Reflected ceiling plan for a backlit mirror: electrical rough-in coordination architects miss

A backlit mirror installed in a Malleshwaram powder room last October exposed a gap that appears on almost every Bangalore residential project: the architect specifies the mirror, the electrical contractor runs the rough-in, and neither has read the other's drawing. The result is a 40mm cavity routed into the back of the mirror frame—the space where the LED strip and transformer must sit—that collides with a live wire chased 35mm deep into the wall. The mirror arrives on site. The cavity is already cut. The electrical rough-in is already in the wall. The site supervisor calls the atelier. Nothing moves without a re-spec and a delay.

This note is about reading a Vetrova backlit mirror shop drawing before you hand it to the electrical contractor, and what to coordinate with them at the rough-in stage so the fitting goes in as drawn.

What the shop drawing shows that the architect needs to see

A Vetrova backlit mirror shop drawing is not an elevation. It is a section through the mirror frame, the wall, and the cavity behind. It shows three things: the glass thickness (typically 8mm or 10mm, toughened), the frame depth (usually 40mm from the back face of the glass to the rear face of the frame), and the location of the wire-chase within that cavity.

The wire-chase is a routed channel, 8mm wide and 6mm deep, that runs from the bottom-right corner of the mirror frame to the transformer. On a 1200mm wide mirror, this chase travels 1200mm horizontally, then drops vertically to the transformer box, which sits either on the floor or on a shelf below the mirror. The transformer itself is 120mm × 80mm × 40mm and requires 230V AC input and a 12V DC output to the LED strip.

The shop drawing specifies the exact placement of this chase—measured from the top edge of the mirror frame and from the side edge—so that when the electrical contractor runs a conduit or a live wire into the wall behind the mirror, they know which 8mm wide strip of the 40mm cavity is reserved for low-voltage wiring and which areas are clear.

The 40mm cavity: why depth matters to electrical rough-in

Standard cavity depth and what it holds

The frame of a Vetrova backlit mirror is routed to a depth of 40mm from the back face of the glass. This 40mm space accommodates: the LED strip (5mm tall, mounted on an aluminium channel), the transformer (40mm tall, mounted vertically or horizontally depending on space), and the low-voltage wiring that connects them. The cavity is not a void. It is a precisely dimensioned box.

On a typical Bangalore residential project—a master bedroom in HSR Layout or a guest bathroom in Indiranagar—the mirror is mounted directly onto the wall. The wall behind the mirror is typically a 100mm brick or block wall with a 20mm plaster finish. Behind that, the electrical contractor runs conduit and live wiring for the main light circuit, exhaust fans, and socket outlets. The conflict arises when that conduit or a live wire is chased into the wall at a depth of 35mm or 40mm, directly behind where the transformer needs to sit.

Cavity depth on custom commissions

On commissions where the mirror is inset into a recessed cavity in the wall—a detail we have executed in BTM Layout and Sadashivanagar projects—the cavity depth can be increased to 60mm or 80mm, which allows the electrical contractor to run conduit deeper into the wall and avoids conflict with the transformer. This requires a structural detail: the wall must be routed or built with a recess, and the mirror frame sits flush with the finished wall surface. The shop drawing for an inset mirror shows the recess depth, the frame depth, and the setback from the wall face.

If your project calls for an inset mirror, specify this to the structural engineer and the electrical contractor before the wall is built or cut. A backlit mirror inset 60mm into the wall requires the electrical rough-in to be chased at least 65mm deep, or routed around the recess entirely.

Wire-chase placement and the transformer location

The wire-chase is the path the low-voltage cable takes from the LED strip, through the frame, to the transformer. On a standard backlit mirror, this chase runs along the bottom of the frame or along one side. The placement is shown on the shop drawing as a dimension from the top edge and from the nearest vertical edge of the frame.

The transformer is the heaviest component and the one that takes up the most space. On a wall-mounted mirror above a vanity, the transformer typically sits on the floor behind the mirror or on a shelf or ledge below the mirror. On a mirror mounted above a floating vanity or in a recess where there is no floor space directly behind, the transformer is mounted vertically on the wall, using a bracket. The shop drawing specifies which mounting method is used and where the transformer sits relative to the mirror frame.

Before the electrical contractor runs any conduit or chases any wire into the wall, they need to know: where is the transformer going to sit, and what is the clearance around it. If the transformer is to sit on the floor, is that floor space clear of conduit? If it is to be wall-mounted, is there a bracket location specified on the drawing? If the transformer is mounted inside the mirror cavity (on a larger commission, or where the cavity is deeper than 40mm), the chase and the transformer location must be marked on the drawing and communicated to the electrical contractor at the pre-rough-in meeting.

The pre-rough-in coordination meeting: what to check

Before the electrical contractor begins work, the architect and the electrical contractor must walk through the shop drawing together. This is not a phone call. This is a site visit with the drawing in hand.

Check these points:

• Mirror dimensions and mounting height. Confirm the mirror is mounted at the height shown on the RCP and the elevation. A mirror that is mounted 50mm higher or lower than specified moves the transformer location and the wire-chase path.
• Transformer location. Confirm where the transformer will sit. Is it on the floor, on a shelf, or wall-mounted? Is there clearance for conduit or live wiring in that location?
• Wire-chase path. Confirm the path of the low-voltage cable from the mirror frame to the transformer. Mark this on the wall with chalk or tape so the electrical contractor knows which areas are reserved for low-voltage wiring only.
• Live wire routing. Ask the electrical contractor where they plan to run the 230V AC input to the transformer. This should not be inside the 40mm cavity or the wire-chase. It should be routed separately, either above the mirror, below the mirror, or to the side.
• Conduit depth. Confirm the depth at which conduit will be chased into the wall. If the wall is plaster-finished, conduit chased at 35mm depth will be only 5mm behind the back face of the mirror frame—too close. Specify a minimum depth of 60mm, or route conduit around the mirror area entirely.

Document this meeting with a site note or email. Photograph the marked-up wall. This becomes part of the as-built record and protects both the architect and the electrical contractor if the mirror installation is questioned later.

Tolerance and the joint line

A Vetrova backlit mirror is fitted to the millimetre. The frame is routed to the exact cavity depth specified. The LED strip is mounted on an aluminium channel that is cut to length on the atelier bench. The wire-chase is routed by hand, and its position is held to a tolerance of ±2mm from the dimension shown on the drawing.

The joint line—the gap between the back edge of the mirror frame and the wall surface—is typically 3mm to 5mm. This gap is filled with a silicone sealant (usually Dow Corning 795, a neutral-cure, non-staining silicone suitable for Bangalore's hard water and monsoon humidity). The sealant fills the gap and prevents moisture from entering the cavity during the June-September monsoon months.

If the electrical contractor has run conduit or a wire into the wall at a depth that leaves less than 5mm clearance from the back face of the mirror frame, the joint line will be compromised. The sealant cannot fill a gap that is less than 3mm wide. Moisture will enter the cavity, and the LED strip and transformer will fail within 12 to 18 months.

Specify a minimum joint-line width of 4mm and a minimum wall depth of 65mm for any conduit or live wiring that runs behind a backlit mirror. This gives the electrical contractor room to work and the sealant room to cure properly.

Bangalore-specific considerations: hard water and monsoon

Bangalore's water supply has a total dissolved solids (TDS) content of approximately 200 to 300 ppm, which is considered hard. This hardness leaves mineral deposits on glass and on silicone sealants over time. The monsoon humidity from June to September creates condensation on the back face of mirrors, especially in bathrooms and powder rooms.

A backlit mirror installed in a Koramangala bathroom with inadequate joint-line sealing will accumulate condensation in the cavity within two monsoon seasons. The transformer will corrode. The LED strip will fail. The sealant will crack and allow water ingress.

To prevent this, specify a sealant that is rated for high-humidity environments and that resists mineral deposits. Dow Corning 795 or equivalent is suitable. Ensure the joint line is sealed continuously around all four edges of the mirror frame. Do not leave gaps at the top corners or at the junction with the vanity or wall trim. After installation, allow the sealant to cure for 48 hours before the bathroom is used.

If the mirror is in a high-humidity area—a bathroom in Whitefield with an exhaust fan that is not vented to the outside, or a powder room with a window that does not open—consider specifying a dehumidifier or increasing the exhaust fan capacity. This is not the atelier's responsibility, but it is the architect's, and it affects the longevity of the backlit mirror.

Questions we get asked

Can the transformer sit inside the mirror cavity?

On a standard 40mm cavity, no. The transformer is 40mm tall, and the LED strip is 5mm tall. There is no room for both. On a custom commission with a cavity depth of 60mm or more, the transformer can sit inside the cavity on a bracket, provided the bracket is specified on the shop drawing and the electrical contractor is informed of its location before rough-in begins. This is not a standard detail and requires a custom drawing and a site inspection before the mirror is routed.

What happens if the electrical contractor runs a wire where the wire-chase is supposed to be?

The mirror cannot be installed. The atelier will discover the conflict when fitting the mirror on site, and the installation will be delayed until the wire is relocated. This typically costs one to two weeks and may require the electrical contractor to re-route the wire, which may affect other circuits or fixtures. Prevent this by holding the pre-rough-in coordination meeting and documenting the wire-chase location on the wall before work begins.

Do we need a separate electrical circuit for the backlit mirror?

Yes. The transformer requires a dedicated 230V AC circuit, typically a 5A or 10A MCB in the distribution board. This circuit should be independent of any other lighting or exhaust circuits in the room. The electrical contractor will specify the circuit rating based on the transformer wattage (typically 60W to 100W for a residential mirror). Coordinate this with the electrical design at the early stage of the project, not during rough-in.

Can the wire-chase be routed on the front face of the mirror frame?

No. The wire-chase is always routed on the back face of the frame, inside the cavity. A wire visible on the front face would be unsightly and would be damaged during cleaning. If there is no room for a wire-chase on the back face (because of conduit or structural elements in the wall), the mirror cannot be backlit as specified, and an alternative detail must be developed.

How often does the LED strip need to be replaced?

The LED strip fitted by the atelier is rated for 30,000 hours of use, which is approximately 10 to 12 years of continuous operation. In a residential bathroom, where the mirror is typically used for 2 to 3 hours per day, the LED strip will last 15 to 20 years. The transformer has a similar lifespan. If either fails, the mirror can be removed, the component replaced, and the mirror reinstalled. This requires the atelier to be contacted, and it typically takes one week.

Commissioning a backlit mirror for your project

If your Bangalore project calls for a backlit mirror, the atelier can work with your electrical contractor to develop a coordinated rough-in plan before work begins on site. Bring the electrical drawing, the RCP, and the mirror dimensions to the atelier, and we will produce a shop drawing that shows the wire-chase placement, the transformer location, and the clearances required. This drawing becomes the basis for the electrical contractor's work and prevents conflicts during installation.