Monday, August 18, 2014

Timeline - Surveying the Building Site

Two Years Ago

Rotary Laser
An early Craigslist find was a rotary laser for $80 that sells at the big boxes for three times more.  It came with the tripod, the leveling rod and the sensor for the rod.  My experience with a rotary laser was nil but it seemed reasonable that it would be the ticket for surveying the building site, instead of paying for a professional survey, and would have myriad uses during construction. 
Tripod station facilitates the excavation

Advantages of a Rotary Laser
The rotary laser has advantages over a conventional transit for the DIYer working alone. The battery operated sensor on the leveling rod beeps loudly when it is level with the laser beam. Consequently, measurements can be made working alone as opposed to the two-person team required for a transit -- one person to sight through the transit and the other to operate the leveling rod.

Tripod Stations
In order to standardize and expedite setting up the laser, I made two tripod stations near the east property line where they would not be in the way of future excavation. Each station comprised two half sheets of salvaged plywood weighted down by stones.  I set up the laser on each platform in turn, marked where the tips of the tripod touched the plywood and drilled holes just large enough to accept the tips.  I reset the laser and marked the tripod legs with permanent marker at the telescoping point for each leg in case the legs were moved between uses. Then to store the laser at the end of the day, the laser could be left on the tripod, the tripod lifted from the plywood and the legs folded together without un-telescoping them.  Each subsequent use of the laser then required only spreading the legs and setting them into the holes in the plywood followed by minimal tweaking of the laser for level as necessary.
Data points (20" x 20" grid) recorded on site

"Surveying" the Building Site
The summer of 2012 was droughty.  Our cool weather grasses were brown and flat for weeks on end which gave me a rare opportunity to survey the building site and the level ground north of the building site.  I used a tape measure to mark off a grid of 20' x 20' squares and mark the intersections with marking paint.  The dead grass was ideal for displaying and holding the paint for the couple of days it took to complete the survey.

The day before surveying, I plotted the grid on a piece of stiff project board that would not blow around in the wind.  I set up the laser on the station highest on the slope.  I then moved about among the paint marks with the leveling rod and detector and recorded each elevation that could be measured from the first station.  Next I moved the laser to the lower station and finished recording the paint marks.
Data points (20' x 20' grid) plotted against sea level
The data points on the project board were transferred to a spreadsheet and given values for elevation above sea level.  The sea level figures were based upon a Goggle Earth value for the highest point on the area surveyed.  The square in the middle of the spreadsheet represented the proposed building footprint.

The data points are not close enough together to plot the contour lines that would be standard for a professional survey.  However, they gave me, as the builder, all of the information I need.  I did not pass the DIY survey on to Steve, who is doing the construction drawings, in order not frustrate him by its lack of sophistication or cause him to stew over proper siting of the building.