A common problem with traditional design/bid/build architecture is that the contractor ends up with so many unknowns. Despite any architect’s best attempts to calculate and design to the nth degree, there are still items that can be contingent on the conditions of the site or the construction industry. One such item is excavation. Depending on the accuracy of bid drawings and the sub-contractor’s site visit during bid,  the sub may have to excavate more or less material in order to properly lay the foundations as designed.

As an example, a recent Dura project required 43 cubic yards (CY) of excavation. If the concrete sub-contractor assumed from the drawings that the excavation would be about 2′ deep x 1.5′ wide x 350 linear feet (LF), then they estimated about 38 CY of excavation. But most contractors know there are unknowns on the site, so they will typically add a reasonable amount to their bid, say in this case, 12%.  At 12% fudge factor, the sub is at 42.5 CY. As it turned out, that extra .5 CY yards of excavation is not too hard to dig once you are mobilized and digging, but it stills costs a sub equipment and labor money to do so.  This example is for a small project, an addition to existing. But what if concrete sub is covering 30,000 SF of area? The contingency costs can really add up: 10% fudge factor on a $200K excavation is $20K. What could you do with $20K?

So how can architects better serve contractors with information that is useful to the building process? And furthermore, how can an architect/contractor relationship work such that the contractor knows they are working with someone who has considered these contingency items and is giving their subs good information to bid on?

This actually starts earlier than you may think.

The owner makes many decisions with the architect. Among the first is the decision to spend some funds up front in order to help the architect complete an accurate design. This will include a survey (not the kind of survey you get when you buy a house, this one is more detailed) and a geotechnical report.  Granted not all sites will require the geotech report, but the survey is essential, and Dura does not complete design work without one. A proper survey locates anything of merit within the site (including existing structures, surface improvements and any significant geographic features like trees or bodies of water); and also provides the bearing lines for the site boundaries. Many times, topographic information is valuable and desired in the survey as well. If your site slopes more than 1 foot within 10′ in any direction, its probably best to have the surveyor include topo info. At the very least, a finished floor elevation of existing structures is required.

Dura requires the survey to be in electronic format, so that survey information is not being manually transferred from the surveyor’s drawing to our drawings. Instead, we on top of their CAD information so that errors are reduced. 

Here’s the kicker: most contractors are going to have a surveyor come out and do their locates when they start staking out the building. They will also have them come in order to check finish floor elevations and adjacent grading. So why not get all this information up front and eliminate changes to the design. Measure twice, cut once.

Most thorough surveys for a decent-sized residential or commercial lot will run under $1000 in our area, depending of course on certain factors. A geotech report is highly recommended for any sort of atypical construction / structural system. They tend to run about the same or higher than a survey. All told, it is a couple thousand dollars spent up front that is well spent if it allows your contractor to proceed with less headaches or changes, which can get costly.

And to the second question: on architect and contractor teamwork and confidence; good design information allows for tighter bidding with less spread between one sub and the next. Now, on occasion, the spread exists for other reasons entirely (how busy a particular sub already is and what the marginal profit is worth to them), but as a hard and fast rule, good drawings produce good pricing.

Of course, problems like these are the reason why 1) BIM, and 2) design/build is so attractive to everyone. Reduce unknowns, value engineer in-house, save time, save money. But a good architect/contractor relationship can yield a similar outcome. Be sure your team is sophisticated enough to handle problems like these before they become costly.

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