March 17 (Reuters) - The Architecture Billings Index, an indicator of U.S. non-residential building activity, rose in February, the American Institute of Architects (AIA) said on Wednesday.

The index rose to 50.4 in February from 49.9 in January.

A reading above 50 indicates an increase in billings.

The index, based on a survey of U.S. architects, reflects the roughly nine to 12 months between architecture billings and construction spending.

"The health of the institutional market has been the key factor for positive business conditions for the design and construction industry in recent months, and it is encouraging to see that sector remain on solid footing," AIA Chief Economist Kermit Baker said.

Industrial companies and their investors track the monthly index as an indicator of future demand for machinery and components used to construct buildings.

The score for an indicator to measure trends in new design contracts at architecture firms in February was 50.

The new projects inquiry index fell to 56.6 in February from 58.7 in January.

(Reporting by Ankit Ajmera in Bengaluru; Editing by Joyjeet Das)