At a glance
| Item | What the source says | Source | Note |
|---|---|---|---|
| Rise of the rear row | Found by sightline geometry from seat, screen and spacing; example 442 mm | Our geometry | Inputs are examples, not standards. |
| Step rise, private stair | 150 to 220 mm; going 220 to 300 mm | ADK 1.3, Table 1.1 | A rise above 220 mm needs a different arrangement. |
| Guard height, dwelling | 900 mm at stairs, landings, ramps, internal floor edges | ADK Diagram 3.1 | Balcony or roof edge: 1,100 mm. |
| Drop that triggers a guard at a flight or landing, dwelling | More than 600 mm | ADK 1.41 | Elsewhere, where reasonably necessary (3.1). |
| Guard in front of fixed seating, assembly | 800 mm within 530 mm of the seats | ADK Diagram 3.1 | Not a home rule. |
| Children under five | 100 mm sphere must not pass; avoid horizontal rails | ADK 3.3 | Guards and stair guarding. |
| Wheelchair space, non-dwelling | 900 × 1,400 mm, 900 mm clear access, level | ADM2 4.12 | Number from Table 3. |
| Row spacing | No source found; from the seat measured fully reclined | n/a | AV designer and seat maker. |
England. Approved Document K 2013 edition and Approved Document M volume 2 (2015 edition incorporating the 2020 and 2024 amendments), read 8 November 2026. Sightline figures are our own arithmetic with example values.
What the regulations say, and what they leave open
In England no regulation sets row spacing or riser height for a home cinema. What the regulations do reach is the platform's edges and steps, because a raised floor is a change of level. Approved Document K (2013 edition) covers steps and guarding in all buildings; Approved Document M volume 2 covers audience seating in buildings other than dwellings, which matters if the screening room is in a hotel, club or other commercial building.
| Question | Where to look | What it says |
|---|---|---|
| Steps up to a platform | ADK 1.3, Table 1.1 | A private stair rise is 150 to 220 mm and the going 220 to 300 mm (maximum pitch 42° noted). Rise and going must be consistent through a flight (1.5). |
| Guard at a platform edge, dwelling | ADK 3.1, Diagram 3.1; 1.41 | Guarding is provided where reasonably necessary at floor edges (3.1). In a single family dwelling the guard height is 900 mm for stairs, landings, ramps and edges of internal floors (Diagram 3.1). At flights and landings in dwellings a guard is asked for when the drop is more than 600 mm (1.41). |
| Guard in an assembly building | ADK Diagram 3.1 | Within 530 mm in front of fixed seating the height is 800 mm; elsewhere 900 mm for flights and 1,100 mm otherwise. |
| Children under five | ADK 3.3 | Where children under five may use the building, a 100 mm sphere must not pass through guarding openings and horizontal rails are avoided. |
| Wheelchair spaces, non-dwelling | ADM2 4.12, Table 3 | Clear space 900 mm wide by 1,400 mm deep per parked wheelchair; 900 mm minimum clear access; spaces horizontal; Table 3 sets the numbers. |
Row spacing, screen height and viewing distance come from the AV designer and the seat maker, not from these documents. The sections below show how those inputs set the platform rise.
Sightlines: finding the rise
A raised rear row sees the screen over the front row only if the line from the rear eye to the bottom of the picture clears the front viewer's head. That line is a straight one, so the rise can be found with similar triangles. With the symbols on the drawing (all in millimetres):
rise = (e + h + c − b) × (D + s) ÷ D − e + b
- e seated eye height above the seat's own floor;
- h height of the top of the head above the eye;
- c the clearance you want between the sightline and the head in front;
- b height of the bottom of the picture above the front floor;
- D distance from the front row's eyes to the screen, and s the eye-to-eye distance between rows, both in plan.
The worked example uses e 1,050, h 120, c 100, b 900, D 3,000 and s 1,800, which gives a rise of about 442 mm. These are example values chosen to show the method: none comes from a standard, and the eye height in particular depends on the seat, its recline angle and the sitter. Take them from the actual seat in the position it is used, and the screen height from the AV design.
| Screen bottom (b) | Row spacing 1,500 | Row spacing 1,800 | Row spacing 2,100 |
|---|---|---|---|
| 800 mm | 455 mm | 502 mm | 549 mm |
| 900 mm | 405 mm | 442 mm | 479 mm |
| 1,000 mm | 355 mm | 382 mm | 409 mm |
| 1,100 mm | 305 mm | 322 mm | 339 mm |
Rise for the second row, same example values and D = 3,000 mm. Three things follow from the arithmetic. A lower screen bottom needs more rise. A larger row spacing needs more rise, because the rear viewer sits further back and looks along a flatter line. And if the bottom of the picture is above the front viewer's head plus the clearance, the formula returns zero and no platform is needed. A third row repeats the calculation over the second row's head, not the first.
Steps, drops and guards
A rise of 442 mm is higher than the 220 mm top of the private-stair range in Approved Document K Table 1.1, so a single riser at that height is outside it. How a platform step is treated, whether as a flight of steps under Table 1.1, or by agreement with building control, is a question for the building control body, not something the Approved Document settles for a cinema platform. Two common ways to meet the arithmetic are two or more equal risers, or a ramp or lifting arrangement where access is needed; confirm which is accepted before the drawings are issued.
Guarding depends on the drop at each edge. The figure shows the 600 mm drop that paragraph 1.41 uses for flights and landings in dwellings and the 900 mm guard height in Diagram 3.1 for a single family dwelling. Paragraph 3.1 says guards are provided where reasonably necessary, so a low front tier may need only visible edge treatment and the rear tier may need a guard. The test is the drop at each edge, the people using the room and building control's view. Where children under five may use the room, openings and rails follow 3.3.
- Edge and steps. Make step edges visible with contrast and low-level lighting; see lighting levels by space. Keep rise and going consistent in a flight (1.5).
- Structure. The platform carries seats, people and sometimes powered recliners. Its loads and the guard's loads are for a structural engineer; Approved Document K 3.2(c) refers to BS EN 1991-1-1 and PD 6688-1-1 for guarding loads.
- Hotel or club screening rooms. If the room is in a non-dwelling, Approved Document M 4.12 asks for wheelchair spaces on a horizontal floor, each 900 × 1,400 mm with 900 mm clear access, and Table 3 gives the number. Approved Document K 1.4 notes that stepped gangways in assembly buildings may need pitches up to 35° for sightlines. Licensing may add requirements: ask the licensing authority.
Row spacing and seat layout
Row spacing is set by the seat, not by a rule. Measure the chosen seat in its fully reclined position, with the leg rest up, and add the walking space the operator wants between rows. A seat that is comfortable in a showroom row can leave no way through once reclined. The same figure feeds the rise calculation above (as s). For a seat in a hotel or club, leave a route to each wheelchair space and keep the spaces level (ADM2 4.12).
A seat that is wider than a standard seat, or two seats joined, changes the eye position across the row: draw the sightlines for each seat that is off the centre line of the screen, not only the centre one. For seat and sofa dimensions see sofa, armchair and bench dimensions and seat height, depth and width.
Sound, services and a mock-up
A cinema platform is a hollow wooden structure in a room built to be loud. These points are for the acoustician and engineer to confirm; the sheet gives no numbers for them.
- The void. A hollow platform can radiate and transmit low-frequency sound. Ask the acoustician whether it is filled, damped or isolated from the structure below.
- Services. Power for recliners, data, speaker cables and ventilation run through the platform; leave access hatches that are not under a seat's footprint.
- Wall and ceiling treatment. See acoustic wall panelling and acoustic doors and Rw ratings.
- Mock-up. A full-size mock-up of the front and rear seat with the platform edge shows sightline and legroom faster than a drawing.
Specification wording
Paste into your schedule or specification and replace anything in [square brackets] with your own figures. Wording is a starting point: your specification governs.
Seating platform [P1] rise [ ] mm above finished floor, derived on drawing [ref] from seated eye height [ ] mm for [seat model, position], screen bottom [ ] mm above finished floor, eye-to-eye row spacing [ ] mm and front-row distance to screen [ ] mm, with a clearance of [100] mm over the head in front. Sightline drawn for the centre seat and for each seat off the centre line. Row spacing measured with the seat fully reclined, leg rest raised.
Steps to platform [P1] to be [ ] equal risers of not more than [220] mm and goings of not less than [220] mm, arrangement agreed with [building control body, reference] before manufacture. Guard of [900] mm at edges with a drop over [600] mm, to loads given by [structural engineer]; where children under five may use the room, no opening to pass a 100 mm sphere and no horizontal rails. Step edges to be visibly contrasted and lit.
Platform structure designed by [structural engineer] for [seating and occupancy loads]; void [filled / damped / isolated] as advised by [acoustician]; access hatches to services outside the seat footprints; cable routes and ventilation as drawing [ref]. A full-size mock-up of the front and rear seat on the platform to be approved on site before the run.
Terms used on this page
- Sightline
- The straight line from a viewer's eye to the point on the screen that must stay visible, usually the bottom edge of the picture.
- Rise (platform)
- The height of a platform tier above the floor in front of it.
- Clearance (C value)
- The vertical distance by which a sightline clears the head of the person in front. The value is chosen by the designer; none is taken from a standard here.
- Private stair
- In Approved Document K Table 1.1, a stair intended for one dwelling: rise 150 to 220 mm, going 220 to 300 mm.
Standards and sources
- Approved Document K: Protection from falling, collision and impact (2013 edition): gov.uk page 3 Jan 2013, no later date. 1.3, 1.4, 1.41, 3.1 to 3.3, Diagram 3.1. Read 8 Nov 2026.
- Approved Document M volume 2: 2015 edition incorporating 2020 and 2024 amendments; 4.5, 4.10 to 4.12, Table 3. Read.
- BS EN 1991-1-1 and PD 6688-1-1: named by ADK 3.2(c) for guarding loads; Approved Document K lists [2011]; status not checked. Not read.
Questions we are asked
How high should the second row of a home cinema be raised?
It depends on the seat, the screen and the spacing, so there is no single figure. Draw the sightline from the rear eye to the bottom of the screen and raise the row until it clears the head in front with the clearance you choose. With example values on this sheet the rise comes to about 440 mm, and it changes by 50 to 100 mm with a change of screen height or row spacing.
Does a home cinema platform need a guard?
Approved Document K 3.1 asks for guards where it is reasonably necessary for safety at the edges of floors. In a single family dwelling Diagram 3.1 gives a 900 mm guard height for edges of internal floors, and paragraph 1.41 asks for a guard at flights and landings with a drop over 600 mm. Whether a given platform edge needs one is a judgement for building control.
Is the step up to a cinema platform treated as a stair?
Approved Document K does not say. Table 1.1 gives 150 to 220 mm for a private stair rise, and a single riser at the heights a sightline needs is above that. Agree the step arrangement with building control, for example two equal risers, before manufacture.
What row spacing should I use for recliners?
We found no published figure. Measure the chosen seat fully reclined with the leg rest up, add the walking space the client wants between rows, and check that the sightline calculation uses that spacing.
Do cinema rooms need wheelchair spaces?
In a private dwelling there is no such requirement in the documents we read. In a hotel, club or other non-dwelling, Approved Document M volume 2 4.12 asks for level spaces of 900 × 1,400 mm with 900 mm clear access, and Table 3 gives the number of permanent and removable spaces.
Do I need an acoustician for the platform?
A hollow platform can radiate and transmit low-frequency sound, so it is worth asking an acoustician whether it should be filled, damped or isolated. We give no numbers for this and found none in the sources read.
Download the factsheet
A two-page A4 PDF with the sightline formula and table, the Approved Document K and M figures for steps, guards and wheelchair spaces, and paste-in wording.