Oak floors shrinkage - when do fillers help ?
That said, drier interiors are not the only cause of shrinkage ...
Other factors that may cause shrinkage of oak floors
In new constructions, factors like sub floor movement, foundation settlement cause many external forces to act on the wooden flooring causing the strips of flooring to lock together or move apart from each other. The extent to which the strips move determines the most appropriate method to repair the floor. If the movement is large, then additional strips may have to be installed. But if the movement is not very large then fillers may be used to solve the problem of shrinkage.
When can fillers be used to solve the problem of shrinkage of oak floors
According to NOFMA ( www.nofma.org), gaps between strips that are less than 3/32" may be filled with a wood floor filler of the appropriate color. And filling cannot be done just in any season - it has to be done when the moisture content of the flooring is at its median stage.
Also, the filler should be sealed with a finish similar to the one on the floor.
If the gaps between the flooring boards is more than 3/32", the filler may either get squeezed out when the boards expand in cold or humid seasons, or the filler may break into chunks with the passage of time.
And all this does imply that ...
The problem of oak floors shrinkage should be handled by expert floor finishers
The solution to the problem of shrinkage of oak floors depends on what caused the shrinkage in the first place, and using fillers may not be appropriate in every case. Experience and expertise is required to judge what caused the shrinkage and then determine the best remedy.