How a re-roof works, step by step

A re-roof looks chaotic from the driveway, but it follows a fixed order. Each layer goes on top of the one below so water always sheds outward. Knowing the sequence helps you read a quote, ask good questions and spot a skipped step.

The steps below follow GAF's installation instructions, the International Residential Code (IRC) and a sample Colorado permit handout. Your city or county may add or drop requirements, so check Colorado climate and codes and what a roof costs for local differences.

How long it takes

GAF says an asphalt re-roof on an average home can often be finished in one to two days. Steep roofs (over 8:12), complex shapes, rotted decking, ventilation upgrades and weather add time. Rotted decking alone can add a few hours to a day. Tile, metal and other materials have their own timelines.

The steps, in order

1. Permit

Most Colorado jurisdictions require a permit for a re-roof. Firestone, for example, requires one for repairs over 100 square feet. Larimer County asks the owner or contractor to sign a form recording fasteners, ice barrier, underlayment and shingle wind rating. Your contractor usually pulls the permit, and the contract should say who does.

2. Delivery and dumpster

Materials and a dumpster arrive, often a day ahead. The bin usually sits on the driveway, often with plywood underneath to protect the concrete. Shingle pallets go on a hard surface.

3. Protecting the property

A careful crew photographs existing conditions first. They tarp gardens and beds below the eaves and cover pools and play areas.

4. Tear-off to the deck

The crew strips the old roof down to the wood. GAF recommends a full tear-off and says code requires it when two or more layers exist, the old roof is wood shake, slate or tile, or it's wet or deteriorated. Tear-off is also the only way to inspect the deck.

5. Deck inspection and repairs

The crew checks the decking, the plywood or OSB the roof nails into. GAF's Timberline instructions call for at least 3/8 inch plywood or OSB. Older homes often have spaced boards left from a wood shake roof. GAF advises against shingling over those, so a solid deck goes on first. Rotted or soft sheets get replaced, usually billed per sheet.

6. Drip edge

Metal edge goes along the eaves and rakes so water drops into the gutter instead of running behind it. Firestone requires it on all edges with 2 inch laps. At the eaves, the ice barrier goes over the drip edge. At the rakes, it goes under.

7. Ice barrier

An ice barrier is a self-adhering membrane that seals around nails. Under IRC R905.1.2, where the local jurisdiction requires it, it runs from the eave to at least 24 inches inside the exterior wall line. GAF's instructions match and add at least 5 inches up walls and chimneys, plus a leak barrier down the center of valleys.

8. Underlayment

The rest of the deck gets synthetic underlayment. GAF calls for one layer on slopes of 4:12 or steeper, and two layers on slopes from 2:12 to just under 4:12. Firestone prohibits shingles below 2:12 entirely.

9. Starter strip

Starter shingles with a sealant strip go along the eaves and rakes. They give the first full course something to seal to, which helps the edge resist wind.

10. Shingles and nailing

Crews snap chalk lines and work up from the eave. GAF's standard pattern is four nails per shingle in the marked nailing zone, and six in high-wind areas or where code requires. Nails must be driven flush. Overdriven nails cut the shingle, and high nails keep it from sealing.

11. Valleys

Valleys carry water from two slopes, so they get extra care. They can be open (metal over a leak barrier), closed-cut (one side runs through, the other is trimmed back) or woven. In every method, nails stay 6 inches from the valley center.

12. Flashing

Step flashing goes in one piece per course where the roof meets a wall, nailed to the deck and not the wall. Chimneys get base flashing with counterflashing over it. Kickout flashing under IRC R903.2.1 turns water away where an eave meets a sidewall. Ask whether old flashing is being reused or replaced.

13. Pipe boots and penetrations

Plumbing vents, exhaust fans and other penetrations get new boots or flashings. Firestone requires plumbing vents to stick up at least 6 inches above expected snow, or 12 inches above the roof.

14. Ventilation

The IRC sets a minimum of 1 square foot of net free vent area per 150 square feet of attic (1/150). It drops to 1/300 if 40 to 50 percent of the venting is high, within 3 feet of the ridge, and the rest is at the eaves, or in some cold climate zones with a vapor retarder. Owens Corning recommends balanced intake and exhaust, with intake at least equal to exhaust. A re-roof is the cheapest time to fix ventilation.

15. Ridge vent and ridge cap

Ridge vent is the exhaust, and soffit vents are the intake. Hip and ridge cap shingles finish the top. Manufacturers require their own ridge caps for system warranties; see who makes roofing.

16. Cleanup

Crews haul debris and run magnetic sweepers over the lawn and driveway for stray nails, ideally every day. Walk the yard yourself before kids and pets go back out.

17. Final inspection

The building department does a final inspection. Some jurisdictions, like Firestone, also require a mid-roof inspection, but that varies; Lakewood, for example, doesn't require one for asphalt. The contractor provides a safe ladder for the inspector. Keep a copy of the permit and the passed inspection with your roof records.

Solar panels

If you have rooftop solar, the panels and racking usually have to come off before tear-off and go back on afterward. That's typically a separate job by a solar installer. Book it early, ask who shuts down and restores the system, where panels are stored, and how the new roof penetrations are flashed. Check whether your solar warranty requires a specific installer.

Getting your home ready

These are practical rules of thumb, not code requirements.

• Move cars out of the garage and driveway the night before. Leave room for the dumpster and delivery truck.
• Tear-off shakes the whole house. Take pictures and fragile items off walls and shelves.
• Dust and old granules can fall through gaps in the attic decking. Cover or move anything stored in the attic.
• Move patio furniture, grills, planters and toys away from the walls.
• Keep pets inside in a quiet room, or somewhere else for the day. The noise is loud and constant.
• Tell neighbors, especially if the dumpster or trucks will be near their property.
• Make sure the crew can reach an outdoor outlet, and unlock side gates.
• Be reachable for decking decisions or surprises once the old roof is off.

After the crew leaves

Walk the job with the contractor. Look for leftover nails, damaged gutters, and any changes to landscaping. Ask for the warranty registration, the permit closeout and a final invoice. If insurance is paying, that invoice is what you send to recover any held-back depreciation; see the claim FAQ. Before you sign anything, our hiring guide covers what Colorado law requires in the contract.

Common questions

How long does a roof replacement take?

GAF says an asphalt re-roof on an average home can often be done in one to two days. Steep pitch, a complex roof, decking replacement, ventilation upgrades and weather can stretch that.

Do I need to be home during a re-roof?

Usually not the whole time, but be reachable. The crew may need a decision about rotted decking, and you'll want to walk the job with the contractor at the end.

Can new shingles go over my old roof?

Sometimes, but GAF recommends a full tear-off, and codes require one when two or more layers already exist or the old roof is wood shake, slate or tile. Some Colorado jurisdictions require tear-off to the deck. Check your local rules on Colorado climate and codes.

Will they replace my decking?

Only the sheets that are soft, rotted or delaminated, which nobody can see until the old roof is off. A good quote lists the per-sheet price up front. See costs.

What happens to my solar panels during a re-roof?

The panels usually have to come off and go back on, which is typically done by a solar installer, not the roofer. Schedule it before the roof job and confirm who handles electrical shutoff, storage and any warranty.