Pier installation details (C) Daniel FriedmanDeck Board Spacing Guide for Durable and Safe Deck Floors

  • DECK BOARD GAPS & SPACING - CONTENTS: 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
  • POST a QUESTION or READ FAQs about deck & porch construction, framing sizing, board spacing, structural connections

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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..

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Spacing the Deck Boards for Drainage & Drying

Summerblue arts camp stage construction (C) Daniel Friedman

This article series includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons. Also see our BOOK REVIEW of that book.

[Click to enlarge any image]

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.

Below is a photo of the stage in use [image file], courtesy Lon Church, Summerblue Arts Program.

Chloe Church at Summerblue Arts Camp (C) Lon Church InspectApedia.comThe original construction, installation and long term performance of this outdoor performing arts stage floor are described in a series of articles given at FOUNDATION DAMAGE by ICE LENSING.

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

Everflashing deck flashing (C) D Friedman, Mark Morsching, Everflashing 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 Protectorâ„¢, 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.

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.


Continue reading at DECK FLOOR LAYOUT or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.




Or see DECK DESIGN & BUILD - home

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