Messages and Online Forum Q&A

foundation techniques continued

From: mmdell@earthlink.net
Category: Select Category From List....
Remote Name: 4.17.82.104
Date: 08 Mar 2001
Time: 09:26 AM

Comments

Sirs, You recently provided me excellent info regarding the use of EPS foam for foundation waterproof membrane protection. It sounds like the termite resistant EPS is overrated and protection can be accomplished via any competent pest control service. R-control makes a product called Perimeter Guard which is termite resistant but has no drainage channels. I'll probobly use this for basement underslab- Which brings me to my next question concerning drainage. As you have hinted I should probobly tell you the ground conditions in So. Maryland, USA( near Washington DC) The soil here is sandy with pockests of clay and sand. The below frostlone temperature is consistant at ~53 degrees. Our frost line is typically about two feet. However, this winter was exceptionally cold and I was told by several contractors that the ground was still frozen four feet down and in some areas 6 feet down.BRRRR. Code for Calvert County Maryland requires french drain atop the footers because of the drains settling and undermining (creating gaps under the foundation footings- so I'm told -My guess is this is because of the sandy soil)

Most of the contractors use corregated plastic drain with drainage holes around the entire pipe. These flexible drains are then sometimes wrapped in a silt proof sleve and then covered with gravel. In reference to the use if internal french drain and weeping holes- I suppose I was not clear. A 12" hollow CMU block is typically used in this area(sometimes double width depending on soil type and wall length) the block is seldom filled with concrete unless backfilling greater than 6-7 feet in height against the foundation wall. Hence, hydrostatic preasure and condensation causes the hollow block to fill with water and settle atop the footer. ( my reason for aggressive external waterproofing) In order to drain, the contractors punch "weeping" holes. along the lowest layer of block which drain the water from the inside of the wall. The water drains into the underslab gravel beside the footer on the internal perimeter of the basement wall. That inside perimeter drains to a sump via the internal drain tile of flexible perforated corregated plastic pipe. The sump is either pumped or gravity drained depending upon the plat grade. Hence, the contractors typically use an external above footer drain and an internal parrelel footer drain tile. My contractor agrees with this approach but does not like to drain the hollow brick under the slab. My guess is he wants the weeping holes on the outer perimeter of the block to be drained(possibly via a tube) into the external french drain. My question is wouldn't this approach compromise the outer waterproof membrane and defeat the purpose of waterproofing. What donsiderations apply to this hollow block drainage. Will the external membrane be sufficient to prevent water accumulation within the hollow block? Or, is some type of drain mandatory? And, what about the wall "breathing/ventilating"? Thank you for your patient tutelege

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