Curtain Wall Framing & Building Envelope

The exterior envelope of a church building is where structural framing meets weather, physics, and the relentless forces of Ontario winters. Curtain wall framing is the non-load-bearing exterior wall system that hangs on the primary structure — steel beams, concrete floors, or a combination of both — and its job is straightforward in concept but demanding in execution: keep the weather out, keep the heat in, resist wind loads, support whatever cladding the architect chose, and do all of this for fifty years without complaint.

On church projects, curtain wall framing shows up everywhere: the tall sanctuary facades with soaring glass, the classroom wing walls clad in brick veneer, the fellowship hall wrapped in metal panel, the office section with stone accents. Each application has the same fundamental structure — steel studs spanning between floor lines, connected to the primary structure with clip angles — but the envelope assembly, cladding system, and detailing vary dramatically.

This guide covers it all. From the clip angle at the base of the stud to the sealant joint around the last window, every layer of the building envelope is detailed here at the level a field crew needs to build it right.

1. What Is Curtain Wall Framing?

A curtain wall is a non-load-bearing exterior wall that is attached to the building’s primary structural frame. It carries no gravity loads from above — no floors, no roof, no beams bear on it. The curtain wall studs span vertically between floor lines (or between spandrel beams), and their only structural job is to resist lateral loads: wind pressure pushing inward, wind suction pulling outward, and seismic forces in some cases.

Beyond resisting wind, the curtain wall serves as the building’s environmental separation — the dividing line between inside and outside. It supports the cladding, carries the continuous insulation, provides the substrate for the air and vapour barriers, and integrates with every window, door, and penetration through the exterior wall. Every layer matters. Every joint matters. Every transition matters.

Why Churches Need Curtain Wall Framing

• Tall sanctuary facades: Worship spaces often feature walls 8–12 m tall with large window openings. These walls must resist significant wind loads while accommodating the structural movement of long-span roof beams above.
• Large glass areas: Churches frequently incorporate extensive glazing for natural light — clerestory windows, full-height feature glass, curtain wall glazing systems. The framing around these openings must be precise and structurally sound.
• Complex geometry: Angled walls, curved facades, tower elements, and canopy connections create non-standard framing conditions that require engineered solutions at every connection.
• Mixed cladding: A single church building might have brick veneer on the main body, stone on the tower, metal panel on the fellowship hall, and curtain wall glazing on the sanctuary front — each requiring different support and detailing from the same curtain wall framing system.

2. Design Principles

Curtain wall framing sits at the intersection of structural engineering and building science. The structural side sizes the studs, designs the connections, and ensures the wall resists wind without excessive deflection. The building science side designs the envelope assembly — insulation, barriers, drainage, and cladding support — to control heat, air, moisture, and vapour flow through the wall. Both disciplines must work together; a structurally adequate wall that leaks water is no better than a watertight wall that blows in during a storm.

Governing Standards

• CSA S136 (North American Specification for the Design of Cold-Formed Steel Structural Members): The primary design standard for CFS member and connection capacity. Every stud, track, clip angle, and bridging member is designed to this standard.
• AISI S240 (North American Standard for Cold-Formed Steel Structural Framing): Covers CFS framing systems — wall studs, headers, bracing, and connections as assemblies rather than individual members.

Ontario Building Code Requirements

• OBC Part 3 (Fire Protection, Occupant Safety, Accessibility): Churches are classified as Group A, Division 2 (assembly occupancy). This classification drives combustibility requirements for exterior cladding, fire separation from property lines, and sprinkler requirements that affect wall assembly design.
• OBC Part 4 (Structural Design): All curtain wall framing on church projects is engineered under Part 4. Wind loads, connection design, deflection limits, and bracing are all Part 4 requirements.
• OBC Part 5 (Environmental Separation): The building envelope — air barriers, vapour barriers, rain penetration control, and thermal insulation — must comply with Part 5. This is where the physics of moisture, heat flow, and air leakage meet code requirements.

Wind Load Design

Curtain wall studs are sized primarily for wind. The National Building Code of Canada (NBCC) provides reference wind pressures based on geographic location, and for most Ontario church projects the design hourly wind pressure (1-in-50-year return) translates to wall pressures in the range of 0.3–0.5 kPa on the main field of the wall. At building corners and roof edges, the pressures increase significantly — sometimes doubling — due to aerodynamic effects. The engineer accounts for these higher pressures by specifying heavier gauge studs or tighter spacing in corner and edge zones.

Deflection Limits

L is the unsupported span of the stud (typically floor-to-floor height). For a 3.6 m storey height with L/360, maximum allowable deflection is 10 mm under full design wind load.

3. Stud Selection & Sizing

Curtain wall studs are heavier than interior partition studs — they must resist the full design wind pressure over their unsupported span while limiting deflection to the values required by the cladding type. The studs are cold-formed steel (CFS), manufactured from 345 MPa (50 ksi) structural-grade steel per ASTM A1003 Grade 50 or equivalent CSA standard.

Typical Stud Specifications

Corner and Edge Zones

Building corners and edges experience higher wind pressures than the main field of the wall. The engineer designates these as pressure zones, and the studs in these zones are typically upgraded — either a heavier gauge (e.g., 12ga instead of 14ga) or tighter spacing (e.g., 300 mm instead of 400 mm). The shop drawings clearly indicate where zone changes occur. Mark these transitions on the floor track during layout — a change in stud gauge is invisible once the wall is sheathed, and using the wrong stud in the wrong zone is a structural deficiency.

Stud Span

Curtain wall studs span vertically between floor lines or between spandrel beams. Typical storey heights on church projects range from 3.0 m for office and classroom areas to 6.0–10.0 m for sanctuary walls. Taller walls may require intermediate horizontal support (girts) to break the stud span into shorter segments, or deeper/heavier studs to span the full height.

4. Connection to Structure — Base (Fixed)

At the base of each storey, the curtain wall studs connect to the floor structure (concrete slab or steel beam) with clip angles that provide a rigid, fixed connection. The base clip resists wind shear forces (the horizontal component of wind load at the base of the stud) and anchors the stud against both inward pressure and outward suction. The base connection does not allow vertical movement — it is the fixed end of the stud.

Clip Angle Specifications

• Material: L-shaped steel angle, minimum 50 mm x 50 mm x 3 mm (2” x 2” x 10ga). Heavier clips for taller walls or higher wind zones — the engineer specifies.
• Stud connection: Two #10 or #12 HWH (hex washer head) self-drilling screws through the clip into the stud web. Screws must fully penetrate the stud and engage a minimum of three exposed threads.
• Structure connection (steel beam): Two TEK 5 self-drilling screws (for steel flanges up to 12 mm) or two bolts through pre-drilled holes (for heavier steel or where specified).
• Structure connection (concrete slab): Two concrete expansion anchors or adhesive anchors per clip, minimum 6.3 mm (1/4”) diameter, with embedment depth per engineering.
• Clip spacing: One clip per stud at each connection point (base and top). Some engineering may require clips at every other stud with continuous track between — follow the shop drawings.

Installation Procedure

1. Snap a chalk line on the floor slab or steel beam at the stud line location, verified against control dimensions.
2. Pre-drill or pre-punch the clip angles on the ground — factory-fabricated clips with pre-punched holes are strongly preferred.
3. Fasten the clip to the structure first (bolts or anchors), aligned to the chalk line.
4. Set the stud into the clip and fasten with HWH screws through the pre-punched holes in the clip’s vertical leg into the stud web.
5. Verify plumb immediately after fastening each stud. Adjust before proceeding to the next.

5. Connection to Structure — Top (Deflection)

At the top of each storey, the curtain wall studs connect to the beam or slab above with slotted clip angles or proprietary deflection clips. This is the critical detail that distinguishes curtain wall framing from load-bearing walls. The top connection must accomplish two seemingly contradictory things: resist wind loads (push and pull) while allowing the structure above to deflect vertically without crushing the stud.

Why Deflection Clips Are Essential

Structural steel beams and concrete slabs deflect under load. A steel beam spanning 12 m with L/360 allowable deflection will deflect up to 33 mm under full design load. A concrete slab continues to creep and deflect for years after construction. If the curtain wall stud is rigidly connected at the top, that deflection compresses the stud axially — a load the stud was never designed to carry. The result: buckled studs, cracked drywall, blown-out sheathing, and a very expensive rebuild.

Slotted Clip Angles

• Design: Same L-shaped clip as the base, but with vertical slots (20–25 mm long) in the stud-side leg instead of round holes.
• Fastening: A bolt or screw through the slot into the stud web, installed with a washer at the mid-point of the slot. The fastener is snugged — not fully torqued — so the stud can slide vertically in the slot as the structure deflects.
• Structure side: The horizontal leg is rigidly fastened to the beam or slab (same as the base clip) with round holes.
• Slot length: Must accommodate the calculated structural deflection plus 10 mm tolerance. For a beam with 25 mm calculated deflection, the slot should be at least 35 mm long (25 mm deflection + 10 mm tolerance).

Proprietary Deflection Clips

• Cemco DFC: Two-piece clip with a slide channel that provides positive lateral restraint while allowing vertical movement.
• ClarkDietrich ASF (Adjustable Slide-Fix): Adjustable clip with a long slot and locking mechanism for field adjustment.
• Equivalent products: Multiple manufacturers offer deflection clips with varying capacities and deflection ranges. All proprietary clips must be engineer-approved for the specific application.

Deflection Allowance Calculation

The deflection allowance at the top clip must account for the maximum expected deflection of the structure above. For a beam or slab spanning L:

• Steel beam: Typical allowable deflection is L/360 (live load) to L/240 (total load). For a 10 m beam at L/360 = 28 mm.
• Concrete slab: Include creep deflection, which can equal or exceed the immediate deflection. Long-term deflection of a concrete slab can be 2–3 times the initial deflection.
• Add 10 mm tolerance to the calculated deflection for construction tolerances and future loading changes.

6. Complete Wall Assembly (Outside to Inside)

A curtain wall is not just studs — it is a multi-layered assembly where every component has a specific function in controlling heat, air, moisture, and vapour. Understanding the purpose of each layer and its position in the assembly is essential for correct installation. Getting the order wrong, or omitting a layer, creates problems that are invisible during construction but devastating in service.

Assembly Layers

1. Cladding: The outermost visible layer — brick veneer, metal panel, ACM (aluminum composite material), fibre cement, stone veneer, or EIFS. Protects everything behind it from direct rain and UV exposure.
2. Drainage cavity / air space: Minimum 25 mm clear space behind masonry veneer (19 mm minimum behind panel cladding) for drainage of any moisture that penetrates the cladding.
3. Air barrier / weather-resistive barrier (WRB): Self-adhered membrane or fluid-applied coating on the exterior face of the sheathing. Prevents air infiltration and acts as the secondary rain screen.
4. Continuous insulation (CI): Rigid insulation board installed continuously over the entire exterior of the sheathing, with no gaps at studs. This is the primary thermal control layer.
5. Exterior sheathing: DensGlass (glass mat gypsum sheathing) or exterior-grade gypsum board. Provides a substrate for the air barrier and lateral bracing for the studs.
6. CFS studs with cavity insulation: Batt insulation (mineral wool or fibreglass) between studs. Provides additional R-value and sound attenuation.
7. Vapour barrier: 6-mil polyethylene or equivalent vapour retarder. In Ontario (Climate Zone 6), the vapour barrier is located on the warm side (interior side) of the insulation. Its position depends on climate — always outboard of the dew point to prevent condensation.
8. Interior finish: Gypsum drywall (12.7 mm or 15.9 mm Type X for fire-rated assemblies).

7. Continuous Insulation (CI) — Detailed

Continuous insulation is the single most important thermal element in an exterior steel stud wall. Without CI, the wall’s thermal performance is a fraction of what the cavity insulation alone would suggest, because steel studs are massive thermal bridges. Steel conducts heat roughly 300 times more efficiently than wood. A 152 mm steel stud wall with R-22 batt insulation but no CI performs like approximately R-8 to R-9 in practice — a 40–60% reduction in effective R-value from the steel studs alone.

Continuous insulation solves this by wrapping the entire exterior of the wall in an unbroken thermal blanket. Because the CI is outboard of the studs, it insulates the studs themselves, reducing the thermal bridging effect to near zero.

CI Material Comparison

Ontario Climate Zone 6 Requirements

• Minimum CI: R-7.5 per OBC/NECB minimum, but typical design targets R-10 to R-15 of continuous insulation depending on wall assembly and cavity insulation.
• Total effective wall R-value target: R-20 to R-25 (combined CI + cavity insulation, accounting for thermal bridging at studs).
• NECB compliance: The National Energy Code for Buildings sets prescriptive and trade-off paths for envelope performance. The building envelope consultant determines the CI thickness required to meet the energy target for the specific project.
• Polyiso derating: When polyiso is used in Ontario, the R-value must be derated for cold-temperature performance. At −15°C, polyiso performs closer to R-4.5/inch rather than the rated R-6/inch. Many consultants avoid polyiso for the outermost CI layer in Ontario for this reason.

CI Board Installation

• Mechanically fastened: Washer-head screws or impaling pins through the CI board into the studs. Fastener spacing per the CI manufacturer and engineer — typically 300–400 mm o.c. vertically and at each stud.
• Board joints: Stagger horizontal and vertical joints. Tape all joints with manufacturer-recommended tape (or apply foam sealant) to prevent air and thermal bypass at gaps.
• Multi-layer installation: For CI thicknesses over 75 mm, install in two layers with staggered joints. This eliminates through-joints and significantly reduces thermal bypass.
• No gaps: Every gap in the CI is a thermal bridge and a potential moisture pathway. Even a 3 mm gap at a board joint reduces the local R-value dramatically. Fit boards tight and seal every joint.

8. Cladding Support Through CI

The cladding must be attached to the structural framing, but it sits outboard of the continuous insulation. Every fastener or bracket that penetrates the CI creates a point thermal bridge — a direct conductive path through the insulation layer. The goal of modern curtain wall design is to support the cladding while minimizing these thermal bridges.

Thermal Spacer Systems

Cladding-Specific Support

• Brick veneer: Supported on shelf angles at each floor line (or every 3.6 m maximum). Shelf angles are structural steel angles bolted to the slab edge or spandrel beam. Standoff anchors or adjustable brick ties extend through the CI from the studs to the brick. This is engineering-intensive — the shelf angle, standoff, and tie design all require P.Eng. approval.
• Metal panel: Supported on Z-girts or hat channels that span between thermal spacer clips. The Z-girts are oriented vertically or horizontally depending on panel orientation. Panel clips attach to the Z-girts.
• Stone veneer: Supported on engineered anchor systems (stainless steel or thermally broken brackets) that extend through the CI to the studs. Every stone anchor is individually designed for the weight and wind load of the stone panel it supports.
• ACM (Aluminum Composite Material): Similar to metal panel — Z-girt or hat channel sub-framing through CI. ACM panels clip or rivet to the sub-framing.

9. Air & Vapour Barriers

The air barrier and vapour barrier are two distinct control layers in the wall assembly, each with a specific job. They are often confused, sometimes combined into a single product, and frequently installed incorrectly. Getting these layers right is essential for a building envelope that performs over its lifespan without moisture damage, mould, or energy waste.

Air Barrier

The air barrier prevents uncontrolled air leakage through the wall assembly. Air leakage carries moisture, heat, and pollutants. In a pressurized building (which churches often are, due to HVAC systems), warm moist interior air pushed through gaps in the envelope can deposit large quantities of moisture in the wall cavity — far more moisture than vapour diffusion alone. The air barrier is the single most important layer for controlling moisture in the assembly.

• Self-adhered membranes: Products such as Grace Vycor Plus or Henry Blueskin VP100. Applied directly to the exterior sheathing (DensGlass). Self-adhered membranes provide excellent continuity because they seal to the substrate and to themselves at overlaps.
• Fluid-applied membranes: Products such as Tremco ExoAir 230 or Henry Air-Bloc. Sprayed or rolled onto the sheathing as a liquid, curing to form a seamless, monolithic membrane. Excellent for complex geometry and around penetrations.
• Continuity is everything: An air barrier with holes is not an air barrier. Every lap, seam, penetration, transition, and termination must be sealed. The membrane must be continuous from the foundation to the roof, wrapping into every window and door opening, sealing at every pipe and conduit penetration, and tying into the roof membrane at the top of the wall.

Air Barrier Continuity at Transitions

• Wall to roof: The wall air barrier must connect to the roof air barrier (typically the roof membrane or vapour retarder). This transition often occurs at the parapet or roof edge and requires a membrane strip or sealant joint bridging the two systems.
• Wall to window: The air barrier wraps into the window rough opening and connects to the window frame with sealant or membrane. The subsill area is the most vulnerable point — a membrane pan under the window sill is critical.
• Wall to foundation: The air barrier terminates at the foundation wall or slab edge, sealed with membrane or sealant to the concrete.
• At penetrations: Every pipe, conduit, duct, exhaust vent, and louver through the wall requires the air barrier to be sealed around the penetration with compatible membrane or sealant.

Vapour Barrier

The vapour barrier controls vapour diffusion — the slow movement of water vapour through materials from the warm, humid side to the cold, dry side. In Ontario (Climate Zone 6), the vapour barrier is installed on the interior (warm) side of the insulation to prevent warm, moist indoor air from diffusing into the cold wall cavity where it would condense.

• Material: 6-mil polyethylene sheet is the standard vapour barrier for Ontario commercial construction. Alternatives include vapour-retarding primers or smart membranes that adjust permeability based on humidity.
• Location: Always on the warm side of the insulation. In Ontario, this means behind the interior drywall, between the drywall and the stud cavity.
• Sealing: All joints lapped a minimum of 100 mm and sealed with acoustical sealant or vapour barrier tape. Seal to the floor slab, ceiling, and all penetrations.

Testing

Air barrier performance is verified through testing per OBC and NECB requirements. Common test methods include:

• Air barrier material testing: Laboratory testing of the membrane material to confirm it meets the maximum air leakage rate (0.02 L/s/m² at 75 Pa per NECB).
• Field testing: Blower door testing or localized chamber testing on completed wall sections to verify installed air barrier performance.
• Visual inspection: During construction, continuous inspection of air barrier continuity, especially at transitions and penetrations. Every lap, every seal, every patch is checked.

10. Window & Door Integration

Windows and doors are the most vulnerable points in any curtain wall assembly. Every opening creates an interruption in the air barrier, vapour barrier, insulation, and cladding — four control layers that all need to be transitioned around the opening without gaps, laps in the wrong direction, or sealant joints that will fail in five years. Water damage at windows is the number one source of building envelope failures, and the fix is always expensive because it involves removing cladding, CI, and sometimes framing to access the damage.

Head, Sill, and Jamb Flashing

• Head flashing: A drip cap or flashing membrane over the top of the window that directs water outward, away from the window frame. The flashing must extend beyond the window jambs on both sides and integrate with the air barrier above.
• Sill flashing: A sloped pan or membrane under the window sill that collects any water that penetrates past the window frame and directs it outward to the drainage cavity. The sill flashing is the most critical flashing detail — it is the last line of defense before water enters the wall cavity.
• Jamb flashing: Membrane strips along the sides of the opening that connect the head and sill flashings to form a continuous waterproof pan around the entire opening.

Sealant Joints

• Backer rod + sealant: Every joint between the window frame and the surrounding wall receives a closed-cell backer rod sized for the joint width, followed by a polyurethane or silicone sealant. The sealant bonds to both sides of the joint (two-point adhesion), with the backer rod preventing three-point adhesion to the back of the joint (which would cause premature sealant failure).
• Joint design: Sealant joints should be designed for ±25% movement capability. Joint width of 10–15 mm is typical for window perimeter joints. Wider joints for larger windows or higher movement conditions.

Subsill Membrane

The subsill membrane is a self-adhered or fluid-applied waterproof membrane applied to the rough sill of the window opening before the window is installed. It wraps up the sides of the opening a minimum of 150 mm and slopes outward to drain. This membrane catches any water that bypasses the window frame sealant and directs it to the exterior drainage plane. It is the single most important detail for preventing water damage at windows.

Large Church Window Openings

Church buildings frequently feature large window openings — full-height sanctuary glass, clerestory windows, feature windows in lobbies and towers. These large openings create significant structural and envelope challenges:

• Structural headers: Large openings require engineered headers in the curtain wall framing — back-to-back C-studs, boxed headers, or steel angle headers depending on the span and load. Headers must transfer wind loads around the opening to the adjacent studs.
• Multiple king and trimmer studs: Wide openings may require double or triple king studs and trimmer studs to handle the concentrated loads at the jambs.
• Integration with glazing systems: Large church windows often use aluminum curtain wall glazing frames (distinct from the CFS curtain wall framing). The transition between the CFS framing and the aluminum glazing frame requires careful air barrier and flashing detailing.

11. Lateral Bracing of Curtain Wall Studs

Curtain wall studs, like interior partition studs, require lateral bracing to prevent twisting and buckling. The bracing requirements are often more demanding because curtain wall studs are taller, heavier gauge, and subjected to wind loads that create significant lateral forces.

Bracing Methods

• Horizontal bridging (CRC through punches): Cold-rolled channel threaded through the factory knockout holes in the stud webs. Minimum one row at mid-height for studs up to 3.6 m, two rows at third points for studs 3.6–5.0 m, three rows for studs over 5.0 m. CRC secured to end studs or tracks with clip angles.
• Strap bracing: Steel strap screwed to the face of each stud. Less rigid than CRC but faster to install. Must be on the same face of all studs. Typical for shorter walls or where CRC cannot be threaded (e.g., insulated cavities).
• X-bracing: Diagonal steel straps forming an X pattern within the wall plane. Used where the curtain wall must also resist in-plane lateral (racking) loads — uncommon for pure curtain walls but sometimes required at building corners or adjacent to shear walls.
• Shear panels: Structural sheathing (plywood or steel sheet) applied to the face of the studs to create a shear-resisting diaphragm. Used where significant in-plane forces must be transferred through the curtain wall framing.

Bracing at Corners and Returns

Where curtain walls meet at corners or return into the building, the framing requires additional bracing to handle the change in direction. Corner studs receive bridging from both wall planes, and the connection between the two planes must be rigid enough to transfer wind loads around the corner without racking. The engineer details these connections on the shop drawings — they are not field-improvised.

12. Brick Veneer on Curtain Wall

Brick veneer is the most common cladding on Ontario church buildings, and it creates the most complex curtain wall assembly. The brick is heavy (approximately 2.0 kN/m² for standard 90 mm veneer), it requires structural support at every floor line, it needs a drainage cavity behind it, and every piece of metal that connects the brick to the structure passes through the continuous insulation — creating thermal bridges that must be managed.

Shelf Angle Support

• Location: Structural steel shelf angles are installed at each floor line, or at maximum 3.6 m vertical intervals, to carry the weight of the brick above.
• Attachment: Shelf angles are bolted to the slab edge or spandrel beam with anchor bolts. The angle must be designed by the structural engineer for the weight of the brick it supports and the eccentric load created by the offset from the structure face.
• Thermal break: A thermal break pad (Armatherm or equivalent) between the shelf angle and the structure reduces the thermal bridge at this critical connection point.
• Soft joint: A compressible joint (backer rod + sealant) directly below every shelf angle allows for vertical expansion of the brick below and deflection of the shelf angle above. This joint is critical — without it, the expanding brick can crush against the shelf angle and spall.

Brick Ties

• Type: Adjustable two-piece ties are preferred for curtain wall construction because they accommodate the variable distance between the stud face and the brick face (which varies with CI thickness, sheathing, and construction tolerances).
• Spacing: Maximum 600 mm o.c. vertically and 800 mm o.c. horizontally (approximately one tie per 0.48 m² of wall area). Tighter spacing at openings, corners, and edges — per engineering.
• Attachment: The stud-side connector screws through the sheathing and CI into the stud with a long fastener. The brick-side connector embeds in the mortar joint. Adjustable ties allow the two halves to slide relative to each other, accommodating differential movement.

Expansion Joints

• Vertical expansion joints: Every 6–9 m in the brick, and at all corners, changes in wall direction, and adjacent to dissimilar materials. Joint width 10–15 mm with backer rod and sealant.
• Horizontal expansion joints: Below every shelf angle. Joint width allows for the cumulative vertical expansion of the brick coursing below the shelf angle plus the deflection of the shelf angle above.

Drainage Cavity

• Minimum 25 mm clear air space between the back of the brick and the face of the air barrier (or CI, if the air barrier is behind the CI). This cavity allows water that penetrates the brick to drain downward to the flashing and weep holes.
• Cavity clear of mortar droppings: Mortar that accumulates in the cavity bridges the drainage space, blocks weep holes, and directs water inward instead of down. Keep the cavity clean during construction using cavity drainage mats, mortar collection devices, or diligent clean-out at flashing locations.
• Weep holes: Open head joints (unmortared vertical joints) at maximum 600 mm o.c. along the base of each brick section, directly above every flashing location. Weep holes allow water collected on the flashing to drain to the exterior.

Flashing

• Base of wall: Through-wall flashing at the bottom of every brick section, sloped outward to the weep holes.
• At shelf angles: Flashing above and below every shelf angle, directing water outward.
• At window heads: Flashing above every window and door opening, extending past the jambs and turned up at ends to form end dams.
• At window sills: Sloped sill flashing directing water outward, integrated with the subsill membrane.

13. Metal Panel & ACM Cladding

Metal panel and ACM (Aluminum Composite Material) cladding provide a modern, clean aesthetic that many contemporary church designs use for fellowship halls, office wings, gymnasiums, and accent walls. The cladding is lighter than brick, faster to install, and offers more flexibility in colour and profile. The underlying curtain wall framing and envelope assembly remain the same — the difference is in the cladding support system.

Sub-Framing

• Z-girts: Z-shaped galvanized steel members that span vertically or horizontally between thermal spacer clips. The Z-girt provides a flat mounting surface for the panel clips. Z-girts are spaced to match the panel module (typically 600–1200 mm o.c.).
• Hat channels: Hat-shaped members serving the same function as Z-girts. Preferred where the cladding attachment requires a wider mounting surface.
• Thermal spacers: Every Z-girt or hat channel must connect to the studs through a thermal break (Cascadia Clip, Armatherm pad, or equivalent) to maintain CI continuity.

Panel Clip Systems

• Concealed clip: Panel edges engage interlocking clips fastened to the Z-girts. No exposed fasteners on the panel face. Provides a clean appearance and allows for thermal expansion of the panels.
• Exposed fastener: Panels screwed directly to the sub-framing through pre-drilled holes with neoprene washers. Faster but less aesthetically refined. Screws must be installed in slotted holes to allow panel expansion.

Joint Details

• Open joints (rain screen): Many metal panel systems use open joints (3–6 mm) between panels, relying on the air barrier and CI behind the panels to provide weather protection. The panels are the rain screen; the air barrier is the rain barrier.
• Sealed joints: Where a sealed system is required, joints are sealed with compatible sealant (silicone for metal panels) over backer rod.

ACM Fire Concerns

14. Quality Control & Inspection

Curtain wall framing and envelope construction involve dozens of components, hundreds of connections, and thousands of potential failure points. Quality control is not a single inspection at the end — it is a continuous process integrated into every phase of the work. The cost of fixing envelope deficiencies after the wall is complete is 10–50 times the cost of getting it right during installation.

Pre-Installation Checks

• Verify stud sizes, gauges, and steel grades match the shop drawings. Check bundle labels and mill certificates.
• Inspect clip angle fabrication: correct dimensions, hole locations, slot lengths, and material gauge.
• Confirm CI products match the specification: material type, thickness, R-value, manufacturer.
• Verify air barrier and vapour barrier products are correct and compatible with the substrates.
• Review shop drawings with the crew. Every person on the curtain wall crew must understand the assembly sequence, clip details, and critical tolerances.

During Installation

• Clip connections: Correct screw type, count, and pattern at every clip. Deflection slot screws at mid-slot with washers, snugged not torqued.
• Stud plumb and alignment: Check every fifth stud with a level. Cumulative errors in stud alignment show up as waviness in the cladding.
• Bridging and bracing: Installed before sheathing. Correct type, spacing, and fastening per shop drawings.
• Sheathing fastening: Correct screw type and spacing per sheathing manufacturer and structural requirements. Edge screws within 10 mm of panel edges, field screws at specified spacing.

Envelope Inspection

• Air barrier continuity: Every lap sealed, every penetration sealed, every transition (wall-to-roof, wall-to-window, wall-to-foundation) complete and tested. Photograph the completed air barrier before CI installation.
• CI board joints: Tight fit, staggered joints, taped or sealed. No gaps. Check for boards that have been cut too short and shimmed with loose pieces.
• Flashing laps: All flashings lapped shingle-style (upper layer overlapping lower layer by minimum 100 mm). End dams at all flashing terminations.
• Sealant quality: Correct sealant type, backer rod installed, proper depth-to-width ratio (2:1 for sealant depth to joint width), good adhesion to both substrates.

Post-Installation

• Window and door integration: subsill membranes, head flashings, jamb flashings, sealant joints all complete and inspected.
• Brick tie spacing and installation verified (before brick covers them).
• Weep holes open and unblocked.
• Drainage cavity clean of mortar droppings and construction debris.
• Mock-up wall testing (if required): full-scale mock-up of a representative wall section, tested for air and water infiltration per ASTM E1105 or equivalent.

15. Common Mistakes

These are the errors that show up repeatedly on curtain wall and envelope projects. Every one of them has caused expensive repairs, insurance claims, or occupant complaints. Learning them here is considerably cheaper than learning them on the job.

1. Missing or inadequate deflection clips. Studs rigidly connected to the structure at the top get crushed when the beam deflects. The entire wall buckles, the cladding cracks, and the only fix is a complete rebuild. This is the most expensive single error in curtain wall framing.
2. CI board gaps at joints. Every gap — even 3 mm — is a thermal bypass and a potential condensation point. Cold spots behind gaps cause moisture accumulation, mould growth, and staining on interior finishes. Cut CI boards to fit tight and seal every joint.
3. Air barrier discontinuity at transitions. The air barrier stops at the parapet. The air barrier stops at the window rough opening. The air barrier has unsealed laps. Every discontinuity allows air leakage, which carries moisture into the wall cavity. The result: condensation, rot, mould, and energy waste.
4. Brick ties too widely spaced or wrong type. Under-tied brick veneer is a structural hazard — the veneer can separate from the wall under wind suction. Using non-adjustable ties on a curtain wall forces the mason to bend the ties to fit, reducing their capacity and durability.
5. Insufficient drainage cavity behind brick. Mortar droppings filling the drainage cavity blocks water flow to the weep holes. Water backs up behind the brick and eventually finds a path into the wall assembly. Clean cavities during construction — every day the mason works.
6. Flashing reversed (directs water inward). Through-wall flashing that slopes inward instead of outward collects water and delivers it to the wall cavity instead of the exterior. Every flashing must slope to drain to the outside. Check the slope on every piece before the next course of brick covers it.
7. Vapour barrier on wrong side of assembly. In Ontario, the vapour barrier goes on the warm side (interior). A vapour barrier on the cold side (exterior) traps moisture inside the wall cavity — the wall cannot dry inward, and condensation accumulates through every heating season. This error is invisible until the wall is opened for other reasons, by which time the damage can be extensive.
8. Cladding attached directly to studs without thermal break. Mounting Z-girts or shelf angles directly to the studs through the CI without thermal spacers creates massive thermal bridges that negate the benefit of the CI. The CI exists to break the thermal bridge — do not re-create the bridge at every cladding attachment point.

16. Commercial Interior Glazing

Interior glazing on church projects goes far beyond a pane of glass in a frame. Nursery observation windows, office partitions, meeting-room dividers, sidelites, transoms, and mirrors all require the right glass type, the right framing system, and strict compliance with OBC safety-glazing rules. In Ontario, all commercial glazing work must be performed by or under the direct supervision of a certified Glazier & Metal Mechanic (421A) journeyperson — this is a compulsory trade under Skilled Trades Ontario regulations.

Glass Types for Interior Applications

Interior Storefront & Office Partition Framing

Interior storefront framing uses aluminium frames — typically non-thermally-broken for interior applications since there is no temperature differential across the assembly. Standard frame depths are 44 mm or 50 mm face width, with finishes in clear anodized, dark bronze anodized, or powder-coated to match door hardware.

• Office partitions: Full-height or partial-height aluminium-framed glass walls that create enclosed offices while maintaining visual openness. Top and bottom channels anchor to the floor slab and structure above. Vertical mullions at 900–1200 mm spacing depending on glass thickness and height.
• Sidelites and transoms: Glass panels beside and above doors. Sidelites extend the visual openness of an entrance; transoms allow light transfer above a door. Both must meet safety-glazing requirements based on proximity to the door and height from floor.
• Frameless glass partitions: Increasingly popular in modern church office suites. 10–12 mm tempered glass panels secured with top and bottom channels (no vertical framing). Door panels on patch fittings or pivot hardware. Dramatic appearance but significantly more expensive than framed systems and more demanding to install level and plumb.
• Mirrors: Washroom mirrors, dance/fitness studio mirrors, and nursery observation mirrors must be safety-backed per CAN/CGSB 12.1. Mirrors in child-accessible areas must use laminated safety mirror or safety-film backing. Mount mirrors on J-channel or clip systems — adhesive-only mounting fails over time in high-humidity washroom environments.

OBC Safety-Glazing Requirements

OBC 3.3.1.2 mandates safety glazing (tempered or laminated) in specific locations. Inspectors check these on every project — memorize them:

• Within 500 mm of a door: Any glazing panel whose nearest edge is within 500 mm of a door edge must be safety glass. This catches sidelites, transoms adjacent to doors, and borrowed lites near doorways.
• Below 900 mm from the floor: Any glazing with its bottom edge below 900 mm from the finished floor must be safety glass. This is the “someone could walk into it” rule.
• All glass in doors and sidelites: Regardless of size or location, safety glass is required.
• Guards and railings: Glass used as or in guards must be laminated safety glass and must comply with OBC 4.1.5 guard requirements.

Church Applications

• Nursery observation windows: The most common interior glazing request on church projects. Parents want to see their children during the service. Use laminated glass (not tempered) — laminated holds together if a child throws a toy at it, while tempered shatters into cubes that, while safer than shards, still make for an exciting nursery evacuation. Frame height: full height to structure or to a dropped bulkhead. Include a transaction window or pass-through for check-in/check-out.
• Office partitions: Glass-fronted offices along corridors create an open, welcoming administrative wing while providing acoustic separation. Pair glass partitions with solid-core doors and acoustic seals for STC 35–40 performance.
• Meeting rooms: Full-height glazed meeting rooms with switchable privacy glass (electrochromic) or applied frost film give flexibility between visual openness and confidential meetings. Budget option: framed glass with integral blinds.

17. Exterior Storefront & Entrance Systems

The church entrance is the handshake — the first physical interaction every visitor has with the building. A well-designed, properly installed storefront entrance system says “welcome.” A drafty, rattling, leaking entrance says “we ran out of budget.” Exterior storefront glazing must perform structurally (wind loads), thermally (Ontario winters), and aesthetically — simultaneously.

Aluminium Storefront Systems

All exterior storefront on church projects in Ontario must use thermally broken frames — frames with a polyamide (nylon) bridge separating the interior and exterior aluminium to prevent thermal bridging. Non-thermally-broken frames cause condensation, energy loss, and will not meet OBC Part 5 (SB-10) energy-code requirements. Specify low-E, argon-filled insulating glass units (IGUs) as minimum.

Entrance Door Frames

• Narrow stile (75 mm): Interior doors and secondary entrances. Limited hardware options. Not recommended for primary church entrances due to limited durability.
• Medium stile (100–115 mm): The standard for church main entrances. Accommodates panic hardware, closers, and lever handles. The go-to choice for 90% of HCMI church entrance doors.
• Wide stile (150–175 mm): Heavy-traffic and institutional entrances. Maximum hardware flexibility. Accommodates concealed vertical-rod panic devices, heavy-duty closers, and electric latch releases. Specify for main sanctuary entrances expected to handle 500+ people exiting in 10 minutes after a service.

Automatic Entrance Systems

OBC barrier-free requirements and AODA mandate power-operated doors at barrier-free entrances. Options for church projects:

• Low-energy power operators: Electromechanical arms that open the door when activated by a push plate or motion sensor. Opens slowly (low energy) and closes on its own. Most common for church entrances — quieter and less institutional than full-auto doors.
• Full automatic sliding doors: Common in commercial retail but increasingly used in large church vestibules. Header-mounted operator. Requires 2400 mm minimum clear opening width for dual-slide configuration.
• Automatic swing doors: Standard swing doors with electromechanical operators. Maintain the traditional entrance appearance while providing automatic opening. Maximum opening force for barrier-free doors: 38 N per AODA.

Integration with Curtain Wall Systems

Storefront entrance systems frequently butt against or integrate into the curtain wall framing covered earlier in this guide. Key coordination points:

• Head and sill connections: The storefront header must tie into the curtain wall mullion system with a weathertight joint. Use compatible sealant systems — silicone-to-silicone, not silicone-to-polyurethane.
• Thermal break continuity: The thermal break in the storefront frame must align with the continuous insulation plane in the adjacent curtain wall. A misaligned thermal break creates a cold bridge at the transition — visible as condensation or frost on the interior frame in winter.
• Movement joints: Curtain wall systems accommodate structural deflection through slip connections. The storefront-to-curtain-wall joint must also accommodate this movement without breaking the seal. Use backer rod and sealant joints sized for the expected movement range.

Church Vestibule Entrance Design

• Vestibule sizing: OBC requires a vestibule (enclosed air lock) at main entrances for Ontario’s climate zone. Minimum vestibule depth: 2100 mm clear between inner and outer door swings. HCMI standard: 2400–3000 mm for comfortable flow with 200+ congregants exiting simultaneously.
• Sightlines: Full-height glazing in vestibule walls allows arriving visitors to see the welcome desk and lobby from outside — reducing the “walking into the unknown” anxiety that keeps first-time visitors from returning.
• Stained glass integration: Many HCMI projects incorporate stained glass panels — either new or relocated from a heritage building. Stained glass has zero thermal or structural performance, so it installs behind a protective exterior storm-glass panel. Coordinate the storm-glass frame with the stained-glass artisan early — retrofit coordination is extremely expensive. Install the storm glass first, sealed and inspected, then the stained glass from inside.
• Vestibule sequencing: Both sets of doors should have automatic operators. Coordinate sequencing so the inner doors do not open until the outer doors have closed — this prevents the pressure-equalization gust that blasts the greeter’s welcome-table pamphlets across the lobby.

Thermal Performance Considerations

• Frame U-factor: Thermally broken aluminium storefront frames typically achieve U-factors of 3.4–4.5 W/m²K. For Ontario climate zones, specify frames at the lower end of this range to minimize condensation risk.
• Glazing U-factor: Double-glazed low-E argon IGUs achieve approximately 1.6–1.8 W/m²K. Triple-glazed units (1.0–1.2 W/m²K) are increasingly specified on church projects to meet NECB energy targets and improve occupant comfort near large glass areas.
• Solar heat gain coefficient (SHGC): East- and west-facing storefront glazing on churches can create severe overheating during morning and evening services. Specify SHGC of 0.25–0.30 on east/west exposures; north-facing glazing can use higher SHGC (0.35–0.40) to maximize daylight without overheating.
• Condensation resistance: In Ontario, interior humidity from a full congregation (200+ people breathing and singing) combined with exterior temperatures of −20°C creates aggressive condensation conditions. Thermally broken frames and warm-edge IGU spacers are mandatory — standard aluminium spacers will show condensation and frost at the glass edge every winter morning.

18. Standards, Codes & Reference Documents

Every section of this guide ties back to specific codes, standards, and manufacturer requirements. Here is the master reference list for curtain wall framing and building envelope on church construction projects in Ontario.