In this multi-part series we’re going to break down what makes a good window. Why not what makes the “best” window? Because best is of course particular to your home, with many factors to consider and trade-offs to weigh. In this first post, we’ll start with the basics including terminology. The second part will dig into material choices for window frames. Let’s dive in!
First, some terminology. When we talk about windows, we’re talking about several different parts including the insulated glass unit (IGU), the window frame and window sash. The image below highlights the key terminology to know here.
Windows come in all shapes, sizes and designs. Fixed windows, sometimes known as picture windows, do not open, have better insulating values, and are almost always cheaper than operable windows. Single hung windows allow the bottom of the window to slide up, while double hung windows often seen on traditional townhouses, slide open from either the top or bottom. Both are difficult to seal properly. Casement windows, which have side hinges and open outward, are much better for sealing and allow the window to fully open. Awning windows (top hinges which open outward) and hopper windows (bottom hinges which open inward) are great choices when only a small cracked opening is needed. Sliding windows and doors are another option; hardware choice can make a big difference in terms of their sealing capability.
Separate windows can be joined together to fit a single opening; these are mulled windows. Mulled windows can consist of two or more of the same or different window types, for example two small awning windows beneath a large picture window. Mulling, or joining, is typically done during manufacture.
While standard window sizes do exist, they aren't standardized across all manufactures. Most American manufacturers standardize in six inch increments. Standard sized windows usually have shorter lead times. Many of the best windows are made with custom order and are manufactured based on the rough opening measurements of the wall opening. Manufacturers vary on the overall size limitations to their window and door assemblies. Glass door heights above 10 or 11 feet are rare and most windows top out at a maximum of 60 square feet of glazing (IGU) before breaking warranty.
A variety of factors contribute to the overall cost of windows including, operability type, materials, IGU quality, thermal performance and size. Window costs can vary widely. Windows of the same size and operability can vary as much as 3x in price depending on the manufacturer, quality of design, and materials. Fixed windows can be half the cost of other, operable window types. Standard size windows typically cost 10-20% less than custom sized windows. We’ll cover the pricing tradeoffs of some of the other contributing factors in the next installments of our window series.
In addition to cost, another important consideration is lead time. Timing may be less of a constraint when you decide to replace a couple windows in your home, but critically impact the timeline of a ground up or major renovation. During the last few years lead time on many window manufacturers has exploded from a relatively standard 10-12 weeks to as high as 30 weeks (~7 months)! Planning ahead and working with an architect will help ensure you consider options that meet your project’s budget and timeline.
Read part two (forthcoming) for what you need to know about window frame materials.