The best way to keep moisture from entering the roof covering material is to install a vapor barrier. The subfloor for roofs is an essential component of roofs, but it also plays a key role when attached to the walls of buildings. Subfloor for roofs should be one of your top choices; it has many other advantages besides being used as a guide for the roofs of your structures. It appears that the decrease in humidity and the lower temperatures on the inner side of the test roof may have contributed to the different humidity behaviors from those that occur in the field.
This capillary water driven inward is the source of moisture for the roof subfloor and the roof covering. Additionally, the subfloor of the roof makes your roof more durable, so it lasts longer and gives your roof an attractive look. Roofing felts vary greatly in terms of their permeability to water vapor; the typical subfloor used under asphalt shingles in residential construction is quite permeable. In ventilated roofs, this is usually seen in the folding of the shingles first thing in the morning, when moisture migrates to the roof covering and the joints close.
Camelot shingles were manufactured by GAF Manufacturing, one of North America's leading manufacturers of roofing materials. Therefore, roofing felt also serves as a waterproofing material, protecting your building from water leaks. This is followed by the relaxation and opening of the roof covering. Later that same day, the deformation disappears.
The conclusion of the BSC report is an argument in favor of installing an impermeable moisture barrier under roof tiles, perhaps instead of traditional, permeable roofing felt. In cold or temperate climates, this is not a problem, since the combination of strong humidification caused by rain or snow is combined with solar heating at high outside temperatures, say the authors, who continue to argue that the folded roof tiles seen in the morning (caused by moisture returning from the roof terrace) relax during the day. However, in unventilated roofs in hot and humid climates, authors argue that water from the roof surface is extracted upwards in liquid form, by capillary action, between layers of rows of overlapping tiles, where it eventually passes through the vapor barrier and through the roof cover to the interior of the roof cavity. With a few exceptions, polyethylene and polypropylene-based roofing subfloors are impervious to vapor and would work as outdoor vapor retardants.
Just like roofing felt provides extra protection for your roofs, it also provides extra protection for your walls.