Installing Tongue And Groove Fir

Old 11-22-05, 09:01 AM
Thread Starter
Join Date: Oct 2005
Posts: 13
Upvotes: 0
Received 0 Upvotes on 0 Posts
Installing Tongue And Groove Fir

Hi Gang,

Happy Thanksgiving to all.

I will soon install solid tongue and groove douglas fir in our TV room over a new 3/4 " plywood sub-floor. The boards have been sitting on the painted cement basement floor for a month. I put spacers between each board so all surfaces of each board can breath. I don't want to go out and buy a wood moisture meter. Do you think letting the boards sit like that for that long will give me enough assurance that the moisture content is right? The TV room is upstairs but we have a forced air furnace with a humidifier so I am fairly confident that the humidity is pretty uniform throughout the house.

Also, do I nail the boards tight against each other or do I leave a space for expansion? We live in Minneapolis and the humidity varies quite a lot between summer and winter. We do not use the AC a lot in summer and the house gets quite humid at times. We have fir floors in the upstairs (installed when the house was new back in the '30s) and their joints are all open quite a bit which we don't mind.


Old 11-22-05, 10:14 AM
Join Date: Aug 2000
Location: USA
Posts: 15,047
Upvotes: 0
Received 2 Upvotes on 2 Posts
Humidity tends to vary among rooms in a home. There is no way to guess. Humidity has to be measured with a hygrometer and should be maintained between 35-55% year round. Should humidity be greater, dehumidifiers should be used.

Wood should sit in rooms where it is going to be installed for several days in order to acclimate (adjust) to temperature and humidity of the individual rooms. A moisture meter is the only way to know for sure the moisture content of subfloor and hardwood flooring. There should be no greater than 4% difference if installing strip flooring and no greater than 2% if installing plank.

Leaving a 3/4" expansion gap around the perimeter of rooms is important for expansion should humidity rise. During dry, heating months boards tend to contract and may leave a gap. Tongue and groove hardwood flooring should be pulled tight before nailing.

Go to for installation instructions.

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: