Insulation Options For New Room With Vaulted Ceiling

[Parmageddon]

Hi all, 

After doing some searching last night I came across this forum and already digested a bunch of really informative threads. Wasn't sure whether to put this in the Heat or sound insulation area as i'm actually looking to do both, though wanted to directly ask for some guidance on the best way to get great thermal/sound insulation on a build thats currently underway at our home.

As a part of some renovations/alterations we're doing, we've added a sort of new cloakroom area at the front of the property. It will have a sloped roof with 3 velux windows in there the ceiling will be vaulted on the inside.

Some images of the plans and current front elevation snapshot of progress below to help describe. (note: roof pitch is about 18 degrees or so, ignore the 24' ref on the images below)

 

 

 

 

 

 

And as you'll see on the images below, the construction beneath the felt is 150mm rafters packed with 125mm of kingspan and a 25mm air gap. Ofcourse the 3 big pieces of kingspan below are temporary and will be coming out in place of the velux windows when they arrive. (note the space between the veluxes will be 230mm or so)

 

 

 

 

 

 

 

 

 

 

Now, the main reason i'm making this post is because the front of the house does point at a main road thats close by which can get really noisy, and while ofcourse I appreciate the interior/exterior is no where near finished, as it's currently SO loud in there it's forced me to start considering how I best want to make this super heat/sound insulated (within reason ofcourse!)

 

I've added a couple videos below to show the layout a bit better and the noise levels too, (currently 55db when cars go past, rain super noisy etc.)

 

 

 

 

Again, I know i'm probably jumping the gun by getting spooked this early, but it'd be great to hear (no pun intended!) steps I can take with this layout to help it stay warm and quiet. I've listed below my current considerations, and some questions at the very bottom.

:- Vertical windows glass will be acoustic laminate (10.8 laminated pane on the rear, 6.8 glass at the front)
:- Gaps around windows filled with acoustic expanding foam
:- Velux windows we opted for glazing option 62 (noise & comfort) their most expensive option and had a 0.93 value from memory.
:- All walls are planned to be double boarded in soundbloc 12.5mm, may even do triple as space isn't an issue there.

Q1) - Can I add more insulation below the rafters? and if so how much realistically speaking?

Q2) - If yes to Q1.... is there a building control limit on how low I can drop the inner vaulted ceiling? (making the cavity between the ceiling felt deeper)

Q3) - Below the rafters, would it be considered sensible to use something like Kingspan Kooltherm that has the plasterboard build into it? and if so can you then do another layer of soundbloc plasterboard below that too?

 

I'm sure there'll be loads of things I havent even thought of, so really keen to hear suggestions on anything and everything I can do here. And so sorry for the essay! it is a subject that's giving me a bit of house-anxiety to be entirely honest.

 

 

thanks so much

Parma

 

 

 

 

 

Edited March 4, 2022 by Parmageddon

[Iceverge]

Hi Parma, 

 

Welcome to the forum. 

 

I'm not an expert but i'll have a punt anyway.

 

Q1. Yes but don't trap moisture in the timbers. I would probably opt for an airtight membrane joined to your wall airtight layer at the edges, 

 

Follow this with a layer of 50mm rockwool between battens, resilent bars and 2 layers of soundblock. The the trouble is all your openings will need to be detailed correctly. Tape the airtight layer to the frame and seal the plasterboard up tight to the frames with acoustic sealent. No gaps. 

 

With tiles on the roof it will improve a fair bit I imagine too. Again the windows and skylights are really the weak points. 

 

Q2. Don't know. 

 

Q3. Not for sound insulation. You need something heavy ( plasterboard) and something to absorb the sound ( rockwool) and something to decouple to reduce structurally transferred noise ( resileint bars) 

 

 

 

[Parmageddon]

4 hours ago, Iceverge said:

 

Q1. Yes but don't trap moisture in the timbers. I would probably opt for an airtight membrane joined to your wall airtight layer at the edges, 

 

Follow this with a layer of 50mm rockwool between battens, resilent bars and 2 layers of soundblock. The the trouble is all your openings will need to be detailed correctly. Tape the airtight layer to the frame and seal the plasterboard up tight to the frames with acoustic sealent. No gaps. 

 

 

Q3. Not for sound insulation. You need something heavy ( plasterboard) and something to absorb the sound ( rockwool) and something to decouple to reduce structurally transferred noise ( resileint bars) 

 

 

 

 

Thanks Iceverge, it's my first time going through the process here, so apologies for any silly questions and thanks for your welcome and help, appreciate it.

Most of what you said makes sense to me, though by 50mm rockwool, you mean the slabs right?, oppose to the rolls. 

:- if the 50mm rockwool is inbetween battens, am I correct to assume you mean attach the battens to the rafters but with the the airtight membrane separating them? 

 

:- Resillient bars are more for impact and vibration from memory? my issue is high pitched airborne hisses, but I suppose the bars are super cheap and easy to install.

 

:- I feel like there's a bit of balance to play here between thermal and acoustic insulating? Like the kingspan thats in there at the moment is completely useless for soundproofing...but it is there because the builders have said BC will demand its in there for thermal sign off..... So coming back to my question above and taking your guidance too Iceverge....realistically is there anything stopping me doing your 50mm rockwool below the rafters, then another 50mm of kingspan below the rockwool? then double board of soundbloc plasterboard below the kingspan?

 

 

Edited March 5, 2022 by Parmageddon

[Parmageddon]

4 hours ago, Iceverge said:

Hi Parma, 

 

 

With tiles on the roof it will improve a fair bit I imagine too. Again the windows and skylights are really the weak points. 

 

 

 

 

Yeah, now this is where i'm getting confsued.....

 

As youve heard already the unfinished  cloak room in question is super loud!

 

Though really interestingly, the room next to our cloakroom is a living room which not also faces the main road but also has a really big bay window in there and has way more glass than the cloak room has ...... but yet there's no traffic sound in the living room at all! You just can't hear it!

 

See the 2 videos below for comparison,

 

Cloak Room

 

Living Room

 

 

 

What im finding interesting and confusing here is....

 

:- 5-6 cars go by in the living room video and there's just no sound at all... And as far as I know the panes of glass in there are just standard double glazing.

 

:- All the other windows i've specificed for the cloak room should have much better acoustic performance than the ones in the living room....

 

:- My point being if the velux window parts of the roof can be as quiet as that bay window....then i'd be happy in which case I really need to focus on the bits that aren't velux windows. i.e the rest of the roof.....or am I being really silly/naïve here and missing something really obvious?

 

For reference of the velux performance by the way, see image below.

 

 

 

 

Edited March 5, 2022 by Parmageddon

[Iceverge]

8 hours ago, Parmageddon said:

 if the 50mm rockwool is inbetween battens, am I correct to assume you mean attach the battens to the rafters but with the the airtight membrane separating them

Correct. 

 

I don't think slabs or rolls make much difference. 

 

8 hours ago, Parmageddon said:

Resillient bars are more for impact and vibration from memory? my issue is high pitched airborne hisses, but I suppose the bars are super cheap and easy to install.

 

 

Yes but should help further isolating the plasterboard and stopping it from acting like a "speaker". Also it will help with rain noise. You need to do everything you can to prevent the inner surface of the house from vibrating. The air gap created by the resilient bars makes sure that any vibrations aren't been taken through the insulation either. 

 

8 hours ago, Parmageddon said:

- I feel like there's a bit of balance to play here between thermal and acoustic insulating?

 

Unfortunately looking at the pics I think it's really neither here nor there. You could triple the insulation in this part of the roof but it would pale into insignificance beside the thermal bridge of the lintel as indicated below. PIR and phenolic insulation typically only perform to their stated U-Value under laboratory conditions. In reality their thermal performance will be much closer to mineral wool than producers would have you believe. 

 

 

 

7 hours ago, Parmageddon said:

What I'm finding interesting and confusing here is

 

Most of the noise is probably coming directly through the roof of the porch. It looks like at the moment all you have is 125mm of PIR and a sheet of plastic. Tiles will help but the big difference will be when the plasterboard is applied.

 

I have no reason to suspect the Velux windows won't reach their stated performance in isolation. As ever the key is detailed installation. Any air paths must be sealed and you must have a continuous layer of plasterboard. It should be mounted with a medium that allows isolation of vibrations eg acoustic mastic, rubber strips or resilient bars. A cavity inthe structure can be good to prevent vibrations but should contain a dampening medium like Rockwool to reduce the drum effect. 

 

Hope this helps. 

[Parmageddon]

Thanks again Iceverge. 

 

So taking above into account I think i'm gonna do the following

 

Vaulted Ceiling (layered top to bottom)

 

Tiles

Felt

25mm airgap

125mm kingspan between rafters

25mm airgap

100mm rockwool (RW3) below rafters

resilient bars

Soundbloc plasterboard 12.5mm 

Tecsound 50  ( https://www.soundstop.co.uk/ZTECSO50S.php )

Soundblock plasterboard 12.5mm

 

Total thickness from top of the rafters to the bottom of the 2nd layer of plasterboard would be =  280mm or so.

Walls

 

brick

100mm cavity packed with Rockwool

block

Soundbloc plasterboard 12.5mm 

Tecsound 50  ( https://www.soundstop.co.uk/ZTECSO50S.php )

Soundblock plasterboard 12.5mm


And as suggested above, all glass for windows and velux will be acoustic laminate double/triple glazed. 

Does the above sound reasonable/good?

Edited March 6, 2022 by Parmageddon