Adjustable manhole top

An adjustable manhole top comprising:

• (a) a cylindrical sleeve having an internal, manhole cover-supporting rim towards one end, a plurality of spaced elongated ribs extending longitudinally along an internal surface of the sleeve below the rim;
• (b) a support rim comprising a planar base to be rested on the upper edge of a manhole foundation and a cylindrical wall extending upwardly from the base, a portion of the base extending inwardly, beyond the inner surface of the wall for supporting the sleeve, the wall being of a diameter so as to co-operate with the sleeve and prevent relative lateral displacement thereof;
• (c) an annular height adjustment ring to sit on and be supported by the inwardly extending annular portion of the base;
• and
• (d) riser blocks secured to and upwardly extending from the height adjustment ring, the riser blocks each having an upper surface with steps therein at a plurality of pre-determined elevations, the blocks and steps positioned so as to supportably receive the lower ends of corresponding ribs of the sleeve at the same one of said predetermined elevations,
• the cylindrical sleeve and the annular height adjustment ring each being relatively rotatable with respect to each other and with respect to the support base so as to permit alignment of the ribs and the steps and thus adjustment of the elevation of the manhole cover.