50mm Ceiling void

[MortarThePoint]

I had considered not having a ceiling void under our hollowcore (see below) but think I do need it really, but plan to keep it to a relative minimum. That raises the question of what the minimum is. Is there a reg that needs to be followed?

 

There are lots of downlighters that support shallow voids (e.g. https://www.downlightsdirect.co.uk/shallow-downlights.html?depth_range=1-50), so I don't think lights will set the minimum void size. I have seen people mention downlighters that are only around 20mm. Any wiring needs a minimal gap.

 

An insulated 15mm water pipe ends up 13+15+13=41mm (22mm --> 48mm) so that suggests a 50mm ceiling void.

 

Not needed, but waste pipes are "40mm" typically, but at solvent well joints mean it would need 50mm plus any fall. I don't need any of this though.

 

Seems like the water pipes are the driving factor. I could take a long route to avoid having the water pipes in the ceiling void. Would it be bold to have a 25mm ceiling void? I was thinking 50mm was best, but with timber prices having gone nuts, I expect 2x2 to be double the 90p/m I paid in December and it needs a fair length as I expect to install at 400mm c/c.

 

I could have a larger void (50mm) in the rooms that the water pipes would need to pass through and a smaller void (25mm) in the other rooms.

 

 

Edited August 31, 2021 by MortarThePoint

[MortarThePoint]

Just finished phoning around for prices and the timber for the void would cost:

• 50mm void (47x50) £4.13/m2 (£1.65/m)
• 38mm void (38x50) £3.23/m2 (£1.29/m)
• 25mm void (25x38) £2.01/m2 (£0.81/m)

In more normal times all of those prices would probably be halved. Painful to pay more than 4x2 prices for 2x2.

 

[PeterW]

Down lights need space for the transformers and to be able to tip them into the void so 50mm is your minimum. 
 

Why though are you going at 400mm centres ..? There is no deflection so 12.5mm board is fine on 600mm centres. 

[MortarThePoint]

  On 31/08/2021 at 07:25, PeterW said:

Down lights need space for the transformers and to be able to tip them into the void so 50mm is your minimum. 
 

Why though are you going at 400mm centres ..? There is no deflection so 12.5mm board is fine on 600mm centres. 

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600mm centres would be great. I thought 12.5mm needed 400mm c/c, perhaps that's 9.5mm plasterboard then.

[PeterW]

All you (n)ever wanted to know about plasterboard 

 

https://www.british-gypsum.com/literature/white-book

 

And it’s 600 centres for 12.5mm - is none of this documented in your spec plans ..??

[MortarThePoint]

Opinions seem a bit divided over 12.5mm plasterboard on 600mm c/c:

 

https://www.plasterersforum.com/threads/600mm-centres.61316/

 

Seems a bit perverse to go for 15mm plasterboard @600mm c/c to save timber cost, but may end up the better choice.

 

600mm saves 33% over 400mm

480mm saves 17% over 400mm but is not a standard spacing so a bit weird

[Mr Punter]

Hollowcore is normally a bit bowed so you can get rid of it by packing the 2 x 2.  600ctrs and 15mm p/board.

[PeterW]

  On 31/08/2021 at 07:44, MortarThePoint said:

Opinions seem a bit divided over 12.5mm plasterboard on 600mm c/c:

 

https://www.plasterersforum.com/threads/600mm-centres.61316/

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Yep - opinions
 

You’re comparing apples and oranges - hollowcore doesn’t flex, and the battens are solid fixed so you won’t have any flex to worry about. 12.5mm will be fine on 600 centres on battens on hollowcore. 

I’ve asked before, but do you have any construction plans for this or have you only got the basic architect plans and bare minimum for BRegs ..??
 

 

[MortarThePoint]

  On 31/08/2021 at 08:22, PeterW said:

Yep - opinions
 

You’re comparing apples and oranges - hollowcore doesn’t flex, and the battens are solid fixed so you won’t have any flex to worry about. 12.5mm will be fine on 600 centres on battens on hollowcore. 

I’ve asked before, but do you have any construction plans for this or have you only got the basic architect plans and bare minimum for BRegs ..??
 

 

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Basic architect 'construction drawings' 

[Conor]

Why don't you use metal suspended ceilings? I don't see how you could get a flat and straight ceiling with timber.

 

Stick all your services in, then get the metal brackets and edge channels installed at the height required. It's very fast.

[MortarThePoint]

  On 31/08/2021 at 08:34, Conor said:

Why don't you use metal suspended ceilings? I don't see how you could get a flat and straight ceiling with timber.

 

Stick all your services in, then get the metal brackets and edge channels installed at the height required. It's very fast.

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Architect included a 150mm MF void, but seems pointless (no ducting). MF needs at least 100mm I think.

 

To get it flat I was planning to pack each mounting as @Mr Punter suggests. To mount the timber to the underside of the HCF I was planning on something like these masonry screws at 400mm c/c.

[Conor]

  On 31/08/2021 at 08:46, MortarThePoint said:

 

Architect included a 150mm MF void, but seems pointless (no ducting). MF needs at least 100mm I think.

 

To get it flat I was planning to pack each mounting as @Mr Punter suggests. To mount the timber to the underside of the HCF I was planning on something like these masonry screws at 400mm c/c.

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We're using gypline brackets for a 40mm ceiling. The guys had this room done before I'd finished my morning cup of tea and buildhub browsing.

 

Edited August 31, 2021 by Conor

[Mr Punter]

The MF stuff is good but chippies don't like it.

[MortarThePoint]

  On 31/08/2021 at 08:47, Conor said:

We're using gypline brackets for a 40mm ceiling. The guys had this room done before I'd finished my morning cup of tea and buildhub browsing.

 

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Looks great, what system is that? Do you have a link to the brackets?

[Conor]

  On 31/08/2021 at 10:37, MortarThePoint said:

 

Looks great, what system is that? Do you have a link to the brackets?

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It's from gyproc. All I know because it was a supply and fit from our MF contractor. Think it was about £12m2.

[wozza]

If using an MF system, you can make your own hangers to whatever length you want.  Have a look at MF Ceiling systems - plenty of videos out there and its easy to do.

 

I have three voids, 1 is about 80mm, 1 is about 50mm both on vaulted ceilings and the other isn't really a void as such- I just used the sections (MF5s I think they are) with plastic spacers / packers to counter batten / level the underside of a ceiling that had uneven joists so its now nice and level

Edited August 31, 2021 by wozza

[Adam2]

  On 31/08/2021 at 08:47, Conor said:

We're using gypline brackets for a 40mm ceiling

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Looks nice  - Looks like you're using duct for the cables to avoid issues with ICF I guess - what did you use to cut out the ICF - hot knife type thingy? I have lots of this to do as well as MF ceilings to get sorted

[Conor]

yep, hot knife. sparks loved working with it.

[Adam2]

  On 31/08/2021 at 15:11, Conor said:

yep, hot knife. sparks loved working with it.

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Sorry to OP re off topic so last one - what did you buy?

[Dudda]

I'm guessing you don't have heat recovery @MortarThePoint

 

I'd definitely get a quote for the MF ceiling. It's very quick as stated by others.

[Conor]

  On 31/08/2021 at 15:14, Adam2 said:

Sorry to OP re off topic so last one - what did you buy?

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Cheapy off Amazon. £125 I think. You need one with a flexible blade "groover" to make channels for conduit and pipes.

[MortarThePoint]

  On 31/08/2021 at 16:20, Conor said:

Cheapy off Amazon. £125 I think. You need one with a flexible blade "groover" to make channels for conduit and pipes.

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Sounds neat, easier than chasing blockwork!

[MortarThePoint]

  On 31/08/2021 at 12:10, Conor said:

 

It's from gyproc. All I know because it was a supply and fit from our MF contractor. Think it was about £12m2.

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Sorry you did say that.  Found an installation video. The brackets look to be GL2 and the channel is GL1 (sections can be joined by GL3) and a perimeter of GL8 (also used for pattresses). GL1 brackets seem to normally go in at 600mm x 1200mm centres. GL3 joins sections of GL1 as required.

 

In parts (Speed Pro not BG):

• GL1: 1.67m/m2, £1.14/m, £1.90/m2 https://www.builderdepot.co.uk/metal-lining-channel-3600mm-gl1
• GL2:  1.4/m2, 12p each, 16p/m2  https://www.builderdepot.co.uk/195mm-gypframe-gypliner-brackets-gl2-box-of-100
• GL3: 0.3/m, 0.5/m2, 12p each, 6p/m2 https://www.builderdepot.co.uk/gypframe-gypliner-channel-connectors-gl3-box-of-50
• GL8: £0.83/m https://www.builderdepot.co.uk/metal-track-3000mm-gl8

An arbitrary 4m*4m room would cost 16m2*(£1.90/m2 + £0.16/m2 + £0.06/m2) + 16m*(£0.83/m) = £47.2 or about £3/m2 plus screws. BG may be more expensive as likely a better brand (?).

 

47x50 timber at 600mm c/c would be £2.75/m2 so GypLyner does compare well with the timber cost. Perhaps not so favourably historically, but based on where timber prices are now...

 

Whilst the timber feels easier to install to a flat level surface, under the hollow core camber the ease of adjusting the metal frame looks very attractive.

 

[PeterW]

Speed Pro and Gypliner are the same thing, and at trade price - those builder depot prices are a bit pricy - it’s as cheap as timber but faster to install. 

[PeterW]

  On 31/08/2021 at 08:34, MortarThePoint said:

Basic architect 'construction drawings' 

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So who’s done the BRegs drawings as some of this such as the detail on the ceilings for fire protection etc needs to be properly detailed.