What Goes Wrong
A roofing or siding job can look perfect for months before problems appear. By then, water is inside your walls and the damage has begun. This guide covers the mistakes we have seen—both in contractor work and in homeowner expectations—that lead to expensive repairs.
The mistakes that hide for years
The worst roofing and siding mistakes are the ones you cannot see. A roof that looks good from the street might have been installed with felt underlayment instead of synthetic, or with fasteners every eighteen inches instead of six. The shingles will look fine for three years, then a storm comes and the ones that were not fastened down properly peel off. A siding job that looks fine on the day can still be installed wrongly in ways that only show up after the first hard winter—water gets behind panels because they were not overlapped correctly, or fasteners were driven too tight and did not leave room for expansion. By the time the problem shows up, the damage is water damage—mold, rot, structural deterioration—and the contractor who did the original job is no longer in business to fix it. This is why watching the work while it happens matters more than inspecting it after.
Homeowners often make the mistake of assuming that all contractors who have been in business for a while must know how to do the work right. That is not true. Some contractors have been doing the wrong thing the same way for twenty years. Others cut corners because they bid the job too low and are losing money on every house. Still others simply do not know better. The difference between a contractor who will get it right and one who will not is usually the information they volunteer about how they will do the job and the details they know to ask about on your house.
When a second opinion pays for itself
Some mistakes you can catch yourself during the job. You can ask the contractor to show you what they are installing and why. You can ask them to walk you through the phases and explain the details. You can visit other jobs they are doing in your area and talk to those homeowners. But some mistakes require professional judgment. If a contractor's work does not feel right to you—if they cannot explain their process, if they refuse to get a permit, if they want most of the money up front—trust that feeling. You do not need to understand the technical details to know that something is off. A second opinion from another contractor, or from a building inspector before the work starts, costs money up front but saves far more when it prevents a bad job from happening. This is one area where the cheapest choice is almost always the most expensive choice in the end.
What to watch for on a siding job
A siding job that looks fine on the day can still be installed wrongly in ways that only show up after the first hard winter. For the detail on how vinyl siding is meant to be fastened and finished, see the Polymeric Exterior Products Association's Vinyl Siding Installation Manual. The manual covers the overlap and fastening pattern that allows panels to expand and contract with temperature changes. When contractors skip this detail, the panels lock up in cold weather and create stress at the seams where water gets in.
Fastening: Each panel is fastened in a loose grid, not top-to-bottom. The fastener goes through the slot, not through the hole—slots allow the panel to move. If you see fasteners driven tight or nailed through the finished edge of the panel below, that is a sign the installer does not know the trade.
Overlap: Panels overlap one inch, which is how water sheds downward instead of getting trapped behind panels. If the overlap is less than an inch, or if the panels are installed with the overlap facing up instead of down, water will find a way inside. This is one of the most common mistakes because it is simple to get wrong and the job looks the same either way—until winter comes.
The inspection points that matter
If you are watching a siding or roofing job, three things separate the work that will last from the work that will not. First, watch the prep work. Good contractors remove the old material cleanly, repair the underlying structure, and install proper underlayment before anything goes on top. Second, watch the fastening pattern. On a roof, shingles are fastened in four places per shingle in a grid. On siding, fasteners go through slots so panels can move. If the installer is rushing through fastening or using a single fastener per section, they are cutting corners. Third, watch the flashing and transitions. The edges of the roof and the places where different materials meet are where water gets in. If the contractor is not talking about flashing detail, ask them about it. Their answer will tell you whether they have built this before.
What it will cost to fix mistakes
The cost of fixing a failed siding or roofing job is usually two or three times the cost of doing it right the first time. If you paid six thousand dollars for a siding job and it was installed incorrectly, you will spend eight to ten thousand dollars to remove it, fix the water damage behind it, and install siding correctly. If you discover the problem early—within the labor warranty period—the original contractor might be obligated to fix it at no cost. If you discover it years later, you are paying out of pocket for both the repair and the damage assessment. A labor warranty of five to ten years from a licensed contractor is cheap insurance. A contractor who will not offer a warranty on their labor is telling you that they do not expect their work to hold up.
The biggest mistake: not asking the right questions
How many houses like mine have you finished in the last two years?
A vague answer is a red flag. They should be able to name the neighborhood and the street, and offer to have you visit similar jobs nearby. If they cannot, they have not built many houses like yours.What underlayment will you use?
They should name a brand, specify synthetic not felt, and confirm it covers the entire roof or house. If they say "standard underlayment" or "the one that comes with the material," they are not thinking about this detail and something will fail.What is included in your labor warranty and for how long?
Five to ten years on labor is standard. If they offer less than five years, they are cutting corners. If they offer no labor warranty at all, they are not confident in their work.Will you get a building permit?
A project that requires a permit and does not get one is a sign the contractor is trying to avoid inspection. You can often call the building department yourself and ask if a permit has been pulled.