What Is Line-Of-Sight Occlusion? (Angle Specs)
Line-of-sight occlusion means blocking the straight path between a chosen observer and a target with an opaque screen. There is no universal privacy angle: the needed height and width depend on eye position, target size, screen location, and movement. Calculate where sightlines cross the screen, then check coverage and building-code limits.
A screen can look tall enough from one spot yet leave a clear view from a doorway or an oblique angle. The reliable approach is to define who might see what, map the full range of sightlines, and place an opaque barrier across them. I treat “angle specs” as project measurements, not a standard angle that works in every room.
Planning the Observer–Target Sightlines
A sightline is the straight path from an observer’s eye to a point on a target. Occlusion occurs when an opaque screen crosses that path. Start by recording the observer locations and eye heights, the target’s edges and height, and the floor levels; one viewpoint alone cannot establish full coverage.
What should you measure?
Include plausible viewing positions, not just the room’s center. A person may stand, sit, approach a doorway, or move sideways. Likewise, define the target as an area, not a single point. A screen that blocks the target’s center may still leave its edge visible.
For each observer position, note:
- Eye height above the local floor, in metres or feet.
- Observer-to-screen distance, (d).
- Observer-to-target distance, (L).
- Target height or range of heights, (z_t).
- Target’s left and right edges in plan view.
- Changes in floor height, door position, or screen position.
Use consistent units. The formulas below assume a level floor and that the observer, screen, and target are measured along the same horizontal sightline. If floors slope or change level, work from surveyed elevations rather than assuming a shared floor datum.
Is there a standard privacy angle?
No. The vertical viewing angle describes one observer-to-target ray. It does not, by itself, specify a screen’s height or prove that a target is hidden. Screen position matters: moving a screen closer to the observer changes where the ray crosses it.
Key takeaway: Set the observer and target limits first. Then calculate the screen dimensions for those limits.
Setting Screen Position, Height, and Clearances
Screen height follows from the ray’s elevation at the proposed screen plane. Calculate that crossing point for the target’s highest and lowest relevant points, then extend the screen far enough to cover the required rays. These are geometry-based dimensions, not code-prescribed privacy measurements.
How do you calculate the vertical crossing?
For a level floor, use:
[ z_s=z_e+(z_t-z_e)(d/L) ]
Here, (z_e) is observer eye height, (z_t) is target-point height, (d) is observer-to-screen distance, (L) is observer-to-target distance, and (z_s) is the ray height at the screen. The screen must cross the ray at that height.
For example, assume an eye height of 1.60 m, a target point 1.00 m above the floor, a screen 1.00 m from the observer, and a target 4.00 m from the observer. The ray reaches the screen at:
[ 1.60+(1.00-1.60)(1.00/4.00)=1.45\text{ m} ]
So an opaque screen must cover the ray at 1.45 m above the floor. That value is not a universal screen height. Check the full target and observer range, and account for the screen’s actual bottom edge and any gaps.
The vertical angle from horizontal is:
[ \theta=\arctan((z_t-z_e)/L) ]
This gives the ray angle, not a “privacy angle” to apply to all projects. Calculate it for each important combination of eye position and target point. A seated observer, for instance, may produce a different ray than a standing observer.
How do you size the screen in plan view?
Draw lines from each observer position to both lateral edges of the target. Where those boundary rays meet the proposed screen plane defines the needed width for that observer. Repeat for the full observer-position range. A screen that blocks a straight-on view may be bypassed when someone shifts sideways.
Set a project-specific margin for movement and installation tolerance. The amount depends on how far people can move and how precisely the screen can be placed; it is not a universal code value. Include that margin in your drawing, then test the edges from actual viewing positions.
| Design check | What to calculate or inspect | Why it matters |
|---|---|---|
| Vertical coverage | Ray height at screen for high and low target points | Prevents a view over or under the screen |
| Side coverage | Boundary rays to both target edges | Prevents a view around a screen edge |
| Observer range | Standing, seated, doorway, and shifted positions | Captures changes in eye location |
| Installation margin | Project-defined allowance for movement and tolerance | Accounts for small shifts in use or placement |
Key takeaway: The screen must intersect all specified rays, across its full height and width.
Building the Occluding Screen
An occluding screen is a fixed or movable opaque panel placed across calculated sightlines. Its framing, fasteners, and substrate must suit the real loads and the building surface. Do not assume a panel is secure because it looks solid; confirm the attachment method and avoid cutting or loading structural members without proper review.
Where should the screen go?
A screen closer to the observer may intercept a ray at a different height than one near the target. Compare candidate screen planes with the same sightline calculations before choosing a location. Also check door swings, circulation, access panels, ventilation openings, and nearby utilities before fixing the layout.
How should it be attached?
Use framing and hardware that are rated for the loads and substrate in the specific installation. The appropriate choice depends on panel size, weight, use, and the wall, floor, or ceiling construction. If the design requires cutting framing, anchoring overhead, or changing a structural element, get qualified review before work begins.
For a movable screen, include its full travel in the plan. A panel may block a ray when closed but leave the target exposed when partly open. Mark the intended operating position and verify that its hardware does not create a hazard or obstruct required circulation.
Key takeaway: Confirm the screen’s location, support, and movement before construction, not after finishing.
Verifying Coverage and Code Constraints
Verification means testing the built screen against the same observer positions, eye heights, target edges, and screen plane used in the design. Check straight-on and oblique views, and repeat after doors, furniture, or screen parts move. Also confirm local code requirements; geometry does not replace code review.
What building-code checks apply?
Model codes do not set a general architectural “occlusion angle.” The governing rules depend on the adopted code, occupancy, and project. Review zoning and building requirements that apply to the site, and check egress, accessible routes, guards, fire protection, and ventilation where relevant.
As a U.S. model-code example, the 2021 International Residential Code, Section R311.2, requires the required egress door to provide at least 32 inches of clear width and 78 inches of clear height. A screen or its hardware must not reduce the required clear opening. Confirm the locally adopted edition and the rules that apply to the building.
Do not use an added return or extension if it blocks a required route, door opening, sprinkler discharge pattern, or ventilation opening. Where fire protection or accessibility rules apply, verify the design with the authority having jurisdiction or a qualified professional.
How do you test for an oblique-view bypass?
Stand at each marked observer point and look toward both edges of the target. Then shift sideways through the defined observer range. If a view passes around the screen, revise its position or width and recalculate. Before adding a return, check that it does not obstruct egress, accessible circulation, or required fire protection.
Illustrative layout checks
In a hypothetical living room, a screen between a hall and a seated area may block the view from the hall center but fail when a person steps toward the door jamb. I would plot rays from both sides of the hall opening to both target edges, then check the screen plane against each ray.
In another hypothetical layout, a screen may meet the side-coverage test but allow a view over its top from a higher landing. I would recalculate for the landing’s eye height and the target’s highest point. These examples show why a single nominal angle is not enough; they are not fixed designs or code dimensions.
Key takeaway: Recheck the complete set of rays after installation and after any layout change.
A Practical Measurement Sequence
A short field process helps keep drawings, calculations, and installation aligned. Record the assumptions so another person can repeat the check. If the observer range, target, or screen location changes, update the calculations instead of relying on the original dimensions.
- Survey: Mark observer locations, plausible eye heights, target boundaries, floor levels, and viewing conditions.
- Calculate: Work out vertical ray crossings and draw plan-view boundary rays for each observer position.
- Mark: Identify the screen plane, required height and width, and project-defined tolerance.
- Review: Check egress, accessible routes, door swings, guards, fire and sprinkler coverage, ventilation, utilities, and structural support.
- Build and test: Install with suitable support, then inspect from each specified position, including oblique views.
- Recheck: Repeat if doors, furniture, or screen components move.
The result is a documented coverage test, not a guarantee that every possible view is blocked. If a new observer position or target is added, include it and test again.
Frequently Asked Questions
These answers clarify how to interpret angle calculations and screen dimensions. The key distinction is between describing a sightline and sizing a barrier: the angle describes the ray, while the screen’s location and extent determine whether it blocks that ray.
What does line-of-sight occlusion mean?
It means an opaque object blocks the straight path between a selected observer position and target point.
What is the correct privacy angle?
There is no universal privacy angle. Calculate sightlines for the actual observer positions, target area, and screen location.
How do I calculate screen height?
Find the ray height at the screen using (z_s=z_e+(z_t-z_e)(d/L)). Repeat for the target and observer limits.
Does a larger angle always need a taller screen?
Not by itself. Screen height depends on where the screen sits along the observer-to-target path, plus the eye and target heights.
How do I stop someone seeing around a screen?
Plot rays to both target edges from the full range of observer positions. Extend or reposition the screen only after checking circulation and code limits.
Should I include seated and standing eye heights?
Yes, if both viewing conditions are plausible. Use the relevant range rather than relying on one nominal eye height.
Is line-of-sight occlusion a building-code requirement?
Not as a general angle rule. Local code may still govern egress, accessibility, guards, fire protection, and other affected features.
Can a screen reduce required door clearance?
No. It must not reduce a required clear opening or block a required route. Check the locally adopted code and project requirements.
How often should I recheck the sightline?
Recheck after installation and whenever the observer position, target, door, furniture, or screen changes.
(This article was written by one of our staff writers, Garrett Vance. Visit our Meet the Team page.)
