How to Choose and Plan an Interlocking Exterior Cladding System

Tongue and groove exterior siding can create a clean, close-jointed façade, but the profile is only one part of the wall. The same interlocking edge appears on interior paneling, ceilings and flooring, so “tongue and groove” does not establish that a board belongs outdoors. Nor does a tight joint make the cladding waterproof.

A reliable selection process starts with the exact product documentation. Confirm exterior approval, orientation, exposed face, fastening, finishing, movement, drainage and warranty requirements before comparing prices. Calculate quantities from installed coverage—not the nominal width in the product name—and price the complete wall assembly rather than the boards alone.

This guide is strongest where the available documentation is specific, particularly for Western red cedar. It does not establish code approval, fire or wind performance, severe-exposure suitability, or a complete flashing design for any uncited product. Those questions require current manufacturer instructions, applicable technical reports and locally adopted code.

Mortar Desk publishes general building-material reference information. Product claims, retailer listings and installation guidance are treated separately because they do not carry the same evidentiary weight.

What tongue-and-groove exterior siding is—and what the joint does not do

A tongue-and-groove board has a projecting tongue along one edge and a matching groove along the other. During installation, the tongue of one board enters the groove of the next. This interlock aligns adjacent boards and generally creates a flatter, closer-jointed surface than profiles based primarily on overlapping boards.

Shiplap works differently: its rabbeted edges overlap and commonly create a more visible reveal or shadow line. Bevel siding uses tapered boards installed in overlapping courses, while channel siding uses an overlap shaped to form a recessed channel. These terms describe edge geometry and appearance; they do not, by themselves, establish durability or weather resistance. A commercial comparison of tongue and groove with shiplap illustrates the basic difference between an interlocking joint and overlapping rabbets.

Joint appearance varies by product. Common seller labels include:

• V-joint, which forms a pronounced V-shaped shadow line;

• flush or tight-joint, which minimizes the apparent seam;

• nickel-gap or reveal, which intentionally expresses a shadow line;

• radius, beaded and square-edge patterns, whose precise geometry varies by mill.

These names are not perfectly standardized. Do not assume that two products described as center-match, reveal or beaded have identical joints. Compare dimensioned cross-sections and physical samples, including the exposed face and intended visible side.

Most importantly, the interlocking face is not the wall’s primary weather barrier. Tongue and groove exterior siding does not replace a continuous water-resistive barrier, flashing around openings and penetrations, a drainage path or ventilation required by the selected wall system. Exterior guidance for both tongue-and-groove and shiplap identifies drainage layers, flashing, suitable fasteners and finish selection as separate assembly considerations—not functions performed by the board joint alone (Mountain Milling’s exterior overview).

The wall therefore needs a planned route that directs incidental water down and out rather than relying on exposed caulk as its sole defense.

Exterior performance depends on the complete assembly:

• exact cladding material and profile;
• water-resistive barrier and its continuity;
• window, door and penetration flashing;
• corner and trim geometry;
• fasteners, furring and attachment substrate;
• base and top terminations;
• drainage and ventilation provisions;
• finish and cut-end treatment;
• local wind, rain, salt, heat and wildfire exposure; and
• inspection and maintenance.

A precisely milled joint cannot compensate for missing head flashing, an unintegrated sill or a blocked drainage route. Treat the siding as the visible layer of a managed wall, not as a self-contained waterproof skin.

Verify exterior suitability before comparing products

Retail collections are useful for discovering products, but they are not substitutes for technical documentation. A single collection can contain exterior siding, interior paneling, ceiling boards, flooring, shiplap and related cladding. Some listings may be suitable for several applications; others may not.

For example, one retailer’s tongue-and-groove siding category includes wood, composite and fiber-cement filters, along with horizontal and vertical orientation filters. That catalog structure shows how products are marketed and sorted. It does not prove that every result is approved for every exterior wall, orientation, climate or code condition.

Do not infer exterior approval from any of these terms alone:

• tongue and groove;
• paneling;
• cladding;
• all-weather;
• water resistant;
• wood-look;
• vertical or horizontal; or
• exterior appearance.

“Water resistant” is not the same as waterproof. Neither term confirms compatibility with a particular wall assembly. Likewise, an exterior project photograph is not a fastening schedule, installation manual or technical evaluation report.

Before buying, obtain and review:

1. The exact product data sheet. Match the manufacturer, model, material, thickness and profile to the quoted item.
2. An exterior-application statement. Confirm approval for the intended wall use, not merely soffits, ceilings or sheltered decorative areas.
3. Permitted orientations. Verify horizontal, vertical or diagonal use.
4. The current installation manual. Check its revision date and confirm that it covers the exact product generation.
5. Substrate requirements. Determine whether attachment is permitted over sheathing, studs, blocking, wood furring, metal framing or a proprietary support system.
6. Fastening requirements. Verify fastener type, metal, head, shank, length, penetration, spacing and placement.
7. Finish requirements. Identify requirements for factory finishing, field finishing, back priming, cut-end treatment and renewal.
8. Warranty terms. Read exclusions concerning installation, ventilation, coatings, cleaning, movement and environmental exposure.
9. Applicable technical reports. Obtain the actual report if the project requires documented fire, wind or code performance.
10. Trim and accessory details. Confirm starter pieces, corners, vents, clips and termination components.

Match every document to the precise material, profile, thickness and wall application. Instructions for cedar do not automatically apply to pine, modified wood or composite. Ceiling-panel instructions do not establish approval for a rain-exposed wall.

Project-specific documents are also needed to answer questions such as:

• Is the attachment schedule adequate for the design wind pressure?
• Are the fasteners and accessories suitable for coastal salt exposure?
• Does the product comply with locally applicable wildfire provisions?
• Does the assembly have a required fire, flame-spread or ignition-resistance classification?
• Is the vapor-control strategy appropriate for the climate and interior conditions?
• Must the project use a tested assembly rather than individually selected components?

Manufacturer instructions and locally adopted code take precedence over generalized retailer or reference guidance. If documentation is incomplete, treat that as an unresolved purchasing risk rather than borrowing instructions from a different product.

Before placing a full order, obtain a physical sample or enough material for a small mock-up. Check:

• actual thickness and overall width;
• exposed face after engagement;
• joint depth and shadow;
• smooth, rough or re-sawn texture;
• finish color under site lighting;
• variation among boards;
• concealed versus visible fastening;
• fit with corners and window trim; and
• appearance of cut ends and field touch-up.

A mock-up can expose conflicts before they become expensive. A concealed fastener may split the tongue, the chosen trim may not cover a required clearance, or the installed reveal may look wider than it appeared online.

Materials and species found in the market

The market can be organized into four broad groups: natural wood, modified or specialty wood, wood-free composite and other cataloged categories such as fiber cement. These labels help structure a search, but category presence is not proof that an individual product is approved for an exterior wall.

Natural wood

Supplier catalogs include Western red cedar and other cedars, Eastern white pine, Southern yellow pine, spruce, Douglas fir, cypress, hemlock, ash and oak. Availability varies by region, grade, profile and mill. A species shown in a tongue-and-groove collection may be offered as interior paneling, flooring or custom millwork rather than exterior siding.

Natural wood also varies within a species. Grade changes knot content and visual consistency; grain orientation influences movement and appearance; moisture condition affects installed dimensions; and surface texture changes the appearance of a finish. A species name alone is therefore an incomplete specification.

Modified and specialty wood

Catalogs also show Accoya and thermally modified ash, spruce, pine and hemlock. Modification methods and product constructions differ, so these materials should not be treated as one interchangeable class. Their attachment, finishing and movement requirements may differ from those of conventional softwood siding.

One specialty lumber catalog, for example, lists pine, ash, spruce, cedar, hemlock, red oak, Accoya and thermally modified products alongside shiplap, flooring and other cladding. The mixed catalog reinforces the need to inspect the documentation for each product rather than assigning one intended use to the entire collection.

Wood-free composite

Retail listings include composite tongue-and-groove siding in multiple wood-look colors. These are engineered systems, not simply synthetic versions of a wood board.

Do not assume that every composite is waterproof, maintenance-free, fade-free or longer-lived than wood. Those conclusions require product-specific documentation and credible comparative evidence. Confirm the permitted application, attachment method, ventilation, cleaning, repair options and warranty conditions.

Other cataloged categories

Some retailers include fiber cement within tongue-and-groove filters. That establishes category presence only. Obtain the exact model, profile drawing and official exterior instructions before treating a listing as an exterior tongue-and-groove wall product.

A practical comparison framework

Avoid ranking these categories by lifespan, decay resistance, fading or maintenance burden without comparable service data. Supplier claims can identify questions to investigate, but they do not create a neutral ranking across dissimilar products.

Apply the same caution to a long warranty or “no finish required” statement. Read the official terms, exclusions, environmental limits, installation conditions and maintenance duties. A headline warranty duration is not useful if the proposed wall falls outside the covered application.

Use this decision sequence:

1. Eliminate products without documented approval for the intended exterior application.
2. Eliminate products incompatible with the substrate, orientation or drainage assembly.
3. Confirm that required ratings and local approvals are available.
4. Compare appearance, supply, finish options and repairability.
5. Compare realistic maintenance obligations.
6. Compare total project cost, including accessories and labor.

Profiles, grades, textures, and the dimensions that control coverage

Nominal width is a product name, not necessarily the width visible after installation. Part of a board’s overall width is consumed by the interlocking joint, so estimating must use the exposed or pattern-face width.

Three dimensions may appear:

• Nominal size: the conventional designation, such as 1x6.
• Finished or actual size: the measured overall thickness and width.
• Exposed or pattern face: the width each installed board adds to the wall.

The exposed face controls coverage. Two nominal 1x6 products can require different quantities—and have different costs per covered square foot—if their exposed faces differ.

Supplier listings commonly include nominal sizes such as 1/2x4, 1x4 and 1x6, with wider products also available. Exact dimensions depend on the mill pattern and moisture condition.

A documented Western red cedar example shows why the distinctions matter. Nominal 4-, 6- and 8-inch boards have listed dry exposed faces of 3, 5 and 6-3/4 inches. The same reference gives a dry finished thickness of 11/16 inch and finished widths of 3-3/8, 5-3/8 and 7-1/8 inches, respectively. These are dimensions for the cited cedar patterns, not universal tongue-and-groove sizes (Real Cedar profile reference).

Profile, grade and texture affect both appearance and ordering:

• V-joint: pronounced linear shadow.
• Flush or tight-joint: subdued seam.
• Center-match: a seller-specific matched-edge pattern that must be interpreted from the drawing.
• Nickel-gap or reveal: an intentionally expressed seam.
• Radius, beaded or square-edge: pattern names whose exact geometry varies by mill.
• Clear grade: selected for fewer visible natural characteristics.
• Knotty grade: permits knots and greater visual variation.
• Smooth face: planed appearance.
• Rough or re-sawn face: more textured finish appearance.

Request a dimensioned cross-section showing the tongue, groove, joint shadow, overall width and exposed face. Confirm which face is intended to remain visible and whether the product is genuinely reversible.

A complete request for quotation should state:

• material or species;
• intended exterior wall use;
• manufacturer and exact product;
• profile name and drawing;
• nominal size;
• actual thickness and width;
• exposed or pattern-face width;
• grade and grading standard, where applicable;
• moisture condition;
• visible face and texture;
• unfinished, primed or factory-finished condition;
• finish color and sheen;
• board lengths or length distribution;
• square-end or end-matched treatment;
• cut-end treatment requirements;
• quantity and ordering allowance;
• matching trim, vents and fastening accessories;
• delivery location and access constraints; and
• required delivery date.

Require the seller to identify substitutions. A board with the same nominal dimensions but a different exposed face can change quantity, joint layout, trim fit and cost.

Horizontal, vertical, and diagonal layouts change the wall assembly

Several wood products support horizontal and vertical installation, and some permit diagonal layouts. That does not mean every tongue-and-groove board can run in every direction. Orientation changes water behavior, support direction, fastener loading, cuts and trim details, so approval must be confirmed for the exact product.

Horizontal installation

For documented Western red cedar installation, work begins at the bottom and proceeds upward with groove edges facing downward. The instructions also establish width-based fastening rules and require fastening at each bearing point. These are cedar-specific details, not a universal sequence for proprietary composite or modified-wood systems (Real Cedar installation guide).

Horizontal cladding commonly attaches over vertical furring so the spaces behind the boards preserve a downward route for incidental water. The wall base must allow drainage and, where specified, ventilation while excluding insects. Product-specific wood-cladding guidance describes vertical furring for horizontal siding and drainable or cross-furred supports for vertical siding (Pioneer Millworks installation guidance).

Plan the horizontal layout around:

• starter course and base termination;
• window and door heads, jambs and sills;
• penetrations;
• inside and outside corners;
• supported board ends;
• roof-to-wall intersections; and
• top termination and ventilation.

A downward-facing groove does not make missing flashing acceptable. The face joint and the concealed drainage system perform different jobs.

Vertical installation

Vertical siding requires attachment points running across the boards. Uninterrupted conventional horizontal battens, however, can obstruct downward drainage. Depending on the selected system, the design may require drainable horizontal battens or a two-layer lattice with vertical furring for drainage and horizontal furring for attachment.

For the cited cedar method, the first vertical board begins at a corner with its grooved edge toward the adjacent wall. It is set plumb and fastened to horizontal blocking or furring. Any trimming of the first groove must be coordinated with the corner detail.

A vertical layout also changes:

• base and top treatment of board ends;
• story breaks or horizontal end joints;
• board rhythm around windows;
• load transfer through furring;
• continuity of drainage past supports; and
• access for later board replacement.

Diagonal installation

Do not proceed merely because a supplier says tongue and groove can be installed diagonally. Confirm that the exact exterior product, attachment system and substrate permit it.

What a rainscreen means

A rainscreen is a drainable—and commonly ventilated—space behind the cladding. It provides a route for incidental water and can permit air movement behind the boards. It is an assembly concept, not evidence that one cavity depth works for every product and climate.

One manufacturer’s general wood-cladding guide identifies 3/8 inch as the minimum cavity for its system and describes 1/2- or 3/4-inch furring as typical. Those dimensions are product guidance, not universal requirements. The same guide states that local codes supersede its recommendations.

For the selected system, resolve:

• cavity depth;
• furring material and width;
• attachment of furring to framing;
• support spacing;
• base drainage and ventilation;
• top ventilation;
• insect screening;
• continuity around windows and doors;
• cavity interruptions;
• roof-to-wall transitions; and
• compatibility with exterior insulation.

Draw these details before ordering because trim depths and fastener lengths depend on the complete wall build-up.

Fastening, acclimation, and seasonal wood movement

Blind nailing means driving a fastener through the tongue so the next board’s groove conceals it. Face nailing means fastening through the visible board face. Blind fastening produces a cleaner surface, but it is not automatically permitted for every width, species, profile or exposure.

For Western red cedar, the cited instructions permit one blind siding nail at each bearing for boards up to 6 inches wide and call for two face nails on wider pieces. They also require fasteners to penetrate at least 1-1/4 inches into solid wood. These rules are specific to the referenced cedar siding and should not be transferred unchanged to pine, Accoya, thermally modified wood, composite or fiber cement; see the Real Cedar installation guide linked above.

Other manufacturers specify different schedules. Pioneer Millworks, for example, recommends two face nails at each furring strip for the wood-cladding products covered by its own general guide. The difference demonstrates why no universal tongue-and-groove fastening schedule is defensible.

For the selected product, verify:

• fastener metal and coating;
• head style and diameter;
• smooth, screw or ring shank;
• fastener length and penetration;
• driving angle;
• spacing along each board;
• number of fasteners at each support;
• distance from edges and ends;
• visible or concealed placement;
• predrilling requirements;
• approved substrate;
• furring attachment;
• treatment at board ends; and
• wind-load-specific requirements.

Corrosion resistance is exposure- and material-specific. Do not substitute a fastener based only on length or an “exterior” label. Commercial wood-siding guidance may recommend stainless steel for its described applications, but the exact alloy and schedule still have to match the selected product and exposure (Mataverde installation guidance).

Acclimation and moisture planning

Natural wood changes dimension as it gains and loses moisture. Movement depends on species, grain orientation, board width, installation moisture, finish and seasonal exposure. Wider flat-sawn boards may behave differently from narrower or differently sawn material.

Treat acclimation as a product-specific requirement rather than prescribing one universal number of days. Determine:

• how boards must be stored;
• whether bundles must be opened;
• how material should be covered and ventilated;
• whether moisture readings are required;
• whether factory-finished boards need special handling; and
• what site conditions are acceptable at installation.

A moisture meter may be useful where the product instructions support moisture checks, but one target cannot be prescribed across every species and climate.

Do not promise a perfectly constant year-round reveal. A discussion involving a particular vertical mahogany profile illustrates how gaps can narrow, disappear or vary as wood moves, but the proposed calculations were disputed and do not support a universal expansion allowance (industry discussion of seasonal reveals).

Warning signs that warrant investigation include:

• splitting around concealed fasteners;
• buckling or boards lifting from the wall;
• narrowing or disappearing reveals;
• unusually wide or uneven joints;
• finish bridging across moving seams;
• cracked finish at board edges;
• staining around fasteners;
• rust or other corrosion;
• trapped debris at the wall base; and
• boards binding against trim.

Adding face nails, cutting gaps or caulking joints without identifying the cause may conceal symptoms while interfering with drainage or movement.

How to estimate coverage and compare board prices

Estimate siding from the exact exposed face, not nominal width.

Required linear feet before waste = net wall area in square feet × linear feet per square foot

If the supplier does not provide a coverage factor, derive it from exposed width:

Linear feet per square foot = 12 ÷ exposed face width in inches

One linear foot of board covers its exposed width across one foot of length.

Cedar reference factors

The documented Western red cedar factors are:

Use these factors only when the quoted product has the same exposed face. The dimensions and coverage factors come from the Real Cedar profile reference linked earlier.

Worked 100-square-foot examples

For a 5-inch exposed face:

1. 12 ÷ 5 = 2.4 linear feet per square foot
2. 100 × 2.4 = 240 linear feet

The order requires about 240 linear feet before waste and other allowances.

For a 6-3/4-inch exposed face:

1. 12 ÷ 6.75 ≈ 1.78
2. Using the cited rounded factor: 100 × 1.77 = 177 linear feet

The order requires about 177 linear feet before waste.

From gross wall area to order quantity

Begin with gross wall area and subtract openings where appropriate:

Net wall area = gross wall area − deducted opening area

Then calculate base footage:

Base linear feet = net wall area × coverage factor

Add the project’s stated ordering allowance:

Order quantity = base linear feet × (1 + project allowance)

Enter the allowance as a decimal. An allowance of A% becomes A ÷ 100. Do not insert a generic percentage without considering:

• wall shape and orientation;
• diagonal cuts;
• board lengths and random-length distribution;
• supported end-joint locations;
• grade and permitted defects;
• unusable damage;
• color or grain matching;
• profile direction;
• pattern matching;
• future repair stock; and
• packaging or minimum-order rules.

A simple rectangular wall using long boards may need a different allowance from a façade with many windows, returns and short sections. Require the supplier or installer to state the assumed allowance so quotations can be compared on the same basis.

Converting linear-foot price to square-foot price

Normalize a linear-foot price with:

Board cost per square foot = price per linear foot × coverage factor

In the retailer evidence reviewed for this article on August 19, 2026, one 1x6 premium Eastern white pine tongue-and-groove product was listed at $1.95 per linear foot, while one 1x6 knotty red cedar product was listed at $3.60 per linear foot. At a factor of 2.4 linear feet per square foot:

• Pine: $1.95 × 2.4 = $4.68 per square foot
• Cedar: $3.60 × 2.4 = $8.64 per square foot

These are dated retailer snapshots, not current national averages. Local stock and delivery availability require a ZIP code or store selection, and the figures should be rechecked immediately before publication or purchase (Ring’s End siding listings).

The conversions cover boards alone. They exclude ordering allowance, delivery, tax, samples, finish, fasteners, clips, furring, vents, water-resistive-barrier work, flashing, trim, labor, access equipment, maintenance and repairs.

Installed-cost worksheet

Comparing board prices without these lines can favor a product that requires costly accessories, extra finishing or a more labor-intensive support system.

The final specification and pre-order checklist

A product is ready to order only when both the visible board and the concealed assembly have been specified.

Go-or-no-go checklist

• [ ] The exact product is documented for the intended exterior wall use.
• [ ] The proposed horizontal, vertical or diagonal orientation is approved.
• [ ] The wall assembly is compatible with the product.
• [ ] Locally applicable code requirements have been reviewed.
• [ ] Required fire, wind or other technical documentation has been obtained.
• [ ] Nominal, actual and exposed dimensions are recorded.
• [ ] Quantity has been calculated from exposed coverage.
• [ ] The ordering allowance has a stated basis.
• [ ] Board lengths and end-joint locations have been planned.
• [ ] The substrate and furring arrangement are defined.
• [ ] Fastener type, length, penetration and schedule are confirmed.
• [ ] Base, top, corner and opening details are drawn.
• [ ] Drainage, ventilation and insect-exclusion details are resolved.
• [ ] Finish and cut-end treatment are specified.
• [ ] Warranty conditions have been reviewed.
• [ ] Cleaning, inspection and maintenance obligations are acceptable.

Do not leave openings, corners, penetrations, wall bases, end joints or roof transitions to improvised caulk. Determine how each detail drains, moves and connects to the water-resistive barrier.

Caulk and board-end decisions

Available guidance disagrees about caulking. Some advice supports caulking selected same-plane siding-to-trim joints while preserving drainage at head flashing. Other guidance warns against caulk where it could trap water, obstruct drying or fail as wood moves. A Green Building Advisor discussion of cedar siding joints demonstrates the disagreement over scarf joints, butt joints, trim joints and drainage.

There is therefore no responsible universal rule that exterior tongue-and-groove joints should always—or never—be caulked. The answer depends on:

• product instructions;
• whether the joint is board-to-board or siding-to-trim;
• trim geometry;
• flashing behind the joint;
• whether the detail is intended to drain;
• board movement;
• finish compatibility; and
• access for inspection and repair.

The same applies to board ends. Possible details include supported butt or scarf joints, approved end matching, cut-end treatment, backing, flashing or deliberately drainable joints. Select the detail from current product instructions and the project design.

Layout plan

Prepare a board-by-board or course-based layout identifying:

• supported end-joint locations;
• board-length distribution;
• visual staggering;
• alignment at windows and doors;
• orientation of reversible profiles;
• treatment of short pieces;
• corner sequence;
• cut-end coating;
• transition locations; and
• boards retained for future repairs.

Replacement stock should match the profile, dimensions, grade and finish. Store it to prevent damage while preserving product identification.

Delivery inspection

Before accepting or installing the order, check:

• manufacturer and exact product;
• exterior-use documentation;
• profile and joint drawing;
• grade;
• moisture condition, if specified;
• thickness, overall width and exposed face;
• ordered lengths and length distribution;
• straightness and machining consistency;
• tongues and grooves for damage;
• factory-finish color and consistency;
• shipping or moisture damage;
• accessory compatibility; and
• total quantity.

Separate questionable material before installation.

Maintenance record

Create a permanent project file containing:

• manufacturer and product name;
• species, grade and profile;
• finish manufacturer, product and color;
• batch or lot information;
• receipts;
• data sheets and installation manuals;
• warranty documents;
• approved cleaning method;
• touch-up procedure;
• prescribed inspection and renewal schedule;
• installation photographs showing flashing and furring;
• fastener specification; and
• locations of stored replacement boards.

Frequently asked questions

Does tongue-and-groove exterior siding need a rainscreen?

Do not assume the interlocking joint eliminates the need for drainage behind the siding. Many exterior wood systems use a drainable and ventilated cavity, but whether one is required—and its dimensions, furring arrangement and vent details—depends on the exact product, wall design, climate and locally adopted code.

For horizontal boards, vertical furring commonly preserves downward drainage. Vertical siding may require drainable horizontal battens or cross-furring so attachment points do not become continuous ledges. Follow the selected manufacturer’s assembly details rather than adopting a universal cavity depth.

Which way should the groove face on horizontal tongue-and-groove siding?

For the documented Western red cedar method, begin at the bottom, work upward and orient the groove edges downward.

Treat that as cedar-specific guidance. Confirm orientation for composite, modified-wood and other proprietary systems, particularly where boards use clips, starter profiles or reversible faces.

Can tongue-and-groove siding be installed vertically?

Yes, multiple wood products permit vertical installation, but the exact product must be approved for it. Vertical boards require horizontal attachment points while the concealed assembly must still allow water to drain downward.

That may require drainable horizontal battens or a vertical-and-horizontal furring lattice. Plan the corner start, plumb alignment, base, top termination, openings and fastening schedule before ordering.

How many linear feet of tongue-and-groove siding are needed for 100 square feet?

Divide 12 by the exposed face in inches, then multiply by 100:

Linear feet = 100 × (12 ÷ exposed face in inches)

A 5-inch exposed face requires about 240 linear feet before waste. A 6-3/4-inch exposed face requires about 178 linear feet by direct calculation, or approximately 177 linear feet when using the cited supplier’s rounded 1.77 coverage factor.

Add a project-specific allowance for cuts, defects, board-length optimization, pattern matching and repair stock. Never substitute nominal width for exposed face.

Should exterior tongue-and-groove joints be caulked?

There is no universal yes-or-no answer. Board-to-board joints, siding-to-trim joints and gaps at flashing perform different functions. Caulk may be specified at certain protected trim joints but prohibited where the assembly must drain or movement would cause premature failure.

Follow the exact siding and trim instructions. Identify which joints are sealed, flashed, treated at cut ends or intentionally left able to drain. Never use caulk as a substitute for continuous flashing, sill drainage or an integrated water-resistive barrier.

Final decision

Verify that the exact product is documented for the intended exterior application. Compare its material, profile, exposed face, finish, approved orientation and maintenance requirements. Confirm a drainable, properly flashed wall assembly, calculate quantity from exposed coverage rather than nominal width, and compare complete project costs instead of board prices alone.

Fastening, movement allowances, caulking, clearances, severe-exposure requirements and warranty compliance must come from the selected product’s current instructions and locally applicable code. Mortar Desk describes its role as a building-material reference rather than a contractor or engineering adviser; project-specific requirements should be confirmed with the manufacturer, a qualified installer and the local authority having jurisdiction.