Causes of Deck deterioration 
 The most common source of deterioration of decks is water. Moisture causes the wood to expand and when it dries out it contracts.
This can cause fasteners to pop, and boards to warp, crack and split. If the deck remains constantly wet, a perfect environment exists for fungus and bacterial to establish itself and rot to begin. In a worst case, wet rot will result in wood members turning to mush over time.
Maintenance to prevent this can be as simple as sweeping your deck regularly, clearing away puddles and any dirt and leaves that retain moisture and don't dry out easily.

Sun
 is also a cause of deterioration to decks. Ultra violet rays can break down the bonds between wood cells. But fortunately sun damage isn't as serious as water damage because the rays only penetrate about 1/100th of an inch into the wood, really only affecting the surface.
And the interesting thing is that this damaged surface actually protects the healthy wood below. So if you sand it away, fresh wood is exposed and will be damaged. So the best deck maintenance for a wood deck in a sunny area is a good coat of sealant or stain.
Insects
 can also cause serious damage to decks depending on your area. Cedar and redwood are insect resistant but not insect proof. There is a difference.
The best material for decking members that are in close proximity to the soil are pressure treated lumbers. So depending on your climate zone, focus your deck maintenance strategy accordingly. 

Deck building code requirements are not something that should be ignored just because you are building a deck and not a house. Even basic deck building construction techniques involving joist spans, post size and loads, beam sizes and spans between deck posts, decking board dimensions, height of railings and load capacity are all discussed in the building code.

Deck Handrails A 2x4 or 2x4 flat, or on edge does not constitute a proper handrail according to the deck building code. So if you truly want to follow the code, check out this list.

• Must be between 1.5” to 2” in either width or thickness
• Handrail must be at least 1.5” away from wall and its outside edge not more than 4” from wall
• At least one handrail required if stairs are less than 43” wide
• At least two handrails required is stairs are 43” or greater
• No handrail required for deck stairs with 3 risers or less
• If more than 3 risers, only one handrail is required (subject to the width requirements above)

Deck stair rails also have special requirements under the building code.

• 4” maximum space between balusters
• A 6” ball must not pass between the triangular space created underneath the bottom rail, the riser and the tread
• At least 32” (not more than 36”) measured vertically above a line drawn through the outside edges of stair nosing – So be sure to extend (cantilever) the top rail over the nose of the last tread
• At least 36” above landings

The building code has different standards for residential and commercial stair treads. Basically residential stairs can be steeper and have narrower treads. But if anything, consider building deck stairs with wider treads and lower rises. It just feels better.
Here is a list of the key points.

• At least 1” thick if used with notched stringers
• At least 1.5” (2x material) thick for open risers and stringers spaced 30” or more apart
• At least 1” nosing if the unit run (not the actual tread) is less than 10”
• At least 9 ¼” (2x10) wide

Width
At least 35” between wall faces or guardrails or a protruding hand rail
Unit Rise and Unit Run
Unit rise and run refer to the overall vertical and horizontal change between each stair tread – not the actual tread size.

• Maximum unit rise of 7-3/4”
• Minimum unit run of 8 ¼”
• Minimum tread width of 9 ¼” (2x10)
• No more than 3/8” difference between any rises (but you should always make them equal)

Stringers
The building code specifies that wood stringers meet minimum sizes for obvious reasons. Here is a list of the key points.

• 1.5” thick (2x material) minimum if no supports along its length
• 1” thick minimum if supported along its length
• 3.5” minimum effective depth size (the narrowest part after cutting all the rise and run notches) 9 ¼” width (2x10) minimum
• Stringers must not have direct contact with ground unless treated with wood preservative
• Stringers must be secured at top and bottom
• 36” maximum space between stringers with open rises
• 48” maximum space between stringers with closed rises

Check your local building code for the maximum spacing of stringers with open rises because it is quite common to see exterior stairs with open rises that are 48” wide.