Properly installed decks prevent water damage to the home, settling and injury. Decks are generally considered temporary structures and typically have a 25 year life expectancy before renovation or replacement is needed. Higher end materials, good installation, and regular maintenance can extend their life expectancy. Below are some of the most important 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.
- Joist 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 should be in good condition (no corrosion).
- Beams need hanger hardware also (this is especially important)! It is common to see missing hangers at beams during our inspections.
- Wood ledgers are allowed by code and they are cheaper and easier to install than metal hardware. Pressure treated wood ledgers can corrode over time (but so can hangers!) and the ledgers can easily be replaced if needed.
- Only 8d and 10d hanger nails should be used with hanger systems.
- 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.
- Unless the deck is free standing the deck ledger should be bolted to the home to prevent settling or catastrophic failure
- 1/2 carriage (through bolts) or lags (screw type) with washers should be used or an equivalent structural screw.
- 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 length of joist span.
- Special fasteners can be used to fasten a deck ledger to block or concrete.
- Deck ledgers should not be bolted directly over siding, stucco or stone/brick veneer.
- Bolts should be used at post/beam/bracing connections to prevent movement.
- 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.
- 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 as 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 be used to separate the metal flashing from the pressure treated wood.
- Copper is more expensive and is also prone to corrosion
- Stainless steel is the most durable metal flashing material however it is expensive and hard to find bent metal flashing off the shelf at big box stores. 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 a properly installed porch roof or awning and 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 shouldn’t be 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.
- 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.
- Openings should not be greater than 4″ at the railings or in between the stair treads to prevent fall hazards for children- especially above 30″ height.
Decking and fasteners
- Decking should be in good condition, properly 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 2 fasteners per deck per joist.
- Fasteners should be countersunk below the surface of the decking to prevent movement or injury.
- 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.
- Homeowners should consider concrete or masonry patios instead of wood decks when the finished level needs to be close to grade.
Deck Posts and Footings
- Deck posts that are 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 post from sitting in standing water (and causing 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 especially important 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