Properly installed decks prevent water damage, settling, and injury to the home. Decks are generally considered temporary structures with a 25-year life expectancy before renovation or replacement is needed. Higher-end materials, sound installation, and regular maintenance can extend life expectancy. Below are some of the most essential details for decks (although this is not comprehensive)
Metal Fastening systems
- Metal fasteners (joist or beam hangers) should be used at joist/beam connections unless a 2×2 wood ledger is used.
- Joists or beams should not be supported by nails only as they will settle and fail (sometimes catastrophically).
- Stainless steel is more expensive but lasts longer than galvanized as galvanized hangers can react with the copper in pressure-treated wood and corrode prematurely.
- Hangers rated for interiors should not be used as they are more prone to corrosion.
- Hardware should be of the proper size, type, and spacing and in good condition (no corrosion).
- Beams need hanger hardware also (this is especially important)! It is expected to see missing hangers at beams during our inspections.
Wood Ledgers Strips
- Wood ledger strips can often replace joist hangers and are allowed by code. They are cheaper and often easier to install than metal hardware (during new construction). Wood ledger strips must be a minimum of 2″ x 2″.
Hanger Nails
- Only 8d and 10d hanger nails should be used with hanger systems. (or specially rated hex screws — see photo)
- Metal deck fastening systems (hangers) require special fasteners or nails that have adequate shear strength to prevent sudden failure
- Wood screws, roof nails, bright finish nails, or other fasteners not intended for hangers should not be used.
- There shouldn’t be any missing nails, and all the nails should be driven flush to the hardware.
- Hanger nails should be the same material as the hangers to prevent galvanic corrosion.
Bolts
- Unless the deck is free-standing, the deck ledger should be bolted to the home to prevent settling or catastrophic failure.
- Decks should not be bolted through brick veneer.
- 1/2-inch carriage bolts (through bolts), lag (screw type) with washers, or an equivalent structural screw should be used.
- Code-compliant structural screws should have a hexagonal head.
- As a general rule, bolts should be spaced 16″ on center (alternating high and low) or closer, depending on the joist span length.
- Special fasteners can fasten a deck ledger to block or concrete.
- Deck ledgers should not be bolted directly over siding, stucco, or stone/brick veneer.
- To prevent movement, bolts should be used at post/beam/bracing connections.
- Stainless steel bolts are less prone to corrosion than other materials
- In some cases, it is better to create a free-standing deck rather than secure it to the house to prevent possible water damage over the long term.
Flashing
- When decks are fastened against the wood framing of the house, flashing should be used to prevent decay.
- Typically, vinyl flashing is used, and this material is long-lasting, affordable, easily purchased, and does not corrode.
- Aluminum and galvanized flashing should not be installed directly against pressure-treated wood. It can react with the copper chemicals in pressure-treated wood (and alkaline masonry materials) and cause corrosion.
- When aluminum or galvanized flashing is used, a peel-and-stick butyl product should separate the metal from the pressure-treated wood.
- Copper is more expensive and is also prone to corrosion
- Stainless steel is the most durable metal flashing material- it is expensive and often must be special-ordered. For some contractors, it may be worthwhile to purchase a roll of stainless steel and to use a brake to create bent ledger flashing
- When decks are installed over siding, additional flashing is needed. See detail for best practice flashing over siding
- See detail for best practice deck flashing over masonry
- Clearances should exist between the siding and decking (min. 3/4″) to prevent possible decay.
- In cases where deck flashing is missing, an adequately installed porch roof or awning can help prevent water damage.
- In many cases, it would be better to create a free-standing deck rather than secure it to the house to prevent possible water damage over the long term.
Railings and Handrails
- Railings and handrails should be present when the deck is 30″ or more from the ground.
- Railings should be 36″ high, secure, in good condition, and with no openings greater than 4″ to prevent possible falls/injury.
- Cable railings should be regularly tightened and not spaced more than 4″.
- Post caps should be installed over wood posts to prevent decay (plastic or metal).
- Wood handrails are prone to cupping, splintering, and decay. Homeowners may consider upgrading to composite decking materials at handrails to prevent possible decay and injury over the long term.
Cross-bracing
- When decks are higher than 4′, steps should be taken to prevent lateral movement by installing cross-bracing.
- Cross bracing can be installed vertically at posts or horizontally under the joists.
- Cross bracing should be bolted to posts when installed vertically
Stairs and Landings
- Landings at exterior doors should be at least 3′ by 3′.
- Stair risers should be of consistent height and no higher than 7-3/4″ from tread to tread.
- Stair treads should be of a consistent height and should be no less than 10″ deep.
- Treads should be of a proper thickness or otherwise adequately supported to prevent sagging, failure or injury.
Decking and fasteners
- Decking should be in good condition, adequately fastened/secured, and supported.
- Decking should not be loose, cupping, or decayed.
- Ideally, decking is stained/painted every 5-10 years or as needed.
- Deck fasteners should be spiral/ring shank nails or screws to prevent movement- there should be at least two fasteners per deck per joist.
- Fasteners should be countersunk below the surface of the decking to prevent movement or injury.
Framing
- Deck framing should be pressure-treated or otherwise decay-resistant.
- Framing should be firmly attached to other framing with hardware, bolts, or structural screws.
- Framing should be adequately sized and spaced, not sagging, and properly supported.
- Framing should be in good condition (no decay, unfastening, splitting, etc…).
- Ideally, framing should be at least 8″ above grade to prevent premature decay and for good inspection/maintenance/repair access.
- When the finished level needs to be close to grade, homeowners should consider concrete or masonry patios instead of wood decks.
Deck Posts and Footings
- Deck posts supported by shallow footings (blocks) are prone to frost heave and uneven settling.
- Deck posts should be supported by concrete footings that extend below the frost line and at least 12″ below disturbed soil.
- Ideally, the concrete footings or piers extend at least 8″ above grade to prevent wood posts from decaying.
- When wood posts are installed over concrete footings/piers, post base hardware should be used to prevent the posts from sitting in standing water (which can cause decay).
- If wood posts are installed at or below the grade, the wood posts should be pressure-treated and rated for ground contact (note: even pressure-treated wood rated for ground contact can decay over time).
- It is essential for wood posts for porches and additions to have at least an 8″ clearance above grade to prevent decay and settling over the long term. Downspout drainage should be directed away from porch post footing areas to prevent decay and settling.
