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How to Buy, Inspect, Install, Repair Doors, Windows & Skylights

  • WINDOWS & DOORS - home - CONTENTS: Inspecting, Installing, Diagnosing, Repairing Skylights, Windows & Doors
  • POST a QUESTION or READ FAQs about how to recognize different types of windows, how to choose & install windows & skylights & how to inspect & repair leaks, condensation & other window problems
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Guide to doors & Windows:

How to buy, install, inspect, build or repair doors, skylights & windows. This article series explains how to build, diagnose, inspect, install, and repair skylights, windows, and doors.

We begin with a photo guide summarizing different architectural window types & designs. We include examples of sources of window condensation, damage, rot, leaks, and other damage.

Green links show where you are. © Copyright 2017, All Rights Reserved.

Guide to Inspecting, Installing, Diagnosing, Repairing Skylights, Windows & Doors

Sketches of & Index to Names to Window Parts

Window casing details (C) Daniel Friedman Window weight and sash sketch (C) Daniel Friedman

[Click to enlarge any image]

Our sketches of basic double-hung window parts (above left and below left) appeared in Basic Housing Inspection and later in other window guides. Our sketch of repair of window sash cords and weights shows how older double-hung windows operated with sash weights and came from the same source.

Article Contents

Our photo (below left) from a lumber company display illustrates some of the basic wood framed window and sash components including the window jamb, bottom rail, sill and trim - keyed to the sketch at below right.

Window parts (C) Daniel Friedman Window parts (C) Daniel Friedman

Photo Guide to Major Types of Windows: window names, window photos, window properties

For more details about window types, names and architectural features, see our illustrated table
at Window Types - Photo Guide.

Definition & illustration of Awning Type Windows

Awning-type windows (photo at left) operate by a crank and open outwards from the bottom, hinged at the sash top.

Awning windows that open out from the bottom, as most do, can be left open in light rain with less chance of water entering through the window opening itself, allowing ventilation in rainy weather.

Window parts (C) Daniel Friedman Awning type windows (C) Daniel Friedman

As we illustrate and expand at Window Types - Photo Guide, depending on their pivot or axis point and opening direction, awning type windows may be defined more narrowly as austral windows, pivot windows, and projecting windows as well as identified as top opening (hinged at bottom, rain comes in when open) or bottom opening (hinged at top).

At above right a sliding pivot type awning window opens at both top and bottom.

Definition & illustration of Basement Windows & Window Wells

Window parts (C) Daniel FriedmanBasement windows vary among many of the styles listed here, but because they are normally close to or even below ground level, special installation detail and attention to handling of roof spillage are critical to avoid leaks, rot, and indoor water and mold problems.

At left the illustration shows a basement window that needs a window-well installed.




Definition & illustration of Bay Windows

Window parts (C) Daniel FriedmanBay windows project out from the building wall and may incorporate both fixed vertical glazing and operable sashes of any type, usually double-hung or casement style.

As you will observe in these window type photos, a bay window is angled (an angled-bay window) using angled sides and a flat main center section in construction.

As we explain below, a rounded window of this type should be called a bow window, not a bay. (Unless it's my stomach)

If the roof over a bay window is not maintained, or if the window is not properly installed, leaks and condensation are likely.

This bay window uses fixed center glass and double hung sashes at either side.

Don't confuse a bay window (including a flat central segment) and a bow or curved window.

Definition & illustration of Bow Windows compared with oriel windows

Bow windows project out from the building wall and may incorporate both fixed vertical glazing and operable sashes of any type, though in the curved frame of a bow window the sash may also be specially constructed and glazed to follow that arc, or the operable units in the bow window may simply be small individual panes that operate as sliders or awnings.

Window parts (C) Daniel FriedmanAt left our bow window, shown on a home in Boston, MA, is constructed with the bow extending to floor level.

And at the right of the bow window is a smaller oriel window, also a bow but whose window opening does not extend to floor level.

Like a bay window, If the roof over a boy window is not maintained, or if the window is not properly installed, leaks and condensation are likely.



Definition & illustration of Casement windows

Casement-type windows are hinged and like awning windows, casements also operate by a crank.

Window parts (C) Daniel Friedman

But casement windows but are hinged at one side and open outwards like a door. Traditional casement windows on most buildings are constructed of steel sashes and frames, but casements are also constructed of wood, vinyl-clad wood, and solid vinyl.

Watch out: steel framed casement windows such as the unit shown above are usually low in energy efficiency, sporting single glazed panes, no thermal break in the steel frame to slow heat loss to the building exterior, leaky, and often rusted or painted stuck as well.

Definition & illustration of Dormer Windows

Dormer (C) Daniel Friedman

Dormers (photo above left) are not a window-type but rather are an expansion of space under the roof area of a building

Nearly any type, even (this slate roof example) of window can be installed in a dormer. Dormers as a means of gaining space and light to make an attic area into living space have been around for a long time.

Definition & illustrations of Double-Hung Windows

Double hung window shown from the building interior (C) Daniel Friedman

Double-hung windows use two moveable sashes, an upper and lower unit that slide past one another.

Above is a single pane type double hung window in a Poughkeepsie NY home built ca 1925. That window used traditional sash weights.

Below is a modern vinyl or plastic double hung window sash whose sashes are supported by springs rather than sash weights.

Double hung window shown from the building interior (C) Daniel Friedman

Watch out: when inspecting a home for window problems don't assume that all new or recently-installed sashes are operable without doing some actual testing. On both sash weight and spring type window sashes may come crashing down if the sash weight rope or spring is broken.

Because those window support components are hidden from normal view, testing the window for proper operation is important.

Definition & illustrations of Eyebrow Windows

Eyebrow window (C) Daniel Friedman

Eyebrow windows may be fixed or operable and are built protruding through the slope of a roof surface.

Our photo above shows a lovely antique eyebrow window on a roof in New York state. Eyebrow windows may also appear as small peaked installations but the classic is rounded such as we show above.

An "eyebrow" window is a miniature dormer in essence but requires less supporting framer than a larger dormer.

An eyebrow window is not a dormer or dormer window (see Dormers, above).

Eyebrow window (C) Daniel Friedman

Definition & illustration of Fixed Glass or Fixed Glazing Windows

Fixed glass window (C) Daniel FriedmanFixed glass windows may be vertical or sloped and in many lexicons include fixed skylights.

Our photo (left) illustrates fixed vertical glazing on a diner in Poughkeepsie, New York.





Definition & illustration of Ox Eye Windows

Shown just below, the eye-shaped window in the center of our photo is an ox-eye window in the wall of the Hacienda Tenexac in Tlaxcala, Mexico, constructed ca 1532, shortly after the arrival of Hernán Cortés de Monroy y Pizarro.

Eyebrow window (C) Daniel Friedman

Looking more closely at the wall top (click to enlarge this or any image) and you'll also notice musket firing slots built into the parapet.

Definition & illustration of Single hung windows & window sashes

Single-hung windows are similar to double-hung units but only one sash, usually the lower one, is movable.

Double hung window (C) Daniel Friedman

Definition & illustration of Skylights, roof skylights, fixed or operable

Skylight in copper roof, Vassar College (C) Daniel Friedman New skylight in copper roof Vassar College (C) Daniel Friedman
Patched skylight flashing (C) Daniel Friedman


Skylights (above and at left) are an example of sloped glazing, normally built into a roof surface.

Our skylight photos above show an older style wire-reinforced and vented skylight in a copper roof (above left), and at above right, a series of custom-built copper-clad skylights in a re-roofed section of a similar building, both on the Vassar College Campus in Poughkeepsie, NY.

Skylights may be operable for ventilation or fixed.



Definition & illustration of Slider Windows

Slider type windows use sashes that slide horizontally like "bypass doors", one sash passing the other on the inside or outside. These slider widows on a log cabin we renovated in Minnesota were site-built, leaky, and replaced entirely.

Patched skylight flashing (C) Daniel Friedman

Definition & illustrations of Storm Windows

Patched skylight flashing (C) Daniel FriedmanStorm windows are additional windows, fixed or operable, that are hung or installed over the main window sash to reduce heat loss through the window.

A "triple-track" storm window incorporates a movable screen and upper and lower widow sashes.

Each layer of glazing added to a window cuts heat loss through the window glass by about one third, but if the window is drafty any energy savings will be lost until the drafts are found and sealed.




And see STORM WINDOW WEEP HOLES - why we need weep holes to avoid sill rot at storm windows

For a table illustrating nearly all window types, names and architectural features, see Window Types - Photo Guide


How to inspect, diagnose, and repair skylights, sloped glazing, vertical glazing, energy-losing windows, and leaky basement windows

Steel casement windows with lead putty glazing (C) Daniel Friedman

Below we show two problem windows at building basements. If your basement windows seem to be points of leakage into the building, see WINDOW LEAKS INTO BASEMENT.

Basement window defects C) Daniel Friedman Window below ground (C) Daniel Friedman

Leaky steel framed skylight Vassar College (C) Daniel Friedman

If your skylights leak or seem plagued with condensation there is a risk of hidden rot or even mold contaminated ceiling or roof insulation.


See SLOPED GLAZING DETAILS - proper installation details for sloped windows and skylights and

see SKYLIGHT LEAK DIAGNOSIS & REPAIR - how to avoid leaks, rot, damage at skylights


If you are building or installing vertical windows such as the fixed glass triangular windows shown in this photograph,
see VERTICAL GLAZING DETAILS - proper installation details for vertical fixed glass windows to avoid leaks, rot, condensation, heat loss.

Fixed vertical window glass (C) Daniel Friedman

Doors: door type examples of entrances & basement walkouts

Details about doors are found at

Our photo (below left) shows a modern solid-wood multi-lite exterior door used at an enclosed porch. Because of weather exposure and rain splash-up from the entry platform, and because there is no protective storm door installed at this entry, the wood door must be kept coated with paint or polyurethane to avoid water damage, swelling, or rot.

Multi Light porch door (C) Daniel Friedman Multi Light porch door (C) Daniel Friedman

Our second exterior door photo (above right) shows an expedient, but insecure means of securing antique interior doors made from a converted ( ca 1910) swing-type garage door.

Window & Door Leaks & Damage

Exterior door flashing leak damage (C) Daniel FriedmanFor some home buyers, especially of older homes, un-disclosed problems with windows and doors (leaks, rot, energy loss, operability) can be a real "sleeper" that later turns out to be a source of major headaches and big costs.

At a home inspection in New York we found an entire development in which nearly every wooden window in the 1960's - 1970's homes was badly rotted.

The same siding installation company had made the same mistake - hundreds of times. A flashing error at window tops and sides sent wind-blown rain into the window frame, leading to rot and in some cases termite damage as well.

Windows and doors that are leaky or poorly constructed can be a big energy loser on buildings as well. Here we provide a series of articles on the inspection, diagnosis, installation, and repair of problems at windows and doors on residential buildings.

Exterior building doors, with focus on selecting and installing energy-efficient doors are discussed in detail

At left our photo shows rot and damage that will eventually occur if a sliding glass door threshold is installed without a pan flashing and is left for a decade or more with little attention to maintenance of sealants nor paint coating.

The common pine brick mold wood trim around this door as well as a common pine door threshold were particularly prone to water absorption and rot.

Definition & illustration of Basement Walkout Doors

Photograph of - simple errors like this missing downspout elbow and extension can lead to a flooded basement

Basement walkout doors were originally usually site-built using sloped wood (photo, below left); if your basement door is in as terrible shape as the unit shown here.

The worry about leaks into the building basement should take second place to the immediate life-safety hazard of a rotted door like this one.

Modern basement walkout doors are purchased as a pre-fab steel unit from manufacturers such as Bilco™ and may be set on a site-built or pre-fabricated masonry stairwell.






Definition & illustration of Door & Window Sill Rabbet Cuts & Flashing Details

Our window sill photo (below left, courtesy Carson Dunlop Associates), shows the traditional rabbet cut or slot on the underside of the window sill.

Window sill showing drip cut (C) Carson Dunlop Associates

This window sill detail is intended to aid drainage off of the window sill by reducing the tendency of water to follow, by capillary action, the underside of the sill back to drain down the building wall.


and FLASHING WALL DETAILS include details to avoid leaks at building windows

Details are at WINDOW FLASHING & SEALING Guide


Continue reading at CONDENSATION on WINDOWS, SKYLIGHTS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Or see WINDOW TYPES - Photo Guide

Or see these

Doors & Windows Articles

Suggested citation for this web page

WINDOWS & DOORS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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