From pilot to contractor (25): Avoiding a slide down a slippery slope

Everywhere I turn around my new house project, I see water or moisture management issues. Weeping tiles around the foundations, waterproofing basement walls, drip ledges over doors and windows, ventilation of attic space… the list goes on, even with my exterior landscaping plan.

Since there is significant clay content under my hillside pool and patio living space, water drainage management is a serious matter. Because of the clay, water is not easily absorbed – it either pools on the surface, making it very slippery, or the water moves rapidly downhill, taking a freshly-graded layer of topsoil with it after a heavy rainfall.

Water on my elevated patio must be able to escape to lower ground. Trapped water freezes in winter and thaws in the spring, causing expansion and contraction resulting in heaving and movement. In summer, water trapped in heavy clay soil can cause walls and patio stones to shift and sink.

What we needed was an ‘Exit Strategy’

Prior to laying the patio stones, Dan Delong (owner of DNG Construction), not only designed a rainwater drainage plan to keep water away from my house and the pool coping, he also installed a drainage system under the retaining walls at the edge of the hillside.

Dan chose to backfill all sides of my pool and along the hillside edge of the patio with up to 4-feet of clear gravel. In addition, the patio stones were laid on an additional 12 inches of HPB (High Performance Bedding aggregate), a material with 98% compaction and that can be subtly sloped to perfection. Each tier of the Armour Stone retaining wall structure, itself a potential obstacle to water drainage, was seated on at least 2 feet of gravel. At the base of each tier, weeping tile was installed so water could not only percolate down below the surface but ultimately under the Armour Stone and down the hill below. To prevent this water from washing away any compacted material, filter cloth was laid below the gravel beds and brought up the sides to the top of the Armour Stone.

Dan guarantees his walls and patios for five years. He’s never had a major service call-back after 10 years in the business. He says the only way to make assurances like that is by taking the time to plan a solid water drainage plan and to use the highest quality materials. Detailed planning and quality execution begins with respect for water’s power to expand and contract through the seasons, and its sensitivity to the slightest changes in pitch.