• Iowa is a UNPAID BALANCE lien state.
• Effective 1/1/13 "Residential Construction" means construction on single-family or two-family  dwellings  occupied or used, or intended to be occupied or used, primarily for residential
  purposes.
•  If the 90-day lien period has lapsed, a subcontractor may still perfect a mechanic’s lien. file the claim with the clerk of the District Court, and give written notice to the owner. Liens perfected after the  90 days period shall be enforceable to the extent of the balance due from the owner to the contractor at the time of the service of such notice.
• Private projects: A supplier per Iowa statute seems to be defined as a subcontractor which should give a supplier to a supplier rights. There is no case law on this issue. Statute 572.1 (11) “Subcontractor” includes every person furnishing material or performing labor upon any building erection, or other improvement, except those having contracts directly with the owner.  
• Bond Claim Notice: No part of the unpaid fund due the contractor shall be retained unless such claims are supported by a certified statement that the general contractor has been notified within 30 days after the materials are furnished.
• In case of highway improvements by the county, claims shall be filed with the county auditor of the county letting the contract. In case of contracts for improvements on the farm-to-market highway system paid from farm-to-market funds, claims shall be filed with the auditor of the state department of transportation.
• 573.7 Claims for Material or Labor on public projects:  A person furnishing only materials to a subcontractor who is furnishing only materials is not entitled to a claim against the retainage or bond under this chapter and is not an oblige or person protected und the bond pursuant to section 573.6.

Oil & Gas Liens:

• The mechanic's lien statute is applicable to labor and materials furnished in connection with gas and oil wells or pipelines. Liens do not attach to realty, but only to lease, wells, buildings, appurtenances, and pipelines.