The USDA Rural Housing Service provides loans to very-low-income homeowners to repair, improve, or modernize their homes or provides grants to elderly very-low-income homeowners to remove health and safety hazards.

Visit this web page for eligibility requirements, loan and grant amounts, etc.
https://www.rd.usda.gov/programs-services/single-family-housing-repair-loans-grants/ca

Program Fact Sheet - https://www.rd.usda.gov/sites/default/files/fact-sheet/508_RD_FS_RHS_SFH504HomeRepair.pdf

Handbook - HB-1-3550 - https://www.rd.usda.gov/files/hb-1-3550.pdf

Eligible dwelling size: 440 minimum to 2,000 maximum square feet. These may be waived on rare occasions, so people with smaller or larger dwellings may apply. Source: Handbook HB-1-3550, Chapter 5, page 12 (pdf page 245).