How to Soundproof a Ceiling
This page shows how to install a soundproof ceiling by using our high performance space saving Oscar Iso-Mount system. A full isolated floating soundproof ceiling is now possible with as little 6mm ceiling height loss. All the work can be done from the room below by a local builder or competent DIY person.
To make things even easier many of the items required to soundproof a ceiling can be ordered from our online shop.
Oscar Acoustics has over 40 years’ experience in the building acoustics industry, working on such projects as Greenwich Royal Observatory, Warner Bros film studios, Tate Modern, The O2 Dome and Arena. We now offer our knowledge to you, the builder, developer and competent DIY person with our Oscar Iso-Mount acoustic hangers for floating ceiling soundproofing.
Oscar Iso-Mount Review
“The whole transaction has been simple and easy. I fitted the ceiling this weekend and it’s made an instant difference. So much so that I had to ask the owner of the flat above if he had been using the room above. I will recommend the product to my friends and will use it on other ceilings in my flat. Keep up the good work.”Jim Hood
Step by step Iso-Mount floating ceiling installation
(omitting electrical works)
The Oscar Iso-Mount acoustic hanger is specifically designed for floating ceiling installations onto timber floor joists, working only from the room below.
Important safety information:
- Only competent persons fully conversant with the use of personal protective equipment should carry out the floating ceiling installation.
- Consult the manufacturers of the plaster board for fixtures to be fixed directly to the plasterboard.
- Use fastenings as recommended by the plasterboard manufacturer.
- Celbar loose fill void insulation (as recommended), is also an excellent thermal insulator. Bring this to the attention of your qualified electrician who may have to allow for heavier cables and ventilation gaps around down lighters, (too be avoided if possible as this will allow sound through).
Iso-Mount floating ceiling components/Iso-Mount assembled
Prep work for floating ceiling installation:
1. Remove the existing ceiling, (if refurbishment work), to expose the structural timber joists and the underside of the floor of the room above. Check the condition of the underside of the flooring system of the room above and seal any gaps or holes to provide an airtight seal using Oscar Seal acoustic sealant ref: OAS/1
2. Using either a laser level or long spirit level, check the level of the joists.
The following drawings give further explanation before the installation notes continue...
Iso-Mount floating ceiling installation
NOTE: Fit the floating ceiling Iso-Mounts to one side of the joist only; this can be either side.
Proceed fixing the Iso-support brackets to the joists using 1 of 2 methods:
If you are satisfied that the joists are level, proceed by fixing the Iso-Support Brackets, measuring from the underside of the joist. This can be anywhere between 16mm above the underside of the joist to the underside of the Iso-Support Bracket, (as in diagram 1 above), and 4mm below the underside of the joist to the underside of the Iso-Support Bracket, (as in diagram 2 above). The 16mm above option gives the minimum ceiling height loss of approximately 5mm and the 4mm below option gives a ceiling height loss of approximately 26mm but with more clearance.
Fix the Iso-Support Brackets 100mm (4 inch), away from the wall and equi spaced at no more than 650mm centres (25.6 inches), if joist centres are 400mm (15.75 inches).
NOTE: If in doubt, fix an additional bracket and evenly reduce the spacing.
You can vertically adjust the positions of the Iso-Supports to compensate for reasonable deflection in the joists. This is to achieve as flat a ceiling as possible for appearance; it does not affect the noise transfer reduction of the new ceiling.
Identify the lowest position of the lowest joist and mark a vertical line up the side of the joist at this point. Measure 16mm up the line from the underside of the joist and mark a horizontal line. Fix the first Iso-Mount centrally on the vertical line with the underside of the Iso-Support Bracket sitting on the horizontal line 16mm from the underside of the joist; this gives the minimum loss in ceiling height of approximately 5mm, (less than 0.25inch)* - Fix lower if ceiling height loss is not critical. If you have chosen minimum ceiling height loss, the first Iso-Support must be fixed at the lowest point of the ceiling joists.
DO NOT fix any Iso-Supports higher than 16mm above the bottom of the joist, as this may allow the sheets of plasterboard (when fixed), to touch the joists and create a path for noise transfer.
The first Iso-Mount fixed at the lowest point of the ceiling joists is the datum for the height of the remaining Iso-Support Brackets. Taking the level from the underside of the fixed Iso support (datum), mark a horizontal line along the joist using a long spirit level or laser, marking the positions of the remaining Iso-Mounts: 100mm (4 inch), away from the wall and equi spaced at no more than 650mm centres (25.6inches), if joist centres are 400mm (15.75inches).
If in doubt fix an additional bracket and evenly reduce the spacing.
If you have chosen minimal ceiling height loss, the base of the datum Iso-Support bracket will be above the bottom of the joist. A method of transferring the level to other joists is to use magnets to increase the depth and allow transfer of levels by spirit level or laser.
The magnet shown is a 27mm dia x 25mm deep pot magnet. You will need at least 2 which we can supply for your convenience; they are useful tools.
3. Ensure the Iso-Support floating ceiling brackets are fixed so that the level is maintained in all directions.
4. Assemble the floating ceiling Iso-Mounts by pushing the Iso-Rubber into position on the Iso-Saddle - the rubber is held in place by the side guides and the 4 triangular grippers and sits on the raised dimples. Then position the Iso-Saddle (with rubber assembly), onto the base of the Iso-Support Brackets. The Iso-Rubber sits flat and is held in place by 4 triangular grippers and side guides. Click to see Iso-Mount Assembly photo and diagram.
Fixing the C Channels - proprietary 48mm drylining channel
(These are the channels that the plasterboard will fix to):
1. Hook a length of C Channel onto the side (nearest the joist), of two Iso-Mounts that are at least 1 metre apart. Then squeeze the C Channel and saddle between your thumb and fingers and the channel will snap-fix into position.
2. Repeat the above along the length of each joist as required.
3. The C Channels run parallel to the joists for the full length of the joists.
NOTE: The C Channels must not touch the walls as this will create a path for vibration and noise transfer; leave a gap of about 20mm (3/4 inch), between the C Channel and the wall. Connection between the C Channel and the wall or joist will mean that the sound proof floating ceiling is no longer floating.
- The fixed C Channel is level and clear of the walls at both ends
- The Iso-Mounts are still correctly assembled
- The bottom of the fixed C Channel is below the joist by a minimum of 4mm or greater if the loss in ceiling height is not critical
NOTE: under load the Iso-Mounts will deflect downwards by up to 2mm (0.08 inch).
4. Joining lengths of C Channel should be done in line with the manufacturers standard instructions.
5. The C Channels now provide a floating ceiling grid for the installation of the first layer of gypsum panels.
Fixing Oscar Foam
This fixes around the walls and the plaster board abuts to it, isolating your sound proof floating ceiling.
6. Mark a horizontal line around the wall at the calculated level of the underside of the floating ceiling, i.e. level with the underside of the lower plasterboard. When using 2 layers of 12.5mm plasterboard this will be 25mm, (1 inch), below the underside of the C Channels.
7. Install 25mm wide x 10mm thick self-adhesive Oscar Foam along this line with the bottom of the foam on top of and sitting on the line.
NOTE: This will prevent direct contact between the plasterboard (next job), and the wall: a potential path for vibration and noise transfer. Oscar foam and the Oscar Iso-Mount combined is what creates the floating ceiling.
Fix ceiling boarding first layer
NOTE: FIRST READ INSTALLING CELBAR ~ Option 1 (see below)
8. Install 1 layer of high density Gypsum board in line with manufacturer’s standard instructions. Make sure that the boards around the edge of the ceiling compress the 10mm (3/8inch), thick Oscar-Foam as much as possible: 10mm compressed to 5mm (3/16”), is good; this is to seal gaps tightly but prevent the plasterboard from touching the walls and transmitting vibration.
It is very important that you do not screw through the plasterboard into the joist instead of the channel. This will again create a path for vibration to run and prevent your floating ceiling from working to the best of its ability.
The preferred and tested void fill material for floating ceiling sound proofing is Celbar. Celbar is a recycled fibrous loose fill flock that is environmentally friendly, has low embodied energy and does not itch. Celbar is an excellent acoustic and thermal insulating material.
There are 2 options when installing Celbar:
Option 1 - Either the Celbar is packed in by hand by the installer
Option 2 - Oscar Acoustics blow fill it with a specialist machine
- As the installer fixes the first layer of plasterboard he/she empties bags of loose Celbar and places it in the floating ceiling void by hand as each board is being fixed. Be sure to pack it in tight by hand or with a tool such as a wooden broom head.
- The installer leaves a small section of board to finish; he/she cuts holes 100mm [4 inch] in the board at a position centrally between the joists and fills this last area by hand. Replace the 100mm dia blank into the hole and screw fixing it in position using a short piece of batten positioned above the plasterboard. Be sure not to allow the batten or screws used to touch the joists or ceiling sound proofing mounts thus creating a path for vibration travel through your floating ceiling. Use gypsum filler to seal the disc cut-outs and board joints.
- Apply the second layer of plasterboard; stagger the joints and compress the Iso-Foam but do not allow the boards to make direct contact with the walls.
- Seal joints, plaster skim and decorate.
NOTE: 100mm (4 inch), holes are not critical, it is just an opening for easy hand access into the floating ceiling; a person with large hands may require a larger diameter hole.
*This is often preferable for large areas and/or deep voids*
- With the first layer of plasterboard installed and butting joints sealed, the floating ceiling is now ready for the installation of Celbar by Oscar Acoustics or any licensed installer. This will require holes of 100mm dia to be cut in the ceiling board so Oscar can insert hoses into the floating ceiling. The cut out discs of board are retained. At least 1 hole between each joist, or more if required to ensure the void is full of Celbar. Where noggins split the void space in two, cut holes at either end of the void space.
- On completion of the Celbar fill, replace the 100mm dia blanks into the holes and screw fixing in position using a short piece of batten positioned above the plasterboard. Be sure not to allow the batten or screws used to touch the joists or floating ceiling sound proofing mounts thus creating a path for vibration.
- Use gypsum filler to seal the disc cut-outs and board joints.
- Apply the second layer of plasterboard, stagger the joints and compress the Oscar-Foam but do not allow the boards to make direct contact with the walls creating a vibration path around the floating ceiling mounts.
- Seal joints, plaster skim and decorate.
For non UK installations email email@example.com requesting the name of your local Celbar supplier/installer. Celbar is manufactured by International Cellulose Corporation with a worldwide network of licensed installers.
- Oscar Iso-Mount Assemblies
- 25x10x 7mtr rolls Oscar-Foam, (1x 3/8x 275 inches)*
- Oscar-Seal Acoustic Sealant OAS/1
- Celbar Acoustic Void Fill
Local builders merchants:
- Standard 12.5mm, (1/2inch) Plasterboard. Heavy density acoustic board is not necessary
- 45mm Dry Lining Channel
- Manufacturers include British Gypsum, GypLiner type GL1 lining channel and GL3 Channel connectors.
- N.B. GL8\wall support channel is not required
To buy any of the Oscar Acoustics items in our, 'How to soundproof a ceiling' page above, please click here.
Celbar void space fill is a very effective thermal insulator and where there are multiple habitations very little heat energy will be lost to adjoining units. Thermal transmittance through a typical ceiling will be better than U = 0.20W/m2K.
Celbar can also be installed through the floor above when access is available and is normally installed by lifting floorboards.