Door in Cannaregio Venice showing bottom panel seal against water entry during aqua alta (C) Daniel FriedmanFlashing Details for Exterior Doors & Windows
Best Practices

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Door & window flashing & sealing:

This article describes the proper flashing details for exterior doors to avoid air leaks, rot, decay, and energy losses at doors.

In this article series we discuss the selection and installation of windows and doors, following best construction and design practices for building lighting and ventilation, with attention to the impact on building heating and cooling costs, indoor air quality, and comfort of occupants.

We review the proper installation details for windows and doors, and we compare the durability of different window and door materials and types.

Page to photo: an entry door in Cannaregio in Venice showing the door bottom sealing insert panel used to block water entry at the door bottom during periods of aqua alta.

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Guide to Exterior Door Flashing Details

As detailed in Best Practices Guide to Residential Construction Chapter 3, BEST PRACTICES GUIDE: WINDOWS & DOORS:

Doors are flashed the same as windows on the sides and top, and similarly at the sill. Clad door frames are flashed like clad windows (see our window flashing illustrations below, Figures 3-13, Figure 3-15, Figure 3-16) and solid wood frames are flashed like traditional windows with brickmold (Figures 3-17 also below).

[Click to enlarge any image]

(C) J Wiley, S Bliss

Figure 3-13: Installing Flange-type Doors or WIndows Over House-Wrap

(C) J Wiley, S Bliss

Figure 3-15: Installing Flange-type Doors or Windows Before the House Wrap is Applied

(C) J Wiley, S Bliss

Figure 3-16: Installing Flange-type Doors & Windows with Felt Paper

(C) J Wiley, S Bliss

This article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons.

See WINDOWS & DOORS our home page for window and door information, and also see WINDOW TYPES - Photo Guide for a photographic guide to window and door types and architectural styles.

Figure 3-17: Installing Doors & Windows with Brickmold Trim

Unless a door is well-protected by a porch or large overhang, good pan flashing at the sill is critical to prevent water from seeping into the floor framing.

Doors leading to patios and decks are particularly vulnerable to wetting around the sill from splashback and, in cold climates, from snow buildup.

Pan Flashing for Exterior Doors & Windows - Rot below a Sliding Glass Door

Sliding door sill installed with no pan flashing (C) Daniel Friedman

Above: this aluminum sill for a sliding glass door was installed over the plywood subfloor of the author's New York offices in the 1970's. The carpenter used no pan flashing. Below our next photo shows the extensive rot that ensued.

Prefab plastic door pans typically come in three sections that are fused together at the required length with solvent-based cement. Metal pans require a brake to form and should be caulked or, preferably, soldered at corners.

Sliding door sill rot (C) Daniel Friedman

In fact the absence of effective flashing at this 20-year-old sliding glass door (photo above) led to the need for a complete door, door jamb, and trim replacement on this Poughkeepsie home.

When the new door was installed we included a sit-built pan flashing and membrane flashing around the door for a more durable replacement.

Peel-and-stick membranes have become increasingly popular due to their ease of use and flexibility. Whether to use a metal pan, plastic pan, or peel-and stick membranes is a matter of personal preference as all work well (see Figure 3-26 below).

(C) J Wiley, S Bliss

Figure 3-26 - above, flashing details above and below an exterior door

(C) J Wiley, S Bliss

Figure 3-27 - above, pan flashing and threshold details below an entry door

Whatever material is used, all pans should have a dam on the ends and along the inside edge

On the exterior, the pan flashing should lap over the deck or masonry flashing below. If forming a pan with peel-and-stick membrane, carry it up the sides at least 6 inches, and turn up the inside edge so it is held in place by the underlayment or finish flooring (Figure 3-27 above).

Also see 

Window and Door Resources: where to buy window and door products

As noted in Best Practices Guide to Residential Construction Chapter 3, BEST PRACTICES GUIDE: WINDOWS & DOORS:

Manufacturers of Windows & Doors

Windows and Patio Doors

Door Manufacturers & Products Guide

Exterior door without need for pan flashing (C) Daniel Friedman Brooklyn NY

Photo: an example of an exterior door exposed to weather that can get by with no pan flashing whatsoever. This metal door, installed in a soldiers and sailors monument in Brooklyn, New York, opens over a stone threshold that is yet another step above grade level.

Both the threshold and the step drain towards the exterior.

A modest angle-flashing affixed to the door bottom directs wind-blown rain down the door and out to the exterior. [Click to enlarge any image]

Industry Associations for Windows & Doors

-- Adapted and paraphrased, edited, and supplemented, with permission from Best Practices Guide to Residential Construction.


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