In insulating gypsum lath, the foil side should be installed facing toward:

In insulating gypsum lath, the foil side should be installed facing toward:

• A. framing members
• B. room interior
• C. exterior sheathing
• D. finished surface

Answer: (A)

The main idea here is how the foil layer in insulating gypsum lath functions within the wall assembly. The foil acts as a radiant barrier and vapor retarder, so its orientation matters for performance and for how the plaster bonds. Installing the foil side toward the framing members places the reflective surface in the wall cavity itself, between the lath and the studs. This keeps the barrier in the air space where it can effectively reduce heat transfer and limit moisture diffusion into the insulation, while also keeping the foil out of the plaster’s bond area so finish work isn’t compromised. If the foil faced the room interior or the exterior sheathing, the reflective layer wouldn’t be positioned in the cavity where it would most effectively influence heat flow and moisture movement, and it could interfere with plaster bonding or become more easily damaged during finishing.

The main idea here is how the foil layer in insulating gypsum lath functions within the wall assembly. The foil acts as a radiant barrier and vapor retarder, so its orientation matters for performance and for how the plaster bonds.

Installing the foil side toward the framing members places the reflective surface in the wall cavity itself, between the lath and the studs. This keeps the barrier in the air space where it can effectively reduce heat transfer and limit moisture diffusion into the insulation, while also keeping the foil out of the plaster’s bond area so finish work isn’t compromised.

If the foil faced the room interior or the exterior sheathing, the reflective layer wouldn’t be positioned in the cavity where it would most effectively influence heat flow and moisture movement, and it could interfere with plaster bonding or become more easily damaged during finishing.