An important tool for the construction of tight wavelet frames is the Unitary Extension Principle first formulated in the Fourier-domain by Ron and Shen. We show that the time-domain analogue of this prin- ciple provides a unified approach to the construction of tight frames based on many variations of multiresolution analyses, e.g. regular refinements of bounded L-shaped domains, refinements of subdivision surfaces around irregular vertices, and nonstationary subdivision. We consider the case of nonnegative refinement coefficients and develop a fully local construction method for tight frames. Especially, in the shift-invariant setting, our construction produces the same tight frame generators as the Unitary Extension Principle. 2000 MSC: 42C40 primary, 42C15, 42C30 secondary Keywords: Wavelet frames, Unitary Extension Principle, irregular MRA, nonstationary MRA