Externally-bonded fiber reinforced polymer (FRP) laminates and grids have been proven to greatly enhance the out-of-plane flexural capacity of unreinforced masonry (URM) walls that behave as simply supported walls without arching action. URM infill wall systems subjected to out-of-plane loads may be considered to fall into one of two categories:(1) slender wall systems without arching action, and (2) non-slender walls with arching action. When the slenderness ratio (height/thickness) of the infill wall is low an arch will form between the boundary elements resulting in the ability of the wall system to carry significantly higher out-of-plane loads. It has been reported that when the slenderness ratio (h/t) is larger than 20, the effect of arching action is negligible (Angel et al., 1994). For walls having low height-to-thickness slenderness ratios and built between rigid supports, the FRP contribution decreases because the effect of arching. Due to arching, the increase of capacity in walls strengthened with FRP laminates and grids may be considerably less than expected. The behavior of FRP strengthened walls prone to arching action is often controlled by localized crushing of masonry at the supports. This paper presents an analytical approach for determining the out-ofplane capacity of masonry walls strengthened with FRP laminates considering the arching mechanism and the stiffness contribution of the wall system. The paper also discusses limitations of FRP strengthening when arching will be present. Results of on-going and past experimental programs were used to compare the proposed methodology.