There can be several reasons why you might hear floorboards creaking upstairs when no one is present:
Temperature and humidity changes: Wood expands and contracts with changes in temperature and humidity. These changes can cause the floorboards to shift slightly, resulting in creaking sounds. This is particularly common in older houses or in areas with significant climate variations.
Settling of the house: Houses can settle over time due to factors like changes in soil conditions or the natural aging of the structure. This settling can lead to slight movements in the floorboards, causing them to creak.
Structural issues: In some cases, creaking floorboards can indicate underlying structural issues. This could include problems with the floor joists, subfloor, or the supports beneath the floor. If you suspect this to be the case, it might be worth having a professional inspect the area to identify and address any structural concerns.
Thermal expansion and contraction: Temperature fluctuations throughout the day can cause the floorboards to expand and contract, resulting in creaking sounds. As the boards rub against each other or against the nails holding them in place, the friction can produce the creaking noise.
Natural settling of the wood: Wood is an organic material that can change over time due to various factors such as moisture content, aging, and wear. As the wood naturally settles and adjusts, it can produce occasional creaking sounds.
It's important to note that occasional creaking sounds from floorboards are often considered normal and may not necessarily indicate a serious issue. However, if you notice persistent or worsening creaks, significant structural changes, or other signs of concern, it's advisable to consult a professional to assess the situation and provide appropriate guidance.