What kind of loan is it? Here is some guidance. Hope this helps:
From WA state licensing & permits:
Building a garage, shop or room addition?
An L&I is required. L&I may be required for any electrical wiring extended into the addition. Be sure all electrical work is done by a licensed electrical contractor.
Are you buying or selling a manufactured or mobile home?
If you are preparing to buy or sell a manufactured or mobile home, you may be asked by your realtor, lender, or appraiser to get an L&I inspection to identify unpermitted work or, you may decide you need one.
An HRI is an inspection only to identify unpermitted alterations.
Any unpermitted work or corrections the inspector finds will require additional permitting.
From Fannie Mae:
Manufactured Housing Property Eligibility Requirements:
Manufactured homes that have an addition or have had a structural modification are eligible under certain conditions. If the state in which the property is located requires inspection by a state agency to approve modifications to the property, then the lender is required to confirm that the property has met the requirement. However, if the state does not have this requirement, then the structural modification must be inspected and be deemed structurally sound by a third party who is regulated by the state and is qualified to make the determination. In all cases, the satisfactory inspection report must be retained in the mortgage loan file.
From HUD/FHA:
Additions to Manufactured Housing:
If the Appraiser observes additions or structural changes to the original Manufacture Home, the Appraiser must condition the appraisal upon inspection by the state or local jurisdiction administrative agency that inspects Manufactured Housing for compliance, or a licensed structural engineer may report on the structural integrity of the manufactured dwelling and the addition if the state does not employ inspectors.
From FreddieMac:
A Manufactured Home must meet the following requirements:
If any structural modifications or add-ons have been made to a 1-unit dwelling and any portion of the dwelling is a Manufactured Home, the Mortgage securing such property must be delivered as a Manufactured Home in compliance with the requirements of this chapter.
Any structural modifications to an existing Manufactured Home must be approved by a licensed professional engineer or the local, State or federal authority.
Any improvements, modifications or repairs that affect the safety, soundness or habitability of the Manufactured Home must be completed prior to the sale of the Mortgage to Freddie Mac.