A277 is a certification standard, not a building code.
Z240 is the actual building code for mobile homes.
From the BSSB:
View attachment 10496
So to apply Pt9 to these buildings seems to me a stretch. And because I live in a swamp with clay soils that are very prone to frost jacking, there is always differential movement between trailers and additions that leads to mould from either bulk water entry or air barrier failure.
OK, so with exception of foundations, siting, and mountings, these buildings
are exempt from the BC code.
That is a BC specific amendment to the code and does not exist in either the national code or the Ontario code (the only other two I own).
We should differentiate between the CSA 240.2.1 (structural requirements) and the CSA 240.10.1 (site anchorage). It appears that the structural requirements are dealt with differently between our codes.
The CSA Z240.2.1 that deals with structural requirements is not referenced at all by the national code and only referenced in Part 3 for the Ontario code. The BC code does reference it is Part 9 through.
Now we are a little bit better equipped to answer the original question: can modifications happen to these buildings? Yes, provided the modifications comply with CSA Z240.2.1.
Here is the national commentary on factory constructed buildings (A-1.1.1.1.(2)):
A-1.1.1.1.(2) Factory-Constructed Buildings. The NBC applies the same requirements to site-built
and factory-constructed buildings. However, it can often be difficult to determine whether a factory-constructed
building complies with the Code once it has been delivered to the construction site because many of the wall,
roof and floor assemblies are closed in and so their components cannot be inspected. CSA A277, “Procedure for
certification of prefabricated buildings, modules, and panels,” was developed to address this problem with
regard to residential, commercial and industrial buildings. This standard describes a procedure whereby an
independent certification agency can review the quality control procedures of a factory and make periodic
unannounced inspections of its products. The standard is not a building code, only a procedure for certifying
compliance of factory-constructed components with a building code or other standard. If a factory-constructed
building bears the label of an accredited certification agency indicating that compliance with the National
Building Code has been certified using the CSA A277 procedure, the accepting authority will have some
assurance that the concealed components do not require re-inspection on site.
On the other hand, standards in the CSA Z240 MH Series, “Manufactured homes,” do resemble a building code.
Most of the individual standards in the series contain requirements regarding many issues also covered in the
NBC. Some of these Z240 MH Series provisions are performance requirements with no quantitative criteria,
some simply reference the applicable NBC requirements, while others contain requirements that differ from
those in the NBC. Because it would be illogical to have two different sets of requirements for buildings—one set
that applies to site-built buildings and one set that applies to factory-constructed buildings—the NBC does not
reference these Z240 MH Series standards. One of the individual standards in the Z240 MH Series deals with
special requirements for manufactured homes related to the fact that these houses must be moved over roads,
which is an issue the NBC does not address. Therefore, labeling that indicates that a factory-constructed house
complies with the Z240 MH Series standards can NOT be taken as an indication that the house necessarily
complies with the building code in effect for the location where the house will be sited.
The NBC does reference CSA Z240.10.1, “Site preparation, foundation, and installation of buildings,” which is
not actually part of the CSA Z240 MH Series. This standard contains requirements for surface foundations
where buildings—not just houses—comply with the deformation resistance test provided in CSA Z240.2.1,
“Structural requirements for manufactured homes.”