Plain-English definitions for 85 terms used by roofing, siding, window, gutter, and metal building contractors. Every definition is written so you can quote it directly on a job site or in a spec.
85 terms · A–W · All tradesAn extra freight fee added on top of the base LTL rate for non-standard delivery requirements, such as delivery to a residential address, a limited-access location, or when a liftgate is needed to lower the pallet. Common accessorials include residential delivery, inside delivery, and appointment fees. Trimgy includes standard accessorial estimates in its freight quote based on the delivery zip code.
A non-ferrous metal used for custom trim when corrosion resistance and light weight are priorities. In sheet metal fabrication, aluminum is specified by decimal thickness in thousandths of an inch — .032", .040", .050", or .063" — rather than by gauge number, which is used for steel. Aluminum does not rust, but it can pit or oxidize; anodizing or painting with Kynar prevents surface degradation on exposed exterior applications.
Aluminum that has been electrochemically treated to build up a hard, corrosion-resistant oxide layer on the surface. Anodizing does not add paint or coating — it hardens the aluminum's natural oxide film — producing a matte metallic appearance in clear, bronze, or dark bronze. It is commonly specified for architectural trim applications where a natural-metal look with long-term durability is required.
A flashing that runs horizontally across the base of a vertical surface — such as a chimney, dormer, or parapet — where it meets the roof surface. Apron flashing is typically bent with a sloped top leg that sits under the cladding above and a bottom leg that laps over the roofing material below. It is distinct from sidewall flashing, which is used at the sides of vertical penetrations rather than across the base.
The rear vertical portion of a sill pan or other receptor flashing that runs up the face of the rough opening or wall behind the window or door unit. The back leg's height is critical: it must extend above the highest anticipated water line inside the rough opening to prevent water from migrating behind the unit. A minimum back leg height of 1" is standard on most sill pan specifications.
A sheet metal angle installed at the base of a metal building wall panel to close the gap between the bottom of the panel and the foundation or floor slab. It provides a weather seal, holds the panel in position against lateral loads, and gives the building a finished appearance at grade. Also called base angle, base trim, or base rail depending on the manufacturer.
The amount of flat sheet material consumed during a bend, which is added to the sum of the flat leg dimensions to calculate developed width. Bend allowance depends on material thickness, bend radius, and bend angle — for a 90° bend in 24 ga. steel with a 1/8" inside radius, the bend allowance is approximately 0.16". This is the flat-pattern engineering that ensures the finished part's leg dimensions match what was drawn.
The amount subtracted from the total of all leg dimensions to arrive at developed width, accounting for the material that "enters" the bend radius. It equals the difference between the outside setback and the inside setback for a given bend. Fabricators use bend deduction tables based on material thickness and die opening to calculate the correct flat blank size before bending.
A rectangular or square-section gutter built into or onto the roof structure, common on commercial and industrial buildings with large roof areas. Unlike K-style or half-round gutters, box gutters are custom-fabricated to large cross-sections to handle high flow volumes. They are typically soldered or welded at seams for leak-free performance and require precise custom dimensions for each installation.
A metal fabrication method that uses a press brake to bend flat sheet metal into angles and profiles by clamping the material between dies and pressing a punch through it, one bend at a time. Brake forming produces custom profiles in low-to-medium volumes without tooling costs, making it the standard method for all custom architectural sheet metal trim. Any profile made of straight-line segments can be brake-formed.
A hem where the folded lip is pressed completely flat against the back of the sheet, fully closing the folded edge. A closed hem requires approximately 3/4" to 1" of additional developed width per edge and produces a neat, rigid, finished look. It is stronger than an open hem and is commonly specified on the exposed edges of coping caps, fascia trim, and architectural panels.
The width of the flat metal coil from which sheet metal trim is slit and brake-formed. Coil width sets the upper limit on the developed width of any custom profile — a profile whose legs sum to more than the available coil width must be fabricated in multiple pieces. Standard steel coil widths for brake-formed trim range from 12" to 48"; aluminum coil is often available in narrower widths.
A sheet metal cap installed on top of a parapet wall, masonry wall, or curb to prevent water from entering the top of the wall. Metal coping is mechanically attached to a continuous aluminum cleat and lapped at joints to allow thermal movement. Critical dimensions include the top flat, inside leg (interior face of the wall), and outside leg (exterior face), all of which must be coordinated with the actual wall thickness measured on site.
A flashing installed in a reglet or embedded in masonry above a base flashing to cap and seal the upper edge of the base flashing assembly. Counter flashing is typically removable or adjustable to allow for building movement and differential settlement. It terminates the waterproofing assembly at wall-to-roof interfaces, chimney flashings, and anywhere a base flashing abuts a vertical surface.
The total flat coil width consumed when a finished trim profile is unfolded flat, including all leg dimensions plus the material consumed in each bend (bend allowances) and any hem deductions. Developed width is the key input to material cost — a wider developed width means more sheet consumed per linear foot, which directly increases price regardless of the profile's visible face height. This is why a hemmed profile costs more than the same profile without a hem.
A vertical pipe or rectangular tube that carries water collected by a gutter down from the roof to grade or a drainage system. Downspouts are fabricated from the same material as the gutter and connect at the top via an elbow. Standard light commercial downspout sizes are 2×3" and 3×4" rectangular; round downspouts are paired with half-round gutter systems. Downspout sizing must be matched to the roof drainage area to prevent overflow.
A sheet metal flashing installed at the eave and rake edges of a sloped roof that directs water away from the fascia and into the gutter. Standard profiles include Type C (basic L-shape), Type D (T-shaped with a drip lip extending over the gutter), and Type F (wide face with vertical drip for fascia protection). Drip edge is installed under the roofing felt at the eave and on top of the felt at the rake.
A hem where the folded lip is bent outward and downward at a slight angle rather than flat against the back of the sheet, creating a drip point that sheds water away from the panel edge. It is commonly used on the bottom edge of wall panels, fascia trim, and coping caps where water must be directed away from the substrate. A drip hem adds approximately 1/2" to the developed width of the profile.
The lower edge of a sloped roof that overhangs the wall below, where rainwater exits the roof surface and enters the gutter or drip edge. The eave is a primary focus of roof edge flashing design because this is where water, ice dams, and thermal movement all concentrate. On metal buildings, "eave" also refers to the horizontal bottom member of the wall-to-roof transition where the eave strut is located.
A structural steel member at the eave of a metal building that supports both the roof panel and the upper course of wall panel simultaneously. Eave trim is attached at the eave strut to close the gap between roof and wall panels. The eave strut's depth and flange dimensions determine the geometry of the eave trim profile that covers it.
A sheet metal trim piece that runs along the eave of a metal building to close and seal the gap between the roof panel and the wall panel at the eave strut. It typically has a top leg sliding under the roof panel, a face covering the eave strut, and a bottom leg overlapping the wall panel. Eave trim is typically the highest-volume custom trim piece on a metal building erection project.
A bent fitting that connects the gutter outlet at the bottom of the downspout drop to the vertical run of the downspout, typically offset from the face of the fascia. Standard elbows are available in 45° and 90° configurations and in matching downspout sizes. On larger commercial gutter systems, custom elbows are sometimes specified to accommodate non-standard offset dimensions.
A raised lip at each end of a sill pan flashing that prevents water from draining out the sides of the sill pan and into the wall assembly. End dams are the most commonly omitted detail in sill pan fabrication and the most common cause of sill pan water-intrusion callbacks. Minimum end dam height is typically 1" above the drainage holes; the corner where the end dam meets the back leg must be watertight.
A sheet metal trim installed at the gable end (endwall) of a metal building where the roof panel terminates at the rake edge. It closes the exposed edge of the roof panel, provides a weather seal, and gives the building a finished appearance at the gable. Also called rake trim, verge angle, or endwall flashing depending on the manufacturer and regional convention.
A J-shaped metal channel used in siding installation to receive and support the cut edge of panels where they terminate at a horizontal surface such as a soffit, window head, or door head. Unlike J-channel, which receives the panel from the front, F-channel slides over the exposed cut edge from the side. It is typically extruded aluminum or brake-formed galvanized steel.
The elapsed time from when a custom sheet metal order is confirmed and paid to when the finished trim ships from the fabrication shop. Lead times vary by shop backlog, material availability, order complexity, and season; typical custom brake-formed trim lead times range from 2 to 10 business days. Freight transit time is additional and depends on the carrier and destination distance.
The vertical face board at the lower edge of a sloped roof, running horizontally along the eave and typically covering the ends of the roof rafters. Metal fascia trim is often a brake-formed flat panel with a hemmed bottom edge and a back leg that slides under the roofing and over the gutter hanger. Fascia trim width — the visible face height — is typically 4" to 12" depending on rafter depth and architectural profile.
A thin sheet metal component installed at joints, transitions, or penetrations in a building envelope to prevent water infiltration. Flashing directs water away from vulnerable areas by bridging the gap between dissimilar materials or assemblies. Common types include sidewall flashing, counter flashing, valley flashing, head flashing, apron flashing, and diverter flashing — each designed for a specific building transition.
Sheet metal trim installed around the perimeter of openings in a metal building wall panel — doors, windows, louvers — to close the exposed panel edges and provide a weather seal. It typically consists of four custom pieces: two jamb trims (sides), a head trim (top), and a sill trim (bottom), all brake-formed to match the panel thickness and the frame dimensions of the specific opening.
A horizontal sheet metal trim piece installed at the top of a wall just below the soffit, covering the transition between the wall cladding and the underside of the roof overhang. It may be flat, profiled, or vented depending on the design intent. Frieze board trim is typically specified in the same material and gauge as the siding panels to achieve a consistent appearance.
The raised front lip at the outer edge of a sill pan flashing that prevents water collecting in the pan from draining over the exterior face of the building. The front dam height determines how much water the sill pan can retain; it should be lower than the back leg and end dams so that if the pan fills, water drains outward rather than into the wall assembly. The weep holes or slots in the front dam are critical to long-term drainage function.
A steel sheet continuously hot-dip coated with an alloy of approximately 55% aluminum and 45% zinc. The aluminum provides corrosion barrier through a sealed film; the zinc provides sacrificial galvanic protection at cut edges and scratches. Galvalume offers significantly better bare corrosion resistance than galvanized steel and is the dominant substrate for unpainted architectural trim, metal building panels, and Kynar-painted products.
Steel sheet coated with a layer of zinc through a continuous hot-dip galvanizing process. Zinc protects the underlying steel by acting as a sacrificial anode — it corrodes preferentially, protecting the steel at cut edges. Galvanized is less corrosion-resistant than Galvalume in most environments and is typically used where economy is the primary driver; still common for drip edge, flashing, and agricultural trim applications.
A numerical designation for the thickness of sheet metal, where higher gauge numbers indicate thinner material. In steel, 26 gauge is approximately 0.0179" thick and 24 gauge is approximately 0.0239" thick — each gauge step represents roughly 30% more metal. Aluminum does not use gauge numbers; aluminum sheet is specified by decimal thickness in thousandths (.032", .040", .050", .063"). Gauge selection affects structural performance, cost, oil-canning risk, and fabrication capability.
A horizontal structural member in a metal building frame that spans between columns and supports the wall panels. Girts provide lateral support and serve as the attachment point for wall panels, insulation, and trim. The girt spacing and size determine the wall panel's spanning capability and the required fastener pattern for trim attached to the exterior face.
A flashing that extends from the roof edge underneath the roofing material and over the front face of the gutter, preventing water from running behind the gutter. A gutter apron differs from a standard drip edge in that it has a longer top leg extending further under the roofing and a bottom leg that hooks over the gutter lip. It is the preferred eave flashing when a gutter is present, providing a more complete weather seal than drip edge alone.
A semicircular gutter profile used on traditional, historic, and high-end light commercial buildings. Half-round gutters provide excellent flow capacity for their face width and have no corners where debris can accumulate. They are typically hung from round-bottom hangers and paired with circular downspouts; available in aluminum, copper, and galvanized steel in 4", 5", and 6" face widths.
A flashing installed horizontally above a window, door, or other wall opening to shed water away from the top of the opening and direct it to the sides. Head flashing typically has a sloped top leg integrating with the weather-resistive barrier above, a face covering the opening head, and a drip edge on the bottom. The end returns are critical — they must prevent water from draining behind the window casing at the corners.
A folded edge on a sheet metal part created by bending the material back onto itself. Hems serve multiple purposes: they eliminate the sharp cut edge (preventing injury and corrosion initiation), add stiffness to the panel edge, and in some cases create an interlocking joint. Common hem types include open hem, closed hem, drip hem, Pittsburgh lock, and S-lock — each with different structural and aesthetic properties.
The additional flat sheet width consumed when creating a hem, which is added to the visible face dimension to calculate developed width. A closed hem on the bottom edge of a panel requires approximately 3/4" to 1" of sheet width that is not visible in the finished part. Hem allowances must be included in developed width calculations to order the correct coil width and to arrive at accurate material pricing.
A sheet metal trim piece installed at the vertical corner where two wall panels meet at an inside (concave) corner. It covers the gap between the panel edges, prevents water infiltration at the corner joint, and provides a finished appearance. Inside corner trim is typically an L-shaped or J-shaped profile that slides behind each panel; on metal buildings it is often a two-piece assembly to accommodate the panel rib profile.
A J-shaped metal channel used in siding installation to receive and conceal the cut edges of horizontal siding panels at windows, doors, corners, and other termination points. The panel's cut edge slides into the open slot of the J and is held by the channel's leg. J-channel is available in aluminum and steel in standard face widths of 3/8" to 1/2"; the face covers the gap between the panel edge and the adjacent frame or trim.
A vertical flashing installed at the side of a window or door rough opening to prevent water from migrating into the rough opening from the sides of the unit. Jamb flashings overlap the sill pan end dams at the bottom and are overlapped by the head flashing at the top, creating a shingle-lapped waterproofing sequence. In new construction they are typically self-adhering membrane; for commercial or high-performance applications, custom sheet metal jamb flashings are specified.
A vertical sheet metal trim piece installed at the side of a window, door, or other opening to cover the gap between the window frame and the wall cladding. On metal buildings with framed openings, jamb trim is a custom brake-formed piece matching the wall panel thickness. On light commercial siding applications, jamb trim is typically flat aluminum coil stock or preformed aluminum casing.
The most common commercial K-style gutter profile, featuring a flat bottom, angled back, and a front face with an ogee (S-curve) profile that resembles crown molding. K-style gutters are available in 4", 5", and 6" face widths; the 5" profile is standard for most commercial applications. They carry more water than a half-round of the same face width due to their rectangular cross-section.
A small flashing installed at the bottom end of a sidewall flashing run where a sloped roof meets a vertical wall, to divert water away from the wall and into the gutter. Without a diverter flashing, water running off the roof at this point is channeled behind the siding and into the wall cavity, causing rot and water damage. It is one of the most commonly missed flashing details on commercial construction and a leading cause of exterior wall water damage.
A high-performance fluoropolymer coating based on polyvinylidene fluoride (PVDF) applied to sheet metal trim and panels for long-term color retention and weather resistance. Kynar 500-based coatings carry a 30-year finish warranty in commercial applications and are the industry standard for painted metal building panels and architectural trim. Available in hundreds of standard colors and custom color-matches through a factory coil-coating process.
A straight, unbent segment of a brake-formed trim profile, measured in inches from one bend to the next or from a bend to the cut edge. The length and sequence of legs defines the cross-section of any sheet metal trim profile. When ordering custom trim, each leg must be specified in length and direction (up, down, left, right) relative to the previous bend. In Trimgy, every line segment drawn on the grid represents one leg of the trim cross-section.
A unit of measure equal to one foot of length along the trim profile's run (not the developed width). Trim is priced and ordered by the linear foot; ordering 200 LF of 4-inch drip edge means 200 feet of trim that measures 4 inches on its face. LFT is the standard quantity unit for all brake-formed and roll-formed sheet metal trim.
The total length of trim ordered, expressed in feet. In a custom trim order, linear footage is the quantity multiplied by the per-linear-foot price (which is based on developed width, gauge, and material) to calculate total material cost. Linear footage is distinct from the area of sheet consumed — area equals linear footage multiplied by developed width.
Sheet metal trim used at the interior-facing edges of metal building wall or roof panels — at openings, skylights, or partial-height walls — to cover the raw panel edges with a finished interior appearance. Liner panel trim is typically lighter gauge than the structural panel and may be a different color. It is custom-fabricated to match the depth and geometry of the specific opening frame.
Less-Than-Truckload freight shipping, in which a shipment is too large for parcel shipping but too small to fill an entire truck, so it is combined with other shippers' freight on a single truck. Custom sheet metal trim ships LTL because the long bundle lengths (10' to 12') cannot go through parcel carriers. LTL rates depend on total weight, freight class, origin-destination lane, and any accessorial charges. Trimgy calculates LTL freight to your delivery zip before checkout.
A multiplier applied to the base material price to account for the cost difference between different metals and coatings. In Trimgy's pricing engine, Galvalume steel is the baseline (modifier = 1.0×); aluminum is approximately 1.5–2.0× depending on thickness; Kynar-painted steel is approximately 1.4–1.7× depending on color and finish type. Material modifiers reflect the combined effect of raw material cost and processing cost differences.
The natural metallic surface of aluminum or steel as it comes from the rolling mill, without any additional coating, painting, or anodizing. Mill finish aluminum has a shiny surface that oxidizes over time to a dull silver-gray. It is used in concealed flashing applications where appearance is not a factor — sill pans, cavity flashings, and substrate-integrated flashings. Mill finish steel (uncoated) is almost never used for exterior trim because it rusts rapidly.
A visual distortion of flat sheet metal panels or trim that appears as wavy, rippled, or buckled areas in an otherwise flat surface, caused by internal stresses in the coil. Oil-canning is a cosmetic issue inherent to thin sheet metal products and does not affect structural performance or weathertightness. It is more visible on painted surfaces at low sun angles and can be mitigated by using heavier gauge, narrower panels, or a striated (embossed) surface texture.
A hem where the folded lip is bent back at approximately 180° but not pressed completely flat against the back of the sheet, leaving a narrow gap between the hem and the panel. Open hems are quicker to form than closed hems and are used on edges that will be concealed or where a slight gap is acceptable. They add stiffness to the edge and eliminate the sharp cut edge but are less finished in appearance than a closed hem.
A sheet metal trim piece installed at the vertical corner where two wall panels meet at an outside (convex) corner. It covers the exposed panel edges, prevents water infiltration at the corner, and provides a finished appearance. Outside corner trim is typically an L-shaped profile with equal or unequal legs; the leg lengths must match the wall panel reveal to achieve a flush appearance from both elevations.
The wood or plastic platform on which custom sheet metal trim is bundled and strapped for LTL freight shipment. Because trim sections are typically 10' to 12' long, the pallet length is fixed at the bundle length; pallet width varies with the quantity and size of trim bundles. Trimgy calculates pallet dimensions from the total linear footage ordered to generate an accurate LTL freight quote before checkout.
A low wall extending above the main roof level around the perimeter of a flat or low-slope roof, typically built up from the exterior wall below. Parapets require coping caps on top to prevent water from entering the top of the wall, and base flashings at the roof-to-wall junction at their base. The height, width, and construction of the parapet determine the dimensions of all flashings required at and above it.
A coping cap installed on top of a parapet wall on a low-slope or flat-roof building. Parapet coping must slope slightly toward the roof interior to drain water inward rather than over the building face. Joint treatment — lapping, soldering, or expansion joints — is critical for parapets that experience significant thermal movement over their length.
A factory-formed interlocking hem that creates a mechanical seam used to join two sheet metal panels or ducts edge-to-edge. One panel has a hook-shaped hem and the other has a cap that snaps over it; when pressed together the seam locks mechanically without fasteners or solder. The Pittsburgh lock is the standard seam for HVAC duct fabrication and is used in architectural sheet metal applications where a hidden mechanical joint is required.
Polyvinylidene fluoride — the fluoropolymer resin used as the binder in high-performance architectural coatings for metal panels and trim. Kynar 500 and Hylar 5000 are the proprietary PVDF resin brands used by coating applicators on metal coil. PVDF coatings have exceptional UV resistance, chalk resistance, and color retention, making them the specification-grade standard for metal building facades and architectural trim that must retain color for decades.
A horizontal structural member in a metal building roof that spans between rafters (rigid frames) and supports the roof panels. Purlins are the attachment surface for roof screws and, at the ridge, for ridge cap trim. The purlin spacing and depth determine the roof panel spanning capability and the required fastener pattern for attached trim and accessories.
The sloped edge of a roof at the gable end, running from the eave up to the ridge. The rake is where rake trim (or endwall flashing) is installed to seal the exposed edge of the roofing material against wind-driven rain. Rake trim must account for the roof pitch — the steeper the pitch, the more acute the angle of the trim's intersection with the wall below.
A sheet metal trim piece installed along the sloped gable (rake) edge of a sloped roof, covering the exposed edge of the roofing material and providing a weather seal at the rake. On light commercial roofs it is often called a rake drip edge; on metal buildings it is called endwall flashing or verge angle. Rake trim must be specified at the correct pitch angle to lie flat against both the roof panel and the end wall below.
A narrow horizontal groove cut into a masonry wall or cast into concrete to receive the top edge of a counter flashing. The counter flashing is inserted into the reglet and the opening is sealed with caulk or lead wedges to prevent water entry. Reglets can also be metal extrusions surface-mounted to the wall face when cutting into the masonry is not practical or desired.
A sheet metal profile installed along the peak of a sloped roof to cover and seal the joint where two roof surfaces meet at the ridge. Ridge caps must allow for thermal movement and are typically attached with concealed clips or lapped at joints. On metal buildings, ridge cap often includes a foam closure that seals the corrugated or ribbed profile of the roof panel at the peak to prevent bird and pest entry.
A metal fabrication process that feeds coil stock through a series of consecutive roll stands, each progressively bending the metal until the desired profile is achieved at the exit. Roll forming produces consistent, high-volume profiles at low per-unit cost but requires expensive custom tooling for each profile — economical only for large production runs. Standard stock trim like K-style gutter and J-channel is roll-formed; custom one-off profiles are brake-formed.
The framed opening in a wall into which a window, door, or other unit is installed, sized slightly larger than the unit to allow for shimming and leveling. Rough opening dimensions are the primary inputs for specifying custom sill pans, jamb trim, and head flashing — the sill pan width must match the rough opening width, and the sill pan length must match the rough opening depth from front to back.
A seam profile that joins two flat sheet metal panels edge-to-edge by bending each edge into an S-shape so the two panels hook together along the S-curve. S-locks create a hidden mechanical seam that can accommodate thermal movement better than a soldered or riveted joint. They are used in roofing, HVAC duct fabrication, and some architectural trim applications where a concealed field joint is needed.
A gutter fabricated on-site in a single continuous piece using a portable roll-forming machine, eliminating the lap joints required in sectional gutter installation. Because there are no intermediate seams, seamless gutters have fewer potential leak points than sectional gutters and are the preferred method for professional gutter installation. Seamless gutters are typically available only in standard K-style and half-round profiles that fit the roll-former tooling.
Factory-fabricated gutter sold in standard lengths (typically 10' sections) that must be joined on-site with connectors and sealant. Sectional gutters are less expensive than seamless and available through retail channels but have more joints that can develop leaks over time. They are typically installed by homeowners or general contractors rather than specialty gutter contractors.
A detailed technical drawing prepared by a fabricator or contractor showing the exact dimensions, materials, and construction details of a custom-fabricated element, submitted for review and approval before fabrication begins. For custom sheet metal trim, a shop drawing shows the cross-section profile with all leg dimensions, material specification, gauge, coating, and total linear footage. Trimgy generates the digital equivalent of a shop drawing as part of every order, transmitting it directly to production.
A flashing installed at the bottom of a wall opening (window, door, or louver) to collect and drain water that enters the rough opening. Sill flashing ranges from a simple L-shaped angle to a full three-dimensional sill pan with back leg, end dams, and front dam. Simple sill flashings are used in commercial storefront systems; three-dimensional sill pans are required under windows in high-performance commercial construction.
A three-dimensional custom sheet metal flashing installed at the bottom of a window or door rough opening to collect any water that bypasses the window unit and drain it outward. A complete sill pan includes a sloped bottom, back leg, end dams, front dam, and drainage holes or slots. Sill pans must be sized to the exact rough opening width and coordinated with the window unit depth to function correctly — there is no standard off-the-shelf sill pan size for non-modular rough openings.
The underside of a roof overhang, filling the space between the fascia board and the wall face, closing the rafter tail space from weather, pests, and debris. Soffit panels may be solid or vented (perforated) to allow attic ventilation. Residential soffit is typically aluminum or vinyl in widths from 8" to 24"; commercial applications may use metal panels matched to the cladding system.
A block or trough placed at the base of a downspout to receive the discharged water and direct it away from the building foundation. Sheet metal splash blocks can be custom-fabricated to any length and profile. They are a low-cost alternative to underground drainage connections for light commercial downspout terminations where positive drainage away from the foundation is achievable by grade alone.
A narrow strip of sheet metal or vinyl installed horizontally at the bottom of a wall before the first course of siding panels, providing the locking feature that the first panel engages. Without a starter strip, the bottom siding course would not lock to anything and would hang loose or bow outward. The starter strip must be level and at the correct height to establish the panel course alignment for the entire wall.
L-shaped sheet metal assembly at the continuous junction of a sloped roof field and a vertical surface (chimney, dormer, parapet, or wall). The horizontal leg integrates with the roofing field — membrane, underlayment, or panel system — while the vertical leg mounts behind the wall cladding or counterflashing. Fabricated in overlapping sections per SMACNA minimum geometry (4" horizontal leg, 4" vertical leg, 6" section overlap), sidewall flashing directs water from the wall junction back onto the roof field without allowing infiltration into the wall cavity.
The permissible variation in a specified dimension, typically expressed as ±1/16" or ±1/8" for brake-formed sheet metal. Brake-formed trim holds tighter tolerances than roll-formed stock but is still subject to variation from spring-back, coil camber, and machine calibration. For critical fit conditions such as a sill pan inside a pre-hung window rough opening, dimensions and tolerances should be explicitly specified rather than left to fabricator discretion.
A flashing installed where two different roof assemblies, wall materials, or building planes meet — such as where a lower roof meets an upper wall, or where a metal wall panel transitions to brick or stucco. Transition flashings are typically custom-fabricated because the dimensions are unique to the specific building geometry. They must account for the differential thermal movement of the two materials they bridge.
A flashing installed in the valley — the V-shaped low point where two sloped roof surfaces meet — to direct the concentrated water flow that occurs at that intersection toward the eave. Open valley flashing (visible metal) uses a continuous W-shaped or V-shaped metal piece; closed valley flashing uses woven or cut shingles over a self-adhesive membrane. Valley flashing must be wide enough to extend beyond the cut edge of the roofing material on both sides and allow for thermal expansion.
A membrane or sheet material installed over wall sheathing under the exterior cladding to prevent liquid water from entering the wall assembly while allowing water vapor to diffuse outward. Common WRB materials include building wrap (spunbonded polyolefin), felt (No. 15 or No. 30 asphalt felt), and fluid-applied membranes. All sheet metal flashings — sill pans, jamb flashings, head flashings — must integrate correctly with the WRB to maintain a continuous water-resistive layer around every penetration.
A small opening at the bottom of a sill pan, window frame, or masonry wythe that allows water accumulated in the sill pan or wall cavity to drain outward rather than backing up into the wall assembly. On a sill pan, weep holes are typically 1/4" diameter punched holes or slots at the front of the pan bottom, protected from insect entry by a mesh or slotted baffle. Weep holes must remain unobstructed by sealant or debris to function — sealing them is one of the most common installation errors.
Decorative sheet metal trim applied around the exterior perimeter of a window or door opening, covering the gap between the window frame and the wall cladding and providing a finished appearance. Unlike jamb flashing and sill pans, which are functional waterproofing, window casing trim is primarily aesthetic and typically brake-formed to a flat or profiled face with returns that wrap the window frame. It is common on metal-panel buildings and aluminum-clad commercial construction.