Exterior Cavity Walls Applications
Spray Polyurethane Foam on Exterior Walls
The objective of this case study is to discuss an insulation technique that works particularly well on buildings designed with a brick veneer as the finished surface of the exterior walls. The actual exterior wall can be constructed with concrete block or a combination of metal studs and one of several exterior sheathing materials.
The significant aspects of this technique are two-fold. 1.) Install insulation on the outside of the building rather then the inside. 2.) Use spray polyurethane foam as the insulation rather then other materials on the market like rigid foam boards. Brick ties are attached to the exterior sheathing, the exterior insulation is applied and the brick veneer is added, leaving an air space between the brick veneer and the insulation for drainage.
Insulating the outside of a building has many advantages:
Because the insulation is on the outside and there is no cold surface on the backside of the exterior sheathing, condensation inside the wall cavities is avoided.
Once the decision has been made to insulate on the exterior, designers must choose from several insulation products and techniques. The major products are:
Following is an evaluation of these materials which considers the important performance criteria.
Rigid foam boards
Rigid foam boards are a good insulation material but, if installed improperly, the effectiveness of the material is compromised. With numerous seams, joints, and cuts necessary to fit the foam sheets together, the possibility of leaving a void in the thermal envelope is significant.
Another major problem with foam boards as the insulation method for masonry buildings is the brick ties. Each brick tie causes a penetration in the thermal envelope. Often, the brick tie makes a larger hole than necessary in the rigid foam board. These holes, if left unsealed, compromise the thermal envelope.
While rigid foam board can serve as the air barrier if it is properly cut, fit, and the joints and penetrations sealed, it cannot serve as the vapor retarder.
Rigid fiber boards
Rigid fiber board is a mineral-wool insulation made from basalt and slag. Like rigid foam boards, the product is manufactured, shipped, and installed in sheet form. Installers of this product face the same installation issues as rigid foam boards present, such as the need for careful fitting and sealing of all penetrations. There is also the problem of sealing penetrations caused by brick ties.
Like rigid foam board, rigid fiber board can serve as the air barrier if properly cut, fit, and the joints and penetrations sealedIt can not serve as the vapor retarder.
Spray Polyurethane Foam
Spray polyurethane foam has the application flexibility and insulation properties that make it the best choice for exterior insulation applications.