How thick should a media wall be?
A media wall finishes 200 to 300mm out from the existing wall face. That figure is a stack: a 100mm stud minimum to hold acoustic insulation, whatever the fire cassette needs behind its aperture, 12.5mm plasterboard, 3mm of skim, then cladding. Thickness and depth are the same measurement, and a Victorian chimney breast already supplies most of it.
How far out should a media wall be?
Thickness and depth are one measurement, and the trade using both words loosely is why two quotes for the same wall can look nothing alike. We quote the finished projection: the distance from the face of your existing plaster to the front of the new structure. Our standard build comes forward 200 to 300mm. As a stack that reads stud depth, then 12.5mm plasterboard, then about 3mm of skim, then the finish. Painted plaster adds nothing to the face. Vertical slatted oak adds about 40mm once you count the slats and the backing board they sit on, and £400–£800 to the price. A 150mm stud clad in slats therefore lands at about 205mm, not 150mm.
The figure repeated across most UK guides is 100 to 150mm, which is a studwork dimension with plasterboard added afterwards and nothing else accounted for. At 150mm overall you have roughly 135mm of timber to work in. Put 100mm of insulation and a recessed fire behind that and the numbers do not add up. If someone has quoted you a 150mm wall carrying both, ask to see the section.
What sets the minimum thickness?
Three things set the floor, and the deepest one wins. Acoustic insulation comes first: we pack 100mm Rockwool into the framework as standard, so the stud cannot be shallower than 100mm. The insulation dictates the timber rather than the other way round. On a Clapham terrace that is £150 on the quote. In a converted flat we specify Rockwool RWA45 at £200, which cuts ongoing bass transmission to the neighbours by 60 to 70 per cent, and we add mass-loaded vinyl behind the plasterboard on the party-wall side. A wall built too thin to take insulation drums when the bass plays, and that is the fault we get called back to fix more than any other.
The fire sets the second floor. A recessed water-vapour cassette such as the Dimplex Optimyst wants roughly 250 to 300mm behind its aperture, which is what pushes a build to the top of that range; a slim wall-effect unit wants a fraction of it. Buy the fire, take the depth off its current datasheet, then frame around it. Third is the screen. An 85-inch set on a full-motion arm loads the fixings with 40 to 50kg, so plywood goes into the framework across the whole mount footprint, which adds £100–£200. Where the flue above is still in use we leave a ventilation gap behind the framework under Building Regs Part J, and that gap is depth as well.
How much floor space does the depth cost?
Multiply the projection by the width of the wall and you have the floor area you are giving up. Nobody puts that arithmetic on a quote, and it is the part worth sitting with. A 250mm wall running across the 4.2m living room of a Bromley 1930s semi takes 1.05 square metres. In a room of about 14.7 square metres that is seven per cent of the floor, permanently. It is usually a trade worth making, but make it deliberately rather than notice it once the sofa no longer fits.
In a Victorian or Edwardian terrace the sum comes out differently, because the chimney breast already stands 300 to 450mm proud of the alcoves. Build inside that existing line and the floor loss is nil, since you are filling a void the house came with. Ceiling height changes how the same depth reads. Under the 2.9 to 3.1m ceilings of late-Victorian Clapham a 300mm wall looks deliberate; against the 2.7m average of a Balham Victorian terrace it starts to close the room in, so we hold the depth down and fit a slim wall-effect fire rather than a deep recessed model.
From our London projects
Bromley is our most expensive borough, typically £5,400–£6,500. Bigger rooms and bigger screens carry most of that, but depth plays its part: with no chimney breast in most 1930s semis, every millimetre has to be built rather than borrowed. A four-bed semi on Bromley Common with a 4.2m living room took an 85-inch screen, a wide fireplace and a sound bar hidden in the recess for £6,400 over twelve days. Where the breast already exists you are not buying depth, you are using what is there: a three-bed Victorian terrace on Clapham Common North Side took a 65-inch recess and oak slats inside the existing breast line for £5,200 over ten days, with no floor given up. Down in SE20, a first-floor flat in a converted Victorian house on Anerley Road had no breast at all, so the whole projection went onto a flat internal wall with Rockwool RWA45 and mass-loaded vinyl behind the board, at £4,200 over eight days.
The tightest tolerances are in Clapham, where front sitting rooms measure 3.2 to 3.8m wide and the breast is only 1.2 to 1.4m across. We survey those personally because the wall has to land within 5mm of the breast on both returns, and an extra 12mm on the face shows up as a step where the new work meets the old plaster.
More on price the cladding and joinery choices, or media walls in Clapham, or book a free site survey. You can also generate a free design mockup for your own room, or head back to the Media Wall Installers London homepage.
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