Which plat does Houston require?

There are two plat requirements in chapter 42, not one. Sec. 42-20 attaches to dividing property; Sec. 42-22 attaches to building or enlarging. They have different triggers and different exemption lists, and a project can need both, one, or neither.

Are you dividing property?

Are you dividing property into more than one lot or tract?

No Yes

Does one of Sec. 42-21’s three exceptions apply?

None of them A reserve tract in an already-approved plat, with no one-foot reserve, not for single-family use A remainder tract in an approved general plan, or one filed at the same time A public street dedication done by street dedication plat

Does it require or propose a new street?

No Yes

Does it require or propose dedicating an easement for public water, wastewater collection or storm sewer lines?

No Yes

Is it a vacating plat?

No Yes

Is it a replat?

No Yes, but it does not require notifying adjacent owners under chapter 212 Yes, and it requires notifying adjacent owners under chapter 212

Is it an amending plat?

No Yes

How many lots does it create?

Four or fewer More than four

Does every lot front on an existing street?

Yes No

Are you building?

Are you building new, or enlarging any exterior dimension of a building, structure or improvement?

No Yes

Does one of Sec. 42-22’s six exemptions apply?

None of them It is within the central business district An alteration adding no more than 100 sq ft and not encroaching into the building line A detached single-family unit on a lot in a recorded plat, complying with article III and with that plat A parking lot, or an expansion of one A retaining wall, masonry wall or fence under eight feet A temporary classroom building at a public school

Nothing here triggers either requirement

Subdivision plat

Not triggered

Sec. 42-20(a) attaches to the subdivision of property. If you are not dividing property, it is not engaged — though a development plat may still be, below.

Development plat

Not triggered

Sec. 42-22 attaches to new construction or the enlargement of any exterior dimension of a building, structure or improvement. Without that, it is not engaged.

What this rests on

What it cannot tell you

Whether deed restrictions add requirements of their own. They are private, enforced by whoever holds them, and city approval of a plat is no defence to a suit on one.
Whether the property sits in the extraterritorial jurisdiction rather than the city. Both Sec. 42-20 and Sec. 42-22 reach the ETJ, but other parts of chapter 42 treat it differently.

The thing most summaries get wrong

Class I, class II and class III are usually described as a hierarchy you are sorted into by the size of your subdivision. Sec. 42-23(a) says otherwise: class I and class II plats are optional and may be used in lieu of a class III plat. A class III plat stays available to anyone. What the criteria in Sec. 42-23(c) and (d) decide is which of the two lighter options you may choose — not which one you are assigned.

What genuinely forces a class III plat is narrow and listed in Sec. 42-23(b): a new street, a dedicated easement for public water, wastewater collection or storm sewer lines, or a vacating plat.

This is how the code reads; confirm with the city — or ask a builder who's actually pulled this permit in Houston. The authoritative text is the Houston Code of Ordinances; permitting questions go to Houston Permitting Center.