. Temperature effects RH afterall. That said it's always advised to build with movement in mind.

Swings in RH percentage of 10-15% aren't going to have a huge impact on movement. The larger movement issues occur in climates like MN where inside RH is 50-60% in the summer and as low as 10% in the winter. Houston is pretty well always humid so going from 60-70 outside to 40-50 inside isn't as much of a concern.

It honestly doesn't matter a whole lot kiln dried vs air dried they both will move. Kiln dried is slower to pickup moisture and dumps it a bit faster but it's going to move the same as air dried material. Kiln drying the lumber doesn't change how the wood moves. That said KD lumber is usually graded and better lumber grades will handle movement generally better than lower grades but that's not always the case. It's complicated.