Constructability Considerations in Walking/ Rolling Surfaces

The purpose of this paper is to outline and identify those issues that would present a significant impact or impose some undue hardship on the construction industry. This paper is written from the vantage point of builder or contractor, not necessarily that of a developer. The following topics are addressed in this writing:

1- MATERIALS
2- WORKMANSHIP / TRAINING
3- INDUSTRY STANDARDS, ACCEPTED PRACTICES
4- FLATNESS, LEVELNESS AND MEASUREMENT
5- CODE ENFORCEMENT
6- COST IMPACT OF ADAAG ON CONSTRUCTION

1- MATERIALS

All paving materials perform well in flat or modestly sloped applications. Even in severe running slope conditions the requirement for limited cross slope is not affected by materials. Building materials utilized in walking and rolling surfaces lend themselves effectively to flat surfaces yet are sufficiently versatile to allow rolled or bent planes, and three dimensional slopes. Paving products are by design well suited to meeting ADAAG requirements.

Improvements in materials, production technologies, and installation techniques alleviate impediments to meeting slope/cross slope limitation. Cross slope limitations and surface rollability are generally achievable in commonly-used surfacing materials; however the use of rough, split-face granite units and similar irregular paving materials cannot provide the flatness and smoothness that are necessary on an accessible route. Performance characteristics of modern materials and installation techniques have allowed greater flexibility and creativity than ever before. Surface smoothness, warning zone textures, and technological advancements in manufacturing have given the construction industry a variety of materials that are readily available and relatively simple to install. The variety and relative differences in cost permit a range of products applicable to current standards for access, smoothness, versatility and serviceability. A broad array OF synthetic and polymer-modified cement products have debuted in recent years giving further versatility to the surface paving industry.

Concrete

Concrete is likely the most versatile and cost-efficient building material in use for pavement of walking or rolling surfaces. Though more expensive initially than asphalt, concrete has a significantly greater life expectancy and can be tooled to more precise tolerances. Concrete is widely available and installation techniques are well practiced.

Fiber Reinforced Concrete or Ferrocement

Fiber additives have improved the flexural stress and strain of Portland cement matrixes (1). Fiber additives include mineral (fiberglass), metallic, plastic, and even natural (cellulose) materials; all of these innovations impart relatively higher strength in thinner-than-standard applications. Thinner applications yield versatility in ramping against existing elevations or surfaces.

Improvements in fiber reinforcement technology also allow for thinner applications in geographic regions that previously have been susceptible to temperature extremes.

Color/ Texture additives and stamping techniques

Color additives enhance appearance of “poured in place” concrete and allow for a broad range of surface treatments. They are relatively inexpensive when viewed against the product and installation costs as a whole. Color additives and stamping techniques have little or no effect on the performance of the product in terms of application or durability. These products and techniques can be used for creating warning zones in paved surfaces at impending changes in elevation or when approaching automobile traffic zones, although it has proven difficult to meet technical specifications consistently in these site-formed surfaces. Tolerances for impressed concrete surfaces may need to be different from those proposed for manufactured tiles and pavers, which can achieve more precise control of small dimensions. Surfaces impressed in imitation of brick or stone have a tendency to “pillow”, making it difficult to achieve a flat, smooth finish for optimal rollability.

Asphalt

Innovations in the chemical makeup of asphalt pavement products have led to greater flexibility in the application of this common surfacing material. Recycled rubber from automobile tires added to hot mix asphalt have created a softer yet more durable surface. Other advancements like warm mix technology imported from Europe since 2002 have made asphalt a more environmentally friendly product.

Porous asphalt is an effective tool to storm water management. This product allows permeability of these products to help control surface runoff. Porous asphalt as well as standard mixes are capable of meeting current ADAAG standards for smoothness, flatness and slope ratio, although it is more difficult to achieve planar surfaces.

Surface smoothness characteristics, while easily achieved at installation, can deteriorate relatively quickly and be costly to maintain. Some requirement for maintenance is dictated by most local and national building codes, although enforcement remains a problem in many urban areas.

Pre-cast Pavers

Available in a variety of sizes, shapes and colors, pre-cast pavers are widely used by both developers and municipalities to allow greater flexibility in design and performance as well as efficient maintenance and repair. Manufacturers have been quick to produce a variety of textured warning products for the visually impaired that remain architecturally pleasing and standard in their installation and configuration. The modular nature of unitized pavers as well as loose laid installation enable cost effective removal and replacement, but “lippage” at edge and joint conditions, or joints that are chamfered or raked, can produce undesirable vibration for which no limits have yet been established, although some research has been completed. Some limitations in surface texture are necessary to control vibration in sidewalk surfaces.

Natural Stone

Dramatic improvements in stone cutting equipment over the past decade have only improved the surfaces available in natural stone products. Faster saws, water-jet stone cutting technology and improvement in manufacturing of hardened carbon steels all contribute to greater versatility in granites, limestone and other natural stones. Slope and smoothness characteristics are very satisfactory with these materials, provided that wise initial choices are made. It is impossible to achieve near-planar conditions with split-face granite block, cobbles, and similar stone units. Standards are needed so that better design and field choices can be made. At least one granite manufacturer has been able to provide detectable warnings in granite slab curb ramps – there’s a very nice installation at the White House. Again, tolerances for this material may need to be different than those for detectable warnings manufactured as tiles and pavers, since they are produced by removing material rather than forming it.

2-WORKMANSHIP / TRAINING

One of the obstacles to achieving satisfactory walking/ rolling surface installations is the continuing decline of a skilled workforce. Ignorance of ADAAG standards is also a contributing factor. The increased speed of construction project scheduling has created a crisis in craftsmanship, training, and development. Relatively low unemployment rates for the past quarter of a century have reduced the number of American born young men and women pursuing a career in the construction industries. Since reaching a post war high of 9.7 % in 1982 and 1983 national unemployment has averaged less than 5.5%. (Often dipping below 4.5 %) (2). There are more employment options available to a better educated workforce than in decades past. This factor, lower cost immigrant labor and natural attrition have reduced the number of skilled journeymen in all construction trades. Apprenticeship training has also declined significantly as the percentage of the non-union workforce versus Union trained apprentices in the trowel trades continues to increase. With the exception of some trade unions there are few agencies in the construction industry to regulate workforce training. Though many companies have established training and recruitment programs, the shortage of experienced, skilled workers could be the single biggest problem facing the construction industry today. This skilled labor crisis extends to project management and supervision as well.

3- INDUSTRY STANDARDS, ACCEPTED PRACTICES

Industry Standards

Defined as commonly accepted practice within a specific trade or discipline. These accepted practices vary from region to region across the country and are therefore the subject of some debate. ACI and CSI specifications remain the best measure of any “Industry Standards” and should include the kinds of surfaces measures we need to plan for ADA compliance. Many trade and product associations have developed written standards to apply where ACI/ CSI leave off. The tolerances outlined in these publications provide the best trade practices available. Unfortunately there is no arbiter to settle the disputes that often arise over what is or is not an accepted industry practice. Although no publication or specification will ever cover all practical situations, it would be desirable to expand industry specifications to include specific tolerances by material type and application.

4- FLATNESS, LEVELNESS AND MEASUREMENT

DEFINITIONS

Rolling or bending of surfaces Defined as the deviation from a true flat plane when applied three dimensionally. For example: a sidewalk originating level at a sill or threshold entering a building situated on a sloping street will have three different reference points with which to align: A level flat line between each of the points where two corners meet the entrance(s), and one each where the two opposite corners meet the sloping curb line. If the slope ratio is 1:48 (the optimal condition) at the higher end of the slope, where the sidewalk meets the curb, and the street has a slope ratio of 1:48 (quite minimal in many regions), then the slope ratio at the low end of the sidewalk where it meets the curb will be 2:48 or 1:24. The surface has to bend from a true flat plane to meet these points. At which point should the cross slope be measured? Contractors need more definition of measurement protocols.

What happens when meeting a cross slope requirement becomes the responsibility of a builder or developer and no longer falls into the once-usual practice of “acceptable given the circumstances”? Rolling of surfaces can be an effective way to maintain a minimal cross slope against an overall slope that exceeds the optimal (1:48). For example: A sidewalk is 24 feet (wide) from the entrance point of a building to the face of the curb. If the overall slope from sill to top of curb is 6”, then the natural slope of that sidewalk would meet the 2% slope requirement. If, however, the overall slope is 18”, then a portion of the walkway -- say 8’(wide) -- could be installed at the preferred 1:48 slope ratio and the remaining 16 ft could be pitched at a ratio of 1:12 (1 inch per foot), assuming that a complying route to the entrance is also provided. Perhaps a standard application can be devised for locating the flatter portion either close to the building or close to the curb. In this manner, some degree of reliability could be established. Construction this type of rolled surface is not difficult, but it seems that draft guidelines expect more planar than the warped and blended surfaces we are used to.

Existing surfaces and points of connections

Defined here as those existing physical limitations that would be considered outside of the work area but impart limiting factors or conditions that will remain as is.

Building entrances, driveway entrances, tops of curbs and architectural features as well as existing natural barriers often pose the greatest challenges to slope and cross slope requirements. Creative incorporation of special features such as fountains, planting areas, and security barricades can be helpful in softening extreme slope conditions where existing conditions preclude compliance with the new construction standards in ADAAG.

How flat is flat?

New technology and standards developed in the 1980’s have created some controversy in the architectural and building communities. The creation of the FF and FL system in response to requirements for superflat floor surfaces required in some industrial applications has opened virtually a whole new concept in measurement of “flat” surfaces.

What are FF and FL?

The following excerpt from The Ceramic Tile Institute of America (3) provides an understandable description of this complex system.

Flatness (FF) and Levelness (FL) F-Numbers

F-Numbers are used to specify flatness and levelness in floors. FF refers to flatness (bumpiness or waviness) while FL refers to levelness (tilt). They are always given in the order FF / FL. The numbers are linear with the higher the number, the flatter or more level the floor. A floor with a specified flatness of FF30 is twice as flat as a floor of FF15. Typically, F-numbers range from 12 to 45. The flatness number controls surface bumpiness by limiting the number of successive 1-foot slope changes measured along sample measurement lines. The levelness number controls conformance to design grade by limiting departures from design grade over distances of 10-ft. The difference between flatness and levelness is shown below in Figure 1i[i].

Figure 1. Flatness and Levelness of Floors.
(3)

How flat does a walking/rolling surface have to be for comfortable, least-effort passage? FF and FL are measured via sophisticated electronic equipment that detects deviation from a true flat surface as small as ten thousandths of an inch. The standard “straightedge” method of measuring slope and cross slope may seem to be a satisfactory way to measure tolerances of walking/rolling surfaces, but how many discrepancies are permitted in that length? And where is it measured? And with what equipment and degree of precision? We need more specific measures to ensure that actual construction complies. Furthermore, vibration or smoothness would not be effectively measured under a straight edge as illustrated in Fig 1 above. The FF method would be a better indicator of smoothness in this instance. However, current specifications require measurement of FF within 72 hrs of placement (4). Curl, heave and settlement would have dramatic effects on such precise measurement. Is such precision really of value in sidewalk pavement? Most unit paver products would not even meet the criteria for testing FF and FL.

5-CODE ENFORCEMENT

Building officials have been reluctant to allow deviation from many state accessibility code requirements due to the precise language and dimensions in the ADA. Fear of litigation has led many municipalities to enforce a hard line attitude with their personnel when it comes to field judgments in the face of absolutes. This has led to significant problems where no tolerance is defined in the industry documents referenced in ADAAG.

This is not to say that all building code enforcement officials are producing tape- measured inspections at every turn. Many inspectors have in fact applied some degree of common sense when the new construction standard is unachievable, but the spirit of the law has been respected. Those individuals making these judgments must do so at their own peril.

While some exclusion or variance from building code requirements is available to planners, designers, and contractors in most municipalities during the review process, some conditions cannot be foreseen. Seldom is there a process for review available to the contractor or some written latitude in judgment afforded to the building code official in the field.

BOCA and IBC both grant some latitude to “the jurisdiction having authority”. And the alterations requirements in ADAAG allow some flexibility in meeting new construction standards “to the maximum extent feasible”. But industry guidance would be more appropriate – if only it existed for walking and rolling surfaces with respect to the qualities we need to provide.

6- COSTS

The cost impact on the construction industry by the imposition of accessibility, slope and cross slope guidelines could be significant if an inflexible maximum, without allowances for appropriate tolerances, is applied. The contractor’s liability should be limited to the quality of the product and its installation according to defined industry practices. Right now, it is all guesswork. Installers cannot be liable for failures in design to meet accessibility requirements. Contractors have an obligation and responsibility to meet the requirements per the specifications of design documents only.

The costs associated with achieving current ADAAG standards should not be considered a significant factor where conditions do not preclude compliance. Pavements are desirable in most applications for their appearance, ease in maintenance, and long-term durability. Paving products can be manipulated to produce a limitless variety of curbs, slopes, and shapes that are beneficial to delineation or separation of pedestrian passage ways, changes in elevation, or transition to automotive areas. While some additional costs will often be incurred for more refined finishing, more detailed planning and engineering, and better control of layout and formwork, that fact is not an insurmountable impediment for developers, contractors or builders. The increase in cost to meet slope and access requirements is minimal when weighed against the total value of a construction project, and benefit to the public.

REFERENCES

1- ACI International®, PO Box 9094, Farmington Hills, MI 48333 ~ (248) 848-3700.
http://www.aci-int.org
• ACI 117-90, “Standard Tolerances for Concrete Construction and Materials”
• ACI 117R-90, Commentary on Standard Specifications for Tolerances for Concrete Construction and Materials”.
• ACI 302.1-96, “Guide for Concrete Floor and Slab Construction”.

2- Bureau of Labor statistics http://www.bls.gov

3- CTIOA FIELD REPORT 2002-7-02
SUBJECT: Concrete Tolerance
By: C.V.Yland, Ph.D

4- ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken,
Pennsylvania, USA 19428-2959. http://www.astm.org
• ASTM E1155, “Standard Test Method for Determining Floor Flatness and Floor Levelness Numbers”.
• ASTM E1486-96, “Standard Test Method for Determining Floor Tolerances Using Waviness, Wheel Path, and Levelness Criteria”