These days trim wood shrinkage in finish carpentry does cause some problems and has tested the reputation of even the most seasoned finish carpenters. This can be controlled some what if it is properly addressed however the shear speed at which houses get built and the use of new growth lumber these days poses a lot of the problems that are unfortunately some times unavoidable.
Trim wood should be acclimated to the inside environment of the house where it will be installed. This does also apply to the wood of a new wood floor to be installed. What this means exactly is the wood needs time to adjust to the temperature and humidity levels of the house where it will be installed. This in turn reduces the shrinkage of the wood and that helps to keep miters tight and doors working properly. There is much discussion on how long this acclimation period should be and a few variables do come into play here especially with a newly built home. A very minimum of an acclimation period would be 48 hrs. if the environment change of the storage place of the trim wood or the store to the house environment is not a huge difference. Another factor is after the acclimation period it is best to get the wood finished and sealed whether you do it before or after installation.
Ultimately wood is going to shrink and swell according to the seasons. Some places more than others due to the climate differences. The best way to reduce this is to try and keep the environment in the house relatively even with just the temperature although I have seen a new house with new trim work sitting empty with no activity like cooking or showering for a long period of time have major shrinkage in the trim wood due to no humidity. I had trimmed this house and was just sick when I went back for the final; fortunately the builder that I had done the work for understood this problem and took full responsibility. I had been in the finish carpentry business for a long time and had a good reputation of doing good work but some times that reputation doesn’t mean anything to the people that don’t understand these problems.
For the do it yourselfers doing trim work, there are a few things to consider. If you are remodeling or doing renovations to an existing home just simply taking the precautionary measure of acclimating the wood will eliminate the major shrinkage problem in most cases. On new homes it is however nice to know the humidity levels in the house as well as the wood. One easy way to check the wood is with a moisture meter tester. This little meter is relatively cheap or can be borrowed from a contractor that does building or remodeling. The use of a dehumidifier is recommended in a new house or new construction and doing a little research for the moisture content that is recommended for the area that you live in is also advisable. This is due to the different climates in the country and various temperature changes for the different areas. As a finish carpenter it is important for people to understand some of these issues concerned with wood shrinkage whether you are doing the work yourself or hiring a professional to do the work for you ultimately to protect yourself.