[sold5]

Hi,

I am just about to start extending our bungalow to add a new section that includes a cinema upstairs - see pics with sizes. New section is in yellow. Just got planning approved this week.

I need to decide if I will build the first floor in 150mm concrete hollowcore with a 75mm screed on top (separated by 25mm insulation so the top screed is floating), or use 300mm I-beams with a floating floor on top. I'm not sure if normal joists will cover the spans so they might not be an option.

Any advice on how I should progress? Having the cinema room isolated as much as possible is VERY important. Would I need a floating floor on top of the concrete floating screed? Room height will become an issue... I know I'll need to put in a second stud wall with double plasterboard all around, and may use green glue. Other than green glue I'd prefer to stick with standard building materials as in Rep of Ireland so carriage would be an issue, not to mention our prices for anything non standard.

Have I enough space to allow 2 rows of seats? Should I lengthen or widen the room? I based the room dimensions on an "ideal cinema room dimension ratio" I found on the net but the drawings show that I should be able to widen a bit to the left (although will be left with a sloping ceiling at the top of the left wall) and move the chimney breast back a foot or two to lengthen the room.

Note I need minimum 300mm insulation in the roof and possibly will lose even another 75mm inside whats shown if I slab with insulation-backed plasterboard.

Thanks for any advice, I dont want to regret later what I can change now!

Steve

[Ted White]

Hi. You are referring to the concrete slab being poured on the ground? If so, you won't really need any sound isolation treatments on that slab. It's too massive to be a concern.

[albriscoe]

Hi Steve

I`m not an expert here mate but will try to help, if you are planning to use a beam floor if thats what you mean when you say "hollow core", then I have to ask what is the 75mm of screed for, is it for ufch or something.

If it is then 65 mm is adequate and I would go for more insulation between the 2 concrete floor to try to dampen the audio passthrough.

Even better for me would be to use an 100 mm concrete beam, 100 mm insulation then your finished floor, this will maintain your floor height as well.

My cinema room ceiling is my garage floor made up of 250mm beams and 60mm screed with nothing between because its a garage and I can`t hear a thing in the garage. Just normal plasterboard in the cinema room as well.

Size wise your room is great and easily enough room for 2 rows of seats imho.

sounds like a great project

cheers Al

[RipMaster]

Originally Posted by sold5

I need to decide if I will build the first floor in 150mm concrete hollowcore with a 75mm screed on top (separated by 25mm insulation so the top screed is floating), or use 300mm I-beams with a floating floor on top. I'm not sure if normal joists will cover the spans so they might not be an option.
....
Steve

I'm sure you have, but just in case have you calculated the relative weight of each of those solutions and checked that the your supporting walls are ok for that?

Since you are extending a bungalow upwards that might be a factor. If you have not done so already it might be wroth getting structural calculations done and then choose the best soundproofing option given the max weight you can get away with. You can always compensate for insulation in the roof and ground floor ceiling if you need to.

As for two rows of seats, I think that will depend as much on the screen type/size, projector placement and and how much height you have to play with. My own room is of a similar size and whilst there is floor space for two rows of seating, I'm not certain it will work out that way given the need to align the projector with the centre of the screen. Floor space wise I'd tend to agree with Al that you probably do have space for a 2nd row, but be careful not to make the room too cramped by chucking too many seats in there tough. There's always bean bags as an ad hoc front row!

Factors I've picked up so far that need to be considered:

• Screen placement
• Throw ratio
• projector placement in regards screen
• Screen size required/possible given the interplay of constraints
• viewing distances
• head clearance

Looks like a great improvement to the property though, good luck!

[deansocial]

i would do it in timber and insulated with rockwool between. in my experience sound is not stopped by block n beam floors as the vibration just pass through.

[albriscoe]

Surely Dean the timbers would allow the vibrations to pass even more. Also its not vibration were on about hear its audible acoustics.

A concrete mass of say 100mm and 65mm with 100 mm insulation sandwiched between them should be an awful lot more acoustically dead than 300mm timber joists.

Thats what I think anyways

As to the weight carrying question, if they are on a double skin wall with cavity their won`t be a problem, mine are 6.8 metres long and are 225 mm deep x 150mm wide so are massive and all sit on a 4" blockwork wall, and all calcs were designed by a structural engineer

[sold5]

Hi All,

Thanks for taking the time to reply.

By hollowcore I am referring to 150mm to 250mm thick concrete beams about 4 feet wide with circular holes running through them.

Moylough Concrete Galway, Mayo, Clare, Roscommon, Ireland - HOLLOWCORE FLOORING

and the pdf shows 52.7 db acoustic insulation here:

http://www.moyloughconcrete.com/imag...pan_tables.pdf

The screed on top is to get a flat final floor, as the beams are prestressed so bent slightly, and improve sound/ fire performance.

Under the hollowcore beams a dropped plasterboard ceiling is hung from metal threaded bars or stiff wires - so the ceiling below is isolated from the hollowcore beams which in turn are isolated from the floor above by stiff insulation - EPS or wood fibre/ rockwool dense slabs. The plasterboard ceilings below can also be screwed to timber strips that are nailed to the underneath of the hollowcore beams, but this would reduce sound isolation.

My main concern was a possible "drum effect" and the possible low frequency bass getting through the hollowcore floor.

Thanks for any more thoughts!

Steve

[deansocial]

sorry i misunderstood. the hollow core are obviously better that block n beam. Also if the ceiling is MF then that will improve the sound insulation

[RipMaster]

Originally Posted by albriscoe

As to the weight carrying question, if they are on a double skin wall with cavity their won`t be a problem, mine are 6.8 metres long and are 225 mm deep x 150mm wide so are massive and all sit on a 4" blockwork wall, and all calcs were designed by a structural engineer

It was not the walls that I was really worried about, but more the foundations. Since the building was originally a bungalow then would the foundations have been made so as to accommodate a 2nd lift, especially one with a block/beam/screed floor. I could be wrong but without verification there could be some uses there. I'm not saying that there would be issues, merely that is is something that needs to be confirmed structurally.

I'm currently building over 500 sq. meters with mostly block and beam floors and where we've put in a 2nd lift we had to put wider foundations and deeper concrete. There was one section that was a renovation and we were advised that we'd have to re-do the foundations before we could go with a bb floor so ended up using Posi-Joist and a dry screed as it was lighter and avoided having to re-do foundations.

[sold5]

The new extension with the second floor is going beside the old bungalow - the bungalow is not being raised so we should be ok as the extension foundations can be specced to take whatever load is necessary.

[RipMaster]

Originally Posted by sold5

The new extension with the second floor is going beside the old bungalow - the bungalow is not being raised so we should be ok as the extension foundations can be specced to take whatever load is necessary.