Stud Wall Between TWO Flats - Requirements

I'm trying to find out the construction requirements in building a timber wall between two flats. Obviously the wall will need to meet various sound & fire requirements.

Anyone have a current diagram with measurements? I have full access to Building Standard Online, however I can't find the required information there...

Many ways to do it.

150mm wide stud wall, using 100mm studs either side. Like in this pic will save space, and will work for both requirements provided you.

a) completely fill the wall with rockwool slab or other rigid insulation.

b) Double plasterboard and skim both sides, using min. 12.5mm board. Staggering the boards joints.

Caulk the perimeter with fire rated acoustic sealant.

You will get better results for sound insulation (but lose couple of inches floorspace in each room) by using 2 seperate walls, spaced an inch apart.


Personally, I'd go for a lightweight block wall (check the floor can take it!), skimmed on both sides (only one side needs to be finish) and then a seperate stud wall, with the insulation, and double boarding on the room side.


My mate recently put up a new build, the architect had specced a much more complex and costly dividing wall, which cost twice as much as what I've described, and with eqaul (or probably worse) performance)

After it was built I pointed out the unneccesary expense and reminded matey that the architect earns a fixed percentage of build cost

http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADE_2003.pdf

page 40-41

Thank you very much for the assistance there chaps. Any idea how much fire resistance (in time) the stud wall with 2 layers of 12.5mm plasterboard will give?

Also, does 'fire resistant' 'pink' plasterboard need to be used under any requirements. Does anyone use this as an alternative to normal plasterboard?

EViS said:

Thank you very much for the assistance there chaps. Any idea how much fire resistance (in time) the stud wall with 2 layers of 12.5mm plasterboard will give?

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One hour: joints taped and staggered.

Depending how on-the-ball your building inspector is and to a certain extent your morals (assuming you're getting building regs approval) you techincally need to use 12.5mm British Gypsum 'Wallboard TEN' as normal plasterboard isn't dense enough. Alternatively you could use 15mm Fireline (the pink one) but I imagine its more expensive. The wallboard route will give you 60 minutes resistance. Fireline even more although you won't have to provide any more than an hour anyway.

You may wish to have a browse through this: http://www.british-gypsum.com/literature/white_book.aspx although about 95% won't apply:
Also here: http://www.british-gypsum.com/pdf/wb_pr boards_10_07.pdf for board types.

I like to do a job properly thus morals are always high on the agenda when carrying any work for a client (and myself).

In terms of the rockwool insulation, will any rockwool at 100mm in thickness be sufficient to pass noise Part E Regulations?

EViS said:

In terms of the rockwool insulation, will any rockwool at 100mm in thickness be sufficient to pass noise Part E Regulations?

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It depends on what's either side of it. 100mm should be considered a minimum, but your soundproofing will mainly come from the mass and integrity of the walls. In any case, completely filling the void between walls is best practice.

Ha-ha, No offence EVis.
For reasons unbeknown to me insulation manufacturers rarely publish the density of their insulations, you have to ring them up to find out what the minimum thickness is you can get away with. Either 100mm of Rockwool Cladding Roll or Acoustic Partition Slab would be fine though. To be honest I normally specify Crown Acoustic roll as builders tell me its cheap, can't remember exactly what thickness you need will have to have a look at one of me drawings at work tom.

Had a look at what I’ve spec’d in the past, you can get away with 1 layer of 25mm if suspended between the studs or 25mm on each side to the face of the studs or 50mm to the face of the studs ooon 1 side only if using Crown Acoustic Roll. I guess the Rockwool would be the same as obviously the density don’t increase with thickness. As Deluks said though if your client is happy to pay you could fill the whole cavity. I’ve not met a developer yet who’s improved on the minimum standard though.

Fantastic advice there guys. Thank you all ever so much!

freddymercurystwin said:

I’ve not met a developer yet who’s improved on the minimum standard though.

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I've met plenty, and helped some specify much greater than "minimum", because keeping noise down between units turns out to be a surprisingly effective way to increase tenant satisfaction, reduce churn and - ultimately - allow rents to be increased. And, yes, I've seen empirical research done over years between otherwise identical units with more/less sound isolation.

freddymercurystwin said:

You may wish to have a browse through this: http://www.british-gypsum.com/literature/white_book.aspx although about 95% won't apply

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As above, as much or as little of all of that will apply as you want to.

Also be very aware about the requirements of Building Control. You can use - and pay heavily for - the "Robust Details", which will exempt you from on-site testing if you've used them exclusively. It is a complete racket, however, as you must pay a license to use the "details" in order to qualify for the exemption. Otherwise the BCO should test - or witness a test - of the actual performance of your built wall. Failure (which tends to be through details such as flanking transmission in refurb / conversion works) can be expensive - basically unpick and start again.

The big advantage of the White Book stuff linked above is that, broadly, if you follow the "menu" BG lay down to the letter, they're prepared to guarantee that the particular construction will behave as per their tables. So if you need, say, a 60dB reducing wall, and follow their how-to, you will get (at least) a 60dB reducing wall.

If at all possible, use steel studs rather than timber. It is far easier to work with, you can tailor the characteristics (mechanical and acoustic) to your needs, and you have no worries about fire.

Oh, finally: if you're just sitting the partition on an existing floor, there is little chance it will meet either fire or noise regs.

A wall between two flats is a separating wall. At the very least you should look up a standard configuration for a separating wall that has been tested and proved to provide a sound insulation of 43dB - which is the minimum standard.

Having said that, on existing construction, you will often find that a wall built to the minimum is not enough to pass a test. My advice therefore is to go some way beyond the minimum.

My specification for this situation is Lafarge RSP158 Cormet dBcheck partition, It is very easy to build, reasonable cost, the finished wall is very solid and I have had about 40 of these walls tested over the last 2 years or so on different jobs - new build and conversion - and I have never had a failure.

See page 79 of the Drywall Manual

http://www.lafargeplasterboard.co.uk/3 Partitions_1.pdf

Not entirely relevant to your original question but also remember when it comes to testing there is no requirement to test between non-habitable rooms, so some careful designs such as putting bathrooms and kitchens against the dividing walls will keep your testing costs down. There is however still a requirement to build these walls to the minimum requirement though.