We work on a lot of decks with French Doors…and often times we find signs of leaking around a door and under the sill where the water had collected and did it’s evil work creating dry-rot. 

Other times we get a complaint that “your deck is leaking”.

 Inspections find that unless there is a hole in the deck membrane, it ain’t the deck…it’s the French Door.

Gene Summy of TLS Laboratory in Laguna Nigel is a French Door/water intrusion expert. TLS Laboratories has a special talent in tracking down difficult homeowner occupied leaks. Windows, French doors, roofs, walls, decks, chimneys, or any other leak will be tracked down by TLS Laboratories field technicians. Due to the experience in homeowner occupied homes, and water testing during the course of construction TLS Laboratories is able to take the lessons learned into the field and help builders build better homes.

Here’s a piece of Gene’s article published at JLC Magazine. I suggest that you download it and keep it close for the next French Door installation you have.

“In California, contractors have been heard to grumble that there are only two types of French doors: the kind that leak and the kind that are going to leak. When they have the first kind, they call my company, TLS Laboratories in Laguna Niguel. We’ve investigated plenty of leaking French doors over the years, and in our experience it’s usually the installation that’s faulty, rather than the door itself.

A hinged exterior French door is something like a very large jigsaw puzzle with a small number of pieces. If the pieces are assembled correctly, the pair of sash should fully compress the weatherstripping against the jambs and one another. If the fit isn’t quite right, the weatherstripping won’t compress and water will seep in around the sash. If a door is going to leak, it most often leaks here.

The next most common leakage area is the sill — not over it, but underneath it, usually as the result of insufficient sealant. Pans and proper flashings also help (I’ll talk about them later), but two fat beads of sealant running 6 inches down each trimmer and all the way across the pan — one toward the front edge of the door and another toward the rear edge — will stop a lot of water.” 

Read the rest by clicking here. http://www.jlconline.com/caulks-adhesives-and-sealants/installing-french-doors_1.aspx