Rooftop Deck Construction Guide

ROOFTOP DECK CONSTRUCTION - Best Construction Practices for rooftop decks
- Rooftop Deck & Porch construction details & procedures
- Rooftop Deck Construction Materials Choices
- Rooftop Deck Railings, Code Requirements, Safety
- Roofing material recommendations below walk-on rooftop decks or porches
DECK & PORCH CONSTRUCTION - home
DECK CONSTRUCTION BEST PRACTICES - separate article
DECK DESIGN & BUILD - article series home
Questions & Answers about how to build a walk-on rooftop deck
References

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Rooftop decks & walk-on roofs: This article discusses rooftop deck construction details to avoid building leaks or rooftop deck safety hazards. We include walk-on roof surfaces, roofing membrane to use below a rooftop deck, and construction of rooftop deck railings and posts. Also see WALK-ON ROOF SURFACES.

Details for Building Rooftop Decks

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.

Decks over living spaces can be detailed various ways, but all should have the following elements:

Along-lasting membrane roof sloped at least 1/4inch per foot, designed to drain at the lower end
Decking screwed to sleepers so that it can be removed for inspection or repair
A sturdy railing system that, preferably, does not penetrate the roofing membrane

Single-Ply Membranes for Rooftop Decks

Our rooftop deck photo (above left) shows how the installer provided for future cleaning of debris accumulating below the nearly-flat roof deck. But it is the choice of roof membrane and how the deck panels are supported so as to avoid damaging the membrane that make a rooftop deck work ... or not.

Continuing as detailed in Best Practices Guide to Residential Construction:

A variety of roofing membranes have been used successfully under rooftop decks, but EPDM remains the most widely used on residential roofs.

EPDM owes its popularity to its longevity and durability. It is dimensionally stable and strong over a wide temperature range (it will not expand and contract or tug at flashings), is highly UV-resistant, and can stretch without tearing. In most residential jobs, EPDM is fully adhered to the roofing deck with a contact-type adhesive rolled onto both surfaces.

Seams can be avoided on small jobs, since rolls come as wide as 50 feet. If necessary, however, seams are relatively easy to seal, using a special double-sided seam tape and lap caulk at the exposed joint. To seal around corners and penetrations, use flexible uncured EPDM, which will conform to irregular shapes and seals well to the main roofing membrane (see EPDM, page 96).

EPDM roofing membranes typically come in .045- and .060-inch thicknesses and carry at least a 10-year warranty in residential work. If properly installed, however, the .060 material should last for decades. EPDM’s chief weakness is its vulnerability to petroleum products, such as oils, grease, and solvents. If used under a deck, warn the homeowners not to splash oil or grease from cooking or solvent-based wood finishes on the decking.

EPDM is often installed over a base layer of fiberboard or rigid insulation, but most EPDM membranes can bond directly to a sanded wood underlayment such as a 1/4-inch AC plywood. If bonding directly to plywood or oriented-strand board (OSB), check with the roofing manufacturer regarding treatment of joints in the sheathing and the need for a primer. To allow for some movement at sheathing joints, some manufacturers recommend holding the adhesive back one inch from the joints.

Also see WALK-ON ROOF SURFACES.

Terminations and Flashings for Rooftop Decks

Where the roofing membrane meets the house, run it 10 to 12 inches up the wall under the sheathing wrap. At outside edges, leave a 3- to 6-inch flap, depending on the edge treatment. A large metal drip-edge usually caps the roof along the fascia boards.

Deck Flooring Construction for Rooftop Decks

The decking sits on 2x sleepers, usually laid flat. If you want the decking surface to be level, the sleepers will need to be tapered to compensate for the slope in the roof deck. For a large deck where flat sleepers are too thin to taper, you can use 2x4s or 2x6s set on edge.

To protect the roofing membrane, set the sleepers on strips of EPDM or rooftop walkway matting (available from commercial roofing suppliers). Attach the decking with screws so it can be removed later for inspection or repairs.

The rooftop deck shown in our photo (left) is installed in a restaurant in Mexico City where it must endure very strong sun and intermittent very heavy rain (and an occasional earthquake).

Shading and sun protection are provided by canvas awnings. - DF.

Post and Railing Construction for Rooftop Decks

As with other decks, guardrails must be a minimum of 36 inches high, infill balusters less than 4 inches apart, and the whole assembly strong enough to resist a 200-pound horizontal load (or 20 pounds per linear foot, depending on the local code). Use the longest pieces available for railings. If the deck is small enough, use a single continuous top railing on each side. Then tie the side railings to the house with steel angle brackets to create a rigid railing assembly.

From a waterproofing standpoint, it is desirable to keep the posts outside of the roofing membrane. This can be achieved by bolting the posts to the rim joists or sub fascia in the roof framing (see Figure 4-17 below).

[Click any image to see a larger, detailed version.]

If this is not practical or if it is unacceptable from a design standpoint, then the EPDM will need to be sealed around each post. This is best left to a professional roofer. Typically, the roofer will fashion a metal or membrane flashing collar around the base of each post and seal this to the roofing membrane, as with the boots used for plumbing vents.

-- 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.

Deck & Porch Wood Treatment Companies

Arch Wood Protection www.wolmanizedwood.com Copper-azole and borate-treated wood products with optional water repellent

Osmose www.osmose.com ACQ- and borate-treated wood products with water repellent

Chemical Specialties www.treatedwood.com ACQ-treated wood products with optional water repellent

Suppliers of Composite Structural Lumber for Decks & Porches

U.S. Plastic Lumber, Boca Raton, FL www.usplasticlumber.com Trimax and Durawood structural plastic lumber

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

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

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

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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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