Roofing Construction & Estimating Overview

Covers sheathing and underlayment techniques, as well as secrets for installing leakproof valleys.

Many estimating tips help you minimize waste, as well as insure a profit on every job. Troubleshooting techniques help you identify the true source of most leaks. Over 300 large, clear illustrations help you find the answer to just about all your roofing questions.

Back Cover

by Daniel Atcheson

If you estimate, install or repair roofing in residential or commercial structures, this book will show you the methods and materials the real pros use - the tricks, shortcuts, and estimating formulas that will get you the job, keep your labor and material costs on target, and bring you a healthy profit. In the competitive roofing business, it's not enough to just measure the roof and add 10 percent for waste. The estimating system you'll find here will help you make a quick, accurate take-off with a realistic waste factor.

To make money in this business, you've got to provide a roof that's attractive and durable enough to last for years, with a minimum of maintenance and repair problems. Callbacks are hard on your profit margin and on your reputation. With the help of this book, you'll know which roofing methods and materials will do the job best, and provide the best value.

You'll learn how to estimate and install:

Roof sheathing
Underlayment
Asphalt shingles
Wood shingles & shakes
Mineral-surfaced roll roofing
Tile & slate roofing
Metal roofing & siding
Built-up & elastomeric roofing

Hundreds of large, clear, illustrations and easy-to-understand tables, charts, calculations, examples, and step-by-step installation and repair procedures will help you find the answers to just about all your roofing questions.

The Author

Dan Atcheson, the son of a Texas architect, began working in construction in his teens, as a draftsman and as an apprentice in plumbing, electrical and carpentry. During his career, he has worked in all areas of construction, from earthwork, through framing, to roofing.

He added estimating to his skills in the 70’s, then started teaching construction cost estimating at Texas Tech University. Finally, he began touring the country, giving estimating seminars and speaking at estimating conventions. He now devotes his time to his construction consulting business, and to writing for the construction industry.

His technical papers on construction and estimating have been published in numerous trade magazines, and he has published three other books: Estimating Earthwork Quantities, Earthmoving Equipment Production Rates & Costs, and Estimating Framing Quantities.

Roofing Construction & Estimating Contents

Level Roofs, 7
     Sloped Roofs, 10
     How to Measure Roof Slope, 12
     Perimeter of a Sloped Roof, 17
     Net Versus Gross Roof Area, 17
     Calculating Total Net Roof Area, 18
     Roof Overhangs, Hips and Valleys, 21
     Length of Ridge (Hip Roofs), 22

2   Roof Sheathing, Decking and Loading, 23
     Check the Framing, 23
     Solid Roof Sheathing, 24
     Spaced Board Sheathing, 29
     Roof Decking, 32
     Loading the Roof, 32
     Estimating Roof Sheathing, 34

3 Underlayment on Sloping Roofs, 35
     Saturated Felt Underlayment, 36
     Saturated Fiberglass Underlayment, 36
     Underlayment Requirements, 37
     Drip Edge, 40
     Installing Underlayment, 43
     Estimating Underlayment Quantities, 49
     Interlayment (Lacing), 57
     Eaves Flashing (Ice Shield or Water Shield), 61
     Valley Flashing, 64

4   Asphalt Shingles, 73
     UL Ratings for Shingles, 75
     Deck Requirements, 76
     Asphalt Strip Shingles, 78
     Flashing at Chimneys and Other Vertical Structures, 96
     Fasteners, 106
     Number of Shingles Required per Square, 108
     Number of Shingle Courses, 109
     Estimating Asphalt Strip Shingle Quantities, 113
     Ridge and Hip Units, 114
     Estimating Ribbon-Course Quantities, 124
     Individual Shingles, 127
     Estimating Asphalt Shingle Roofing Costs, 130

5   Mineral Surfaced Roll Roofing, 131
     Installing Mineral-Surfaced Roll Roofing, 133
     Valley Flashing, 134
     Estimating Mineral-Surfaced Roll Roofing, 144
     Waste from Non-conforming Roof Layout, 146
     Estimating Mineral-Surfaced Roll Roofing Costs, 157

6   Wood Shingles and Shakes, 159
     Installing Wood Shingles and Shakes, 164
     Covering Capacity of Shakes, 174
     Covering Capacity of Wood Shingles, 174
     Estimating Wood Shingle and Shake Quantities, 176
     Staggered Patterns, 185
     Sidewall Shakes and Wood Shingles, 185
     Roof Junctures, 192
     Estimating Wood Shingle Roofing Costs, 196

7   Tile Roofing, 197
     Underlayment Under Tile Roof Coverings, 199
     Installing Roof Tiles, 200
     The Starter Course, 202
     Fastening Roofing Tiles, 204
     Flashing at Vertical Walls, 217
     Replacing Broken Tiles, 224
     Estimating Tile Quantities, 225
     Estimating Total Tile Roofing Costs, 229

8   Slate Roofing, 231
     Slate Size, Color and Texture, 231
     Felt Underlayment, 234
     Installation on a Sloping Roof, 234
     Fasteners, 244
     Flashing, 245
     Estimating Slate Quantities, 249
     Estimating Slate Roofing Costs, 254

9   Metal Roofing and Siding, 255
     Modern Metal Panel Systems, 256
     Installing Metal Roofing Panels, 257
     Job-Fabricated Seams, 263
     Estimating Metal Roofing and Siding, 269
     Steel Roofing and Siding Quantities, 270
     Ribbed Metal Panel Quantities, 271
     Miscellaneous Metal Roofing Quantities, 275

10 Built Up Roofing, 291
     Roof Slopes, 292
     Substrate Design, 292
     Back Nailing, 297
     Base Sheets (Vapor Retarders), 298
     Roofing Membranes, 300
     Hot Bitumens, 303
     Cold-applied Bitumens, 305
     Surface Aggregate, 306
     Smooth-surface Roofing, 308
     Cap Sheets, 308
     Aluminum Roof Coatings, 309
     Phasing, 310
     Cant Strips, 311
     Temporary Roofs, 313
     Roof Traffic Pads, 314
     Water-retaining Roofs, 315
     Flashing on Flat Roofs, 315
     Roof Expansion Joints, 319
     Estimating BUR Systems, 323
     Testing BUR Systems, 327
     Built-up Roofing Warranties, 327
     Built-up Roofing Repairs and Re-roofing, 329

11 Elastomeric Roofing, 333
     The Advantages of Elastomeric Systems, 334
     Liquid-applied Elastomers, 335
     Single-Ply Roofing Systems, 338
     EPDM Elastomeric Systems, 337
     CPE Elastomeric Roofing, 342
     CSPE Elastomeric Roofing, 342
     Hypalon Roofing, 343
     PVC Elastomeric Roofing, 343
     Composite Roofing Systems, 343
     Flashings for Elastomeric Roofs, 344
     Estimating Elastomeric Roofing, 345

12 Insulation, Vapor Retarders and Waterproofing, 347
     The Benefits of Insulation, 347
     Insulation Materials, 348
     Reducing Heat Loss, 355
     Insulation Values, 361
     Vapor Barriers, 362
     Weatherproofing Existing Homes, 364
     Caulking and Sealants, 364
     Wall Flashing, 370
     Waterproofing, 37l
     Dampproofing, 377

13 Roofing Repair and Maintenance, 381
     Finding the Source of Leaks, 381
     Repairing Leaks, 384
     Roof Maintenance, 386
     Assessing Hail Damage, 388
     Roofing Demolition, 390
     Re-Roofing, 394
     Estimating Re-Roofing Quantities, 401
     Attic Ventilation, 402
     Gutters and Downspouts, 407

14 Estimating (and Maximizing) Production Rates, 411
     Labor Unit Prices, 411
     Estimating with Published Prices, 415
     Roofing Labor Tips, 420

Appendix A Roof Slope Factors, 428

Appendix B Valley Length Factors, 429

Appendix C Equations Used in This Book, 430

Index, 436

Roofing Construction & Estimating Introduction

Measuring and Calculating Roofs

If you're like some roofing contractors, you estimate roofing quantities by calculating the area of a roof, then adding 10 percent for waste. That might be OK in a fat building market, but in a tight market you'll need a sharper pencil to compete successfully for the good jobs, and then make money on them. In this book, I'm going to show you how to make a quick and accurate takeoff for any kind of roof.

You'll also learn the latest and most acceptable roofing methods in an industry where installation practices are closely related to warranties. That's because material warranties may be invalid if you don't follow the manufacturer's recommendations for installation. Look here for general guidelines, but always follow the manufacturer's instructions to the letter.

New products come on the market every day to solve the complex roof covering requirements presented by modern building technology. Your job is to know as much as you can about those products. You also have to know how to install them so the job passes inspection and presents no future repair and maintenance problems. Callbacks are hard on your profit margin and they don't do your reputation any good either. Know as much as you can about your roofing business, and you'll avoid them.

This book is more than an estimating book for roofing contractors. It develops a system, beginning with Chapter 1, for all types of roofing materials and installation methods. We'll cover the entire roofing trade, including how to manage your crews and keep them safe. So let's get started.

Before you can bid any job, you have to figure your costs. And before you can figure the costs, you have to know the size of the job. So you have to do two things: First, measure the roof and calculate the total area. Then find the lengths of the eaves, gables (or rakes), ridges, hips and valleys.

When you construct a roof on a new building, you can get these measurements from the plans. On repair or replacement jobs, you'll probably have to take your pencil, clipboard and tape measure, haul out your ladder, climb onto the roof, and start measuring.

To avoid mistakes, or a second trip to the job site, develop a system for taking measurements. Use a 100-foot flexible tape which has a 1/2-inch grout hook at the "stupid" end of the tape. Flexible tapes are made of metal, or fiberglass-reinforced nylon fabric. Find a tape that's marked with highlights at 5-inch intervals to match the exposure of most composition shingles.

There is no cardinal rule for the sequence you use to measure a roof, as long as you don't miss anything. Here's a system that works for me:

Start by measuring the length of the eaves. On a gable roof, you only have to measure in one direction. On a hip roof, you'll have to measure the eaves in two directions.

Next, measure the width of the roof. On a gable roof, hook the tape over one of the eaves, and run it over the ridge to the opposite eave. On a hip roof, measure the width the same way. To measure the length, hook the tape to the eaves at the ridge rafter (look ahead to Figure 1-16 on page 13 for an illustration of the parts of a roof), run the tape the length of the ridge and down the opposite ridge rafter. Measure the ridge at the same time.

Now, measure the hips and valleys by hooking the tape to a building comer and running the tape to the ridge. You use these measurements to calculate material requirements such as valley flashing and hip-covering material.

When you measure, some dimensions need to be more accurate than others. For instance, you could miss the length of ridge, hip or valley by a foot or more, and the error wouldn't affect your total bid price too much. But don't make a mistake in the length and width, because that error could be substantial. For example, assume you measure a roof at 100 feet by 200 feet, while the actual measurements are 100'6" by 200'6". The difference between the two measurements is 150 square feet, or 11/2 squares of material.

Always make a sketch of the roof layout, including dimensions, roof slopes, location of penetrations and any unusual circumstances such as rotten deck areas, ventilation problems, or overhanging tree branches or other obstructions.

Once you have the measurements, you'll use them to calculate areas, slopes, angles, and allowance factors. Lets begin with an easy example.

Level Roofs

The dimensions on the plans give you the actual measurements for a level roof. To get the area of a rectangular roof, multiply its length by its width.

Area of a level rectangular roof = L x W

where L is the length and W is the width.

Of course, not every roof you work on will be a single rectangle. You may need to figure the area of a roof like the one in Figure 1-1. There are two ways to calculate this area:

The positive method
The negative method

In the positive method, you divide the roof into rectangular areas, then add the parts to get the total area. See Figure 1-2.

With the negative method, you extend the roof lines to form a single rectangle. Calculate the area of this rectangle, and subtract the areas of the rectangular spaces which lie outside the actual roof. Figure 1-3 illustrates this.

Figure 1-1 & Figure 1-2

Left: Figure 1-1 Roof Plan of Level Roof
Right: Figure 1-2 The Positive Method

Example 1-1: The Positive Method

Divide the roof into rectangles as shown in Figure 1-2. Calculate the area of each rectangle, then add them together:

Area A = 20 feet by 60 feet, or 1,200 square feet
Area B = 20 feet by 40 feet, or 800 square feet
Area C = 20 feet by 20 feet, or 400 square feet

Then, the total area =

1,200 SF + 800 SF + 400 SF, or 2,400 SF

Figure 1-3

Figure 1-3 The Negative Method

Example 1-2: The Negative Method

Extend the roof lines to form one rectangle, as in Figure 1-3. Calculate the total area of that rectangle, then subtract the areas of any rectangles which aren't in the actual roof:

Extended rectangle = 60' x 60' = 3,600 SF

Area A = 40 feet by 20 feet, or 800 square feet
Area B = 20 feet by 20 feet, or 400 square feet

Total area outside the roof layout is 800 SF + 400 SF, or 1,200 SF. Subtract that from the extended area to get the total area:

3,600 SF - 1,200 SF = 2,400 SF

You get the same answer both ways. So you might as well use the easiest method - the one that requires the fewest calculations. For example, in Figure 1-4 you'd have to calculate three areas, then add them together. But in Figure 1-5 you only have to calculate two areas, and then subtract one from the other.

Roofing Construction & Estimating