What you need to do before you start shingling
Before you lay a single shingle, you need a sound roof deck — the plywood or boards underneath — and proper underlayment. Walk the roof in daylight and check for soft spots, rot, or missing sections of deck. If the deck moves when you step on it or feels spongy, those areas need repair or replacement before shingles go down. Any water damage to the wood underneath will cause shingles to fail early, no matter how well you install them.
Underlayment is a water barrier that sits between the deck and shingles. Most building codes now require synthetic underlayment or roofing felt (also called tar paper). Synthetic lasts longer and handles foot traffic better. Felt is cheaper but tears more easily. Unroll it horizontally across the roof, starting at the eaves and working upward, overlapping each row by at least 2 inches. Nail or staple it down every 12 to 18 inches so it stays flat while you work.
You will also need drip edge — a metal strip that channels water away from the fascia board. Install it along the eaves before underlayment, then along the gable ends after underlayment is down. This detail matters: water that gets behind the fascia rots the wood frame.
Key Takeaways
- The roof deck must be solid and dry; soft or rotted wood will cause shingles to fail and must be replaced before you start.
- Underlayment and drip edge are not optional — they are required by building code and prevent water from reaching the wood underneath.
- Shingles are nailed in a specific pattern with a specific number of nails per shingle, and placement matters for wind resistance and water shedding.
- Starter shingles at the eaves and ridge caps at the peak are separate pieces that seal the edges where water and wind pressure are highest.
- Roof pitch, weather conditions, and local building codes all affect how you install shingles, so check your local requirements before you begin.
Installing starter shingles at the eaves
Starter shingles are cut or full shingles installed upside down along the eaves, before the first course of regular shingles. They fill the gaps between the tabs of the first course and create a seal that keeps water from being driven under the shingles by wind. You can buy pre-made starter shingles or cut the top 6 inches off regular shingles and flip them.
Snap a chalk line 11 inches up from the eaves (the width of one shingle minus the exposed tab). Align the starter shingles with this line, nailing them down with 4 nails per shingle, placed 1 inch from the top edge and spaced about 12 inches apart. The nails should go through the nailing strip — the area where the adhesive is — not through the tabs. If you nail through the tabs, you will create a leak point.
Overlap each starter shingle by 1/2 inch as you work across the roof. At the gable ends, cut shingles to fit and nail them down the same way. Once the starter course is complete, you are ready for the first course of regular shingles.
Laying the first course and establishing the pattern
The first course of shingles sits on top of the starter course. Most three-tab shingles (the most common type) are 36 inches wide and have two tabs separated by slots. The pattern you establish in the first course determines how the rest of the roof looks and how well water sheds.
Start at one gable end with a full shingle, aligned with the edge of the roof. Nail it down with 4 nails: one above each tab and one above each slot, about 1 inch below the top edge of the shingle. The nails should be driven straight in, not at an angle, and seated flush with the shingle surface — not so deep that you crush the asphalt.
Lay the next shingle so it overlaps the first by 1/2 inch. Continue across the roof until you reach the other gable end. Cut the last shingle to fit. Once the first course is complete, you will offset the second course so the slots do not line up vertically — this is called staggering and it prevents water from running straight down through the slots.
Staggering courses and maintaining the offset pattern
Staggering is what makes a roof watertight and long-lasting. If the slots in one course line up with the slots in the course above, water can run straight down through them. The standard offset is 6 inches — each course is shifted 6 inches horizontally from the one below.
To stagger, start the second course with a half shingle (18 inches wide). Nail it down the same way as a full shingle: 4 nails, 1 inch below the top edge, through the nailing strip. Then lay full shingles across the roof, overlapping by 1/2 inch. The third course starts with a full shingle again, the fourth with a half shingle, and so on.
Some roofers use a different offset pattern — 3 inches or 4.5 inches — depending on the shingle type and local practice. Check the manufacturer's instructions for the shingles you are using. The key is consistency: every course must follow the same offset, or the pattern will look wrong and water will not shed properly.
Nailing shingles correctly for wind resistance
Nailing is the most common mistake in roof shingling. Too few nails and the shingles blow off in wind. Too many nails and you crush the asphalt, creating leak points. The standard is 4 nails per three-tab shingle, placed in a specific location.
Each nail goes 1 inch below the top edge of the shingle, in the nailing strip (the area where the adhesive is). For a three-tab shingle, that means one nail above each tab and one above each slot — four nails total, spaced roughly 12 inches apart. Drive the nail straight in, not at an angle. The head should sit flush with the shingle surface, not crushing the asphalt or leaving a gap.
If you are using architectural shingles (thicker, with a textured appearance), the nailing pattern may be different — some require 6 nails per shingle. Check the manufacturer's instructions. Using the wrong number of nails voids the warranty and leaves the roof vulnerable to wind damage.
Installing ridge caps and finishing the peak
Ridge caps are shingles installed along the peak of the roof, perpendicular to the courses below. They seal the gap where the two roof planes meet and prevent water and wind from entering at the highest point. You can buy pre-made ridge caps or cut regular shingles into thirds (12-inch pieces).
Start at one end of the ridge and work toward the other. Fold each ridge cap over the peak and nail it down with 2 nails, one on each side of the peak, placed 1 inch from the edge. Overlap each ridge cap by 1 inch as you work across the roof. The last cap at the opposite end should be sealed with roofing cement under the edge to prevent wind from lifting it.
Once the ridge is complete, walk the entire roof and check that all nails are seated flush, all shingles are overlapped correctly, and no nails are missing or driven at an angle. Seal any nail heads that are not covered by the course above with roofing cement to prevent leaks.
Flashing around chimneys, vents, and valleys
Flashing is metal or rubber material that channels water around obstacles like chimneys, vent pipes, and skylights. It is installed before shingles are laid around it, not after. If flashing is installed incorrectly, water will find its way behind it and into the roof structure.
For a vent pipe, slide the flashing boot over the pipe before you lay shingles. Nail the upper edge of the flashing to the roof deck, then lay shingles over the top and sides of the flashing. The shingles should overlap the flashing by at least 2 inches on the sides and 4 inches on the top. Seal the edges with roofing cement.
For a chimney, install step flashing — individual pieces of metal that sit under each course of shingles and direct water down and away from the chimney. The flashing is nailed to the roof deck and the chimney, then shingles are laid over it. At the bottom of the chimney, install a cricket (a small peaked roof) to shed water around the chimney base.
Valleys (where two roof planes meet) need special attention. You can install shingles in a woven pattern (shingles from each side overlap in the valley) or a cut pattern (shingles from one side are cut and laid over the other). Either way, the valley must be sealed with roofing cement and flashing underneath to prevent leaks.
Frequently Asked Questions
How many nails should I use per shingle?
Most three-tab shingles require 4 nails per shingle, placed 1 inch below the top edge in the nailing strip. Architectural shingles may require 6 nails. Check the manufacturer's instructions for the shingles you are using — using the wrong number of nails voids the warranty.
What is the correct overlap between shingles?
Shingles should overlap by 1/2 inch horizontally (side to side). Vertically, each course should be offset by 6 inches from the course below, though some manufacturers recommend 3 or 4.5 inches. Check your shingle manufacturer's instructions for the correct offset pattern.
Can I shingle over an existing roof?
Many building codes allow one layer of shingles over an existing roof, but not two. Before you start, check your local building code. If the existing roof is damaged, wet, or has more than one layer, you must remove it down to the deck. Shingling over a damaged roof will fail quickly.
What should I do if I hit a nail at an angle?
Remove it and drive a new nail 2 inches away from the hole. Do not leave the angled nail in place — it creates a leak point. Seal the empty hole with roofing cement so water does not enter.
How do I know if my roof pitch is too steep to shingle?
Most shingles can be installed on roofs with a pitch up to 21:12 (very steep). Steeper roofs require special installation methods and may need additional fasteners. Check your local building code and the shingle manufacturer's instructions for your roof pitch before you start.