Continuous Exterior Insulation

Continuous exterior insulation (CI) describes insulation that is continuous across all structural members reducing the effects of thermal bridging. It can be installed on any opaque surface on the exterior of the building envelope. Thermal bridging is the interruption of thermal insulation within the building envelope by another material with higher thermal conductivity (e.g., wood studs) that results in increased heat loss through the assembly and localized cold spots on the interior.  Continuous insulation is often installed to increase the effective R value of the wall assembly. 

Continuous exterior insulation will increase the temperature of the wall’s cavity, reducing the potential for condensation in winter.

Permeance is inversely proportional to the thickness of the material, except for foil faced polyisocyanurate, where the permeance derives primarily from the foil face.

Extruded polystyrene insulation (XPS) is an insulation board formed by extruding chemically dissolved polystyrene beads.  XPS is a rigid, lightweight, closed cell, insulating material. Some XPS manufacturers  provide proprietary systems which utilize tapes and sealants enabling it to act  as an air barrier, as well as a water resistive barrier inhibiting water from entering the assembly. Please refer to manufacturer literature. The uniform and fine, closed cell structure results in lower vapour permeability (and higher insulating performance per unit thickness than expanded polystyrene.  Some XPS materials at specific thicknesses qualify as a vapour barrier (i.e., a permeance less than 60/Pa^.s^.m²).  Please refer to manufacturer literature.  Using XPS as an exterior insulation can help improve the moisture performance of the wall assembly by raising the temperature of the cavity and reducing the potential for condensation.  Care should be taken when installing low permeance materials (less than 60 ng/Pa^.s^.m²) that do not provide sufficient thermal resistance on the outside of the wall assembly.  These situations are described in the Building Code (see outboard to inboard ratio of thermal resistance).  Wetting of the wall cavity from air leakage, construction moisture, or bulk water should also be prevented.  For an example of how a wall assembly with extruded polystyrene insulation, and its corresponding information, is displayed on the Effective R Tool, please see Wall ID 12760.

Foil-Faced Polyisocyanurate board is an insulation board made of closed-cell plastic used where high insulating capacity is preferred.  These boards are also rigid and lightweight.  Some polyisocyanurate board manufacturers  provide proprietary systems which utilize tapes and sealants enabling it to act  as an air barrier, as well as a water resistive barrier inhibiting water from entering the assembly. Please refer to manufacturer literature.  Most often, polyisocyanurate boards are foil faced, meaning that one side of the board is laminated with an aluminum facing which can enhance its thermal performance when the foil faces an air space.  This  board and its foil face result in an extremely low vapour permeance (significantly less than 60 ng/Pa^.s^.m²), which may impact the drying potential of the wall cavity but will resist the inward flow of vapour when using moisture absorptive claddings.  Low permeance materials that are installed on the outside of the assembly without sufficient thermal resistance to raise interior cavity temperatures, as described in the Building Code, should be handled with care (see outboard to inboard ratio of thermal resistance).  Wetting of the wall  cavity from air leakage, construction moisture, or bulk water is particularly important for walls with this continuous insulation and should be prevented. For an example of how a wall assembly with foil-faced polyisocyanurate board, and its corresponding information, is displayed on the Effective R Tool, please see Wall ID 15211.

Expanded Polystyrene Insulation (EPS) is an insulation board formed from bonded, polystyrene beads.  EPS, often referred to as beadboard, is a rigid, lightweight, closed-cell insulation material.    This material is more permeable to vapour when compared with XPS because of the way the board is manufactured.  EPS is also commonly used for insulated concrete forms (ICFs).  For an example of how a wall assembly with expanded polystyrene insulation, and its corresponding information, is displayed on the Effective R Tool, please see Wall ID 12798.

Mineral wool is an insulating material manufactured from molten slag or rock.  It is a fibrous material and when it is manufactured as a board, it can be installed on the exterior of a wall assembly, as exterior continuous insulation.  Some municipalities accept that it can act as a drainage plane, draining any water that leaks past the cladding. Mineral wool board is highly vapour permeable (much greater than 60 ng/Pa^.s^.m²) and facilitates outward drying of the assembly.  On the other hand, mineral wool board offers little resistance to inward vapour drive from cladding materials that can store rainwater, like brick.  For an example of how a wall assembly with mineral wool insulation, and its corresponding information, is displayed on the Effective R Tool, please see Wall ID 12840.

References

Continuous Insulation. (1991). In ASHRAE terminology of heating, ventilation, air conditioning & refrigeration. Atlanta, Ga: American Society of Heating, Refrigerating, and Air-Conditioning Engineers.

Expanded Polystyrene Insulation. (2013). In Glossary of housing terms (Rev. ed. of: A glossary of house-building and site-development terms, 1982 ed.). Ottawa: Canada Mortgage and Housing Corporation.

Extruded Polystyrene Insulation. (2013). In Glossary of housing terms (Rev. ed. of: A glossary of house-building and site-development terms, 1982 ed.). Ottawa: Canada Mortgage and Housing Corporation.

Mineral Wool. (2013). In Glossary of housing terms (Rev. ed. of: A glossary of house-building and site-development terms, 1982 ed.). Ottawa: Canada Mortgage and Housing Corporation.

Polyisocyanurate Board. (2013). In Glossary of housing terms (Rev. ed. of: A glossary of house-building and site-development terms, 1982 ed.). Ottawa: Canada Mortgage and Housing Corporation.