Opinions on best way to drop a ceiling

[Thorfun]

On 24/05/2023 at 21:13, Thorfun said:

actually there are a lot more calculations that I posted above. here's a pdf for the joists in question.

 

joist_calcs.pdf 10.07 MB · 1 download

 

it's all Greek to me. I'm hoping someone can tell me what it all means!

@Gus Potter don't suppose you would have the time to take a quick look at this for me please? I'm trying to work out if I can double board my ceilings if I want to. I 'think' that the dropped MF ceiling has minimal impact on the dead load and it looks like the bottom chord is rated at 200N/m² which, to my mind, means a load of ~20kg/m² and so 2 x 12.5mm plasterboard at 8kg/m² each should be within tolerance. assuming resilient bars and any light fittings are negligible as well.

[Gus Potter]

10 hours ago, Thorfun said:

don't suppose you would have the time to take a quick look at this for me please?

Had a very quick spin through the parts of the calcs you have posted. The output is not that clear and to really consider this we need to be able to see all the data that lies behind the the output. In other words to check this we need a lot more transparency and need more info.

 

On the face of it though in terms of the joists themselves it looks like they have spare capacity to take a bit of extra load in terms of strength. But we also need to consider deflection. Looking at the output you may get this to work ok and still be within the limits set by the original designer. It looks like you have about 20% to spare deflection wise and it is deflection that appears to be governing the joist design.

 

There are some vibration checks.. good to see. Adding a bit more dead load should not be a material factor on this relatively short span.

 

However to do this responsibly we need to then trace the extra load all the way down to mother earth and look at how this extra load may impact on the other parts of the structure. For example.. we need to check the joist end supports.. are there lintels below, if so what is their capacity?.. does this extra load cause more bending effects in say the masonry below / above due to the nature of the joist end supports acting possibly at the face of the walls rather than dead centre over the wall.

 

Often all works out ok.. but adding or in fact removing loads from a structure must always be checked. Sometimes if you remove a permenant load it can cause problems.. good example is a basement in water. Remove the ballast and the thing can suddenly float upwards! Another is where you may be relying on weight to stop a roof lifting off. Swap dense masonry blocks for lightweight aerated ones.. often done to reduce heat loss if you can't get the u value calcs to work.. if there is not good communication between the design team this is the sort of thing that gets missed... very easily done!

 

In the round though based on the summary output you have posted it looks like you can add a bit of extra load subject to detailed checking. Advise you proceed with caution.

 

If the joist manufacturer is no longer trading then there are some other avenues / ways a round this with a fair wind but story for another day.

 

 

 

 

 

 

 

 

 

 

[Thorfun]

13 hours ago, Gus Potter said:

Had a very quick spin through the parts of the calcs you have posted. The output is not that clear and to really consider this we need to be able to see all the data that lies behind the the output. In other words to check this we need a lot more transparency and need more info.

 

On the face of it though in terms of the joists themselves it looks like they have spare capacity to take a bit of extra load in terms of strength. But we also need to consider deflection. Looking at the output you may get this to work ok and still be within the limits set by the original designer. It looks like you have about 20% to spare deflection wise and it is deflection that appears to be governing the joist design.

 

There are some vibration checks.. good to see. Adding a bit more dead load should not be a material factor on this relatively short span.

 

However to do this responsibly we need to then trace the extra load all the way down to mother earth and look at how this extra load may impact on the other parts of the structure. For example.. we need to check the joist end supports.. are there lintels below, if so what is their capacity?.. does this extra load cause more bending effects in say the masonry below / above due to the nature of the joist end supports acting possibly at the face of the walls rather than dead centre over the wall.

 

Often all works out ok.. but adding or in fact removing loads from a structure must always be checked. Sometimes if you remove a permenant load it can cause problems.. good example is a basement in water. Remove the ballast and the thing can suddenly float upwards! Another is where you may be relying on weight to stop a roof lifting off. Swap dense masonry blocks for lightweight aerated ones.. often done to reduce heat loss if you can't get the u value calcs to work.. if there is not good communication between the design team this is the sort of thing that gets missed... very easily done!

 

In the round though based on the summary output you have posted it looks like you can add a bit of extra load subject to detailed checking. Advise you proceed with caution.

 

If the joist manufacturer is no longer trading then there are some other avenues / ways a round this with a fair wind but story for another day.

 

Hi @Gus Potter. thank you for the response. i do actually have all of the SE calculations for the TF and i think i have them for the basement. The load bearing walls that the joists sit on are 140mm CLS timber walls. the external walls sit on 250mm reinforced concrete walls which sit on a 250mm reinforced concrete slab.

 

the deflection of the joists were designed to be 8mm so we don't get any sort of bounce in the rooms above.

 

do you think that for peace of mind i should engage a structural engineer for this? i can then give them all the information i have and ask them to calculate if double boarding will screw stuff up? if so, how much do you think something like that would cost?

[Mr Punter]

Given that the floor was designed - I assume at your request - for 8mm deflection, there will be loads of spare capacity for the extra board layer.  It is probably equivalent to having and extra 2 average sized people in the room.  I would just get on with it.

[Pocster]

30 minutes ago, Mr Punter said:

I would just get on with it.

He's a true self builder. Post and ask, post and ask, think about it, post and ask...before you know it a year or 2 has gone and it's still not done......

[Thorfun]

1 hour ago, pocster said:

He's a true self builder. Post and ask, post and ask, think about it, post and ask...before you know it a year or 2 has gone and it's still not done......

so true

Edited May 30, 2023 by Thorfun
typo

[Pocster]

2 minutes ago, Thorfun said:

so true

I saw it !

You said ture - that’s coz you are pissed 🍺 

[MortarThePoint]

A middle ground is a single 15mm layer of Soundbloc (12.6kg/m2) or Soundbloc F (14.1kg/m2). I started a thread when I was trying to understand a lot of PB stuff.

 

Don't forget to add the weight of a 2 - 3mm MultiFinish skim which is 3.4 - 5kg/m2 unless you plane to tape and joint.

[Thorfun]

34 minutes ago, MortarThePoint said:

A middle ground is a single 15mm layer of Soundbloc (12.6kg/m2) or Soundbloc F (14.1kg/m2). I started a thread when I was trying to understand a lot of PB stuff.

 

Don't forget to add the weight of a 2 - 3mm MultiFinish skim which is 3.4 - 5kg/m2 unless you plane to tape and joint.

Your thread is like a bible to me and I refer back to it often!!

 

thanks for the weight of the skim, I was wondering what that would be. 
 

definitely loads more to think about and to consider other options. I could do 12.5mm and 9mm as a middle ground. So many options. 

[Thorfun]

1 hour ago, pocster said:

I saw it !

You said ture - that’s coz you are pissed 🍺 

Was actually in a rush to leave the office. 

[saveasteading]

3 hours ago, Mr Punter said:

equivalent to having and extra 2 average sized people in the room.  

Except that it is permanent so the floor bends a bit, but just once and stays there. If anything it reduces  bounce from movement. 

[Gus Potter]

On 30/05/2023 at 14:33, Thorfun said:

do you think that for peace of mind i should engage a structural engineer for this? i can then give them all the information i have and ask them to calculate if double boarding will screw stuff up? if so, how much do you think something like that would cost?

In terms of structural safety, yes.

 

But we all have a civic responsibility and structural safety is paramount..

 

But let me also appeal to all on these grounds...

 

Why not make sure that you have built something that will really last, maybe a lot longer than it's design life, be proud of it, leave a legacy? Yes I know it's about the money.. but you have put so  much work into this..

 

In terms of your wallet. What happens when you apply for you completion certificate. Who signs to say that the building has been constructed as per the approved plans? If it becomes apparent that you have added undeclared load what then? ..  that can develop into a big problem, habitation certificates, lenders not playing the game etc.

 

If it was me signing off your house I would check you are not pulling the wool over my eyes at not just my expense / risk but for the sake of all the folk who may own the house after you. But the other side of the coin is that I would try my best to get it to work for you and prove it and.. that may take a bit of innovation and lateral thinking.

 

I would play this off a straight bat, rest easy and be proud of what you have built without any worries.

 

Cost for a design review. If you have all the calcs and drawings that is a good start. But there is probably manufacture's data missing. So a bit of due dillegance required here, phoning about for the SE and talking to you to tease out what you have really built.  Say 3 days work with full disclosure from you and payment on the nail. It carries liability so say £400 a day = 1200. depending on who you get there may be vat on top of that.

 

That will be on the ball park to get you the checks you need. What you won't get for that is any kind of warranty that you can then pass onto a third party. There will be caveats.. for example if the checks reveal that there is a flaw in the original design then it's a different scope of works.

 

Also, if you can't access the joist data in particular lines become blurred. Things like this happen if companies have gone bust. There are ways of tackling this but it takes more time.

 

If you go to a larger SE outfit then a graduate rate is say £85.00 per hour.

 

 

 

 

 

 

 

 

 

 

 

 

[Thorfun]

12 hours ago, Gus Potter said:

In terms of structural safety, yes.

 

But we all have a civic responsibility and structural safety is paramount..

 

But let me also appeal to all on these grounds...

 

Why not make sure that you have built something that will really last, maybe a lot longer than it's design life, be proud of it, leave a legacy? Yes I know it's about the money.. but you have put so  much work into this..

 

In terms of your wallet. What happens when you apply for you completion certificate. Who signs to say that the building has been constructed as per the approved plans? If it becomes apparent that you have added undeclared load what then? ..  that can develop into a big problem, habitation certificates, lenders not playing the game etc.

 

If it was me signing off your house I would check you are not pulling the wool over my eyes at not just my expense / risk but for the sake of all the folk who may own the house after you. But the other side of the coin is that I would try my best to get it to work for you and prove it and.. that may take a bit of innovation and lateral thinking.

 

I would play this off a straight bat, rest easy and be proud of what you have built without any worries.

 

Cost for a design review. If you have all the calcs and drawings that is a good start. But there is probably manufacture's data missing. So a bit of due dillegance required here, phoning about for the SE and talking to you to tease out what you have really built.  Say 3 days work with full disclosure from you and payment on the nail. It carries liability so say £400 a day = 1200. depending on who you get there may be vat on top of that.

 

That will be on the ball park to get you the checks you need. What you won't get for that is any kind of warranty that you can then pass onto a third party. There will be caveats.. for example if the checks reveal that there is a flaw in the original design then it's a different scope of works.

 

Also, if you can't access the joist data in particular lines become blurred. Things like this happen if companies have gone bust. There are ways of tackling this but it takes more time.

 

If you go to a larger SE outfit then a graduate rate is say £85.00 per hour.

 

 

 

 

 

 

 

 

 

 

 

 

you make very good and valid points in here @Gus Potter and maybe i'm being a bit guilty of trying to do too much and to tick too many boxes! our kids aren't little and so there isn't a lot of stomping around in their bedrooms (they generally sit on their beds and watch YouTube vids!) and so may double boarding is simply not required. we've already put 100mm of Rockwool between the joists and if i use resilient bars and a single 12.5mm board then that would probably give a nice sound reduction level.

 

then we're building within the original specification and i save money on a second skin of plasterboard and also SE fees!

 

i guess that's one issue with self-building and reading forums is that it's hard to resist the 'ooohhhh.....i need to have that!' temptation when you read about something that sounds like a good idea whether you REALLY need it or not.

[Thorfun]

On 23/05/2023 at 22:37, Thorfun said:

Out of interest was ESP one of those other manufacturers? Had a quote from my BM for both Gyproc and ESP. I said I’d probably go for Gyproc as I figured in this instance you probably get what you pay for but he said he’d never had any complaints about the ESP stuff. 

@nod or anyone else, has anyone used ESP metal frame please? I need to put an order in tomorrow for this stuff and the ESP stuff is between 25% the price of Gyproc. they even name their components in a similar fashion to Gyproc so I'm wondering if they just come out of the same factory!

 

e.g Gyproc wall channel is GL8 and ESP's is ELS8 

 

GL1 or ELS1 

 

GL12 or ELS12 

Edited June 12, 2023 by Thorfun
got my maths wrong!

[Thorfun]

actually, I'm now worried @Nickfromwales is going to call me a tight ar$e again as the quantities I'm buying I'll probably end up saving about £60! I'm wondering if it's worth the ignominy.

[Nickfromwales]

1 minute ago, Thorfun said:

actually, I'm now worried @Nickfromwales is going to call me a tight ar$e again as the quantities I'm buying I'll probably end up saving about £60! I'm wondering if it's worth the ignominy.

[ETC]

On 19/05/2023 at 09:25, pocster said:

Suspended ceiling benefits :

 

Lightweight 

Easy to install 

No plastering

No painting

Access to pipes/cables 

Easy to add sound proofing 

Easy to add and move lighting 

Easy to add ceiling speakers etc.

Probably cheaper than ‘traditional’ ceiling 

 

What’s your problem ?

Ugly as f**k!!!!

[Chanmenie]

15 minutes ago, Thorfun said:

@nod or anyone else, has anyone used ESP metal frame please? I need to put an order in tomorrow for this stuff and the ESP stuff is between 25% the price of Gyproc. they even name their components in a similar fashion to Gyproc so I'm wondering if they just come out of the same factory!

 

e.g Gyproc wall channel is GL8 and ESP's is ELS8 

 

GL1 or ELS1 

 

GL12 or ELS12 

Thanks for sharing that, I need loads of it 

so a 25% saving will make quite a difference to me 

[Thorfun]

3 minutes ago, Chanmenie said:

Thanks for sharing that, I need loads of it 

so a 25% saving will make quite a difference to me 

 

so a bit more deep diving into the details and it looks like the Gyproc stuff seems a little superior as their yield strength is 210N/mm² (https://www.british-gypsum.com/documents/declaration-performance-dop/british-gypsum-dop-m100-uk-gypframe-metal-profiles.pdf) but the ESP Flexural tensile strength (which I presume is the same thing and the units are the same!) is 140N/mm² (https://www.espdrywall.co.uk/wp-content/uploads/2016/08/ELS8.pdf)

 

that seals it for me I think considering the quantities I'm ordering.

[Chanmenie]

13 minutes ago, Thorfun said:

 

so a bit more deep diving into the details and it looks like the Gyproc stuff seems a little superior as their yield strength is 210N/mm² (https://www.british-gypsum.com/documents/declaration-performance-dop/british-gypsum-dop-m100-uk-gypframe-metal-profiles.pdf) but the ESP Flexural tensile strength (which I presume is the same thing and the units are the same!) is 140N/mm² (https://www.espdrywall.co.uk/wp-content/uploads/2016/08/ELS8.pdf)

 

that seals it for me I think considering the quantities I'm ordering.

Interesting as the ESP is thicker steel at 0.6mm  I think the Gyproc is 0.55 mm 

[nod]

They are nothing to do with Gypsum 

It will be a lighter grade than Gypsum 

But do the same job 

Most of the other companies use similar codes to Gypsum and undercut by about 20% 

 

Get your order in Great saving 

There out there Just need to shop around 👏 

[Thorfun]

4 minutes ago, nod said:

They are nothing to do with Gypsum 

It will be a lighter grade than Gypsum 

But do the same job 

Most of the other companies use similar codes to Gypsum and undercut by about 20% 

 

Get your order in Great saving 

There out there Just need to shop around 👏 

Thanks @nod would the ESP resilient bar do the same job as the Gyproc RB1 too? 

[nod]

10 hours ago, Thorfun said:

Thanks @nod would the ESP resilient bar do the same job as the Gyproc RB1 too? 

You can use res bar 

But you still need an mf frame 

We normally use top hat then two x 15 mil sound boards

[Thorfun]

29 minutes ago, nod said:

You can use res bar 

But you still need an mf frame 

We normally use top hat then two x 15 mil sound boards

Sadly my posi joists aren’t designed to take that much weight as discussed previously in this thread. I know better for next time (if there is a next time!) to ask for them to be designed to take a higher load.
 

The resilient bars are for different rooms to the MF dropped ceiling. 

 

anyway, I’ve ordered the ESP MF and Resilient bars. I’m sure they’ll be fine. 

[saveasteading]

It doesn't need to be superior metal, as long as it works.

BG spend a lot on marketing and research which must increase the cost. Also they get specified by Architects so can charge more.

 

The specialist merchants usually stock the big names and a cheaper option. It must be OK......I have specifically asked a manager and was told the cheaper one was fine, but most specifiers don't even know it exists.

It's not complicated...buy galvanised strip, Bend it.