20% fluff may not be e-nuff for all de stuff
adding a 20% fluff factor is a good rule of thumb for heavy clay. It is very close to multiplying by 1.17 which is what I suggested earlier, so we agree about clay.
If you attempt to apply this 20% rule to fluffier soils like loam, sandy loam, or muck, you will produce an estimate that will be off as much as 35%, and you may loose a very important part of your anatomy.
Each soil type fluffs ( swells at break out) at a different rate. That is why most better quality plans tell you exactly what types of soils exist on your site, and where. Civil engineering charts exist which tell you the exact amount of swell to expect for each soil type. The larger sites you work, the more critical this becomes. ( miss a small site bit by 5% and laugh about it at the bar tonight. miss a large site by 5% and maybe go out of business)
When larger companies bid, they use a digital pen to trace all the lines on the plans while telling the computer what information is existing and proposed. The computer then turns the information into digital information and is able to make precise calculations on every volume calculation on your site. Imagine how much more accurate and safe your bid would be if you knew exactly what every volume was.
The computer estimating programs also give you the ability to "balance a site." [ figure out what evevation to build your site so no dirt is imported or exported]
Many surveying companies do not have the math skills to calculate a balanced site in this lifetime so an arbitrary elevation is chosen. If you can offer a balanced site alternative to the plans, you often become the only bidder in a new proposal which saves the developer money and seperates you from the other bidders.
Another big advantage area of computer bids is in roadbuilding. The computer programs allow you to insert dimensions of the specific road profile into the computer and trace the centerline of the road. The computer then does all the cut and fill calculations and gives you an average materials move list, like: move 5670 cu yds an average of 516 feet.
Most non-computerized bids are the product of 1. an educated guess, plus 2. the addition of a fudge factor, and 3. the prayer for a profit.
When you know exactly how much dirt will move and what kind of dirt it is, you can bid much closer without fear of hurting yourself.
Since most of us can't run out and drop $6 to 14K on a computer estimating program, and many of us don't have an honors math degree to make the calculations ourselves, it is often best to change the rules, if possible, and convert the bid to unit and hourly pricing.
Some bids are pre-funding and may be building their budget to apply for project funding. Unit and hourly won't work if they are going to the bank for funding in most cases.
Most out-of-pocket type projects may work well with unit and hourly pricing and since this type project often comes without plans, unit and hourly pricing is a good way to protect yourself and insure your profit. (someone mentioned this earlier but it seemed like it fit in here too.) This approach keeps poor math skills from hurting you, too.
Some demolition jobs are good candidates for unit and hourly, too, because of the difficulty of bidding debris volumes, and small blasting and rock removal jobs fall into this category, too.
Quest and HeavyBid are two of many project estimating softwares.
Happy Estimating
