Passive House Renovation — 1960s Ranch

Converting a 1,800 sq ft single-story ranch to near-Passive House standards. The goal is 90% energy reduction while keeping the original character.

Current Performance

• Blower door test: 12 ACH50 (leaky)
• Heating load: 45 kBTU/hr
• Annual energy: ~$3,200/year
• Insulation: R-11 walls, R-19 attic, single-pane windows

Proposed Envelope Upgrades

Walls

Exterior rigid foam wrap (4" polyiso, R-26) over existing framing. Furring strips + new siding. Total wall R-value: R-37.

Attic

Blow 16" cellulose over existing. Target R-60. Air seal all penetrations first.

Windows

Triple-pane, European tilt-turn. U-value 0.14. Solar heat gain coefficient 0.50 on south, 0.25 on east/west.

Foundation

2" XPS on interior basement walls + sealed crawlspace with vapor barrier.

Mechanical

• ERV: Zehnder ComfoAir Q450 (93% heat recovery)
• Heating/Cooling: Mitsubishi cold-climate mini-split, 2-zone
• Hot water: Heat pump water heater in conditioned space

Budget Estimate

Item	Cost
Exterior insulation + siding	$28,000
Windows (12 units)	$18,000
Attic insulation + air sealing	$4,500
ERV system	$8,000
Mini-split (2 zones)	$7,500
HPWH	$2,500
Total	$68,500

Expected Results

• Target ACH50: <1.5
• Heating load: <12 kBTU/hr
• Annual energy cost: ~$400/year
• Simple payback: ~24 years (but comfort improvement is immediate)