Noise insulation pitched roof / vaulted ceiling

[Bosi]

Hi.

 

We have opened the ceiling in our living room which had previously the ceiling in 2.4m height, with a normal plasterboard and 10cm mineral/glass fibre mix.
The outside noise was less, but still noticeable.

 

We now want to use the full space of the pitched roof to create a vaulted ceiling.

At the moment the rafters have been strengthened and extended to 20cm depth, from which we have left a 5cm void below the felt under the concrete tiles for air ration and added 15 cm celotex insulation.

 

I understand that celotex is great for the heat insulation and that we overreach building specs with the 15 cm, but that it does not do much against outside noise.

As we live on a very busy road we wonder what would be the best way to insulate now the roof sound wise the  best / economical way?

 

Our builder wants to put additional 2cm wooden batons now under the rafters to account for uneven areas, not filled with anything and attach the sound plasterboard to them? Will this work, or just create an sound problem?

 

Currently I am looking into two different thickness sized acoustic boards, depending on what is available on the market currently. 

I read about mass loaded vinyl which is quite expensive, and which seems to be often recommended to add in-between the 2 soundboard plasterboards. 
And in addition I read about resilient bars, where I wonder if they are ok with the weight of two heavy soundboards, and in addition if they are actually helpful against street noise, as this is rather an airborne noise instead of ground-born, , or am I wrong? Or are they rather for ceilings where a room is used above, and so not what I need?

 

What would you recommend to keep out the road noise please?

Kind regards

Manfred

 

 

Edited November 13, 2021 by Bosi

[ProDave]

You won't want to hear this, but rip out the Celotex, fill between the rafters with mineral wool (Frametherm 35 is good for this, stiff enough to stay in place while you board over it) then re use your PIR so sheet over the bottom of the rafters so you really will have lots of insulation and better soundproofing.

[joe90]

Yes, mass (heavy stuff) is also good for sound insulation, the only thing I would do differently on my build would be to double board the ceilings (between floors) and/or sound rails (to disconnect boards from frame.) use ALL the space you can for heat insulation (400mm?).

[Bosi]

1 hour ago, ProDave said:

You won't want to hear this, but rip out the Celotex, fill between the rafters with mineral wool (Frametherm 35 is good for this, stiff enough to stay in place while you board over it) then re use your PIR so sheet over the bottom of the rafters so you really will have lots of insulation and better soundproofing.

Hi and Thank you.

 

It just has been painfully out in

 

So how can I make it work with keeping it in ?   it is anyway just 15 cm space, which would not give enough space for a good insulation of 30 cm for mineral woll i believe.

 

What is the best way to add below the insulation now to get things well sound insulated?

[Bosi]

1 hour ago, joe90 said:

Yes, mass (heavy stuff) is also good for sound insulation, the only thing I would do differently on my build would be to double board the ceilings (between floors) and/or sound rails (to disconnect boards from frame.) use ALL the space you can for heat insulation (400mm?).

Well I wonder about the sound rails, but there is no floor above, it is just the roof, so will they do anything against airborne noise from the traffic? Somehow I understand that they are rather for ceilings between floors or a joint wall / similar?

[Iceverge]

PIR between rafters, sorry for your troubles ?.

 

Anyhou we is where we is innit. 

 

Airtight membrane next religiously sealed everywhere. 45*45 counter batten with rockwool acoustic batts.

 

15mm or more soundboard plasterboard with acoustic sealant to all joints. Maybe 2 layers all joints staggered. Skim. 

[saveasteading]

I would be more inclined to leave the PIR as it is bought and the hard work done,  but then batten out twice to put in a layer of mineral wool, an air gap then a layer of any plasterboard. I don't think it needs acoustic seals as you have created a very long path for airborne sound. The shortcut might be by vibration through the roof via the rafters, so your resilient bar might be a useful insurance to break the contact to the pb.

 

Is the noise high or low pitched, air-borne or including vibration?

[Bosi]

2 hours ago, saveasteading said:

I would be more inclined to leave the PIR as it is bought and the hard work done,  but then batten out twice to put in a layer of mineral wool, an air gap then a layer of any plasterboard. I don't think it needs acoustic seals as you have created a very long path for airborne sound. The shortcut might be by vibration through the roof via the rafters, so your resilient bar might be a useful insurance to break the contact to the pb.

 

Is the noise high or low pitched, air-borne or including vibration?

Most noise we get is from cars etc, not  really vibrations from trucks, and of course loud exhaust from scooters etc.

 

I believe it is rather airborne noise which we need to address.
I made a bad choice with the 150mm celotex, but as you said it cost sweat and labour to put it in nicely, sound foaming even the smallest gaps.

So it is a "damn" good heat insulated room, which is just loud ?

Looking around and ripping out my last hears I think about to add  MLV like this 
Advanced Acoustics Soundproofing Mat 3m by 1.25m by 2mm Thin - 5kg/m2 Mass Loaded Vinyl MLV 3.75sqm Per Roll. 

which I would sandwich between one 12.5 mm and one 15mm soundboard plasterboard. The teksound seems to be less effective given the same depth, or?

This would costs me the least height, which we just gained by opening the ceiling.

 

Or should I go rather for a 50mm dense acoustic mineral wool and two layers of acoustic plasterboard?

 

Thank you for all your thoughts

 

 

[Moonshine]

4 hours ago, Iceverge said:

PIR between rafters, sorry for your troubles ?.

 

This reminds me of the time I was at my brothers house and looking at his renovation work. He had put celotex between the floor joists of a internal floor 'for acoustics'.

I had to put him right and tell him if was going to do naff all.

 

1 hour ago, Bosi said:

Or should I go rather for a 50mm dense acoustic mineral wool and two layers of acoustic plasterboard?

 

If you aren't going to take the celotex out, do the 50mm mineral wool, and two layers of 15mm soundbloc on resilient bars.

 

Edit: if you wanted decent acoustics from the pitched roof you should have done something similar to the isover metac roof system. This can achieve a sound reduction up to Rw 49 dB which is pretty damn good, and I have recommended it in houses with rooms in roofs near airports.

Edited November 13, 2021 by Moonshine

[Bosi]

So it looks like that there is no voice here for the MLV put in-between two  acoustic plasterboard for a more slim solution ?

 

If I add 50mm before the acoustic plasterboard, would you get 5cm knauf acoustic mineral wool or is the Fibrefon Micro 50mm Acoustic much better ( or is it rather for floorboards  and house noise ) instead of road noise?

 

And just to be sure. Will the resilient bars help with street noise, as it somehow feels that the noise is rather air borne?

[Gus Potter]

Hello Bosi.

 

Yes you mention weight.. it would be a good idea to have a look at what your roof structure can carry in terms of extra load. You have strenthened the roof but what has been allowed for in terms of acoustic plasterboard etc?

 

You'll probably get much more noise ingressing through and around the window frames, service penetrations in the roof, put in a stove and the noise comes down the flue, the solum vents under the floor if you have them, your letter box and so on. I would try and identify / quantify all these areas first before spashing out on a fancy roof envelope.

 

Don't forget how you are going to light the place.. no point in spending loads on the roof if you then go and cut holes in it for say down lighters. Yes if you live next to an RAF base then you may need a fancy roof acosutic wise but if the RAF are flying at night regularly then we probably have a bit more to worry about.

 

 

[Polish Builder]

In terms of soundproofing You should always look for products with high density min 45 kg/m3. Ideal would be 100kg.  I have been using this product on last job. My client never complained about noise from the street.

https://insulationgo.co.uk/100mm-rs100-knauf-rock-mineral-wool-building-slab-100kg-density-acoustic-insulation-multi-application-rw5/

 

[ADLIan]

Sorry but denser does not necessarily mean better in term of acoustics. Just about any mineral wool, at a set thickness, will have a similar acoustic absorption figure, perhaps lower than 0.4 at frequencies below 500 Hz, increasing to 0.8-1.0 at higher frequencies. However any slight difference in performance between products is lost once installed in a wall or roof - the plasterboard, tiles, slates, timbers etc having the biggest impact, swamping any difference in the mineral wool.

 

Denser slabs may also 'couple' each side of the construction and actually make the performance worse! The only difference a slab at 100kg/m3 would make would be to your wallet!

[SimonD]

On 13/11/2021 at 19:31, Bosi said:

Most noise we get is from cars etc, not  really vibrations from trucks, and of course loud exhaust from scooters etc.

 

What you really need to do first is understand the nature of the noise you're dealing with and then the sound pressure levels. You can download some basic audio spectrum analysis apps for your smartphone - start there and that will better guide what you need to do. Noise will not just be the sound coming in but also the nature/shape of the room and how it responds to those frequencies.

[saveasteading]

Also, some sounds are more annoying than others. A distant motorway sound just like a waterfall.

There will be a big difference in keeping out all traffic noise, as opposed to occasional big lorries/ sirens etc.