A design method to determine the shear resistance of elongated web openings in cold formed C sections is presented, that is based on Vierendeel bending in the web-flange Tee sections. The results of 6 tests on pairs of C section beams with stiffened and unstiffened openings of 155mm depth and 220mm length are presented. The tests also included a beam with closely spaced elongated openings and a comparative test on a plain C section. The tests showed that the bending resistance of the beam with stiffened openings was close to that of the plain C section.The design method is based on a derived formula for the normal stresses acting on radial planes around the circular part of the elongated opening. The results are compared to the stresses at an equivalent rectangular opening. It is proposed that in Vierendeel bending, buckling at the unstiffened openings may be represented as an equivalent ‘strut’ with an effective length of 0.3 x opening depth. The post-buckling resistance may take account of the redistribution of moments around the elongated openings. It was also found that for the tested beams, the additional shear and bending deflection due to each elongated opening was approximately 3% of the plain beam deflection.