One of my curious friends recently asked me how to plan a deck, so I thought it might be easier to list my thought process here for others to consider.

Need a permit?
Check your local jurisdiction to see if there is any permit needed.

Generally speaking, a deck (with its supporting columns) is considered a construction associated with “public safety”. Therefore, a building permit is required in most jurisdictions regardless of how high the deck is.

In many cases, it might be easier to go directly to the professionals to build a deck (rather than a DIY project) since the project needs a permit anyway.

Update with the current code?
Update yourself with the current state-wide building code.

As a rule of thumb, most local jurisdictions update their "Statewide Building Code" on a three-year cycle through their code development process. So, make sure you get the most updated version and are familiar with any changes amended by the local authorities.

How state-wide codes regulated is different in each state. For example, in Virginia, the state-wide code is governed by the Department of Housing and Community Development. Yet, in Maryland, all the building-related code (also known as MBPS- Maryland Building Performance Standard) is administrated through the Department of Labor. It requires local jurisdiction to use the same edition of the building code. There are 18 months to adopt the new edition. Once the code is adopted, the local has 12 months to enforce the code. (That is almost like a 30-month development cycle.)

Get the local design criteria?
Check jurisdiction's design criteria (so you can play with a full "deck")

Here is a simplified diagram of a deck: decking, rim, joist, ledger, beam, post and footing. You might have known these basics already.

However, some parts of the deck will lead to safety issues or economic choices. Here is why.

Footing and Post

Footing and post are the two elements that impact the structure's soundness the most. Make sure you have this information for your project:

the frost line: The footing depth is based on the local area's design criteria (see image below). Since the regional's frost line is 30", the bottom of the footing needs to be at least 30" below grade.
supporting size: Often the local regulation is more stringent than the model code. For example, only two post size are recommended in Montgomery County: 4x4 posts for a maximum height of 6'-9" and 6x6 posts for a maximum height of 14'. If a post is higher than 2 feet, a diagonal bracing needs to be provided.
additional requirements: The local guideline also requires the deck footing to align with the main structure's settlement. "Deck footing closer than 5' to an exterior house foundation wall must bear at the same elevation as the existing house foundation."

This Table is excerpt from International Residential Code. According to its instruction, “the jurisdiction shall fill in this part of the table.” Therefore you can search the table like the one below on your local jurisdiction official website.

This is an example of ”design criteria” excerpt from “Design Parameter“ via Montgomery County’s Department of Permitting Services.

Joist

direction of joist span: Though there is no specific requirement on which direction that joists should run. I would suggest running the joists perpendicular to the longer side of the exterior wall. (Typically known as the “width” of the deck).
joist layout selection: My other recommendation is to use a deeper joist and wider spacing to have a more economical layout.

Most single houses can have a deck depth ranging from 8 feet to 12 feet, and the width could be as long as crossing the entire house.

Assume your deck is 10 feet by 24 feet with no cantilever condition. When using 16" spacing to layout the joist, you would need 17 of 2"x8"x10' pressure-treated southern pine. When using 24" spacing to layout joists, you would need 11 of 2"x10"x10' pressure-treated southern pine. Though 2x8 lumber's unit price is lower than 2x10 lumber (current market price, $23 and $32, respectively), using 2x10 would cost less than using 2x8 lumbers when calculating the total sum.

Railing

Telling my curious friend, "yes, you would need a railing for your deck" might sound like a piece of silly joke.

But if your deck is 30 inches above the ground, you do need a railing- a guardrail. The origin of this rule is based on the IRC chapter 3. It states: "Required guards at open-sided walking surfaces, including stairs, porches, balconies or landings, shall be not less than 36 inches in height as measured vertically above the adjacent walking surface or the line connecting the nosings." (IRC 312.1.2)

While sometimes, a deck is less than 30 inches above the ground. But using a ramp to connect the deck and the surrounding, you still need a railing- a handrail. Here is how the rule is based, "Handrails shall provided on not less than one side of ramps exceeding slope of 1 unit vertical in 12 units horizontal." “Handrail height, measured above the finished surface of the ramp slope, shall be no less than 34 inches and not more than 38 inches.” (IRC 311.8.3)

Vice versa, if you prefer to build a deck without any visual obstructions. For example, an “infinity” deck. You can strategically place the deck surface below 30 inches from the lowest ground point. Therefore you do not need to apply this railing requirement. (Also, be thoughtful in adding tactile warning devices for people who might have visually impaired situations.)(1)

So? What's the main takeaway

This year, businesses or individuals have been reporting the record-high "labor shortage". As we spend more time working from home, it is not surprised more people decide to do small projects themselves. I did not write this story to "teach "people how to construct a "code-compliant "project; Rather, I hope we can be aware of some safety issues involved while we inevitably take on some project ourselves.

Our deck's structure will also be completely sound when we play with our full deck.

Notes and references:

All the codes referred here are according to IRC 2018.
As a side note, Maryland adopted the International Residential Code 2021 since May 29, 2023.
In the previous edition (2015 R507.8.1), the code only requires "post" to be embedded with a minimum of 12" of surrounding soil or concrete. 2018 IRC gives us more stringent and clearer provision. In R507.3, it states more footing possibility and includes how the post connectors or through-bolts are anchored in the footings. It also gives clear guidance on the minimum footing size based on various loads, which (I consider) is most important.
For the first-time reader, the guardrail and handrail might sound confusing. Here is the distinction: handrails are lower. They are no less than 34 inches and not more than 38 inches. In comparison, guardrails shall be not less than 42 inches high, measured vertically from the adjacent walking surface.
For readers in my jurisdiction, you could check out "Montgomery County Residential Typical Deck Details", if you are interested to learn more about the “Deck“.
“Tactile warning devices“ are often referred to as truncated domes, that adds little bump on the surface to inform visually impaired persons regarding edges of a walkway or entering another area.