Sound Insulation - Is it worth it?

[MdB]

I'm in the process of finishing off the underside of my floor and I'm wondering if it is worth fitting some sound insulation between the joists, below the oak floorboards and above the plasterboard which will be in between the joists.

The above picture is taken looking up at the underside of the floorboards. You can see the batons on either side of the joists which is were the plasterboard is going to be fitted. The question is whether or not fit sound insulation in the cavity.

I have fitted rubber strips between the joists and the floorboards and this will help with impact noise transmitted mechanically through the wood. Adding sound insulation (rockwool) in the cavity will potentially help reduce the air transmitted sound. However, this will be fairly expensive (£100), be a pain to fit as it will need to be cut to fit and according to my builder, it is unlikely to make a lot of difference. I also can't fit it all the way across the ceiling as there are various cable runs which need to be kept insulation free. Finally, we currently don't have any heating upstairs so don't really want to add a layer of insulation which will stop the heat rising.

Because of all of this, I thinking of not bothering. What do you lot think?

 

[FamilyWiggs]

We used SoundBloc plasterboard; 2 layers between the joists. Wasn't a lot more than standard plasterboard and whilst not perfect, it certainly makes a difference.

 

[middi]

I would definetely fit as much insulation as I could stuff in the cavity available. I am rather surprised that your builder said that it will not make much difference in sound travel. IT WILL MAKE A BIG DIFFERENCE !!!!!. Whilst some noise will be transmitted through the floorboards to joists contact the amplified drum effect noise of the void will be buffed out by fitting insulation.

Also I am at a loss when you say that heat will not rise as quickly through the insulation, i would have thought that if individual rooms are well insulated then the correct heat can be individually supplied to each room as required hence more efficient. If you have a free flow of heat convection or conduction that is not regulated you could well end up with more heat that you may need in a room, This excess heat could be retained where the rooms need to be warmer.

Middi

 

[Gervase]

Agree - your builder's talking boswellox. Fit as much as you can under there, and make it as dense as possible.

 

[AMc]

Your builder probably doesn't want to do it because it will be an unpleasant job to do and will slow him down. I'm afraid once you've paid to have the plasterboard fitted, skimmed and painted you'll wish you'd done it and it will cost £1000's to put in £100 of insulation.
I would also specify the sound insulation plasterboard as the minor incremental cost of regular will help and again can't be sensibly fitted once it becomes apparent there is a problem.

You can buy rockwool subsidised by the energy providers (with our money) in the big DIY chains - it says it's not to be used in new buildings but this is a renovation isn't it?
Also £3 a roll delivered here http://www.npower.com/web/diyloftinsulation/index.htm
It's obviously going in the loft though like they say

 

[Penners]

The rubber that you've fitted between the floorboards and the joists will help to attenuate the sound of people walking around above, but I don't think it will make a lot of difference to the sound transmitted upwards, from the room below. There will be a degree of attenuation due to reduced vibration of the boards, but not much.

I would definitely put insulation into the cavity. This will help to reduce acoustic and thermal transmission. Well worth £100, IMO. In fact (just to really wind you up!) I would set the counterbattens lower on the joists in order to increase the depth of the cavity, thus allowing more insulation to be inserted.

 

[ian]

I would definately add insulation. In our case we used 50mm rockwool batts - the difference was very noticable for both "ambient" noise (talking, TV etc) as well as impact noise, footsteps, falling out of bed, etc

 

[Stephen]

I would concur with the views expressed already that you should put in an appropriate accoustic insulation material (not just ordinary insulation). However, I would advise that you ensure that coverage is complete. The problem with sound is that a small gap in the insulation can allow through a disproportionate amount of sound. I do not have the actual figures in front of me but I seem to recall that a 10% gap in sound insulation could (in theory) allow through c. 80% of the sound. Any accoustic specialists on here can clarify this for you. The important thing is not to cut corners and to ensure that coverage is complete.

Stephen

 

[CatherineB]

I am completely higorant of the technology, but I would read your post the other way around - "and for a mere £100 I can put insulation across my entire loft floor - what a bargain!".

At that price, I would go for it. The downside of doing it is small, in relation to what you must have already spent, and the downside of not doing it is potentially huge. "For the want of a nail, the shoe was lost... etc etc".

 

[MdB]

That's the decision I came up with - the insulation has now been paid for and will be fitted next week. Lets hope it doesn't make upstairs too cold.

Thanks for all your comments.