- Q. I'm in discussions with an architect regarding the pros and cons of using Grace Ice and Water Shield or a similar membrane material as a housewrap. These materials are more expensive than Tyvek or 15# felt but can't be beat when it comes to the wind-driven rain we get here in the Florida Panhandle. My architect has cited Paul Fisette's articles on felt, housewraps, and flashings as his reason for requiring felt ("Making Walls Watertight," 12/95; "Housewrap vs. Felt," 11/98). But Paul Fisette works in a "heating" climate, not a "cooling" climate like ours. Would he recommend different details for a hot, humid climate?
A.Corresponding editor Paul Fisette replies: Your observation is correct: Climate has an impact on the specification of a weather barrier system. I would not recommend using a membrane like Grace's rubberized product over wall sheathing in a heating climate. It is impermeable, and it forms a powerful cold-side vapor barrier. If water or vapor leaks into a wall cavity that has a tight "rubberized" covering on the exterior cold surface and an impermeable vapor retarder installed on the warm interior surface of the wall, it will be trapped there.
But in your hot, humid climate, a low-perm membrane applied facing the warm exterior could work. It is important to build the wall so that it's able to dry toward the inside when conditions dictate -- in other words, don't apply a poly vapor barrier or vinyl wallpaper to the interior.
However, given the expense of rubberized membranes, I think I would choose 30# felt. It's stiff and a bit difficult to work with, but it's more forgiving if you get water on the wrong side of the membrane. If you are building in a very exposed location where "sideways" rain is common, I would consider a rain screen design, which balances air pressure and creates a drainage plane. This option is not cheap, but I think it's more effective for severe exposures.
