Deck Board Spacing Guide for Durable and Safe Deck Floors

What is the proper gap to leave between deck boards?
- Why is it important to space deck boards apart by a small gap?
- Steps to protect deck joists from rot
- Best Construction Practices for decks or porches
- Deck & Porch construction details & procedures
DECK & PORCH CONSTRUCTION - home
DECK CONSTRUCTION BEST PRACTICES - separate article
DECK DESIGN & BUILD - article series home
Questions & Answers about deck & porch construction, framing sizing, board spacing, structural connections
References

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How much to space deck floor boards: this article explains proper gap size to leave between deck boards for drainage and drying, and extra steps to take to protect deck joists from rot. We include a description of tightly-butted tongue-and-groove pressure treated deck boards as well as typical 5/4" thick pressure treated deck boards that should be spaced for drainage..

Spacing the Deck Boards for Drainage & Drying

Summerblue arts camp stage construction (C) Daniel Friedman

This article series discuss best porch & deck construction practices, including choice of framing materials, decking or flooring choices & installation, how to select and use deck and porch structural and flooring fasteners, actual deck & porch framing construction details & connections, deck joist & beam span tables, how to build leak-proof rooftop decks, construction of covered & screened porches, deck & porch railing construction & materials, choices of finishes and stains for decks & porches, and past & current deck lumber preservative treatments with related health & environmental concerns. This article series includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons. Also see our review of that book.

When Lon Church constructed this outdoor stage for the Summerblue Arts Camp (Two Harbors MN), we knew that the structure would have to endure severe winters and strong summer sun without the protection of a roof. And because the surface is used as a performing stage, we used 5/4 tongue and groove treated wood for the surface - no gaps for drainage.

Sloping a solid deck floor to achieve drainage

To compensate for the drainage worry, we made sure to slope the stage (from back towards the front or audience side) - and the stage pitch became a theatrical feature. Here is a photo of the stage in use., courtesy Lon Church, Summerblue Arts Program. Steps that were taken to avoid ice lensing and post movement for this structure are described at Ice Lenses, Frost Heaves vs. Frozen Soil Pressure.

Use gaps between deck boards to achieve drainage

But most decks need and can achieve spacing between the deck boards for drainage.

As discussed in Best Practices Guide to Residential Construction:

'When securing the decking, it is important to leave adequate spacing between the boards for water to drain. The goal is to have about an 1/8-inch gap (the diameter of an 8d nail) between boards after the decking has dried to its equilibrium moisture content. If the decking is installed wet, as is often the case for pressure treated material, it is best to install the boards tight, letting gaps form as the wood dries.

When installing kiln-dried stock, use a 16d nail as a spacer to leave enough space for the boards to swell slightly and still leave an adequate drainage space. For wood that has partially air-dried, it is a judgment call. If in doubt, it is best to err on the side of leaving a little extra space for the wood to swell when wet.

Watch out: don't leave wider gaps between still-wet treated lumber deck or porch boards during construction or you may find that as the wood dries, excessive deck board gaps can form a trip hazard, especially for people wearing high heeled shoes.

Protecting the Deck or Porch Joists from Leaves, Rot

In decking applications subject to continuous wet conditions or the buildup of leaves and tree debris, it is best to protect the tops of the joists from moisture.

This can be achieved by laying strips of felt paper or self-adhesive membrane (one approved for UV exposure) over the tops of each joist prior to laying the decking boards.

Photo (left) courtesy of Mark Morsching, Everflashing, shows an Everflashing stainless-steel flashing product installed over the deck ledger. Additional metal flashing is in use to protect the deck joist top from rot. Additional details about deck flashing and more deck flashing images are at Deck Flashing at Building.

To avoid deck joist top rot Morshing applies peel-and-stick flashing membrane material to joists and ledgers during deck construction.

Another proprietary product for this application, Vycor Deck Protector™, is available from Grace Construction Products. Membranes such as Vycor Deck Protector can also be used as a barrier between pressure-treated joists and joist hangers, flashings, or other metal hardware to reduce corrosion.

-- Adapted with permission from Best Practices Guide to Residential Construction.

Deck & Porch Resources, Products, Manufacturers: Where to Buy

See Deck & Porch Products, Manufacturers for our complete/updated listings of manufacturers of porch & deck products, materials, coatings, fasteners, lumber, tools.

Composite Decking System Suppliers

Certainteed Corp. www.certainteed.com Boardwalk solid composite decking with hidden fasteners and optional railing system

Composite Building Products International www.xtendex.com Xtendex hollow composite decking system with optional railing

Correct Building Products www.correctdeck.com Solid composite decking with hidden fasteners and optional railing system

Fiber Composites www.fibercomposites.com Fiberon solid composite decking and optional railing system

Kadant Composites www.geodeck.com Geodeck hollow composite decking and railing system

Kroy Building Products www.kroybp.com Timberlast solid composite decking with optional hidden fastening system

Louisiana-Pacific Corp www.weatherbest.lpcorp.com. WeatherBest solid composite decking, railings, and accessories

Nexwood Industries Limited www.nexwood.com Hollow composite decking and railing systems

Tendura www.tendura.com TenduraPlank solid tongue-and-groove composite flooring for porches; natural finish or primed for painting

Thermal Industries www.thermalindustries.com Dream Composite solid tongue-and-groove composite decking system with optional vinyl railings

TimberTech Limited www.timbertech.com Floorizon hollow composite decking system, solid composite decking planks, and optional railing system

Trex Company www.trex.com Solid composite decking

Weyerhaeuser Building Products www.choicedek.com ChoiceDeck solid composite lumber and optional railings

Plastic Decking Systems

Kroy Building Products www.kroybp.com Classic Manor embossed vinyl decking with clip system

L.B. Plastics www.lbplastics.com Sheerline interlocking vinyl decking system and deck cladding systems

Renew Plastics www.renewplastics.com Solid recycled high-density polyethylene (HDPE) plastic decking with embossed wood-grain texture

Royal Crown Limited www.royalcrownltd.com Brock Deck and Deck Lok interlocking vinyl decking systems

Thermal Industries www.thermalindustries.com Dream Deck interlocking vinyl decking and railing system

U.S. Plastic Lumber Corp www.carefreexteriors.com Carefree Xteriors recycled plastic HDPE decking with embossed wood grain and optional railings

Metal Decking Systems

FSI Home Products Division www.lockdry.com. LockDry aluminum decking and railing system

Prefabricated Deck & Porch Railing Systems

Avcon Structural Railing Systems www.avconrail.com Thermoplastic and aluminum railings

CertainTeed www.certainteed.com EverNew PVC railing system

Global Dec-K-Ing Systems www.globaldecking.com DEC-K-ING aluminum railing system

DecKorators Inc. www.deckrail.com Decorative aluminum balusters and connectors for wooden railing systems. Also, tempered-glass balusters

Duradek www.duradek.com Durarail powder-coated aluminum railing system and walk-on vinyl decking membrane.

FSI Home Products Division www.railingworks.com Aluminum railing systems

Fypon www.fypon.com Polyurethane railing systems in classic architectural styles

HB&G www.hbgcolumns.net PermaPorch cellular-polyvinyl chloride (PVC) railings and posts reinforced with wood or aluminum; cellular-PVC or aluminum balusters Kroy Building Products www.kroybp.com Classic Manor PVC-railing system

L.B. Plastics www.lbplastics.com Sheerline PVC-railing systems and PVC- post cladding

Royal Crown Limited www.royalcrownltd.com PVC railing system with steel reinforcing

Shakespeare Composites Structures www.armor-rail.com Armor-Rail structural fiberglass (FRP) railing system with turned balusters

Thermal Industries www.thermalindustries.com Dream Rail PVC-railing system with optional tempered glass balusters

U.S. Plastic Lumber Corp. www.carefreexteriors.com Recycled HDPE railing system

Hidden Deck Fastener Suppliers

BEN Manufacturing www.premier1.net/~ben69 Dec-Klips fit between deck planks with prongs into edges; nailed into top of joists; electrogalvanized steel

Blue Heron Enterprises www.ebty.com Eb-Ty UV-resistant polypropylene biscuit fits into slots in edge of decking, screws into top of joist Grabber Construction Products www.deckmaster.com Deckmaster angle bracket screws to side of joist and up into decking; available in galvanized or stainless steel

Simpson Strong-Tie www.strongtie.com DBTC deck ties screw down to top of joist with prongs into edges of decking planks; triple-zinc-coated or stainless steel by special order; disposable plastic driving tool

Spotnails www.spotnails.com Tebo stainless-steel fasteners fit between decking boards with prongs into edges of decking; installed with mallet and proprietary tool

TY-LAN Enterprises Inc. www.shadoetrack.com Shadoe Track angle bracket nailed along top of joist and screws up into bottom of deck boards; available in galvanized, powder-coated, and stainless steel

USP Lumber Connectors www.uspconnectors.com Deck Clip screws into edge of one decking board and locks to next board; requires toenailing one edge of each board

Screen Systems for Porches

One BetterWay www.screentight.com Screen-Tight vinyl porch screening system screws to exterior of porch framing; snap-on facings conceal screws and screen splines; available in white, beige, gray, and brown

Sources of Deck Finishes, Stains, Preservative Coatings

Amteco www.mfgsealants.com/amteco.htm Sealers, preservatives, and deck stains

Cabot www.cabotstain.com Clear sealers and deck stains

Cuprinol, a division of Sherwin Williams www.cuprinol.com Sealers, preservatives, and deck stains

The Flood Company www.floodco.com Clear sealers and deck stains

Penofin www.penofin.com Lightly tinted oil-based sealers and stains

Olympic, PPG Architectural Finishes www.olympic.com Clear sealers and deck stains

Wolman Wood Care Products, division of Zinsser Co. www.wolman.com Wolman sealers and deck stains and DAP Woodlife clear sealers

Deck & Porch Industry Associations

American Wood Preservers Association (AWPI) www.awpa.com

California Redwood Association www.calredwood.org

Deck Industry Association www.deckindustry.org

Forest Stewardship Council www.fscus.org Information on certified tropical hardwoods

Rainforest Alliance, Smartwood Program www.rainforest-alliance.org Information on certified tropical hardwoods

Southern Forest Products Association www.sfpa.org

Southern Pine Council www.southernpine.com

Western Wood Products Association www.wwpa.org

Western Wood Preservers Institute www.wwpinstitute.org

-- Adapted with permission from Best Practices Guide to Residential Construction.

see Codes for Stairs for details about stair building codes and specifications.

Frequently Asked Questions (FAQs)

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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Amazon.com and also Wiley.com. See our book review of this publication.
Decks and Porches, the JLC Guide to, Best Practices for Outdoor Spaces, Steve Bliss (Editor), The Journal of Light Construction, Williston VT, 2010 ISBN 10: 1-928580-42-4, ISBN 13: 978-1-928580-42-3, available from Amazon.com
Prescriptive Residential Wood Deck Construction Guide, based on the 2009 International Residential Code, American Forest & Paper Association, Inc., provided by reader Mark Morsching from Everflashing.
Mark Morsching, Everflashing, Tel: 800-550-1667, Email: everflashing@gmail.com. The Everflashing product comes in G-185 and Stainless Steel and is intended for use with treated lumber with copper in it. Everflashing produces a variety of specialty flashing products including flashings for use with decks at deck ledgers and deck perimeters.
Summerblue Arts Camp., Two Harbors MN, Lon Church, Director, c/o: Two Harbors High School 405 4Th Avenue, Two Harbors, Minnesota 55616, United States Email: lon_church@yahoo.com

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

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Building inspection education & report writing systems from Carson, Dunlop & Associates Ltd

Manual for the Inspection of Residential Wood Decks and Balconies, by Cheryl Anderson, Frank Woeste (Forest Products Society), & Joseph Loferski, October 2003, ISBN-13: 978-1892529343, $39.00 at Amazon.com or at the InspectAPediaBookstore
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