This is from the 2015 IRC. NY has it's own codes but it is based on the IRC
SECTION N1101
GENERAL
N1101.1 Scope. This chapter regulates the energy efficiency
for the design and construction of buildings regulated by this
code.
SECTION N1107 (R501)
EXISTING BUILDINGS—GENERAL
N1107.1 (R501.1) Scope. The provisions of Sections N1107
through N1111 shall control the alteration, repair, addition
and change of occupancy of existing buildings and structures.
N1107.1.1 (R501.1.1) Additions, alterations, or repairs:
General. Additions, alterations, or repairs to an existing
building, building system or portion thereof shall comply
with Section N1108, N1109 or N1110. Unaltered portions
of the existing building or building supply system shall not
be required to comply with this chapter.
N1107.2 (R501.2) Existing buildings. Except as specified in
this chapter, this code shall not be used to require the
removal, alteration or abandonment of, nor prevent the continued
use and maintenance of, an existing building or build-
ing system lawfully in existence at the time of adoption of
this code.
N1107.3 (R501.3) Maintenance. Buildings and structures,
and parts thereof, shall be maintained in a safe and sanitary
condition. Devices and systems that are required by this code
shall be maintained in conformance with the code edition
under which installed. The owner or the owner’s authorized
agent shall be responsible for the maintenance of buildings
and structures. The requirements of this chapter shall not provide
the basis for removal or abrogation of energy conservation,
fire protection and safety systems and devices in existing
structures.
SECTION N1109 (R503)
ALTERATIONS
N1109.1 (R503.1) General. Alterations to any building or
structure shall comply with the requirements of the code for
new construction. Alterations shall be such that the existing
building or structure is no less conforming with the provisions
of this chapter than the existing building or structure
was prior to the alteration.
Alterations to an existing building, building system or portion
thereof shall conform to the provisions of this chapter as
they relate to new construction without requiring the unaltered
portions of the existing building or building system to
comply with this chapter. Alterations shall not create an
unsafe or hazardous condition or overload existing building
systems. Alterations shall be such that the existing building or
structure uses no more energy than the existing building or
structure prior to the alteration. Alterations to existing buildings
shall comply with Sections N1109.1.1 through N1109.2.
N1109.1.1 (R503.1.1) Building envelope. Building envelope
assemblies that are part of the alteration shall comply
with Section N1102.1.2 or N1102.1.4, Sections N1102.2.1
through N1102.2.12, N1102.3.1, N1102.3.2, N1102.4.3
and N1102.4.4.
Exception: The following alterations need not comply
with the requirements for new construction provided
the energy use of the building is not increased:
1. Storm windows installed over existing fenestration.
2. Existing ceiling, wall or floor cavities exposed
during construction provided that these cavities
are filled with insulation.
3. Construction where the existing roof, wall or
floor cavity is not exposed.
4. Roof recover.
5. Roofs without insulation in the cavity and where
the sheathing or insulation is exposed during
reroofing shall be insulated either above or below
the sheathing.
6. Surface applied window film installed on existing
single pane fenestration assemblies to reduce
solar heat gain provided the code does not require
the glazing or fenestration assembly to be
replaced.
N1109.1.1.1 (R503.1.1.1) Replacement fenestration.
Where some or all of an existing fenestration unit is
replaced with a new fenestration product, including
sash and glazing, the replacement fenestration unit shall
meet the applicable requirements for U-factor and
SHGC as provided in Table N1102.1.4.
N1109.1.2 (R503.1.2) Heating and cooling systems.
New heating, cooling and duct systems that are part of the
alteration shall comply with Sections N1103.1, N1103.2,
N1103.3 and N1103.6.
Exception: Where ducts from an existing heating and
cooling system are extended, duct systems with less
than 40 linear feet (12.19 m) in unconditioned spaces
shall not be required to be tested in accordance with
Section N1103.3.3.
N1109.1.3 (R503.1.3) Service hot water systems. New
service hot water systems that are part of the alteration
shall comply with Section N1103.5.
N1109.1.4 (R503.1.4) Lighting. New lighting systems
that are part of the alteration shall comply with Section
N1104.1.
Exception: Alterations that replace less than 50 percent
of the luminaires in a space, provided that such alterations
do not increase the installed interior lighting
power.
N1109.2 (R503.2) Change in space conditioning. Any nonconditioned
or low energy space that is altered to become
conditioned space shall be required to be brought into full
compliance with this chapter.
Exception: Where the simulated performance option in
Section N1105 is used to comply with this section, the
annual energy cost of the proposed design is permitted to
be 110 percent of the annual energy cost otherwise
allowed by Section N1105.3.