Abstract A building module 10 comprises a substantially rectangular prism shaped hollow body having rectangular side walls 12, first and second rectangular end walls 14 and 16, and intermediate rectangular support ribs 18. The end walls 14 and 16 and the support ribs 18 are substantially identical, spaced and parallel to each other, and each comprises a plate having large spaced apertures 22. The side walls 12 are perpendicular to the end walls 14 and 16 and the support ribs 18 and are connected to respective side edges thereof. The main module 10 comprises open upper and lower ends 24 which allows filler material such as concrete to enter and fill the main module 10 in use. The apertures 22 allows the filler material to pass through the end walls 14 and 16 and the support ribs 18 to evenly distribute therewithin. The apertures 22 in the end walls and support ribs are also aligned and allow steel reinforcement bars to extend therethrough. The main module 10 comprises corresponding connection means 30a and 30b
