As with most types of construction work, everybody has their opinion on how to backfill a basement. I've heard of, seen, and repaired foundations with variations from pushing the existing clay soils back into the hole after the basement is constructed with no crushed rock, no drain tile, no sand or gravel to the extreme opposite of people using over two hundred cubic yards of crushed rock in their basement construction. Which way is correct? Certainly not the first scenario; and the second scenario is way too expensive and unneccesary. My time proven technique with no call backs over the past twenty one years is this:
First, we always excavate the hole for the basement sixteen inches deeper than the finished floor of the basement. We pour the 12" thick footing on native soil and install 12" of pit run sand or gravel inside the footings (beneath the basement floor). This allows the plumber ample clean material to work in in order to install his pipes, provides an excellent base for the basement floor, and facilitates below slab drainage. After the walls are erected and water proofed, we install the exterior drain tile with elevation at the high point beginning at top of footing and at the low point one half way down the footing where it enters the previously installed "sleeve" through the footing and into the sump pit.
I backfill the exterior with crushed rock from the base of the footing up to within one foot of finished grade, but only between 6" and one foot wide. My theory is that if you have crushed rock next to the wall, any water next to the wall will fall (not percolate or dribble or weep) directly down to the drain tile, run to the sump through the tile, and then will be pumped out of the sump. This technique may seem expensive, but it is really not. As mentioned earlier, I have seen homeowners use over 200 c.y. of rock to accomplish the same type of backfill I mentioned above and that I can do with about 40 cubic yards of rock. It is more expensive than the "typical" excavating contractor's technique of 6" of crushed rock over the tile then either sand or clay backfill up to grade. I have repaired more foundation walls constructed by my competitors than I can count.
I repeat, my method does not allow any water to sit next to the foundation. Others methods allow the water to either perch or slowly trickle down the wall. This enables the ground adjacent to the foundation to potentially freeze and expand. The result is always cracked and leaking walls, foundation shifting, sidewalk heaving / settling, etc.
Back to does my technique cost more. I will answer that question with a question. How much does it cost to repair your damaged and leaking foundation of your new home after your landscaping is done, sidewalks are in, driveway is blacktopped, etc. Not to mention the cost of rebuilding the foundation that your builder just had somebody else build and backfill. So yes, the small up front additional cost of proper construction does cost more. However, the added expense will give you peace of mind in that your foundation will outlast your home. Contact us for further questions or to allow us to quote you or your builder on your basement construction and repair project.