Previous Section | Table of Contents | Next Section

3.0.0 MEASURING STRUCTURES

3.1.0  Sketching and measuring plans
3.2.0  Sketching and measuring elevations
3.3.0  Sketching and measuring sections
3.4.0  Sketching and measuring details
3.5.0  Sketching and measuring roofs

3.1.1  A plan is a horizontal slice through one level of a structure, generally cut at waist height, or approximately 3'-4" from the floor (Figure 3.1).

Figure 3.1: Measured drawing of the first floor plan.
Rock Harbor Lighthouse, Isle Royale National Park, Michigan.

3.1.2  The interior of the plan drawing shows flooring materials (floor boards, tile patterns, concrete, stone or dirt); moldings; door and window frames; door swings; and structural materials denoted by various poché techniques.  Dashed lines are used to indicate elements above the cut line, such as mantels, arches or stairs.

3.1.3  The exterior of the plan drawing shows roof lines above and porch or skirt roofs of the floor immediately below, basement window wells, paving stones immediately adjacent to the structure, and portions of walkways away from the structure.

3.1.4  Most measurements are taken from conveniently located 0 points and are read as "running" rather than "incremental" dimensions.  For ease in notation, dimensions may be written as 3.10.1, 6.1.3, instead of 3'-10 1/4", 6'-1 3/4", etc.  If greater accuracy is required by an object to be drawn at a larger scale, one may write either 1'-3 13/16" or 1.3.13, so long as consistency is maintained.

3.1.5  The establishment of reference lines and points is crucial to accurately measuring the exterior of a structure, which, due to variations in wall conditions may vary from interiors.  There are several methods of placing a building within a "reference polygon."  Figure 3.2 shows that the reference polygon need not have parallel or perpendicular sides, nor must any of the sides be parallel to any side of the target structure.

Figure 3.2: Establishment of a reference box and triangulation points.  Measured drawing
of the Spring House, Mumma Farm, Antietam National Battlefield, Sharpsburg. Maryland.

Method 1: 

1)  Lay out sides AD, A'ABB', D'DCC' and BC with stakes and strings, making sure that a) the stakes at points A, B, C and D do not cause the strings A'B and D'C' to bend, and that b) the strings are level;

2)  determine the precise lengths of all strings;

3)  triangulate distances A'D, AD', B'C and BC'.  All four sides are now located relative to each other without having measured the angles at A, B, C or D;

4)  divide sides AB, BC, CD and DA into convenient increments from which to triangulate points on the structure.

1)  To lay out box ABCD (Figure 3.3), first set up a transit several feet away from one corner at A such that two sides of the structure can be seen.  Sight to a point B' beyond the end of one side and mark its location with a stake and nail.

2)  Swing the transit exactly 90º, sight to a point D' and mark its location with a stake and nail.  Connect points D', A and B' with string.

3)  Using a plumb bob suspended below the center of the transit, center it at point B, preferably at a distance from A which is a multiple of 5 or 10 feet.  Sight back to A, note the bearing, then swing 90º, sight to C' and mark it with a stake and nail. 

4)  Repeat the procedure at C, sighting back to B, then swinging 90º to establish E and D--at the crossing of A-D' and C-E.

5)  Divide each side of box ABCD into convenient increments usingtape with pen marks on the string.  Each corner and all other plan features can now be located from nearby pairs of points on the box.

Figure 3.3:  Establishing a perfectly rectangular reference box with a transit.  Measured drawing of Clifton Farm House, Monocacy National Battlefield, Frederick, Maryland.

Figure 3.4:  Constructing perpendicular datum lines.

3.1.6  It is sometimes useful to construct x and y coordinate axes for use as datum lines.  First, perpendicular lines must be constructed.  The "x-y coordinates" method can be used to locate one or more structures in plan and relative to each other, reference interiors to exteriors, and measure interiors.  To construct perpendicular reference lines at a site, if a transit is not available (Figure 3.4):

1)  Lay out a line AB with stakes and/or nails, and string, checking it for horizontality with a string level;

2)  choose a point C, secure a steel tape measure to a stake, unroll it to a point beyond AB; 

3)  using the tape measure as a compass, swing an arc through two points on AB, marking the intersections p' and p" precisely with pen marks on tape;

4)  point D is half way between p' and p", and CD is perpendicular to AB.

Figure 3.5:  Interior perpendicular datum lines. Jimmy Carter Boyhood Home,
Jimmy Carter National Historic Site, Plains, Georgia.

Figure 3.6:  Measuring a complex floor pattern.  Field sketch of the Parlor,
Monticello, Charlottesville, Virginia.

3.1.8  Large interior and exterior spaces can be measured with a transit or theodolite/EDM (Figure 3.7).  In this case, each point (A1..A13, etc.) was surveyed from at least one  major survey station (A, B, B₂, etc.); major changes in wall direction were surveyed from two stations.  Angles and distances were recorded systematically by station. 

Figure 3.7:  Use of a theodolite/EDM to find distances and angles.
Site survey, Fort Sumter National Monument, Sullivan's Island, South Carolina.

3.1.9  In addition to measuring rooms individually, as many overall dimensions as possible should be taken.  A run through several connected spaces can include wall thicknesses, partition-wall locations and stairs; a separate run should be made for floor boards.  When construction materials differ from wall to wall, or if other irregularities are suspected, wall thicknesses should be measured through as many openings as necessary.

3.1.10  Individual rooms must be measured around their perimeters to locate openings, mantels and other elements.  Tiles, inlays and other regular flooring materials may be sized and counted, but irregular floorboards--such as those often found in barns and older houses--must be measured in runs across the entire space.  Where individual floorboards vary in width, or are not laid parallel to the walls, a number of dimension runs must be taken.

3.1.11  Because of construction material deterioration, settling, wind damage, and other reasons, historic structures are rarely "square"; a building or room perceived to be rectangular in plan may in fact have two acute (< 90º) and two obtuse (> 90º) angles as corners.  Diagonal measurements taken at plan height will reveal the true configuration of the space.  In large open plans with columns it may be more practical to determine the squareness of each bay, since intervening columns and tape sag over a long distance will make corner-to-corner measurements impossible.

Diagonals are also useful in locating fireplaces, built-in furniture, and other features. 

3.1.12  Stair treads in good condition should be spot checked for regularity, otherwise each tread must be measured individually, keeping in mind that the edge of the nose, not the face of the riser will be seen in plan.  The center post and top and bottom rungs of circular stairs should be located relative to known points in the space.

3.1.13  Reflected ceilings are located relative to floor plans by dropping a plumb bob at the corners to the floor.  A tape measure can then be tacked or held at one end, stretched across the ceiling and read from below.  These measurements will also be used to construct section drawings.  If possible, diagonal measurements should also be taken.

3.1.14  Unless it can be demonstrated that appliances such as stoves, furnaces and bathroom fixtures have historical or other contextual significance, they should be drawn schematically, rather than in detail. 

3.1.15  New partition walls, counters and building additions should be measured and drawn as they exist; notes will call out materials and dates on the final drawings.  Evidence of elements no longer extant, such as "paint shadows" or missing trim should be recorded.  Consultation with project historians and others knowledgeable about the structure will determine if missing elements are to be noted on the drawings.

3.1.16  The failure of floor plans to "line up" is often a symptom of buildings changing shape due to various types of structural distortion.  Suspending a plumb bob from the top of a wall may show the wall to be leaning several degrees from vertical, causing floors to move horizontally relative to each other.

3.1.17  Recording circular, elliptical, polygonal and irregular spaces.

In Figure 3.8: 

1)  Locate and triangulate known points such as door frames
     A,B,C,D;
2)  from A and B, locate e, f, g, h, etc., and from C and D locate i,
      j, k, l, m, etc.;

Figure 3.8:  Beginning triangulation of an elliptical space. 
Blue Room, The White House, Washington, DC.

In Figure 3.9:

1)  locate reference points at W, X, Y, and Z;
2)  plot curves by triangulating tile locations a, b, c, etc.

Figure 3.9:  Plotting  irregular curves.
Wishing Well, Scotty's Castle, Death Valley National Monument, California.

A second method is to lay a sufficient number of straight datum lines (strings or measuring tapes) on the floor (AB, AF, CD in Figure 3.10).  Locate the end points relative to nearby known points.  In this case, measure to each mortar joint at right angles to the tape measure.  Connecting the points will produce a plot of the curve. 

Figure 3.10:  Plotting irregular curves from straight datums.  Measured drawing of the 
Joers-Ketchum Rowhouse patio, Rancho Santa Fe, California.

Figure 3.11: Triangulation in a highly irregular space.  Field sketch of the left
flank angle, Ft. Sumter National Monument, Sullivan's Island, South Carolina.

3.2.0  SKETCHING AND MEASURING ELEVATIONS

3.2.1  Elevations represent the planar surfaces of structures as ideally seen without the distortion of photography and natural vision.  Field sketches show structures without planting, shades or shadows, glass, utility cables or screens.  Gutters and other features that obscure the "essential" elevation are to be rendered separately as details.

3.2.2  Rather than delineate every brick course or row of siding or shingles, count the rows to window openings and other significant features, remembering that top rows of brick are often hidden behind gutters and roof overhangs.  Decorative and structural elements, such as finials and column capitals, will appear curvilinear in perspective, but are in fact linear in elevation and must be drawn as such. 

Figure 3.12:  Field sketch of west elevation, Asa Packer Mansion, Jim Thorpe, Pennsylvania.

3.2.3  As in construction drawings, field sketches will refer to details drawn at larger scale for clarity.  Porches, screen doors and window shutters may be drawn separately.  (In many instances, screen doors, gutters and non-historical building elements are "graphically removed" from the final drawing, that is, when it is determined that to draw them would obscure more important features.  Graphic removal must be approved by project leaders and historians.)  Larger structures should be sketched as logically separate elements, e.g. main block--hyphens--wings. 
 

3.2.4  Accurate datum lines are the key to successful measurement of elevations and sections.  A transit or similar surveying instrument is located at a distance from the structure that affords the best view of the maximum possible number of elevational features.  This is especially important for structures with highly articulated surfaces.  Points are marked by datum number with ink on drafting tape or other materials not injurious to the structure.  Snap chalk lines between points;  these lines are the "zero" from which vertical measurements are taken up and down.  USE BLUE POWDER ONLY!  RED AND YELLOW ARE PERMANENT. Virtually all structures will require at least two horizontal datums.  It is therefore imperative to label them clearly on all field notes and preliminary pencil drawings, and to note the vertical distances between the datums.  3.2.5  When the digital measuring pole is used, the dimension may be calculated back to the datum line or directly from the surface on which the pole is standing.  3.2.6  Measuring structures of more than one story in height will often require more than one datum line.  The higher datums can be established with transits located on surrounding higher ground or other structures. 3.2.7  Because roof ridges can be irregular, a datum line can be established between chimneys or other roof projections, and checking horizontality with a string level. More information on measuring roofs can be found in 3.5.0.

Figure 3.13:  Field sketch of the Tea Room elevation, Monticello, Charlottesville, Virginia.

3.2.8   A symptom of lateral wall shifting in its own plane is a rhomboid appearance, that is, the absence of right angles at the corners of walls, doors and windows (Figure 3.14).  To record such an elevation, horizontal datums must be established with plumb bobs or suspended chalk lines.  Determining the plumbness of walls in elevation will also prove useful in developing sections. 

Figure 3.14: A building leaning 3º to 6º out of plumb, requiring vertical control lines for 
measurement.  Store/saloon, Rock Creek Station, Wyoming.  Photographer: Jack E. Boucher, 1974.

3.2.9  Sharing dimensions can save a great deal of time during the measuring phase.  Some elevational features can only be reproduced from plan information, such as spiral stairs and bay windows (see 13.0.0; Appendix E:  Projections From Plans to Elevations.) 

3.2.10  When building elements project forward significantly from the principal plane of the elevation, the elevations of these elements should be sketched and measured separately.  In the final drawings, projected elevations are located relative to principal elevations triangulated measurements and projection from floor plans.

3.2.11  The tops of building walls are often concealed by roof overhangs and gutters.  Recorders may find it useful to indicate the true tops of walls and bottoms of overhangs with a dashed line on field sketches, in order to clearly
 

3.3.0  SKETCHING AND MEASURING SECTIONS

3.3.1  Section drawings or "cross-sections" serve several purposes:  they show the relationships among rooms and circulation routes; reveal structural deformation and major elements of construction; and  show interior elevations if those are not drawn individually by room (Figure 3.15).  These drawings can even help determine the order of construction of complex structures.

Figure 3.15:  Mision San Juan de Capistrano,
San Antonio Missions National Historic Park, San Antonio, Texas.

3.3.2  Section cuts must be chosen on the basis of logic and the amount of information they will convey.  Whenever possible, cuts should run through wall openings, especially exterior doors and windows. 

3.3.3  Sections may be cut as uniform, vertical slices through a structure (Figure 3.15), or "jogged" to cut through important openings and to reveal more important spaces (Figure 3.16).  In a multi-story structure, the jogs may vary slightly from floor to floor, but should be close to each other in the vertical and horizontal planes. 

Figure 3.16:  Stepped or "jogged" section. 
Bright Angel Lodge Cabin, No. 6179-82.  Grand Canyon National Park, Arizona.

3.3.4  Horizontal datums may be established either from outside the structure through openings; transferring exterior datums with string levels through openings; or establishing new interior datums with a transit (space and light permitting) or string level.  Field notes must reflect referencing datums from sections to corresponding elevations.

3.3.5  Vertical datums (control lines) are used to locate walls and determine their plumbness.  A plumb bob is suspended from the tops of walls and columns, and distances from the tip of the plumb bob back to the base of the wall or column is recorded.

3.3.6  Large, open interior spaces such as atriums, auditoriums, barns and churches must be sketched as a series of vertical planes for clarity in producing the field notes, with each overlaid "interior elevation" sketched and measured on separate sheets of graph paper. Datum points must be established on all columns and other elements which are located between the plane of the section cut and the farthest plane of the interior elevation.  The information gathered on these field notes will prove invaluable in producing isometric framing drawings (Figure 3.17 and Figure 3.18.)

Figure 3.17:  Dimensions were recorded at planes A, B, and C
to produce the section drawing in Figure 3.18. 
Barn, Farm One, Eisenhower National Historic Site, Gettysburg, Pennsylvania.

Figure 3.18:  Transverse section.
Columns and other elements in bent B are neither plumb nor in line with those in bent A,
and can therefore be seen between bent A and the end wall.

3.3.7  Exposed framing in attics and similar structures is usually best shown with a cut line on the near side of the ridge.  A tape is strung along the underside of rafters; if all rafters are known to be of the same size, the dimension at the lead edge is sufficient for recording.  However, many older structures will have hand-hewn structural members of varying sizes, so both edges will require recording. Measuring from center to center is not acceptable in such cases.

3.3.8  The curvature of a dome may be plotted by first stringing a tape across the diameter of the drum supporting the dome.  A plumb bob is then suspended from various points along the dome ceiling down to incremental points along the tape.  The length of the string is recorded each time.  The distances from tape to ceiling at 90º to the horizontal tape will provide points along which the curve can be plotted.  As in all hand measuring operations, attention to safety is especially critical in measuring high interior spaces.

3.3.9  The most precise way to record irregular structures such as stone and adobe walls is with vertical, incremental control lines.  The method is similar to measuring domes.  Distances from the line at 90º to it are recorded at the chosen increments.  Notice that on the field sketch, an irregular surface may be drawn as a straight line, because plotting the points will define the true shapes on the final drawings.  (A variation of this technique will also be used to measure landscape features.)
 

3.4.0  SKETCHING AND MEASURING DETAILS

3.4.1  Several criteria may be employed to test the usefulness of each potential detail drawing:

1.  Frequency of occurrence.  Are there typical doors, windows and moldings that are integral parts of the whole structure and provide uniqueness of character to it?

2.  Do the elements demonstrate significance in history or in the realms of architectural, landscape or interior design?

3.  Can the detail drawing explain a unique or unexpected method of construction or design?

4.  Will the project sponsor need the drawing for future maintenance, restoration or publication?

5.  Can the proposed drawing serve as a title sheet element or enhance the set in some other way?

6.  Is the element so complex that recording it will take time from producing other drawings?

7.  Can the element be better captured photographically?

3.4.3  Maximum use of artistic talent is encouraged in field sketching decorative elements.  A limited amount of shading and other rendering techniques can enhance field sketches, but team members should use field photographs to reproduce textures and three-dimensionality.  Shining a flashlight down on the element will produce crisp shading lines suitable for later drawings.

3.4.4  Profile gauges, tracings and pencil rubbings can produce fairly accurate representations of moldings, tiles, ornamental cast iron and stone texture.  If possible, compensate for paint layers that tend to obscure the sharpness of detail. 

Supplemented with photographs and measurements, these artistic techniques can be used to produce striking ink drawings.  These techniques must be implemented with caution in order to avoid damaging historic fabric. 

3.4.5  Both incremental and running dimensions may be used to measure small objects, but incremental dimensions should only be used if the shape of the object prevents running measurement.  The datum point should also be selected for convenience, and not necessarily placed at one end.  On field notes it may be useful to indicate the beginning of a line of running dimensions with an arrow.

3.4.6  Calipers, dividers and carpenter's squares are useful in measuring objects that are round in cross-section, such as balusters, decorative urns and spheres, and columns.   When determining column diameters, care must be taken to account for entasis--the slight convex curvature of the vertical profile of the column--if it is present.  In Roman entasis, for example, curvature begins at one-third the distance from the bottom of the base to the top of the capital; in Greek entasis, curvature begins at the base.  Field notes and detail drawings should reference heights from the base at which diameters were determined (see 12.0.0 Appendix D:  Measuring Circular Objects and Areas.)

3.4.7  If taking precise measurements is less important than capturing the essence of an ornamental detail, photographs used in conjunction with overall dimensions may serve as underlays for drawings.  This recording technique is particularly appropriate for stained glass windows, tiles and similar flat, asymmetrically ornamented surfaces. 
 

3.5.0  SKETCHING AND MEASURING ROOFS

Figure 3.20:  Measuring a gambrel roof.

Architectural scholars have identified over 30 different roof types, which for purposes of documentation can be divided into flat, gable (including gambrel), hip (including mansard and jerkinhead), composite and dome roofs.

3.5.1  Flat roofs are often hidden behind parapet walls, and therefore are usually depicted in section cuts.  The amount and direction of slope may be determined by measuring down from the parapet tops, then double-checking through use of a string and line level.

3.5.2  Gable or ridged roofs (including gambrel, Figure 3.20) can be measured from datums located on the end walls beneath them.  One method of measuring a gambrel roof is to: 

1)  stretch a tape between the lowest points on the roof;

2)  suspend a plumb bob from the center and intermediate ridges to the tape, and note the distance from 0;

3)  note the distances from ridges to tape, and from the tape ends to the datum.  Be sure to use only the top or the bottom of the tape as the intermediate datum, in order not to introduce the width of the tape as an error factor;

4)  document the roof cladding (slate, shingles etc.) by counting courses and spot checking their width.  Note where courses begin and end in relation to the roof structure and other roof features.

Figure 3.21:  Hip roof with concave chamfering on
the belfry of Kanaana Hou Church,
Kalaupapa National Histoic Park, Hawaii.

Figure 3.22:  Calculation of roof height 
using Pythagorean Theorem.

1)  In Figure 3.22, determine if angle ABC = 90º; 

2)  using the technique for constructing perpendicular lines discussed in  3.1.6 (Figure 3.4), find point E, where DE is perpendicular to AB at E in elevation;

3)  likewise find point G. where DG is perpendicular to BC at G in elevation.

4)  measure DE as a straight line through the air, not on the roof surface;

5)  measure BG, which is equivalent to EF and DH;

6)  according to the Pythagorean Theorem, a²+b²=c², 
or (DH²+(EH)²=(DE)², so (EH)²= (DE)²-(DH)²;

7)  EH is the height of point D above line AB at point E, or in other words, if line AB is perfectly horizontal, the height of the peak above the eave line.

Figure 3.23:  Sine method for 
determining roof hights.

3.5.5  When measuring a mansard or similar roof, the heights and horizontality of all eave and ridge lines will require checking. 

3.5.6  The fundamental difficulty in measuring curved roof structures is ascertaining whether the curves are truly circular, and if not, what their true configurations are.  The curves can be triangulated from surrounding elements.

Figure 3.24:  Triangulating the curve of a dome. 
Jefferson Memorial, Washington, D.C.

1)  To measure a dome, lay a cloth or plastic tape measure along the curve in a plane perpendicular to the plane of the base of the dome, keeping it taut (Figure 3.24);

2)  set up one or two braced stadia rods, camera tripods, ladders or other stable devices, and establish triangulation points A, B, C and D in the same vertical plane as the tape. Triangulate from these points up and down the surface of the dome to a consistent set of points on the tape.  Depending on the dome's curvature, it may become necessary to triangulate from more than one location.  (see 12.0.0  Appendex D:  Measuring Circular Objects and Areas.)

Previous Section | Table of Contents | Next Section