<p>The invention concerns a building system for constructing vertical walls using wooden building blocks. The parallelepiped blocks comprise on their upper and lower surfaces a first groove (5a) extending over the entire length of said surfaces. The ridge between the upper surface and the outer surface of the blocks includes a chamfer (12) folding down part of the first groove over its entire length. The system further comprises a first block aligning tongue (6a) designed to be arranged horizontally between the first grooves of adjacent blocks in the wall. The first tongue includes a double-panel incision. The first panel of the incision is engaged in the first groove, the second panel of the incision is pressed against the chamfers of the blocks. The surface opposite the second panel forms an oblique slope for draining off water.</p>
