Heat and sound insulation of a floor above a driveway underpass

[I like floors]

Hi all. 

 

I'm currently renovating a late 60's terrace with a bedroom suspended above a driveway (which provides vehicle access to the garages behind the terrace)

 

• The floor of this suspended bedroom is made up of 7" joists at 16" centres.
• Directly fixed (screws) to the underside of the joists, is some sort of cement board which more than likely contains asbestos.
• To the top of the joists will be glued and screwed a 22mm chipboard floor (with UFH grooves) and a corresponding cement board is screwed on top of the chipboard. 
• Final floor will be glued LVT.
• There has been no provision for ventilation of this floor void  (other than a non tight fitment of the asbestos boards)
• There is a no sign of rot or dampness in the joists (although there has been some woodworm)

 

I'd appreciate some opinions on how to best insulate this floor both thermally and acoustically. 

 

 

 

 

 

 

[I like floors]

I should add that removing the asbestos cement board from below and re-fixing using resilient bars or similar isn't practical (due to height and asbestos) 

 

I should also add that I've already bought the chipboard for the floor (it's Torfloor2 plus) 

 

I realise that this will never be great acoustically.

 

My first idea is to use 100mm PIR plus 25mm acoustic roll (knauff or similar)

[JohnMo]

PIR has almost zero noise stopping capability.

 

I would be more tempted to have a dense mineral wool between studs. Then full sheets of 25mm PIR above the joists if you have head room. This would get rid of any cold bridging, alternatively but it at the bottom of joists. You will need to ensure design is ok for condensation risk.

 

UFH design, make sure it's well thought through. Chipboard is an insulator, the pipe are likely to retain the pipe heat in the location of the groove, and not across whole floor. So you need aluminium spreader plates also. You want zero air gaps anywhere as air is a good insulation also. I did fully follow this advise and UFH in a summer house just didn't perform. So much so I put in other heating.

[Redbeard]

"RWA45 insulation slabs achieve Lambda 0.035 W/mK and are available in seven standard thicknesses from 25-100mm, with a density of 45 kg/m3." 'Raw' insulation value (not taking into account anything 'offered' by the structure or 'depleted' by it (joist thermal bridging, for example)) would suggest a U value of around 0.2W/m2K for full fill.  I'd also look at making everything (e.g. round the joists and any other penetrations of the 'envelope') as tight as a tight thing  in terms not only of 'thermals' but also airborne noise.

[I like floors]

Thanks for the replies.  

I'm not able to fit anything below or above the joists due to the floor type being set (already bought) 

I can only really choose what to put in the 7" void.

Redbeard, if i just stuffed the void with RWA45, would you be concerned about it sitting directly on the asbestos boards? 

Would stopping all air movement around the joists be a problem in terms of rot?