You are here

Building An Extension - External Wall Construction

Customising, building or repairing your own gear? Need help with acoustic treatment or soundproofing? Ask away…

Building An Extension - External Wall Construction

Postby adamc » Thu Sep 02, 2004 4:12 pm

I'm reposting this question on the new forum - hope this is okay - just as I registered with the SOS Forum, it moved !

----
hi,

I'm building an extension on to my house (approx 5m sq, single storey, pitched roof) and would like to soundproof it, to reduce noise coming out of it. Aside from internal soundproofing (room within an room etc) which I plan to do later, I was after some advice on external wall construction.

Currently, the guy who drew my plans has specified 100mm brick (can't be changed - has to match the house) 75mm of cavity insulation and then 100mm Celcon block ("aircrete").

I asked someone at Rockwool about this (as I was thinking of using Rockwool in the 75mm cavity) - and got this response ...
-----
> Insulation in a cavity wall construction is mainly there for enhancing the
> thermal performance of the wall construction, it does very little for the
> acoustic performance. A dense block would provide a better acoustic
> performance compared to a light weight block.
----
does anybody have any advice on this ?

thanks alot

adam


had 2 useful replies on the old forum

Hugh Robjohns: SOS Technical Editor
SOS staff
-----------------------------------
The man is absolutely correct. The gap between outer brick and inner block wall is there for construction reasons, primarily to stop damp getting through. The insualtion is a building regs requirement for thermal efficiency.

To reduce sound transmission you need as much mass as possible in the walls, and hence his suggestion of using heavy dense internal blocks instead of the very light blocks that most builders appear to prefer.

However, while you could ask you builder to use heavy blocks, I doubt there would actually be a hugely significant advantage in terms of sound insulation, and there may well be serious knock-ons in terms of foundation requirements, time to build and raw material costs.

Personally, I'd go for the conventional wall build design, but make sure you have double or tiple glazed windows, double doors (if there is an exterior door), and take great care over the internal room-in-a-room construction.

Hugh

PS, we're all over in the new forum now.... why not join us. Just click on the forum banner in the main SOS web page.

Smiffy
Active Member
-------------
You might like to do a search on this subject in this forum. I recall this was debated in quite some details several months ago.

Picking up on Hugh's last para, I think the outcome back then was that you could invest heavily in soundproofing your walls, but sound was transferred through roofs/ceilings, doors (internal and external) and windows more efficiently than through conventional walls. Therefore wiser to invest in better materials for these than the walls.
adamc
New here
Posts: 9
Joined: Thu Sep 02, 2004 12:00 am

Re: Building An Extension - External Wall Construction

Postby adamc » Thu Sep 02, 2004 4:17 pm

smiffy,

thanks for your reply - I tried searching on the old forum - couldn't seem to find anything on external walls, but have only just started using this forum, so may have mis-searched

adam
adamc
New here
Posts: 9
Joined: Thu Sep 02, 2004 12:00 am

Re: Building An Extension - External Wall Construction

Postby Matt Downing » Thu Sep 02, 2004 4:32 pm

There are quite a few PDF documents at http://www.rockwool.co.uk although they're not easy to link to (or even find) so you'll have to go search there.

BTW - there's a whole forum dedicated to studio design and acoustics in this new world. We have moderators now who might move your post there.

Matt
Matt Downing
Poster
Posts: 44
Joined: Mon Jan 20, 2003 1:00 am
Location: London

Re: Building An Extension - External Wall Construction

Postby RegressiveRock » Thu Sep 02, 2004 5:57 pm

There are a number of good .PDFs on acoutics on the Rockwool web site, the main one is the Acoustic Manual - Part E (2003).

Try that for starters, then research the sections that apply to you most, their are separate documents on Wall design etc...

Hope this helps... ;)
RegressiveRock
Frequent Poster
Posts: 1540
Joined: Wed Sep 01, 2004 12:00 am
Location: Buntingford, Herts
Smoking Goats
https://www.facebook.com/SmokingGoats

Re: Building An Extension - External Wall Construction

Postby Siejen » Thu Sep 02, 2004 6:34 pm

Hi,
One thing you havent yet mentioned is dimensioning your extension. You really want no two walls parallel to minimise standing waves, null spots etc. This will probably be of greater benefit long term than trying to soak them up later with traps or foam...

I've never tried telling a builder that you want the walls squint though... Who knows what could happen!

Iain
Siejen
Poster
Posts: 32
Joined: Thu Sep 02, 2004 12:00 am
Location: Coventry

Re: Building An Extension - External Wall Construction

Postby adamc » Thu Sep 02, 2004 7:35 pm

hi sejen,

I'm currently planning to make the external walls parallel, but could make the inside walls non-parallel (I could just get a really bad builder - they'd soon make the walls non-parallel ! :-) )

The extension is on the back and side of (kind of "L" shaped) a 3 bedroom semi-detatched. The extension at its widest is approx 5 metres internal dimension with approx half of that width on the back of the house and the other half at the back of my driveway (which doesn't join on to any other properties apart from my own) - the bit behind the house goes back about 3.6m meteres internal dimension, the bit at the back of the driveway extends further forward than the back of the house (5 meteres length internal dimension).


I plan to divide the space up into a control room and recording room. At the moment I'm working out of two bedrooms in my house, mostly with singers rather than full bands, but would like to do louder stuff if possible - things are going quite well this year with production work (look at my website www.incompany.co.uk if you're interested) and so I wanted to build a better studio - but also keep it close to home.

thanks for your help

adam
adamc
New here
Posts: 9
Joined: Thu Sep 02, 2004 12:00 am

Re: Parallel walls maybe not so straightforward a solution?

Postby Scottdru » Thu Sep 02, 2004 8:22 pm

Hi,
One thing you havent yet mentioned is dimensioning your extension. You really want no two walls parallel to minimise standing waves, null spots etc. This will probably be of greater benefit long term than trying to soak them up later with traps or foam...

That said . . . from what I've read and heard from some fairly trustworthy sources (and if memory serves), building non-parallel walls mainly helps with the high mid and upper frequencies, and doesn't do quite so much for the low frequencies, as (among other things) the low frequencies are less directional.

Which means you will still need bass traps. And the other thing is that with non-parallel walls you have a more difficult time with doing the calculations.

Not to say don't do it, because this is certainly a common practice . . . but maybe it isn't quite so straightforward or as comprehensive a solution as it might seem. Could cause added complication and expense . . .

I don't claim to be any kind of expert on this . . . but I thought it might be worth bringing up. Hopefully someone with greater expertise than mine will chime in and clarify. :)
User avatar
Scottdru
Frequent Poster
Posts: 1165
Joined: Tue Dec 17, 2002 1:00 am
Location: NYC: isle off the coast of Europe
Scott --Where are we going and why am I in this handbasket?

Re: Parallel walls maybe not so straightforward a solution?

Postby Jon Jon Jon » Thu Sep 02, 2004 10:43 pm

yeah non parallel walls really over complicate things and will cause a lot of problems along the way.

as scott says they don't really affect bass frequencies unless the wall angles are quite drastic. if you just add a slight slant you get standing waves based on the average distance between surfaces. plus you still get a whole host of axial and tangenal modes. the worse thing to do is to make a parallelogram shape as this has no axis of symmetry. meaning that you stereo imaging will be innacurate. A good design would be to aim for a trapeziod shape with the monitors at the shorter parallel side. this way the angled wall aim sound away from the listening posistion. You just need to think what do with the left over space is your orignal room was cuboid. No mattery what shape room you build you will always need diffusers and absorbers
User avatar
Jon Jon Jon
Poster
Posts: 19
Joined: Tue Aug 05, 2003 12:00 am

Re: Parallel walls maybe not so straightforward a solution?

Postby Studio Support Gnome » Thu Sep 02, 2004 11:22 pm

Phatriff is entirely correct, and gets awarded the 5 red balls no one else seems to have seen fit to give him....

Always a pleasure to see you Phatso ;)

Max
User avatar
Studio Support Gnome
Frequent Poster (Level2)
Posts: 2897
Joined: Tue Jul 22, 2003 12:00 am
Location: UK
Now available for consultations and audio engineering jobs .  Also guitar tech work , and “rent-a-shredder” sessions .  Oxfordshire based but can and will travel .  Email maxtech.audio@me.com

Re: Building An Extension - External Wall Construction

Postby DAN » Fri Sep 03, 2004 12:06 am

Hugh is right, denser blocks are far better for sound insulation - however your builder will use Celcon blocks (otherwise known as Thermolite blocks, or aerated blocks) as these are stipulated by building regulations concerning thermal insulation.

As well as filling the cavity with Rockwool (or 2" polystyrene, its just as good) you could also batten out the internal wall and add more fibreglass or polystyrene in between before it is covered with plaster boards.

Also, which I did in my cellar, cover the walls with a ROUGH coat of plaster, as opposed to smooth. This will help to diffuse the soundwaves. The rougher the better.

I might be pointing out the obvious but also tell your electrician to put loads of double sockets in (pref at mid-height) before plastering. You can never have too many. Put them on a seperate ring main also.

Dan
DAN
Regular
Posts: 62
Joined: Thu Sep 11, 2003 12:00 am
Location: Dordogne, France.

Re: Building An Extension - External Wall Construction

Postby Jon Jon Jon » Fri Sep 03, 2004 12:15 am

max you are the MAC of all macs.
User avatar
Jon Jon Jon
Poster
Posts: 19
Joined: Tue Aug 05, 2003 12:00 am

Re: Building An Extension - External Wall Construction

Postby Studio Support Gnome » Fri Sep 03, 2004 12:23 am

Thermally Polystyrene is fine, acoustically, it's next to useless.


Use Acoustic mineral wool

Higher density the better IMHO.

NORMAL pink fluffy Fibreg;lass insulation is only @30Kg/M^3 Proper AMW starts at say 60Kg.M^3 ish (some cheapo stuff is 45) and goes up.
it's dearer than The other stuff, but it's sonically a LOT more effective.


Max

(Cheers PhatRiff.... )
User avatar
Studio Support Gnome
Frequent Poster (Level2)
Posts: 2897
Joined: Tue Jul 22, 2003 12:00 am
Location: UK
Now available for consultations and audio engineering jobs .  Also guitar tech work , and “rent-a-shredder” sessions .  Oxfordshire based but can and will travel .  Email maxtech.audio@me.com

Re: Building An Extension - External Wall Construction

Postby Tim. » Fri Sep 03, 2004 7:16 am

>As well as filling the cavity with Rockwool (or 2" polystyrene, its just as good) you could also batten out the internal wall and add more fibreglass or polystyrene in between before it is covered with plaster boards.

I just thought I’d mention that, for thermal insulation, polystyrene is better (cheaper too) than Rockwool ‘cos polystyrene doesn’t absorb water.

If any material used for thermal insulation absorbs water its thermal properties will be severely compromised (read no insulation at all); cavity walls can sometimes harbour damp.

Tim ;o)
Tim.
Regular
Posts: 403
Joined: Thu Nov 14, 2002 1:00 am

Re: Building An Extension - External Wall Construction

Postby adamc » Fri Sep 03, 2004 10:08 am


that's right - the plans specify Celcon aircrete block, but I did notice on the Celcon website that they do a slightly denser block (750 kg/m3) as well as their standard block (620kg/m3) - but this doesn't sound a huge difference, and given the general feel of responses so far, it sounds best to stick with the "standard" construction and save money for the Room Within A Room.

thanks to everbody for replies so far - what a great forum !

I've stuck a scan of my building plans online if that's any use to anyone - www.incompany.co.uk/index_extension.html


adam
adamc
New here
Posts: 9
Joined: Thu Sep 02, 2004 12:00 am

Re: Building An Extension - External Wall Construction

Postby Guest » Fri Sep 03, 2004 4:02 pm

"Proposed dining room extension"? You have told the wife what's going to happen to the new "dining room" ???? :bouncy:

A few thoughts:

Don't use ordinary/acoustic type mineral wool as a cavity insulation in external cavity walls. As Tim Rainey points out, it'll bridge the cavity and provide a path for damp incursion. Once it gets damp inside the cavity it's a nightmare to do anything about it and ordinary "acoustic" mineral wool when wet will create quite a good coupling between internal and external walls for both thermal and sound transmission. Expanded polystyrene sheet or purpose designed mineral wool sheet is better in this application. The mineral wool sheets are denser than polystyrene and will increase attenuation slightly whilst maintaining thermal insulation and without bridging the cavity; check the information on the Rockwool site for suitable products.

Personally, I'd go for the heaviest blocks I could get past the building inspector/planning dept.! Thermalite/Celcon/similar blocks are the preferred medium for thermal insulation - which is a big consideration (a requirement) for much normal domestic construction. Their relatively low mass is not, however, particularly good for attenuation. If this were not on the plan as a "dining room extension" then you could argue that a different construction is permissible. (Though if you own up to it being a studio you might run into planning problems - I've found that calling it a "music room" is a good ruse ;) ) The construction specified meets domestic attenuation levels and thermal insulation specs and would be the default expectation of the planners. If you owned up to building a studio room you should be able to substitute HD block for Celcon. If there are any queries, point out that the thermal insulation of a room within a room construction inside HD block walls with poly filled cavity will *far* exceed any thermal specs for domestic construction. The reason I'd go for the heaviest walls I could get is that unless you are going for a *really* serious internal construction (which will substantially eat into the available space), this outer shell is your primary barrier for LF attenuation - both incoming and outgoing. Anything other than a very, very, heavy/clever internal room construction will pass LF at quite appreciable levels. A heavier external shell will attenuate this more than a lighter one. If it's not too late, I'd go for a larger cavity with heavier block construction. There again - this might well be over spec for what you want to do in the room. It'd also be much better than (what appear to be) the original walls of the house that form part of the construction so it might be a waste of time - it depends upon how much noise you intend to make and how quiet you need the room to be.

Rather than using the floor construction in the drawing, why not install a proper floating floor - like the one in the link posted by Simon in the Floating Floor thread elsewhere in this forum. If you're going to build a room within a room anyway, properly floating the floor of the original construction of the extension will save you a lot of time, work, and ceiling height and reap big benefits in attenuation. It may bump up your build cost for the extension but it should work out to be a saving in the long run - particularly in time and effort when you construct the internal room. It'll also considerably increase the effectiveness of the attenuation provided by the outer walls.And you get the builders who do the extension to do the really heavy work for you. ;)

How will you be ventilating the room? If you're sound proofing it properly then you won't be wanting/able to open the window for a bit of fresh air. It might be worth looking into air conditioning solutions or if these are too expensive, at least some kind of ventilation system. It's much easier and cheaper to consider and plan this before you start than it is to add it later.
Guest

Next