Editing Window (section)

== Construction ==
[[File:Passivhaus Fenster Beispiele (blank).svg|thumb|Examples of modern plastic and wooden window profiles with [[insulated glazing]]]]
[[File:WaterMill Window LymeRegis.jpg|thumb|Modern wooden framed window fitted in the 14th century [[Lyme Regis]] [[watermill]], [[UK]]]]
[[File:5-chamber plastic window profile.JPG|thumb|upright|5-chamber plastic window profile]]

Windows can be a significant source of heat transfer.<ref name="Window Systems">Carmody, J., Selkowitz, S., Lee, E. S., Arasteh, D., & Willmert, T. (2004). ''Window Systems for High-Performance Buildings''. New York, NY: W. W. Norton & Company, Inc.</ref> Therefore, [[insulated glazing]] units consist of two or more panes to reduce the transfer of heat.

=== Grids or muntins ===

These are the pieces of framing that separate a larger window into smaller panes. In older windows, large panes of glass were quite expensive, so muntins let smaller panes fill a larger space. In modern windows, light-colored muntins still provide a useful function by reflecting some of the light going through the window, making the window itself a source of diffuse light (instead of just the surfaces and objects illuminated within the room). By increasing the indirect illumination of surfaces near the window, muntins tend to brighten the area immediately around a window and reduce the contrast of shadows within the room.

=== Frame and sash construction ===

Frames and sashes can be made of the following materials:
{| class="wikitable"
! Material
! [[Thermal resistance]]
! Durability
! Maintenance
! Cost
! Recycled content
! Comment
|-
| [[Wood]]
| very good
| variable
| low
| average
| high
| a well-maintained wood window built before 1950 can last 50–100 years<ref>{{cite web |title=Saving Windows, Saving Money: Evaluating the Energy Performance of Window Retrofit and Replacement |url=https://forum.savingplaces.org/viewdocument/saving-windows-saving-money-evalu |website=Resource Library – National Trust for Historic Preservation |publisher=National Trust for Historic Preservation |access-date=March 31, 2020}}</ref><ref name="auto">{{cite web |last1=Peterson Wasielewski |first1=Shannon |title=Windows: Energy Efficiency Facts and Myths |url=https://dahp.wa.gov/sites/default/files/Windows%20Energy%20Efficiency%20Facts%20and%20Myths.pdf |website=Washington Department of Archaeology and Historic Preservation |access-date=March 31, 2020}}</ref>
|-
| [[Polyvinyl chloride|uPVC ("vinyl")]]
| very good
| very good{{Efn-lr|PVC and fiberglass frames perform well in accelerated weathering tests. Because PVC is not as strong as other materials, some PVC frames are reinforced with metal or composite materials to improve their structural strength.|name=PVC&fiberglass}}
| very low
| average
| very low
| has a life span of 25–50 years in average<ref name="auto" />
|-
| [[Aluminum]]
| very good{{Efn-lr|1=Modern aluminium window frames are typically separated by a thermal break made of a glass fibre reinforced polyamide. With a 34&nbsp;mm thermal insulation profile it is possible to reach Uf= 1.3 W/m2K for a metal window. This greatly increases thermal resistance, while retaining virtually all of the structural strength.}}
| good
| very low
| low
| typically >&nbsp;95%
| mostly thermally broken by a thermal insulation profile
|-
|Composites
|very good
|good
|very low
|high
|high
|used in modern buildings
|-
| [[Steel]]
| medium
| superior
| very low
| high
| >&nbsp;98%
| typically welded at corner joints
|-
| [[Fiberglass]]
| very good
| very good{{Efn-lr|name=PVC&fiberglass}}
| very low
| high
| medium
|
|}
{{Notelist-lr}}[[composite material|Composites]] (also known as Hybrid Windows) are start since early 1998 and combine materials like aluminium + pvc or wood to obtain aesthetics of one material with the functional benefits of another.
[[File:Bleekman zimmer.jpg|thumb|A typical installation of insulated glazing windows with uPVC window frames]]
A special class of PVC window frames, uPVC window frames, became widespread since the late 20th century, particularly in Europe: there were 83.5 million installed by 1998<ref>{{cite book|last1=Pritchard|first1=Geoffrey|title=Novel and Traditional Fillers for Plastics: Technology and Market Developments|year=1999|publisher=iSmithers Rapra Publishing|isbn=978-1-85957-183-5|page=95|url=https://books.google.com/books?id=U3GWoyuMEckC&pg=PA95}}</ref> with numbers still growing as of 2012.<ref>{{cite web|url=http://www.prweb.com/releases/Vinyl_doors_market/vinyl_windows_market/prweb9415523.htm|archive-url=https://archive.today/20130131182428/http://www.prweb.com/releases/Vinyl_doors_market/vinyl_windows_market/prweb9415523.htm|url-status=dead|archive-date=January 31, 2013|title=Global Vinyl Windows Market to Reach 163 Million Units by 2017, According to a New Report by Global Industry Analysts, Inc. |publisher=PRWeb|date=April 18, 2012|access-date=February 11, 2012}}</ref>

=== Glazing and filling ===

[[Low-emissivity]] coated panes reduce heat transfer by [[radiation]], which, depending on which surface is coated, helps prevent heat loss (in cold climates) or heat gains (in warm climates).

High thermal resistance can be obtained by evacuating or filling the insulated glazing units with gases such as [[argon]] or [[krypton]], which reduces [[Heat conduction|conductive]] heat transfer due to their low thermal conductivity. Performance of such units depends on good window seals and meticulous frame construction to prevent entry of air and loss of efficiency.

Modern double-pane and triple-pane windows often include one or more low-e coatings to reduce the window's U-factor (its insulation value, specifically its rate of heat loss). In general, soft-coat low-e coatings tend to result in a lower solar heat gain coefficient (SHGC) than hard-coat low-e coatings.

Modern windows are usually glazed with one large sheet of glass per sash, while windows in the past were glazed with multiple panes separated by ''glazing bars'', or ''muntins'', due to the unavailability of large sheets of glass. Today, glazing bars tend to be decorative, separating windows into small panes of glass even though larger panes of glass are available, generally in a pattern dictated by the architectural style at use. Glazing bars are typically wooden, but occasionally lead glazing bars soldered in place are used for more intricate glazing patterns.

=== Other construction details ===

Many windows have movable [[window covering]]s such as [[blinds]] or [[curtain]]s to keep out light, provide additional insulation, or ensure privacy.
Windows allow natural light to enter, but too much can have negative effects such as glare and heat gain. Additionally, while windows let the user see outside, there must be a way to maintain privacy on in the inside.<ref name="Design Evaluation Project">Howell, Sandra C. (1976). ''Designing for the Elderly; Windows''. Massachusetts Institute of Technology. Department of Architecture. Design Evaluation Project.</ref> Window coverings are practical accommodations for these issues.