Differential Leveling

Mr. Retherford's Lecture Notes: These are the lecture notes for the Differential Leveling lesson. Pictures are located at the bottom under the attachments tab.

Theory: Building Elevation Location with a Builders Level

I. Definitions:

A. Builders Level (Theodolite) – an instrument used to check and establish grades and elevations. It consists of a telescope that is similar to a scope on a rifle. Attached to the telescope are bubbles, similar to the bubbles that are on a 4’level, these bubbles are used to ensure that the telescope is perfectly level when it is being used. A builder’s level is mounted on a tripod. Sometimes these levels are equipped with a laser that is used to take readings. Picture #1 & 2 Teacher should set up a Builders level at this point in the lesson and explain the process as it is performed.

B. Leveling Rod – A vertical measuring device that has measurements marked on it. When performing leveling and layout duties one person looks through the builders level at the rod and records measurements while one person holds the rod perfectly plumb so that accurate measurements can be taken. After the measurements have been recorded, calculations can be performed to determine the differences in elevation between several points. Picture #1 Teacher should use a leveling rod at this point to measure the difference in elevation of several points in the classroom.

C. Tripod – A three legged mount for the builders level. Picture #1

D. Civil Plans – Civil Plans are a part of a set of drawings that shows man made and natural features of the site that will be used for construction. The drawings will have a direction arrow that points north to help orient the builder. These plans show elevations of the land that the building will be constructed on as well as the elevations that the structure will be at when finished. Show Page 1.4 from Carpentry Advanced Textbook and Hunter Homes Site Plan.

E. Primary Control Points – A permanent point on a job site that can be used as a reference point for locating other elevations. These points should always be located in such a way that they will not be disturbed during the construction process. These elevations are established using point set up by the National Geological Surveying Administration.Show NGS Benchmark Viewer Website

F. Secondary Control Point – A point whose elevation is established by referencing the primary control point. This point should be established and used to establish Working Control Points.

G. Benchmark – Another name for primary and secondary control points. These are know elevations that are used to locate other elevations needed in the construction process.

H. Working Control Points – Points that are located by referencing the primary control points. These are used for construction purposes.

Procedure (Demonstration): Differential Leveling

1. Set up the builder’s level.

A. Use a 2 foot level to level the tripod

B. Attach the Builders level to the tripod and level it using leveling knobs

2. Establish the elevation of the primary control point as marked on the drawings

A. The person holding the leveling rod should hold it straight up and down while another person looks through the Builders Level, reads the measurement, and makes a note of the elevation.

3. Establish a secondary control point.

A. Drive a wooden stake into the ground and drive a nail into is ______below the primary control point

4. Establish the Working Control Points

A. Drive a Wooden Stake at the corners of the mock building that was laid out in the first portion of this project

B. Using the Builders Level mark a line on the stakes that are at the corners of the mock building. These marks should be _________ above the secondary control point.

C. 2X4s should be nailed to the corner stakes at these marks to establish the finished floor elevation as noted on the drawing.

5. Elevations of several other points should be noted and differences between these control points should be calculated