Can a new roof go over the old one in Connecticut?

Short answer: sometimes, but rarely the right call, and never in three common situations.

The residential building code used in Connecticut allows a new roof covering to go over an existing one only within limits. Town building departments across the state summarize the rule in their re-roofing handouts: a full tear-off is required when:

1. The existing roof is water-soaked or deteriorated to the point that it is not an adequate base for new roofing
2. The existing covering is wood shake, slate, clay, cement or asbestos-cement tile
3. The roof already has two or more layers of any type of roof covering

In practice that means no more than two layers, ever, and slate always comes off. Your own building department has the final word, and code editions change, so confirm before planning an overlay.

Why most roofers tear off anyway

Even where an overlay is allowed, a tear-off is the standard recommendation in the Hartford area:

• You see the deck. Rot around chimneys, valleys and eaves gets fixed instead of buried.
• The eave membrane goes on the wood. An ice-barrier membrane is meant to be bonded directly to the decking, which matters in a region that averages around 48 inches of snow a season.
• The new shingles lie flat. Shingles over old shingles telegraph every bump and curl underneath.
• Flashing gets replaced. Overlays tend to reuse or cover old flashing, which is where many leaks start.
• Less weight on old framing. Older houses were not always built for two layers.
• The next roof is easier. One layer comes off; two layers mean more labor and disposal later.

If a roofer proposes an overlay

Ask them to put in writing how many layers are on the roof now, why an overlay suits it, what will happen to the existing flashing and how the eaves will be protected. Compare that proposal with a tear-off proposal before deciding.