Insulation - too good to be true?

[attractivebrunette]

Untitled

• attractivebrunette
• 5 Mar 2011
• 1

Hi guys, I'm insulation the space above my ceiling today. It's a converted house. There is a flat above mine and I don't have access to it. I've taken down the old ceiling and have new plasterboard to put in it's place (I'm obviously going to remove the new spot lights and put blocks on the cable first)

So how do I insulate the space between the joists? There's so many different types on the market I don't know which one to get. Some give an R rating and others don't. This one seems very good http://www.wickes.co.uk/Space-Blanket/invt/161206 but I don't trust the customer reviews. Everyone gives it 10 / 10.

My joists are 30cm apart and 20cm deep. Which is best for me? B&Q seem to have different types of insulation. Should I get this Space Blanket thing or would 'normal' insulation work better?

And how can I put the insulation in place before the plasterboard goes up? Should I put one board at a time then slide some insulation between the joists, then do another bit?

 

[ajrobb]

I suggest you research 'Robust Detail' solutions for floors between flats in converted houses. These satisfy Building Regulations without having to measure acoustic performance. Things to note:

• there isn't going to be a huge saving as flat upstairs should be warm (but why give them heat for free?)
  look up acoustic-grade mineral wool as it is heavier and absorbs more sound
  look up resilient bars for fitting plasterboard
  look up intumescent acoustic sealer
  you may need to provide a 30 or 60 minute fire barrier (check with Local Authority Building Control) ceiling between dwellings
  LABC might tell you to use chicken wire to hold mineral wool against floorboards upstairs

 

[kakdroog]

Having done this recently I suggest you cover as much as possible while you can and have the ceilings down. I used fire graded acoustic wool 100mm between joists leaving a 100mm air gap from the upstairs floor to the wool then covered the entire area with an acoustic rubber membrane 3mm (stapled to joists) to keep the wool in place and as a rubber seal for the resilient bars. Then two layers of acoustic plaster board 15mm staggering the joints also leave a 5 - 8 mm around the walls then fill the joints and the gap around the wall with fire grade acoustic sealant, then plaster and paint and Bob's your uncle.

This will give you the fire barrier and drop the db level well below the part E regulation and save you money on heating etc...

 

[ajrobb]

Without treating the floor upstairs I'm not convinced that you'll handle impact noise sufficient for Part E. Also, I'm sceptical about the fire resistance of mineral wool held in place by a rubber sheet. It might not matter as just the two layers of plasterboard may be sufficient for fire resistance. However, it's possible a rubber sheet could act as 'constrained layer damping', further reducing air-borne noise, if used between the sheets of plasterboard.

As you are working on the fire barrier between dwellings, you probably have to notify LABC.

 

[attractivebrunette]

Okay, this all sounds interesting. There is a real trouble with noise from upstairs so anything that will help reduce that will be welcome.

Kakdroog, why is a 100mm air gap important between the wool and the floorboards for the flat above? The joists are only 300mm deep and I'd like to put as much insulation in there as possible and was thinking of two layers of 150mm rather than 100mm and an air gap.

I like the idea of the acoustic rubber membrane between the plaster board sheets and I've just researched resilient bars which also appear useful.

Ajrobb, impact noise isn't too much of a problem upstairs, it's mainly noise from the television. Thanks for the tip about the rubber sheet between the boards.

 

[TicklyT]

Any insulation you install, whether accoustic or thermal, will be seriously compromised by the multitude of holes you will need to cut in the plasterboard to install those spotlights, and the necessity of keeping the insulation well clear of the light fittings to prevent them from overheating....

....which leads on to the next potential problem - recessed spotlights breaching the integrity of the fire barrier your ceiling should provide.

Maybe a different lighting solution would assist your aim of improving accoustic insulation.

 

[kakdroog]

Well with any sound proofing air is the best dampener if you have 300mm from the top of the joist (their floor) to your ceiling then even better put in 200mm acoustic wool but leave an air gap. Also if you are having spots then get acoustic light hoods that pop over the top of the spot in the ceiling. Most importantly make sure you seal all the gaps and joins properly else the sound will find the gaps and leak through them.

The main reason I did not do the membrane in between the plaster boards is that you have to screw the boards together and into the bars making rather a lot of holes in the membrane breaking down the structure etc. but as you are not after studio quality sound proofing it all helps believe me. Also check out Green Glue (between the boards) I have heard a lot about it and it has all been very good, just make sure it will work for ceilings, last thing you want is it all coming down on your head.

Remember with any sound proofing the heavier and more dense the material the better but also remember that it has to stay up above your head

@ajroob indeed, I agree but the rubber and resilient bars help quite a bit but yes impact is best tackled at floor level, I don't recall the name right now (will dig out the invoice) of the acoustic wool used but it had a very high fire rating so did the rubber membrane. But I can't say that it would meet regs as I have not had it tested...

 

[ajrobb]

Well with any sound proofing air is the best dampener

Air is terrible at damping - think church organ or flute. Mineral wool is used as the dampener for air; as the energy oscillates between movement and pressure, the mineral wool reduces the temperature changes. Holes don't matter, just the mass.

The main reason I did not do the membrane in between the plaster boards is that you have to screw the boards together and into the bars making rather a lot of holes in the membrane breaking down the structure etc.

... leaving 99.9% of the structure unaffected - no problem. It is the shearing between the layers of plasterboard that lets the rubber absorb vibration energy, it is not there as an air barrier.

Also check out Green Glue (between the boards) I have heard a lot about it and it has all been very good, just make sure it will work for ceilings, last thing you want is it all coming down on your head.

Whatever you do has to survive a fire for at least 30 minutes and possibly 60.

 

[kakdroog]

@ajrobb I disagree, an air cavity that is air tight is an excellent dampener lets just say the proof is in the pudding I have done it and it worked a charm.

Either way I can say do it, the improvement on both impact and airborne noise was worth it...

 

[ajrobb]

Let's just disagree on terminology. I say an air cavity is an impedance barrier and the mineral wool is the dampener. Where there is a large change of impedance, energy tends to get reflected rather then propagated and that is very useful.

 

[JohnD]

Good idea to reconsider the idea of making holes in the ceiling for lamps.

Apart from letting noise and fire through, in a couple of years when holes in the ceiling are as fashionable as stone cladding, you will have all the trouble of filling them in and replastering the ceioliong.