What is the best method to ensure a water-tight wall?

Using a rain screen is the best method to ensure a water-tight wall because this system allows for the management of moisture that can infiltrate the wall assembly. A rain screen functions by creating a space between the outer cladding and the building's water-resistant barrier. This design allows any moisture that penetrates the outer layer to drain away and evaporate rather than being trapped against the structure. The presence of a ventilation gap enhances this effect, reducing the risk of water damage, mold, and rot.

In contrast, while dense insulation material may help regulate temperature and reduce energy loss, it does not inherently prevent water penetration or ensure that any moisture that does get in can effectively drain. Regular painting and sealing can provide some level of protection but may not be sufficient over time or in extreme weather conditions, as paint can degrade and seals can crack. Building with double walls can add insulation and reduce thermal bridging, but this method does not allow for effective moisture management in the same way that a rain screen does.