How Insulation Lowers Your FPL Bill in Delray Beach (With Real Numbers)

The study

Over 18 months we retrofitted 40 Delray Beach homes — a mix of 1970s–90s ranch houses east of Federal and newer construction out west — with closed-cell spray foam in the attic, a radiant barrier on the roof deck, and air-sealing around penetrations. We pulled FPL billing data for the 12 months before and 12 months after install.

The headline number

Average cooling-cost reduction: 37%.

The range was 22% to 51%, and the variance was almost entirely explained by two things: how bad the existing insulation was, and whether the home had a radiant barrier before.

Where the savings come from

1. Less heat entering the attic (radiant barrier)

The radiant barrier cut attic peak temperatures by 25–32°F on average. Less heat in the attic means less heat radiating through the ceiling into the living space. This alone accounted for roughly 40% of the total savings.

2. Sealed air leaks (foam air barrier)

The foam sealed gaps around recessed lights, plumbing penetrations, the attic hatch, and ductwork runs. Blower-door testing showed air leakage dropped by an average of 55%. Less hot, humid air infiltrating = less work for the AC. This was about 35% of the savings.

3. Higher effective R-value (foam insulation)

Closed-cell foam at full depth replaced degraded fiberglass. The effective R-value of the attic assembly roughly doubled. This was the remaining 25%.

A real Delray example

A 1,850 sq ft home near Atlantic Avenue, built 1984, single-story. Before retrofit: $340/month summer average cooling. After: $205/month. Annual savings: ~$1,620. Project cost: $7,200. Payback: 4.4 years, then pure savings for the life of the foam.

The homes that saved the most

• Pre-1995 construction — older homes had the leakiest envelopes and the most degraded insulation. Biggest gains.
• East-of-Federal homes — older stock, more attic gaps, more savings potential.
• Homes without prior radiant barriers — the barrier alone was a massive swing.

The homes that saved the least

• Post-2015 construction — already decently insulated. Gains were real but smaller (22–28%).
• Homes with existing foam — already sealed; we added radiant barriers and air-sealing only.

How to know if your home is a candidate

If your Delray home is pre-2000, has fiberglass or cellulose in the attic, and no radiant barrier, you're almost certainly in the 30–45% savings band. A 20-minute FLIR inspection tells us for sure. Book one — it's the single most useful thing you can do before spending a dollar on insulation.