Cement-stabilised soil blocks are far more resistant to water than raw earth, but they are not impervious. Long-lasting earth buildings keep rain off the walls through good design rather than relying on the blocks alone. The old builders’ saying applies: give the building a good hat and good boots.

A good hat: the roof

A generous roof overhang is the cheapest protection you can build. It shields the upper wall from direct rain and shades it from the sun. Overhangs of 600 mm or more are often recommended for earth walls in rainy climates, but your designer should choose the size for your site and roof type.

• Fit gutters and downpipes so roof water does not run down the walls or pool at their base.
• Make sure fascias and eaves details do not trap water against the wall top.

Good boots: plinth and base

The bottom of the wall takes the most abuse from splashing and ground moisture. A raised plinth and a continuous damp-proof course, as described in our foundation guide, keep the soil blocks dry from below.

Shape the ground

Slope the ground away from the building and keep paved or gravelled aprons around it. Avoid planting beds, taps and water drains against walls.

Wall finishes

Plaster, render and paint can add protection, but only if they are compatible with the wall and well maintained. A poorly bonded render can crack and trap water behind it, which is worse than no render at all. Read about finishing options for interlocking block walls before you decide.

Check openings

Windows and doors are common entry points for water. Use sills with a drip, set frames properly and seal joints where the frame meets the wall.

Maintain, do not ignore

Walk around the building each year before the rains. Clear gutters, repair cracked finishes, fix leaks and check the ground slope. Small repairs prevent large problems.

Learn more

For a comparison of soil blocks against other walling, see our articles on soil blocks and burnt bricks and soil blocks versus quarry stone.

• durability
• roof overhang
• waterproofing