Insulating Sheathing for Residential Construction Application Guide for: ® ROXUL COMFORTBOARD™ IS 1 ® ROXUL The Better Insulation™
Prepared by: 167 Lexington Court, Unit 5 Waterloo, Ontario Canada N2J 4R9 Primary Author: John Straube, Ph.D., P.Eng. Illustrations by Building Science Corporation of Somerville, MA unless otherwise noted. DISCLAIMER: Building Science Consulting Inc. and Roxul Inc. have exercised due care to insure that the data and information contained in this document is accurate. However, this document is for general reference use only.
Contents INTRODUCTION: WHAT YOU WILL FIND IN THIS GUIDE 2 BUILDING SCIENCE FOR COMFORTBOARD IS WALLS A functional overview of the building enclosure The “Perfect” Wall 4 4 5 Rain Penetration Control Drained Screen Approach Selection of Drainage Plane Material Recommendations for rain penetration control 6 6 8 8 Air Control Basic requirements of Air Barrier Systems 11 12 Thermal Control Thermal bridging Condensation Control Cladding attachment through Continuous Insulation Recommendations for thermal
Introduction: What You Will Find in this Guide This application guide covers the use of ROXUL TM COMFORTBOARD IS in residential construction for low- and mid-rise buildings in continental North American locations. The use of Insulating Sheathing (IS)—rigid or semi-rigid insulation board products installed to the exterior of the building structure—is becoming more common in all parts of North America with recent changes to energy efficiency requirements in building codes and standards.
Here are some examples of buildings addressed by this guide. Detached House Single unit, light wood frame construction; up to 3 storey’s in height. Typically one or two family dwelling. This type of building is typically covered by the IRC (International Residential Code) building code in the US; and Part 9 of the NBCC (National Building Code Canada) in Canada. Row (Town) House Single unit, light wood frame construction with one or more common party walls up to 3 storey’s in height.
Building Science for COMFORTBOARD IS Walls A functional overview of the building enclosure The building enclosure is defined as the physical component of a building that separates the interior environment from the exterior environment: it is an environmental separator. In general, the physical function of environmental separation can be further grouped into three useful sub-categories as follows: 1. 2. 3. Support, i.e.
The “Perfect” Wall The support/control/finish components of a typical enclosure assembly are presented in a conceptually “perfect” sequence in Figure 1. The concept diagram shows an exterior finish layer (the “cladding”) outside of the thermal, air, vapor, and water control layers, which in turn are to the exterior of the building structure and interior finishes.
Rain Penetration Control There are three recognized design strategies to control rain penetration within and through the enclosure: Storage, Drained Screen, or Perfect Barriers. In a Storage (or Mass) approach, it is assumed that water penetrates the outer surface of the wall and then is eventually removed by drying to the inside or outside. The maximum quantity of rain that can be controlled is limited by the storage capacity available relative to drying conditions.
Figure 2: “Screened” and Drained enclosure walls As drained systems can accommodate a range of claddings and backup systems, this approach to rain control has justifiably received a lot of attention from researchers and practitioners.
Selection of Drainage Plane Material Drainage planes are water repellent materials (building paper, house wrap, sheet membranes, etc.) that are located behind the cladding and are designed and constructed to drain water that passes through the cladding. They are interconnected with flashings, window and door openings, and other penetrations of the building enclosure to provide drainage of water to the exterior of the building.
Figure 3: Annual Rainfall Map (From Building Science Corporation. Based on information from the U.S. Department of Agriculture and Environment Canada) Drained Screen Wall Recommendations Screened wall systems are inherently more forgiving than either mass or perfect barrier systems. Properly designed and built screened wall systems will provide economical and durable rain penetration control.
Window Installation Perhaps the most common rainwater control failure occurs at window penetrations. Regardless of which rain penetration control strategy is used, window and door penetrations through a cavity wall should be drained. Sub-sill flashings (see Figure 4) of various types are widely available for this purpose. For drained systems, the flashing can drain into the drainage gap.
Air Control There are three primary classes of reasons why the control of air flow is important to building performance: 1. 2. 3. Moisture control – water vapor in the air can be deposited within the enclosure by condensation and cause serious health, durability, and performance problems. Energy savings – air leaking out of a house must be replaced with outdoor air, which requires energy to condition it.
Basic requirements of Air Barrier Systems Typically, several different materials, joints and assemblies are combined to provide an uninterrupted plane of primary airflow control. Regardless of how air control is achieved, the following five requirements must be met by the air barrier system (ABS): 1. Continuity. This is the most important and most difficult requirement.
Thermal Control As society demands that residential buildings consume less energy and generate less pollution, minimizing the flow of heat through the enclosure has become an increasingly important function for the enclosure to perform. The control of heat flow is also important for the control of interior surface temperatures, and hence ensuring human comfort and avoiding cold weather condensation.
Figure 6: Thermal bridging can cause local temperature depressions during cold weather, resulting in condensation, mold growth, and staining. For these reasons, continuous exterior insulation is recommended in all residential buildings.
Condensation Control Air leaking outward through the enclosure wall in cold weather will contact the back of the sheathing in framed walls and can form condensation. This condensation can accumulate as frost in cold weather, and subsequently cause “leaks” when the frost thaws and liquid water drains down, or cause rot if the moisture does not dry quickly upon the return of warmer and sunnier weather.
Table 1: Ratio of exterior-interior insulation to control air leakage condensation If the sheathing layers are very vapor permeable (e.g., ROXUL COMFORTBOARD IS over fiberboard or gypsum sheathing, and housewrap) then very little insulation value is required outboard of the stud bay.
Cladding attachment through Continuous Insulation Cladding attachment is a common question when assemblies with exterior continuous insulation (“ ci “) are proposed. Although solutions for semi-rigid stonewool insulation boards are not currently widely used in all parts of North America, they are simple, straightforward, and time tested in Europe and other parts of the world. Two methods of cladding attachment are considered here: a “Thin ci” approach for ROXUL COMFORTBOARD IS thicknesses of 1.
Figure 8: Example of “Thick ci” cladding attachment approach More information on the “Thick ci” approach can be found in the details section of this application guide. For larger buildings and heavier cladding systems, the required structural connections often need a different design approach to accommodate a continuous insulation with minimal thermal bridging. Traditionally, relieving or shelf angles are used to collect the gravity load of heavy masonry veneers every one or two floors.
Recommendations for thermal control by climate zone Figure 9: North American Climate Zone Map (based on ASHRAE Standard 90.
Table 2: R-value Recommendations by Climate Zone for each enclosure element Climate Zone 1 2 3 4 5 6 7 8 Wall 10 15 20 25 30 35 40 50 Vented Attic 40 50 50 60 65 75 90 100 Compact Roof 35 40 45 45 50 60 65 75 Basement Wall 5 10 10 15 15 20 25 35 Exposed floor 10 20 20 30 30 40 45 50 Slab 1 edge none 5 7.5 7.5 10 10 15 20 Windows (U/SHGC) yes 0.35/<0.25 0.30/<0.3 0.30/<0.35 0.24/<0.50 0.18/-0.15/-0.15/-- Sub-slab 2 none none 5 7.5 7.
Vapor Control Although most condensation problems occur because of air leakage, vapor diffusion can also occasionally cause damaging amounts of wetting. However, vapor diffusion is also an important drying mechanism, which may be an important part of a wall assembly design. Vapor diffusion is the movement of water vapor molecules through the microscopic open pore structure of porous materials (glass, solid plastics, and metals are not porous, wood, gypsum, and concrete are).
The most common moisture-related durability issue caused by inward moisture drives is moisture accumulation inside the gypsum wall board as a result of a low permeance coating such as vinyl wall paper, or on the back of low permeance materials installed on the interior of the gypsum wall board such as mirrors, cabinetry, whiteboards, etc. This often results in the formation of mold either on the drywall or the back of the wall covering, and in worst cases, the disintegration of the gypsum wall board.
Recommendations for vapor control by climate zone Different types of assemblies have different vapor control requirements. Although the requirements can be developed through rational engineering analysis, a simplified summary of recommendations, many from the US ICC (International Code Council) “I” codes, is presented below for the “normal” occupancies described above.
A Class III vapor control layer may be used instead of a Class I or II layer on the interior of framed walls in zone 4c and higher, if any of the following criteria are met: Zone 4c (e.g., Vancouver, Seattle or Portland) Sheathing-to-cavity R-value ratio of >0.20 Insulated sheathing with an R-value ≥ 2.5 on a 2x4 framed wall Insulated sheathing with an R-value ≥ 3.75 on a 2x6 framed wall. Zone 5 (e.g. Chicago, Windsor, Boston) Sheathing-to-cavity R-value ratio of >0.
Material Properties ® The following tables summarize the relevant material properties for the ROXUL COMFORTBOARD™ IS insulated sheathing product mentioned in this guide. ROXUL COMFORTBOARD IS Material Properties Table Thermal Resistance Density Compressive Strength 2 o 2 o RSI value R-value 0.72 m K/W per 25.4 mm @ 24 C . 2. o 4.0 hr ft F/Btu per inch @ 75 F Cold Weather RSI value R-value 0.78 m K/W per 25.4 mm @ -4 C . 2. o 4.4 hr ft F/Btu per inch @ 25 F Hot Weather RSI value R-value 0.
About Stone Wool ROXUL stone-wool insulation is a rock-based mineral fiber insulation comprised of Basalt rock and Recycled Slag. Basalt is a volcanic rock which is abundant in the earth, and slag is a by-product of the steel and copper industry. The minerals are melted and spin into fibers. Thermal Insulation Stone wool is an excellent insulator and a vital component in an energy efficient building.
Installation Details The following drawings illustrate common construction details for residential wall assemblies using the products and building science information provided in this guide. The drawings are not project-specific and, of course, are meant to be modified by the project architect to include selected cladding, structural, and other construction materials. Each drawing, however, clearly labels assembly elements by function and a narrative description of each detail is included.
01. “Thick ci” Cladding Attachment System Step 1: Install Drainage Plane Material over the Structural Sheathing Step 2: Install ROXUL COMFORTBOARD IS and Furring (i.e., strapping) Board edges should be butted tightly together. Multi-layers should have joints staggered. (no joint sealing is required) NOTE – if strapping is installed immediately ROXUL COMFORTBOARD IS boards can be temporarily attached to wall.
Step 3: Install Cladding Material Install cladding to furring as per cladding manufacturer’s instructions.
® ROXUL Building Science Notes 01. GENERAL a. Detail is applicable to light-weight cladding systems including vinyl siding, wood siding, and fiber cement siding or panels with ROXUL COMFORTBOARD IS thicknesses greater than 1.5” (38 mm). For heavy-weight cladding systems, see ROXUL CAVITYROCK™ Application Guide. Detail is applicable for ROXUL COMFORTBOARD IS thicknesses less than 1.
02.
® ROXUL Building Science Notes 01. GENERAL a. Detail is applicable to grade-level wall-to-basement or crawlspace stem wall interface. 02. STRUCTURE a. A site-cast concrete foundation wall and floor slab is pictured. A CMU foundation wall is an alternate. 03. RAIN WATER CONTROL LAYER a. A drained-screen approach to rain water control (as illustrated) is recommended. b. The drainage plane material is the primary rain water control layer in the wall assembly.
03. Floor Slab-to-Wall Interface ® ROXUL Building Science Notes 01. GENERAL a. Detail is applicable to grade-level wall to stem wall or slab-on-grade interface. 02. STRUCTURE a. A site-cast concrete foundation wall and floor slab is pictured. A CMU foundation wall is an alternate. 03. RAIN WATER CONTROL LAYER a. A drained-screen approach to rain water control (as illustrated) is recommended. b. The drainage plane material is the primary rain water control layer in the wall assembly.
04. AIR CONTROL LAYER a. The drainage plane may be detailed as the primary air control layer if made continuous. b. Other air barrier system components include the concrete structure, sealant at the rim joist and other framing connections, and the sill gasket. c. If an air permeable cavity insulation is selected an airtight drywall approach should be used. An airtight drywall approach requires all penetrations of the gypsum board to be carefully sealed. d.
04. Inside Corner – Horizontal Section ® ROXUL Building Science Notes 01. GENERAL a. Detail is applicable to above-grade walls with light-weight cladding systems (see 07.b below) over ROXUL COMFORTBOARD IS thicknesses greater than 1.5” (38 mm) for low and mid-rise construction. 02. STRUCTURE a. A wood frame is illustrated in this detail. Alternates for the infill wall structure include light gage metal stud with exterior gypsum board sheathing and a CMU structural wall. 03. RAIN WATER CONTROL LAYER a.
05. 06. 07. 08. approach requires all penetrations of the gypsum board to be carefully sealed. c. Multiple planes of airtightness are recommended where practical to control convection within the enclosure cavity. THERMAL CONTROL LAYER a. ROXUL COMFORTBOARD IS insulation is the primary thermal control layer. b. The amount of insulation recommended varies by climate region (see Table 2) VAPOR CONTROL LAYER a.
05. Outside Corner – Horizontal Section ® ROXUL Building Science Notes 01. GENERAL a. Detail is applicable to above-grade walls with light-weight cladding systems (see 07.b below) over ROXUL COMFORTBOARD IS thicknesses greater than 1.5” (38 mm) for low and mid-rise construction. 02. STRUCTURE a. A wood frame is illustrated in this detail. Alternates for the infill wall structure include light gage metal stud with exterior gypsum board sheathing and a CMU structural wall. 03. RAIN WATER CONTROL LAYER a.
04. 05. 06. 07. 08. iv. vapor permeable “peel and stick” self-adhered membrane v. vapor impermeable membranes may be used depending on vapor control design (see Section 06 below) AIR CONTROL LAYER a. The drainage plane may be detailed as the primary air control layer if made continuous. b. If an air permeable cavity insulation is selected an airtight drywall approach should be used. An airtight drywall approach requires all penetrations of the gypsum board to be carefully sealed. c.
06. Punched Window Interface – Installation Sequence Step 1: Wood frame wall sheathed with OSB or plywood with housewrap as drainage plane. Step 2: Modified “I” cut in housewrap over framed opening (dashed line above) Step 3: Housewrap folded in at jambs and sill and secured tightly. Head flap folded outward; or, tuck head flap under Step 4: Install first piece of sill pan into horizontal slit in housewrap. Pan must fit tightly. Fasten at vertical face of pan only.
Step 7: Back-caulk window. Apply sealant at jambs and head; do not apply to sill to allow for drainage. Or, caulk can be applied to window nailing flange prior to installation. Step 10: Install head flashing; extend minimum 2” past edge of jamb flashing 40 Step 8: Install window plumb, level and square per manufacturer’s instructions. Step 11: Fold housewrap down at head. Ensure head flap has not been damaged during the installation process.
Step 13: Install ROXUL COMFORTBOARD IS insulation. Step 14: Install furring over ROXUL COMFORTBOARD IS insulation. Step 15: Outward leg of cap flashing extends past face of trim (to be added in Step 19). Step 16: Adhesive membrane strip extends past cap flashing. Step 17: Sheathing tape applied over adhesive membrane strip to secure top edge. Step 18: Install next course of ROXUL COMFORTBOARD IS and furring. Drainage gap created by furring. Do not fasten furring through head cap flashing.
Step 19: Trim installed at head and jambs; sloped cap flashing (shown) installed over lower trim at head of window. 42 Step 20: Install vinyl, wood, or fiber cement siding.
07. Wall-to-Balcony Interface ® ROXUL Building Science Notes 01. GENERAL a. Detail is applicable to above-grade walls with light-weight cladding systems (see 07.b below) over ROXUL COMFORTBOARD IS thicknesses greater than 1.5” (38 mm) for low and mid-rise construction. 02. STRUCTURE a. A wood frame is illustrated in this detail. Alternates for the infill wall structure include light gage metal stud with exterior gypsum board sheathing and a CMU structural wall. 03. RAIN WATER CONTROL LAYER a.
04. 05. 06. 07. 08. i. non-perforated housewrap or building wrap ii. building paper iii. vapor permeable liquid or fluid applied membrane iv. vapor permeable “peel and stick” self-adhered membrane v. vapor impermeable membranes may be used depending on vapor control design (see Section 06 below) AIR CONTROL LAYER a. The drainage plane may be detailed as the primary air control layer if made continuous. b. If an air permeable cavity insulation is selected an airtight drywall approach should be used.
08. Wall-to-Roof Interface ® ROXUL Building Science Notes 01. GENERAL a. Detail is applicable to above-grade walls with light-weight cladding systems (see 07.b below) over ROXUL COMFORTBOARD IS thicknesses greater than 1.5” (38 mm) for low and mid-rise construction. A vented attic roof construction is illustrated. 02. STRUCTURE a. A wood frame is illustrated in this detail.
04. 05. 06. 07. 08. ii. building paper iii. vapor permeable liquid or fluid applied membrane iv. vapor permeable “peel and stick” self-adhered membrane v. vapor impermeable membranes may be used depending on vapor control design (see Section 06 below) AIR CONTROL LAYER a. The drainage plane may be detailed as the primary air control layer if made continuous. b. If an air permeable cavity insulation is selected an airtight drywall approach should be used.
References and Resources For more information on ROXUL COMFORTBOARD IS, please visit: http://www.roxul.
ROXUL INC. is the North American Operations of ROCKWOOL INTERNATIONAL A/S. In July of 2013, ROXUL INC. and ROCKWOOL: INTERNATIONAL A/S celebrated 25 years of success in North America. ROXUL INC. is the leading North American manufacturer of stone wool insulation products for the North American market. It has two strategically placed manufacturing facilities, one in Milton (East) and the other in Grand Forks, British Columbia (West).
