Calculate Gutter Size for Your Roof
Size gutters and downspouts based on roof area and rainfall intensity. Prevent overflow and foundation damage.
Gutter Sizing Basics
Gutter size depends on roof drainage area × maximum rainfall intensity. Standard 5" K-style gutters handle most residential applications (up to 5,520 sq ft of roof in moderate rainfall). Homes with large roofs, steep pitches, or high-rainfall areas may need 6" gutters. Undersized gutters overflow during heavy rain — sending water down your foundation instead of away from it.
Downspout Placement
Rule of thumb: one downspout per 600 sq ft of roof drainage area, with no more than 40 feet of gutter between downspouts. Place downspouts at corners and low points. Extensions should direct water at least 4-6 feet away from the foundation — or better yet, connect to an underground drainage system. Poor downspout placement is the #1 cause of basement water intrusion.
Foundation damage from poor drainage costs $5,000-30,000 to repair. Properly sized gutters and downspouts with extensions cost $1,500-3,000 installed. This is one of the highest-ROI home improvements — protecting your foundation protects your largest investment. Check your gutters during the next heavy rain and note any overflow points.
