Roofing Tips: Four Factors to Consider

A roof replacement is one of the largest single expenses a homeowner takes on, and most people go through it once or twice in their life. That means almost nobody has enough experience to know which questions matter.

These four come up on every job, and the answers separate a roof that lasts its full service life from one that fails early.

1. Layering New Shingles Over Old

A roof over, sometimes called a re-roof or an overlay, means installing new shingles directly on top of the existing layer instead of tearing off first. It is cheaper up front because it skips the labor and disposal cost of a tear-off, and that savings is real.

It is also usually the wrong decision. Here is why.

Heat buildup shortens the new shingles’ life

Two layers of asphalt hold considerably more heat than one, and that heat has nowhere to go. Shingles age from thermal cycling, so a layered roof ages faster than the same product installed over bare deck. You pay less now and replace sooner.

It hides the condition of the decking

This is the serious one. The only opportunity to see your roof deck is during a tear-off. Covering it means any soft, delaminated, or rotted sheathing stays exactly where it is, now sealed under two layers of shingles where it will continue to deteriorate unseen.

It adds weight the framing was not designed for

A second layer roughly doubles the dead load of the roof covering. Most framing handles it, but older homes and long spans are worth evaluating rather than assuming.

It often voids the warranty

Check your shingle manufacturer’s requirements before agreeing to an overlay. Many warranties are conditional on installation over a clean deck, and a roof over can void coverage entirely. Verify this in writing, not verbally.

One more practical consideration: most building codes limit a roof to two total layers. If your home already has two, a tear-off is not optional. And when you sell, a home inspector will identify a layered roof and buyers will price it accordingly.

We tear off to the deck on every roof replacement for these reasons.

2. Ventilation

Ask any contractor bidding your job what ventilation is included and why. The answer tells you a great deal about how they work.

Ventilation is a loop with two halves. Cool air enters low through soffit vents at the eaves, hot air exits high through the ridge. Break either end and the system stalls, so exhaust alone accomplishes nothing.

The half most roofs get wrong is intake. Blown-in insulation packed into the eaves seals soffit vents from inside the attic. The vents are still visible from the ground, they are simply no longer connected to anything. A ridge vent with no intake below it is a straw with a thumb over the end.

The other common error is mixing exhaust types. A roof with both a ridge vent and box vents on the same attic space will pull air from the box vents a few feet below the ridge rather than from soffits thirty feet away. The top of the attic cycles, the bottom sits stagnant. When a ridge vent goes on, old box vents should be closed off.

Under-ventilated attics cook shingles from underneath in summer and trap condensation in winter, which produces mold and rotted decking. Most manufacturers also require adequate ventilation for warranty coverage to remain valid. More on ridge vents and roof ventilation.

3. The Wood Under the Shingles

The deck is the plywood or plank sheathing your shingles are nailed to. It carries the whole system, and new shingles over compromised decking will not hold.

Deck problems are almost never visible before tear-off, which creates a specific situation you should understand before it happens: the crew pulls the old roof, finds soft sheathing, and now there is a cost nobody quoted. This is the single most common reason a final invoice exceeds an estimate.

The way to handle it is in the contract. Ask any bidder:

• What is your per-sheet price for decking replacement?
• How many sheets are included in the base bid?
• Will you show me the damaged sheathing before replacing it?

A contractor who answers those clearly is telling you they have done this before. One who says “we’ll deal with it if we find it” is setting up a conversation you will not enjoy having on day two.

Nails also matter here. Shingles fastened into soft or rotted sheathing do not hold, which becomes a wind problem later even if the roof looks correct on completion.

4. Wind Resistance

How much wind resistance you need depends on where you live, but the more useful point is that wind performance depends less on the shingle than on how it was installed.

Shingle wind rating

Architectural shingles are commonly rated from 110 mph up to 130 mph. The upgrade cost between tiers is modest at the time of replacement and impossible to add later, so it is worth deciding deliberately rather than defaulting.

Nailing pattern

Manufacturers specify nail placement precisely, and high-wind applications call for six nails per shingle rather than four. Nails driven too high miss the reinforced strip. Nails overdriven through the mat lose their grip entirely. None of this is visible once the roof is finished, which is why the crew matters more than the brand.

Starter strip

Wind uplift starts at the perimeter, so a proper starter course along eaves and rakes, with its adhesive positioned to seal the first row down, is the largest single factor in wind performance. Cut-up three-tab shingles used as starter is a shortcut that shows up in the first serious storm.

In the Southeast, the relevant threat is usually not sustained coastal wind but sudden downbursts from summer storms and the inland remnants of tropical systems. Both produce short bursts well above 60 mph. Read more about wind and storm damage.

What to Ask Before You Sign

Four questions, one per factor above:

• Are you tearing off to the deck, and does my warranty require it?
• What ventilation is included, and are you addressing intake as well as exhaust?
• What is your per-sheet decking price, and how many sheets are in the bid?
• What is the wind rating of the shingle, and how many nails per shingle are you using?

The answers matter, but so does the manner. A contractor who welcomes these questions has thought about them. One who deflects has told you something too.