A novel timber I-joist with a castellated web is presented. While castellated webs are common in steel joists, this concept is new to timber joists. The openings provided by the castellation process provide for the easy passage of services during construction or subsequent remodelling of a building. The manufacturing process is described together with details of tests on twelve 241 mm and eleven 305 mm deep joists. The load-deflection response, failure loads and modes of failure are given. The mean failure moment and shear force for the 241 mm deep joists were found to be 8.2 kN m and 6.0 kN, respectively. The corresponding values for the 305 mm deep joists were 12.5 kN m and 6.9 kN. The predominant failure modes were tension failure in the web at the corner of the openings and shear failure in the web at mid-depth between the openings. The effect of the web openings on the joist stiffness is not significant but the shear capacity is reduced. The reduction in shear capacity compares favourably with the shear capacity of commercial joists of equivalent sizes with circular or rectangular openings. (C) 2011 Elsevier Ltd. All rights reserved.