Sound insulation in roof renovation

[geraldthehamster]

Can anyone suggest a material or combination of materials, and a method, that would maximise both heat and sound insulation, on the inside of my sloping roof?

I'm renovating the first floor of my house, which you would probably call a chalet bungalow, consisting of ground floor rooms surmounted by a 45 degree pitched roof, formerly containing partitioned bedrroms, which I have ripped out, in order to change the layout and to insert dormers into the rear-facing roof pitch.

My query concerns insulation for the sloping part of the wall/ceiling at the front (where the dormers aren't). Working up from the eaves, there will be an upstand of around 800mm, which I may make into cupboards, then 2 meteres of 45 degree-sloping wall/ceiling, then 2 metres of flat ceiling over to the other side of the roof.

Both the sloping and horizontal rafters are 3 x 2. There is a big purlin half way up the roof. There is no problem in insulaiung between and over the rafters to a depth of 6 or 7 inches. Bang in a load of Kingspan, vast amounts of rock wool over the flat ceiling, and all will be cosy. However...

The front of the roof (where the dormers aren't) faces a busy road. As these rooms will be bedrooms, I want to maximise the amount of sound insulation provided, without compromising the heat insulation. I am under the impression that Kingspan-type insulation is not the best sound insulation.

Regards Richard

[keith_765]

What ever you do , DON'T CRAM IT FULL WITH ROCKWOOL RIGHT UP TO THE BACK OF THE ROOF. You must leave a air flow gap. Rockwool is a perfect sound proffer on its own.

[The Natural Philosopher]

Actually its a crap soundproofer, on its own.

[Hugo Nebula]

On Sun, 6 Jan 2008 08:34:25 -0800 (PST), a particular chimpanzee, geraldthehamster randomly hit the keyboard and produced:

The two best sound insulators are mass and isolation. An 'independent ceiling with more than the normal level of plasterboard should help. Try 25-30mm of sound-block plasterboard on resilient bars under the rafters.

[blue]

have a look at

[keith_765]

Advanced acoustic solutions to meet building regulations Rockwool stone wool has an open fibrous structure making it ideal for absorbing and regulating noise. Rockwool products reduce ear-deafening noise from machines or the activities of people, and provide ambient situations that allow normal conversation.

Rockwool SOUNDPRO RANGE range is specially designed to provide a comprehensive choice of sound insulation that meet the requirements of the New Approved Document E (ADE).

[keith_765]

Noise should be dampened to such an extent that it no longer interferes with the activity you set out to do. Just 30 dB is disturbing to sleep. Noise with sound levels of 35 dB or more interferes with the intelligibility of speech in smaller rooms. Inside buildings, the recommended maximum average for indoor background noise levels is 35 dB.

The widespread use of hard reflecting building materials in modern architecture amplifies the problem of noise indoors. For example, Rockwool is used in walls, roofs and floors to dampen the noise from next door neighbours and in enclosures around noisy machines.

SoundPro range includes Rockwool and Rockfon products for walls, ceilings, roofs, around machines, and under floors effectively to dampen noise from, or to, the neighbours.

[geraldthehamster]

So, are you chaps suggesting that I should insulate the whole depth of my sloping wall/ceiling with rock wool? Just the existing 3 inch depth, minus air gap, or battened out to the 6 or 7 inches that I suggested? I can see that this would provide good sound insulation, but how does rock wool compare to Kingspan as a heat insulator? Will it doing it all with rock wool satisfy my building inspector?

I was thinking maybe that I might insulate between the rafters with rock wool, then put 4 inches of Kingspan underneath. Incidentally, what I pulled out was plasterboard with rock wool jammed in behind it with no air gap - there was no trace of condensation on the roofing felt (circa 1963), or damp on the timbers.

I emphasise that my question concerns the sloping bit - not the flat ceiling rafters.

Regards Richard

[Dave Plowman (News)]

Cheapest way is two layers of thick plasterboard.

[John Rumm]

Assuming you have not got a breathable sarking then you need the air gap.

You can get celotex type products that are faced on one side with a heavier than normal bitumus foil, and have a dense cork layer on the other. Using this as your under rafter layer before a couple of layers of plasterboard ought to give fairly substantial acoustic attenuation.

[geraldthehamster]

Ok, thanks. I think perhaps the absence of condensation was due to the fact that the top storey of my house has been unheated an unused for the past several months.

So basically I'm screwing through an inch of plasterboard, and two to four inches of celotex, into the rafters, using long fixings? Any issues with this holding, or with the added weight on my 3 x 2 rafters, or the 8 x 3 purlin that spans 4.3 metres and bears interlocking concrete tiles (ie it's already underspecified by modern standards)?

Regards Richard

[harry]

You do talk s**te - alternatively you will be able to back up this statement with some figures?

[RobertL]

Ideally, as a previous poster has said, the (dboule) plasterboard should not be screwed to the rafters but rather to a 'floating' support frame that is not mechanically coupled to the rafters. the frame could be wood beams parallel to but between the rafters for example.

Robert Robert

[geraldthehamster]

Right, so - bearing in mind we are talking of a 45 deg. sloping surface, I potentially have insulation between the 3x2 rafters, with an air gap, "resilient bars" that are not "mechanically" coupled to the rafters - also with insualtion between (and/or over?) them, then my two sheets of PB. To what are my "resilient bars" attached, and how?

I'm interested in the suggestions involving am independent structure, provided I can do this without encroaching too far into the room (ie I could build a foot-thick wall/ceiling but would end up a little cramped).

Regards Richard

[John Rumm]

Yup, that can work - depends a bit on how much insulation you have under the rafters. When I did my loft I had 50mm between the rafters (with

50mm air gap behind - 100mm rafters), and 35mm under them. The plasterboard was simply screwed through the insulation into the rafters with no extra wood required. If you have 100mm of insulation below, that may become less easy.

The insulation is not that heavy. The plasterboard is obviously reasonably heavy (although nothing compared to the weight of the tiles), but it is a well distributed and uniform load.

[RobertL]

I'd d fix them to the existing roof woodwork at the ridge and eves attaching them to new a horizontal beam at those places fixed to the rafters on 2" spaces. then the new 3x2 will have a 2" gap at the slates. I'd fill the space with insulation leaving a gap at the slate side and having a vapour barrier at the PB side. Not sure about ridge ventilation

"Noise control in residential buildings", by D.A.Harris, suggests roughly a 24dB attenuation by adding a layer like this (at mid frequencies).

Robert

[Hugo Nebula]

On Mon, 07 Jan 2008 03:04:39 +0000, a particular chimpanzee, John Rumm randomly hit the keyboard and produced:

Unless the OP has counterbattens over the breathable membrane, he will still need a gap. Maybe not the full 50mm if he has a vapour barrier under and the void sealed, but enough to allow the membrane to drape.