With a drainage membrane on exterior of foundation walls, is backfilling with gravel still recommended?
William Costello| Posted inGreen Building Techniqueson
We’re in an area where gravel runs pretty high in cost (monopoly effect.) On the exterior of our basement walls we’ll have sprayed in place Tremco Tuff’n’dry H8, with Tremco Warm’n’dri drainage board installed prior to back filling. So is it still a no brainer to backfill with gravel or might we be able to skip this and save some cash? We haven’t excavated yet, but soil in this area is classified as “silt loam” – in other words it’s not a heavy clay, but it’s not light, sandy soil either. Our builder says he’s had good results with using these products and just using the original excavated material as backfill. Any thoughts?
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Replies
You would still have a drain to daylight at the footing level, correct? There is a product sold at the big box stores that is a perforated pipe wrapped with silt fabric, and containing a loose medium that allows water to find the drain. Perhaps you could check it out, I have never used it.
We typically use native fill above the two ft. Deep layer of French drain stone. Unless there is rocky soil that would compromise the waterproofing layer.
Yes, we'll have a drain to daylight at footer.
Seems to me that gravel will increase the amount of water getting to the footing drains and cause them to clog faster. In either case, I'd add a less porous cap to the top of the backfill zone (ie, encourage surface water to move outward, not downward).
William,
If you have a dimpled drainage board on the exterior side of your foundation wall, and a footer drain that leads to daylight, you can get away with backfilling your foundation with the soil you find on site.
-- Martin Holladay