This is almost certainly due to condensation buildup on the underside of the panels. The condensation that forms is not a direct result of the Suntuf panels, but rather the surrounding environment in which the panels are installed.
To learn what condensation is, why it occurs, and a few suggestions that can help minimize it, click here to download Palram Tech Brief #5007.
All foam PVC trimboard products expand and contract to some degree. Foam PVC expands and contracts linearly – along the length of the material – in reaction to changes in temperature. If you follow our installation guidelines, you can limit the variance to just 1/8IN in either direction per 18FT of run. Note that longer runs of uncut boards will expand and contract more than shorter runs.
Always consider the temperature at the time of installation, and gap the boards accordingly. If you do not fasten PVC trimboard properly, and if you do not account for future movement, problems with gapping or buckling can occur. This is especially true if the board is very hot or very cold on installation.
There is no hard and fast calculation, but you will need less gapping when installing hot boards, and more gapping when installing cold boards. Always use "hidden" joints like scarf or ship lap joints to minimize the appearance of gaps.
When gaps are glued on a long run of Palight, allow space for expansion and contraction at each end of the run. Download our installation guide for more details on proper gapping.