Blind Solutions Academy · C20 · A4 Quick Reference

Concealed-Blind Detailing Cheat Sheet

Pocket dimensions, clearances, fixing details and decision trees on four pages — the working numbers for the desk and the site.

Page 1 · Pocket dimensions & tube selection

Sizing the pocket

Depth = rolled fabric Ø + 15–25 mm

The cardinal rule. Size to the FULLY-ROLLED fabric diameter, never the empty tube.

Width = glass + 2×(bracket + end clearance)

Add the motor head + idler; the pocket is always wider than the glass.

Throat (slot) = 20–25 mm clear

Wide enough to clear the fabric, narrow enough to limit light leak; bead the plaster edge.

Working clearance ≥ 15 mm

Around the rolled fabric so it never binds against the pocket walls.

Tube	Typical use	Rolls thicker?
32 mm	Short, light blinds	Lowest capacity
38 mm	General purpose	Mid
45 mm	Tall / heavy fabric	Largest pocket

Drop / fabric	Tube	Rolled Ø	Min depth
2 700 mm, 3% screen	45 mm	~80–90	110 mm
2 400 mm, dim-out	45 mm	~95–105	130 mm
3 000 mm, blockout-lined	45 mm	~110–120	145 mm

Head-height cost: every 120 mm of pocket = 120 mm off glazing OR ceiling height. Check against SANS 10400-O daylight before dropping the head.

Page 2 · Clearances, tolerances & light leak

Coordination numbers

Side light leak & remedy

Blind runs 15–20 mm narrower each side

Free-hanging = two bright lines down the jambs. Fatal on AV / bedroom blackout.

Remedy: side channel + overlap

F-channel or recessed U-channel + 20–25 mm fabric-to-reveal overlap + throat shadow.

Shadow gap = dimension it

A dimensioned reveal (15–20 mm typical) reads as architecture; a discovered gap reads as a defect.

Deflection & span

Member	Limit
45 mm tube span	~3 000–3 500 mm max
Supporting steel / lintel	span/360
Over limit?	Intermediate support / larger tube / couple

Central light gap (multi-blind)

20–40 mm between coupled/linked tubes — minimise or mask with a mullion. Disclose to the client.

Corner: blinds cannot turn 90°. Return short of the corner or introduce a corner post.

Page 3 · Fixing details & the concealed drive

Fixing & motor

Fixing substrate rule

Bracket → real structure ONLY

Never fix to plasterboard lining or ceiling grid alone. Reach a steel angle / sub-frame back to slab or lintel.

Accommodate slab/lintel deflection

Pocket clearance absorbs span/360 live movement so a moving structure never jams the blind.

Access strategies (extraction test)

Strategy	Access
Snap-on fascia	Tool-free, elegant
Hinged lid	Full run access
Demountable tile	Suspended grid
Access panel	Sealed-ceiling fallback

Motor & power

Rated torque ≥ calculated demand (+ margin)

Demand ↑ with fabric weight, drop, tube Ø. Undersize = stall in a sealed pocket.

Mains 230 V → fused spur in pocket at FIRST FIX

Power + data must arrive before the ceiling closes. LV/battery changes the cabling story.

Standard	Covers
SANS/IEC 60335-2-97	Powered blind/shutter safety
EN 13120	Internal blind performance & safety

Control: RF (Somfy RTS / io), wired, or KNX / BMS dry contact — each imposes its own first-fix cabling.

Page 4 · Decision trees & standards

Choosing the detail

Concealment-family decision tree

Is there depth above the ceiling?

Yes, services-light → flush ceiling-recess pocket

No / shallow slab void → dropped bulkhead or joinery box

Deep masonry reveal? → window-head reveal pocket

No service access ever? → cavity (between-glass) blind

Accept replace-unit-on-failure cost → proceed

Wide-opening decision tree

Opening > 3 000–3 500 mm?

Add intermediate support, OR

Larger tube, OR

Couple / link blinds → dimension 20–40 mm central gap → disclose

Light-leak decision tree

Room needs blackout / AV-grade dark?

Yes → side channels + overlap + throat shadow + dim-out/blockout fabric

General glare control → screen fabric, no channel needed

Edge line acceptable? → flush pocket, dimension the shadow gap

SA standards quick map

Standard	Use
SANS 10400-XA	Energy: combined SHGC compliance
SANS 204	Rational-design fenestration / SHGC
SANS 10400-T	Fire: cavity barriers across compartment lines
SANS 10400-O	Daylight / ventilation floor on head height
SANS/IEC 60335-2-97	Powered-blind safety
EN 13120	Internal blind performance

Honest position: external shading beats internal; claim the concealed blind's true tested SHGC contribution and document it for the assessor.