flooring upstairs seems to have gaps appearing everywhere between the floorboards!

What is the finish - stain or natural?

Hi there, firstly can I just check when you say 'floorboards' do you mean; 1.the pine boards nailed to the joists that are under any floor coverings, or 2. do you mean wooden flooring? If you mean floorboards (1) and your house is of relatively recent construction, they have probably fitted the boards 'wet' and they have now dried out. Which is not uncommon and should not be a problem. If you mean wooden flooring(2), unless there has been a large shift in humidity in the house, causing the flooring to swell and then shrink, then it has been incorrectly fitted. Possible poor fitting being; a.Uneven subfloor which would cause excessive movement in the floor and cause the joints to come apart. b. Poor fixing, i.e. insufficient glue or poor nailing of joints would cause them to work apart. These are the likely causes based on the information you gave. Wherever the gaps appear, the floor will have to be refitted. If this is a small area of the whole floor isolated repairs may be feasible. If this is widespread across the area, the whole area will have to be done, in which case it may prove the floor becomes unsuitable/uneconomic for repair and will have to be replaced! Just one other thing to mention, I wouldn't recommend filling the gaps with 'filler' until the underlying problem has been identified and addressed. Good Luck Robert