>20yrs of HST obs. of Cepheids in SNIa host gal.

The targets include nine newly imaged SN Ia hosts using a novel strategy based on a long-pass filter that minimizes the number of HST orbits required to detect and accurately determine Cepheid properties.

We carried out a homogeneous reduction and analysis of all observations, including new universal variability searches in all SNIa hosts, which yielded a total of 2200 variables with well-defined selection criteria, the largest such sample identified outside the Local Group. These objects are used in a companion paper to determine the local value of H_0_ with a total uncertainty of 2.4%.