An asphalt driveway should be installed on stable soil, otherwise, it will fail and the life span will be greatly reduced. Adding asphalt driveway base material or any other type of structural base to unstable sub-grade can stabilize the soil and in turn lengthen the life expectancy of the asphalt driveway. However, whether base should be installed or should not be is a difficult question to answer. It really depends on what the soil is like in your area. You must be prudent when getting bids because there are two things to look out for:
1) Contractors who don’t include base in their estimate when it really should be installed.
2) Contractors who try to sell us base where it just isn't necessary.
Let me give you an example.
Here in Denver, there are two types of soil we pave on. The first, which is along the front range far east of the mountains. The soil in some areas can be considered to be expansive soils that tend to be a bit unstable and move a lot. It's hit or miss. Some contractors will include 3 to 6 inches of base in their bids to stabilize the sub-grade and minimize any cracking that may occur in the asphalt. On the other hand, the soil just west right into the foothills and into the mountains is completely different. It’s mostly made up of decomposed granite which is almost identical to that of base. You couldn't ask for a better, more stable sub-grade material. So most contractors will not include the installation of base in their estimates.
Now, I say most contractors because, again, there are some contractors who will include base in their bids and oversell the importance of it to increase their profits. But there are also contractors who will not include base in their bids so they can "Get in, get paid and get out" fast!
So, how do you know whether base should or shouldn't be included in your bids?
The best way to determine whether the region you live in requires base or not is one of two ways: The first and least expensive way is to get 3 estimates from reputable contractors. If all of the estimates have base installation on their proposals, then it’s more than likely needed. On the other hand, if 1 or 2 out of 3 have base installation on their proposals, then we’ll need to do a little investigation to find out why. Start with the contractor that doesn't include base installation on their proposal and ask them for 3 references near your home. Request that each reference is 2 to 3 years older than the next. What we’re looking for is longevity. If the driveways have an excessive amount of cracking, failed areas, low spots and are bumpy, that's probably a sign that the soil is unstable and base should be installed. I would eliminate that contractor from the choices and then investigate the other 2 contractors work. If those driveways are in great shape then that should be a good sign that base is a standard practice in your area. On the other hand, if the 1st contractor's driveway looks great, then the other two may be overselling it. Either way, it may take some thorough investigation on your part!
The only sure fire way to determine if the area you live in requires base is to hire a soil engineer. But that can cost hundreds if not thousands of dollars. But even then, there’s not a 100% guarantee that the asphalt will not fail unless the soils engineer is willing to guarantee it in writing, which in most cases... they won't.
Base can be very important! Before you hire any contractor... avoid asphalt paving scams and see our report on “The Most Common Ways Asphalt Installation Contractors Rip Us Off and How To Avoid Them”.
Or make it easy and request an asphalt installation estimate from one of our Trusted Contractors!