What each window needs: privacy, light, heat and how the room is used
A window treatment does several jobs at once. This chapter names them for one window at a time, from the direction the window faces and how the room is used, and ranks them so the one you would not trade away chooses the treatment.
- Start here: the essentials
- The jobs a window treatment does
- Which way the window faces, and when the sun reaches it
- How the room is used, and at what hours
- What else is at the window
- Ranking the needs
- The window across the seasons, and the whole home
- See it
- Practice
- Your windows
- Check your work
- Knowledge check and scenario
Start here Essentials
At minimum this chapter asks you to look at one window carefully, at the hours that matter, and write down what it needs in order. One window in one room is enough. Everything marked Go deeper is optional on a first pass.
- Note the room, the direction the window faces and what is outside it. A street, a neighbor's window, a yard, a tree. Use a phone compass or a map for the direction (Which way the window faces).
- Go outside after dark with a lamp on inside and see what shows. Write down whether you can see the room, a silhouette or nothing (The jobs a window treatment does).
- Write the room's uses and the hours of each. Sleeping, working at a screen, sitting in the evening, and when each happens (How the room is used).
- Rank the needs and circle the one you would not trade away. That one chooses the kind of treatment; the rest choose among options (Ranking the needs).
Minimum time: about 30 minutes, plus five minutes outside after dark. Done when: the window survey has one row for the window with its needs ranked.
1. The jobs a window treatment does Understand
A curtain, shade, blind or shutter is asked to do several different things with one piece of material, and most disappointments come from choosing it for one job and then discovering it was also expected to do another. The list is short, and it is old. A museum vocabulary defines curtains as hangings used for privacy, light and draft control, or decoration (the Getty's Art & Architecture Thesaurus entry for curtains). A historian of nineteenth-century American interiors lists the same jobs with dirt and pests added, and notes that most American rooms had no curtains until at least the middle of the eighteenth century (Curtain Call, a University of Delaware material culture paper). The jobs have not changed much since. What has changed is the range of products that do each one well and the others badly.
We use seven needs in this manual. Each one is a question you answer about one window, not a feature you shop for.
| Need | The question to answer | When to look | What it decides later |
|---|---|---|---|
| Privacy by day | Can someone outside see into the room in daylight, and from where? | Midday, from the street, path or neighbor's side | Whether a sheer, a light-filtering fabric, a top-down shade or film is enough |
| Privacy at night | With lamps on inside, what shows from outside? | After dark, standing outside | Whether the window needs an opaque layer that closes |
| Daylight and view | How much light and outlook do you want, and at what hours? | Morning, midday and late afternoon | How open the treatment has to be, and whether it has to clear the glass entirely when open |
| Glare | Does sun land on a screen, a seat or a face? | At the hour it happens | Whether to filter, redirect or block, and whether to move the screen instead |
| Darkness for sleep | Does anyone sleep in the room while it is light outside, or under a streetlight? | During the sleep hours | Opacity, and how the edges are closed |
| Heat and cold | Is the window hot in summer sun or cold to sit near in winter? | A sunny summer afternoon; a cold winter evening | Insulating or reflective kinds, and whether they will be opened and closed by season |
| The look | What should the window add to the room, or stop taking from it? | Any time, from inside | Fabric, heading, height and proportion, once the other needs are met |
Privacy is two needs, not one. By day the street is usually brighter than the room, and people outside see their own reflection or a dim interior. After dark, with lamps on, the room is the bright side, and the same window shows the room to anyone passing. A window film trade association's guide says the daytime privacy from highly reflective film virtually disappears once the home is brighter inside than out (the International Window Film Association's 2026 education guide). Physical principle That is why Start here sends you outside after dark: it is the one observation that most often changes the answer. Privacy by day and by night works through it window by window.
Light and darkness are separate needs too. A bedroom can want morning light on weekends and full darkness on the days someone sleeps in it after a night shift. One treatment can do both only if it has two settings, or two layers. Daylight, glare and darkness sorts out the opacity words (sheer, light filtering, room darkening, blackout) and what each one stops.
Heat and cold depend on how the treatment is used. The U.S. Department of Energy's consumer guide advises closing curtains and shades at night in cold weather and opening them on sunny winter days, and closing draperies on windows in direct sun in warm weather (the Energy Saver Guide, 2022). A treatment that is left in one position all year does a different job from one that is moved twice a day. Record whether anyone in the home will actually do that. Heat, cold and condensation has the studies and what they found.
A child in the home is a rule, not a need. It does not compete with the others in the ranking. It removes options before the ranking starts, because corded coverings are a strangulation hazard to young children and the U.S. Consumer Product Safety Commission says cordless coverings are the only option that eliminates it (CPSC's window covering cords page). If a child lives with you or visits, write that on the survey row now; Cords, children and fire deals with it.
Terms used here. A window treatment or window covering is anything hung at or on a window to control light, view, privacy or heat: curtains and draperies, shades, blinds, shutters and films. The casing or trim is the molding around the window opening. The sill is the ledge at the bottom of the opening inside the room. Glare is light bright enough, against what is around it, to make it hard to see a screen, a page or a face. The glossary has these and the rest.
2. Which way the window faces, and when the sun reaches it
The direction a window faces decides when direct sun comes in, how low it is in the sky when it does, and which season brings the most of it. That shapes glare, heat and fading more than any other single fact about the window.
Finding the direction
Stand inside, with your back to the room, looking straight out through the glass. The direction you are looking is the direction the window faces. A phone's compass app gives it in a few seconds; hold the phone flat and away from speakers and steel. An online map works as well: find your building, find the wall with the window, and read which way it faces against the map's north arrow. Round to the nearest of north, east, south and west, and write "northeast" or "southwest" if it is clearly between two. If the window is in a corner bay or a slider that wraps a corner, write each pane's direction.
What each direction brings
The sources we use describe the Northern Hemisphere. South of the equator the midday sun is in the northern sky, so read north where the table says south.
| Window faces | Direct sun | What it tends to bring |
|---|---|---|
| East | Morning, from a low sun | Low sun that reaches deep into the room; glare and overheating early in the day; most exposure in summer |
| West | Afternoon and evening, from a low sun | The same low-sun glare and overheating, late in the day when the house is already warm; most exposure in summer |
| South | Around midday, high in summer and low in winter | Easier to shade in summer while keeping daylight; the most exposure in winter, which is welcome warmth and also winter glare |
| North | Little direct sun | Steady daylight; easier to shade while keeping the light; often the cold window in winter |
A university daylighting lecture puts it plainly: north and south windows are easy to protect from sun while admitting daylight, and east and west windows face a low rising or setting sun that threatens severe glare and overheating (University of Oregon, window orientation slide). The window film association's guide adds the seasons: in the Northern Hemisphere, summer exposure is highest on east and west windows and winter exposure highest on south ones (IWFA education guide, 2026). Physical principle The "little direct sun" on the north row and "often the cold window" are our summary of the same geometry, not a measured figure.
What changes the pattern
The table is a general pattern. Your window is a particular one. A tree, the building across the street, a deep eave, a porch roof or the next-door wall can shade a window that the compass says should be sunny, and a pale wall or a parked car across the street can bounce light into a north window. Eaves matter by season: the same trade association notes that low winter sun can come in under eaves that block the high summer sun, and can put glare on computer screens (IWFA, low winter sun and glare). So the direction is a starting guess, and your own observation settles it.
Test it Look at the window at three times on one day: morning, around midday, and late afternoon. At each, note whether direct sun is on the glass, where the patch of sun lands in the room, and whether it lands on a bed, a seat, a screen or a rug. Three looks on one day are enough for a first pass. The Go deeper section below covers doing it again in another season.
Learn Color Design's chapter Observe your light describes the same habit of watching a room at different hours, for choosing color, and is worth reading if the look of the room ranks high for you.
3. How the room is used, and at what hours
Two identical windows facing the same way can need opposite things, because of what happens in the room and when. The direction tells you what the sun does. The room's use tells you whether that matters.
For each room, write who uses it, for what, and at what hours. Be specific about the hours: "evenings" is less useful than "7 to 11 p.m., lamps on, sitting on the sofa facing the window."
| Use | Hours | The need it raises | Example |
|---|---|---|---|
| Sleeping at night | About 10 p.m. to 7 a.m. | Privacy at night while lamps are on before bed; darkness at dawn for an east window, or under a streetlight | An east bedroom where the sun is up before the alarm |
| Sleeping by day | Morning to early afternoon | Darkness for sleep while it is fully light outside; privacy matters less while the room is dark | A night-shift worker's bedroom |
| Sitting in the evening | Dusk to bedtime | Privacy at night, often from the street; afternoon glare first for a west room | A living room at sidewalk level |
| Working at a screen | Working hours | Glare at particular hours; daylight the rest of the time | A home office with a monitor facing an east window |
| Bathing | Any time | Privacy by day and by night, every time; damp | A bathroom facing a neighbor's window |
| A child's sleep and play | Naps by day, nights | Darkness for naps; cords out of reach; furniture away from the window | A nursery |
Three patterns come up often enough to name.
Someone sleeps while it is light. A shift worker, a new parent catching up, a child's afternoon nap. Darkness usually wins the ranking here, because the sun on the window and the sleep hours overlap. The U.S. National Institute for Occupational Safety and Health's training for nurses on long hours advises a sleep room so dark you cannot see your hand in front of your eyes, with blackout shades or drapes (NIOSH, sleep tips for night shift workers, last reviewed 2020). That is workplace health guidance for shift workers, not a medical finding about your sleep; Daylight, glare and darkness says what it does and does not settle.
The room is lit while the street is dark. A living room or a ground-floor bedroom in the evening. Privacy at night usually wins, and the answer has to close, not just filter.
A screen faces the window, or has the window behind it. Glare usually wins for a few hours a day and does not matter the rest of the time. That makes it a candidate for a treatment that adjusts, or for moving the screen, rather than a treatment that blocks the window all day.
Write down, too, who will open and close the treatment and how often. A shade that needs lowering at 7 a.m. every day in a room nobody enters at 7 a.m. will be left down, and then it is doing a different job from the one it was chosen for.
4. What else is at the window
The window opening is not empty. Things on the frame, the wall and the floor near it decide later what can be mounted where, and they are easier to note now than to discover on installation day.
| What to note | Where to look | What it can limit later |
|---|---|---|
| Cranks and handles | On casement and awning windows, at the sill or the side | A treatment mounted inside the frame may hit them; a crank may need clearance to turn |
| Sash locks | On double-hung windows, where the two sashes meet | They stand proud of the glass and use up some of the frame's depth |
| Alarm sensors and contacts | On the frame or sash | Brackets and tension rods have to clear them |
| Heat registers, radiators, baseboard heaters | Under or beside the window | Long curtains over them block warm air, and anything that can burn needs clearance from a heat source |
| Outlets and switches | On the wall below the sill or beside the trim | Floor-length curtains may cover them; a motorized shade may want one |
| Space above the trim | From the top of the casing to the ceiling or crown molding | Where a rod or an outside-mounted shade can go, and how high |
| Space beside the trim | From the casing to the next wall, door or corner | How far a rod can extend, and where open curtains can stack |
| Depth of the frame | From the glass or sash to the room edge of the frame | Whether a blind or shade can mount inside the frame |
| Is it a bedroom's escape window? | Any bedroom window that opens | Nothing fixed should stop it opening |
Inside the frame or outside it. Two words come up from here on. An inside mount fits a blind or shade within the window frame, so the casing stays visible. An outside mount fixes it on the wall or the casing, covering the opening and some wall around it. Whether an inside mount is possible depends on the frame's depth against the maker's minimum, and that minimum varies widely by product. Bali's measuring guide for wood and faux wood blinds gives 3/4 in as the minimum inside-mount depth (Bali wood and faux wood measuring guide), while Levolor's custom cellular shades need between 1/2 in and 2 in depending on the lift, and more to sit flush with the frame (Levolor cellular technical guide, 2022). Product-specific Your maker's guide wins. For now, write the depth and anything that sticks out into it; Measuring for blinds and shades measures it properly.
The space above. An outside mount needs a flat place for its brackets. Hunter Douglas says outside-mount brackets need at least two inches of level surface above the window trim, or they mount on the frame itself (Hunter Douglas, inside vs. outside mount). Product-specific A curtain rod needs room above the trim too. If the casing runs almost to the ceiling, write that down, because it changes both.
Heat sources. The U.S. Fire Administration advises keeping anything that can burn at least 3 feet from heat sources, naming radiators and space heaters among them (U.S. Fire Administration, heating fire safety). The Department of Energy's guide says to keep registers and radiators clear of drapes for heating as well (Energy Saver Guide, 2022). And a window above a heat source is often there for a reason: Natural Resources Canada explains that air moving across the glass keeps it warmer, which is why heaters are placed under windows, and that closed drapes, deep sills and nearby furniture can trap cool air at the glass and lead to condensation (Natural Resources Canada, condensation). A radiator under the window is a fact that shapes the choice; note it.
The escape window. Building codes based on the International Residential Code require every sleeping room to have at least one operable emergency escape opening that opens from inside without keys, tools or special knowledge. A Washington State permitting consortium's tip sheet for the 2021 code states the requirement; the code says nothing about curtains, and adoption varies by place (MyBuildingPermit.com, emergency egress openings tip sheet). Ask the authority Our working rule, which is an inference from that requirement and not code text: in a bedroom, note which window is the one you would leave by, and do not choose anything for it that is fixed across the opening or that needs tools to move.
If you are measuring a whole room for furniture as well, Learn Space Planning's Measure and draw the room records windows, radiators and outlets from a corner, and those measurements serve here too.
5. Ranking the needs
Once a window's needs are written down, put them in order. The method is simple and it is ours: the one need you would not trade away chooses the kind of treatment, and the others choose among the options that kind offers. Preference
The reason for ranking rather than listing is that needs conflict, and a list hides the conflict until you are standing in a shop. Daylight and darkness pull in opposite directions. So do view and daytime privacy. A sheer gives light and daytime privacy and fails at night; a blackout shade gives darkness and night privacy and takes the daylight when it is down. If the list says "privacy, light, darkness, the look", any of four kinds seems to fit. If the ranking says "darkness first, privacy at night second", the choice narrows to opaque kinds that close the edges, and the look chooses among those.
How to find the first need
- Ask what would make the window a failure. Not "what would be nice", but what would make you take the treatment down. For a shift worker's bedroom, light at 9 a.m. For a living room on a sidewalk, being watched at 9 p.m. For a home office, not seeing the monitor at 8 a.m.
- Check it against the hours. A need that bites only when nobody is in the room can drop down the list.
- Check it against what you saw outside. If nothing shows after dark because the window faces a blank wall or a high fence, privacy at night may rank low even in a bedroom.
- Write the rest in order. The second and third needs decide between kinds that both meet the first; the look usually comes last, not because it matters less but because it can be met within almost any kind.
Where two needs both seem to come first, the usual answer is two layers or one treatment with two settings: a sheer and a lined curtain on one rod, a shade that lowers from the top as well as rising from the bottom, a shade with two fabrics. That is a decision for Curtains, shades, blinds and shutters; here it is enough to write that the window has two first needs.
Write the ranking on the needs sheet of the window survey, in the column "The first need", with the rest in Notes. If you are not sure yet, write "not sure" and come back after the look outside after dark. Most uncertainty ends there.
This chapter helps you describe what a window needs. It does not say what a window "should" have, and the ranking is yours, not a rule. The direction table is a general pattern for the Northern Hemisphere; trees, buildings, eaves and porches change it, and your own look at three times of day settles it for your window. Whether a lease or an association allows a given treatment is a question for the lease and the people who manage it, not for this chapter.
6. The window across the seasons, and the whole home Go deeper
A second look in another season. The three looks in one day describe the window in one season. The sun's path changes through the year, and the same trade association notes that in winter a lower sun can bring more direct sunlight under eaves and into a room (IWFA, low winter sun and glare). If you have moved in during summer, repeat the three looks in midwinter before ordering anything expensive for a south or west window, and add a "Season routine" note to the survey row: what you would open and close, and when, in each season.
A sun-angle sketch. On paper, draw the window in section: the wall, the glass, the eave or porch roof above if there is one, and the floor of the room. Then draw a line from the edge of the eave past the bottom of the glass. Sun steeper than that line is shaded by the eave; sun lower than it comes in. You do not need angles from a table: watch where the patch of sun falls on the floor at midday in each season and draw the lines through it. The sketch shows why a south window can be shaded in June and sunny in December without anything on it changing.
A whole-home survey. The survey works one window at a time, and a first pass should stay with one room. Once that room is done, adding the rest has two uses: it shows where one product line could serve several windows (fewer samples, one order), and it shows which windows can wait. A whole-home pass takes longer than it looks; do it room by room, at the hours each room is used, rather than all in one afternoon.
7. See it See it
Priya surveys her bedroom window. Priya rents a ground-floor apartment, her first. Her bedroom has one double-hung window. Her phone compass says it faces east, onto the street, and the sidewalk is about 6 ft from the glass. Inside the frame it measures 34 3/8 in wide at the top, 34 1/4 in in the middle and 34 1/2 in at the bottom, and 58 1/2 in high at the left, 58 3/8 in in the center and 58 5/8 in at the right. The frame is 2 3/4 in deep, and the sash lock stands 3/4 in proud of the sash. The trim is 2 1/2 in wide, and there are 14 in from the top of the trim to the ceiling. The landlord's 1 in vinyl mini blinds hang inside the frame.
She works three night shifts a week and sleeps until early afternoon on those days. She looks at the window at 8 a.m., at noon and at 4 p.m. on a day off: direct sun is on the glass at 8 and lands across the foot of the bed, gone by noon, and the street is in shade at 4. After dark, with the bedside lamp on and the mini blinds closed, she stands on the sidewalk: thin bright lines show between the slats, and she can make out the shape of the lamp and a shadow when she walks past it.
Known: the measurements; the facing; that morning sun reaches the bed on the days she sleeps through the morning; that the closed blinds leak light after dark; her lease terms, which forbid holes without written permission and require the landlord's mini blinds to be in place at move-out. Assumed: that the blinds' cords are not a hazard in this home, because no children live with her or visit (her assumption, true while that stays so). Open: how early direct sun reaches the window in midsummer, which only a look on a June morning settles; whether the landlord will allow a no-drill bracket, which her written request settles; whether a tension rod will hold inside a frame with a sash lock, which the rod maker's published depth and load figures settle.
Her ranking: darkness for sleep first, because sun on the bed at 8 a.m. on a sleep day is the failure she would take a treatment down over; privacy at night second, because she is home in the evenings on her days off and the street is 6 ft away; daylight third, for her days off; the look last. She writes "darkness for sleep" in The first need and the rest in Notes. The ranking narrows her choice to opaque kinds that close at the edges; it also tells her that one opaque layer, closed, serves both of her top needs at night.
- Window orientation is a major issue, a University of Oregon daylighting lecture slide: one paragraph on why east and west windows are the hard ones.
- Advanced Solar Control Education Guide 2026, the International Window Film Association: the seasons by orientation and the day and night privacy reversal, written for film dealers.
- Energy Saver Guide (2022), U.S. Department of Energy: the window covering advice for cold and warm weather in a few lines.
- Curtain Call: Drapery and Hardware of the Late Nineteenth Century, University of Delaware: what curtains were for before the products existed, for the history-minded.
8. Practice Practice
Minimum: one window, three looks in one day plus one look from outside after dark, and one row on the needs sheet with the first need chosen. Time: about 30 minutes of work spread across a day, plus five minutes after dark. Materials: a phone with a compass app or a map, a steel tape measure, a pencil and paper or the survey page open on the phone, and a lamp in the room.
- Name the window and find its direction. Give it a name you will recognize later ("bedroom, street side"). Read the direction from the compass or the map and write it on the windows sheet.
- Note what is outside it. Street, sidewalk, neighbor's window, yard, fence, tree, and roughly how far away.
- Look three times in one day. Morning, around midday, late afternoon. Each time, note whether sun is on the glass and where it lands in the room.
- Write the room's uses and hours. Who, what, when. Include who will open and close a treatment, and when.
- Note what else is at the window. Cranks, locks, sensors, heat sources, outlets, the space above the trim and beside it, and the depth of the frame. Write anything that sticks out into the frame in "In the way".
- Go outside after dark with the lamp on. Stand where a passer-by or neighbor would. Write "yes", "partly" or "no" under "Seen at night" on the needs sheet, and the same for what you saw by day.
- Rank and circle. Put the needs in order and write the first one in "The first need". If two tie, write both and note "two layers?" in Notes.
9. Your windows Your windows
This box uses the rooms, goals and facing from your setup to say which window to start with.
10. Check your work Check your work
Criteria
- Does the survey row name the room, the window and the direction it faces?
- Did you look at the window at the hours its room is used, not only when it was convenient?
- Does the row say what shows from outside after dark, from your own look, not a guess?
- Are the room's uses written with hours?
- Is anything that will limit mounting (locks, cranks, heat sources, little space above or beside) noted?
- Is there one first need, or two marked as a tie, with the rest in order?
- If a child lives in the home or visits, is that on the row?
Worked example
Priya's row (fictional) against the criteria. Room, window name and direction: yes, "bedroom, street side", east. Hours: she looked at 8 a.m., which is inside her sleep hours on shift days, so the look that matters most was taken at the right time. After dark: from her own look on the sidewalk, "partly", with the light lines between slats noted. Uses with hours: sleeping 8 a.m. to about 1 p.m. three days a week, and nights on the other four; evenings at home on days off. Limits: the sash lock's 3/4 in in a 2 3/4 in frame, the landlord's blinds that must stay, 14 in above the trim. First need: darkness for sleep, with privacy at night second. Children: none, and she has written that the cord check is based on that. The row passes. The one thing it leaves open is the midsummer morning, which she has marked to look at again.
Common mistakes
- Surveying at the wrong hour. A bedroom checked at noon on a Saturday says nothing about 7 a.m. on a work day. Look when the room is in use.
- Treating privacy as one need. A window that is fine by day can be a lit stage at night. Only the look from outside after dark tells you.
- Ranking by product. "I want Roman shades" is a choice, not a need. Write what the window has to do, then let Curtains, shades, blinds and shutters find the kinds that do it.
- Missing what sticks out. A sash lock or a crank found on installation day can turn an inside mount into an outside one, or an order into a return.
- Forgetting who opens it. A treatment chosen for a twice-a-day routine nobody keeps ends up doing one job all the time.
What is still unresolved
- Which layer gives privacy for each window by day and after dark, and what to put up tonight: Privacy by day and by night.
- How dark, how light, and how to deal with glare and the gaps at the edges: Daylight, glare and darkness.
- Which kinds meet the first need, and which are ruled out: Curtains, shades, blinds and shutters.
- Exact measurements for an order: Measuring for blinds and shades and Measuring for curtains.
- Whether your lease or association allows a treatment: your lease and the landlord or manager, asked in writing.