A Full Guide to DIY Roof Installation

Introduction

Re-roofing with asphalt shingles is a straightforward enough job, but it isn't one without potential hazards, and you can take that from someone who has fallen off a roof. Luckily, my injuries were minor — mostly bruises — but it could have been worse. As a result, I run through a checklist of conditions before I'll consider doing roofing work:

The pitch has to be low enough to walk on safely. Professional roofers consider any pitch lower than 8/12 walkable (8" of vertical rise per foot of horizontal distance), but my cutoff is 6/12. Anything above that I consider a job for pros with the right safety equipment.
A hoist is available to lift shingles onto the roof. Just thinking about carrying multiple bundles, each weighing from 50 to 80 pounds, up a ladder and dragging them into position makes my back ache. Not to mention that manually bringing shingles onto the roof presents another opportunity for a fall.
The weather is dry and not too windy or hot (ideal temperatures are between 50 and 80 degrees). A wet roof is a slippery roof, the hot sun is hazardous — to you and the roofing material — and working in windy conditions is just asking for an accident. Needless to say, roofing when it's cold enough for ice is also out of the question.
The terrain around the foundation is stable and flat enough to support a ladder and isn't covered with shrubs and other vegetation that prevent easy access.

When all these conditions are met, replacing the roof on your house is a viable DIY project, and you can save a bundle by hiring friends or local workers to help you instead of a roofing company. Be advised that you'll probably need a building permit before starting. You'll also need to conform to local regulations, which vary by region and climactic zone.

Safety Precautions

Besides the conditions I've already mentioned, there are a number of other important safety considerations for DIY roofers:

Be wary of high roofs. The roof I fell off was a little more than 10 feet above the ground, and if it had been much higher, I could have been more seriously injured. If your roof is high enough to give you vertigo, consider hiring pros for the job, so you can live to enjoy your new roof.
Purchase safety equipment. A fall protection kit including a harness, rope and hook only costs about $100.
Wear rubber-soled shoes at all times, and get some knee pads. Your knees will thank you.
Provide hard hats for workers on the ground to protect them from falling debris. Always look and call out before throwing anything off the roof.
Position ropes and extension cords so they're not underfoot.
Make sure your ladder can support your weight plus the weight of a bundle of shingles in case you have to carry one up.
Extend the ladder at least three feet above the roofline and tie it to the eave, so it won't move. Never step on any rung that extends above the roof.
Set up scaffolding to install the drip edge and first few courses of shingles.

The Basic Procedure

This article provides a complete step-by-step procedure for installing new roofing. Here are the basics in a nutshell:

Tear off the old roofing. Rent a dumpster to make life easier and avoid having to make several trips to the dump in a truck.
Replace damaged or rotted decking.
Install any new vents you might need. If your attic doesn't have enough ventilation, this is a good time to install new roof vents, and if you've always wanted a skylight, now's your chance.
Lay underlayment. Codes in regions with extreme weather call for self-adhesive waterproof underlayment, also known as an "ice barrier." Otherwise, a single layer of 15-lb. felt underlayment (tar paper) is usually sufficient unless local codes call for 30-lb., which is heavier and more water-resistant.
Install flashing in valleys and around dormers.
Nail in the shingles.
Apply roofing sealant where needed.

Now that you know what's involved, let's get into the details.