A home inspection is a snapshot in time of the condition of a home and an opinion of the performance of the various systems that make up the home. The systems of the home include readily identifiable components like the plumbing system, electrical system, floors & ceiling, but also roof & attic, foundation, HVAC, and the structure to name a few. A home inspector will "inspect" these systems and components that make them up and determine the functional performance.
As an example, if you walk into a room and turn on the light switch and the light comes on, then that component of the electrical system is performing its function as intended. When the light does not come on, it is deficient. It is not known if the light bulb is bad, the switch is bad, the wiring is bad, or something else. A home inspector will report that condition as deficient, but will not troubleshoot to identify why. A recommendation may be made to contact a licensed electrician to inspect and make repairs. It could be a bad breaker in the panel.
The house will be systematically inspected system by system against a known standard which in Texas is the International Residential Code (IRC). This document is the same set of standards city inspectors will use when a home is built. These standards draw up on various other industry specific code documents from the governing bodies for the other licensed trades - electrical, plumbing, and HVAC. Additionally, the IRC has sections related to how strong the house has to be to resist wind loads, snow loads, how deep to dig a foundation, what the structure of the home should be, and hundreds of other topics.
In Texas, the Texas Real Estate Commission (TREC) defines the minimum level of inspection via the Standard of Practice. This specifies the minimum level an inspector must inspect a house at. The inspector can always do more, but not less than specified in the standard.
A home inspector in Texas must complete nearly 400 hours of training and testing including 60 hours of classroom training and mock inspections. Once the coursework is completed, the licensing test can be taken and a license issued if the test is passed. In Texas the pass rate is about 56% now, so this is not an easy feat. Home inspectors are not "Code Inspectors" or "Code Enforcers". Per the SOP, an inspection is:
(3) For the purposes of these standards of practice a real estate inspection:
(A) is a limited visual survey and basic performance evaluation of the systems and components of a building using normal controls that provides information regarding the general condition of a residence at the time of inspection.
(B) is not intended to be a comprehensive investigation or exploratory probe to determine the cause or effect of deficiencies noted by the inspector; and
(C) does not require the use of:
(i) specialized equipment, including but not limited to:
(I) thermal imaging equipment;
(II) moisture meters;
(III) gas or carbon monoxide detection equipment;
(IV) environmental testing equipment and devices;
(V) elevation determination devices; or
(VI) ladders capable of reaching surfaces over one story above ground surfaces; or
A home inspector is a licensed, highly trained and knowledgeable person who evaluates the performance of a home using a Standard Of Practice and the International Residential Code and provides an opinion on the functional performance of a home at a particular time.