Deck 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
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.
'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
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.
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.
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(Aug 30, 2012) ray linn said:
We have a 38-1/2" span on a bridge supported by timber on each side. ( straight bridge )
What thickness of lumber will we need to span the 38-1/2" ? Thxs.
Your flooring span question omits any statement of live and dead loads, does not specify the timber dimensions nor the timber spans, connections, and it exceeds the standard framing spacing for conventional wood framing (normally joists on 16" o.c. or 24" o.c. all of which makes me worry that no design professional has considered your overall design. For bridge construction I'd want to consult a structural or civil engineer with familiarity with bridges since a mistake anywhere in the design could kill someone.
But I can note that in my experience the deflection in standard 2x lumber, such as 2x8's over 38" span between supports under normal un-laden human foot traffic won't be noticeable. Without any other information I'm doubtful that anyone can say for sure if that meets the design loads for your bridge.
" Table 3.18A Floor Joist Spans for Common Lumber Species", American Wood Council, , 222 Catoctin Circle SE Suite 201 Leesburg, VA 20175, USA, Email: email@example.com retrieved 30 June 2015, original source: http://www.awc.org/Publications/update/WFCM2001FullPage.pdf
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Questions & answers or comments about deck & porch construction, framing sizing, board spacing, structural connections.
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Mark Morsching, Everflashing, Tel: 800-550-1667, Email: firstname.lastname@example.org. 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: email@example.com
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