Fire Rated Cavity Closers

[Jammy5]

Three story building, advised fire rated cavity closers on all openings. Are they really required or will normal insulated cavity closers suffice?

 

If they are, can some one recommend something more cost effective than 150mm TIMLOC FR30 Cavity Closers that about £20-25 per length (windows are 1.8 x just over 1.2m, so can't even get 2 sides from a length). 4 lengths per window x ALOT of windows = Big cost!

 

Many thanks,

Jamie

[Gus Potter]

5 minutes ago, Jammy5 said:

Three story building, advised fire rated cavity closers on all openings.

Assume this is a timber frame? 

 

Your cavity closing is going to be driven by your external leaf / cladding arrangement.

 

https://envirograf.com/product-category/fire-barriers/cavity-barriers/

 

They have a good offering which I spec from time to time. 

 

BUT to be blunt.. if you are asking about this stuff on BH then please be careful before you swap materials out with your designers spec.

 

To be safe by all means look for similar and cheeper products but ALWAYS check with your designer that it is ok to use an alternative material.

 

Yes fire protection is expensive.. but it has to be implemented. Many think.. well we are young and fit so will exit the building.. but you put the fire service at risk and wallet wise.. your insurer may not pay out if you cut corners and are unlucky enough to have a fire. 

 

 

 

 

[Jammy5]

It's a three story, traditional block/brick build if that helps any?

[ADLIan]

There are exemptions for the cavity barrier requirement/performance - please see the section on ‘compartmentation’ in Approved Doc B

[Jammy5]

On 26/01/2026 at 22:05, ADLIan said:

There are exemptions for the cavity barrier requirement/performance - please see the section on ‘compartmentation’ in Approved Doc B

 

Thanks @ADLlan. Having read the standard am I correct that you were pointing me towards section 5.18 of Approved Doc B and specifically where it states:-

"This does not apply where a wall meets the conditions of Diagram 5.3."

 

Diagram 5.3 then states:-

"materials used to close the cavities in this arrangement do not need to achieve a specific performance in relation to fire resistance". 

 

Having constructed a traditional block that is more than the 75mm stated per leaf, and knowing I used fire rated cavity closers at the top of the wall then I interpret this as fire rated cavity closers aren't required.

 

Can anyone care to point me at anything I've missed, as this seems a nice little win (thanks to @ADLIan)?

 

 

[ADLIan]

That’s the one!

[Jammy5]

3 minutes ago, ADLIan said:

That’s the one!

Hero! 

[ETC]

Don’t forget that a cavity barrier can be as simple as timber and plasterboard.

[Jammy5]

Recognised construction details are showing an insulated cavity closer though for my sap value. Could I just put a 20-25mm piece of insulation across it at full width and then I'd need a DPM laid over the top prior to fitting the window?

 

Then I assume you're saying a 38mm window board and plasterboard reveals is acceptable?

 

Does the UPVC/Aluminium window cover the other element of the cavity, rather than the timber window sill inside?

 

[ETC]

[ADLIan]

@Jammy5 you will need photo evidence of this junction. Be very careful of using an alternative (though outwardly similar) detail!!!

 

@ETC if the detail complies with Diagram 5.3 above there is no fire resistance requirement for the cavity closer around openings so no need for CS board.

[Gus Potter]

On 26/01/2026 at 21:32, Jammy5 said:

Three story building, advised fire rated cavity closers on all openings.

Jammy.

 

You are winging it mate.

 

You have posted no drawings for example. 

 

I do this as a day job. From the questions you are asking it is clear you have no clue, not even taken the time to talk to your designers. But you maybe did not pay them enough in the first place and are now chasing you tail and trying to get a fudger by milking the good will on Build Hub.

 

Accept that you need to pay for professional advice here. 

 

You might get away with this stuff to start with but is going to come back and bite you in the arse!

[Jammy5]

2 minutes ago, Gus Potter said:

Jammy.

 

You are winging it mate.

 

You have posted no drawings for example. 

 

I do this as a day job. From the questions you are asking it is clear you have no clue, not even taken the time to talk to your designers. But you maybe did not pay them enough in the first place and are now chasing you tail and trying to get a fudger by milking the good will on Build Hub.

 

Accept that you need to pay for professional advice here. 

 

You might get away with this stuff to start with but is going to come back and bite you in the arse!

Gus,

 

I paid for an architect, they don't even respond to my messages or calls anymore so I'm kind of stuck. If you have advice on how this should be working and if I should be pursuing legal action for their lack of involvement then let me know?

 

Yes you're right I don't have a clue! I thought these forums were for people to help? If not then I apologise.

 

I'm unsure what drawings would you like me to post?

 

I'm going to use the insulated cavity closers as per the recognised construction details. My question was, do they have to be fire rated or not. I was simply just asking @ETC what he was meaning in his reply so I could understand better.

 

I'll try and obtain confirmation from my designer, I doubt I'll get a response but even if I do, what if he won't admit it's not required even though reading Part B it's not applicable around doors/windows in my situation?

 

Thanks, and like I said I'm trying to learn and understand. I appreciate everyone's help on here. I'm certainly not trying to wing it, I'm trying to understand the difference between how it's written and how these can be reasonably applied. It's sometimes not straight forward 

 

Thanks,

 

Jamie

[ETC]

You need to close the cavity to the perimeter of ALL external doors and windows with an 1/2HRFR cavity barrier irrespective of what insulation is in your cavity. The only “get out” for not installing a cavity closer is at the eaves and verge ONLY and that is on condition that the cavity is fully filled with insulation (pumped bonded bead being one example).

However, until I see conclusive evidence that the insulation in a cavity is non-combustible I will always ask for the cavity to be closed at the eaves and verge.

Edited 22 hours ago by ETC

[Nickfromwales]

24 minutes ago, Jammy5 said:

I thought these forums were for people to help? If not then I apologise.

 

40 minutes ago, Gus Potter said:

You are winging it mate.

@Jammy5, excuse Gus, he's old and grumpy, but is well intentioned. As am I....well, old-ish.

 

@Gus Potter, kinder words, softly spoken.....  

 

26 minutes ago, Jammy5 said:

I paid for an architect, they don't even respond to my messages or calls anymore so I'm kind of stuck. If you have advice on how this should be working and if I should be pursuing legal action for their lack of involvement then let me know?

Go at these lazy pricks with some gusto. Go call them out. If you need a professional confidante to support I'll help you out. These kind of architects piss me soooooooooooo badly off, bunch of pretentious wankers most of them. I've chewed so many up, and spat them out, and my qualifications allow me to drive a vehicle on UK roads.

[Nickfromwales]

3 minutes ago, ETC said:

You need to close the cavity to the perimeter of ALL external doors and windows with an 1/2HRFR cavity barrier irrespective of what insulation is in your cavity. The only “get out” for not installing a cavity closer is at the eaves and verge ONLY and that is on condition that the cavity is fully filled with insulation (pumped bonded bead being one example).

However, until I see conclusive evidence that the insulation in a cavity is non-combustible I will always ask for the cavity to be closed at the eaves and verge.

This.

[ETC]

45 minutes ago, ADLIan said:

 

 

@ETC if the detail complies with Diagram 5.3 above there is no fire resistance requirement for the cavity closer around openings so no need for CS board.

See my reply above - and read the diagram again - carefully!

[ETC]

2 minutes ago, Nickfromwales said:

 

@Jammy5, excuse Gus, he's old and grumpy, but is well intentioned. As am I....well, old-ish.

 

@Gus Potter, kinder words, softly spoken.....  

 

Go at these lazy pricks with some gusto. Go call them out. If you need a professional confidante to support I'll help you out. These kind of architects piss me soooooooooooo badly off, bunch of pretentious wankers most of them. I've chewed so many up, and spat them out, and my qualifications allow me to drive a vehicle on UK roads.

Post their identity. £1 says they’re not registered!

[Nickfromwales]

11 minutes ago, ETC said:

£1 says they’re not registered!

Be honest. You must get a bee in your bonnet, as do I, watching these barely-qualified pricks take good money, in good faith, and deliver disappointing sack-full's of dog turds?

[Jammy5]

15 minutes ago, ETC said:

Post their identity. £1 says they’re not registered!

I'll give them one last go before I do that bud. I'm really peeved off with the situation I've been left in, it's been the steepest learning curve of my life!

[Nickfromwales]

14 hours ago, ETC said:

Post their identity

Nothing would give me greater pleasure.

 

For one previous client, the architect was a family friend, who said he would support on "mates rates". I got brought in when the wheels were starting to fall off the project (YAY!!!) and immediately confronted this individual for his dispondence.

 

"I'm doing this as a favour so they'll just have to wait, I explained this to them". Tosser.

 

I said it wasn't a problem as I had the clients agreement that we should lose this bell-end and introduce some new blood. All I wanted was the .DWG's converted to PDF's, and some stupid faux-pas corrected before hand. Not the world, and the sky and the chuffing moon.

 

After embarrassing him sufficiently, low and behold, the requisite information started flowing. Prior to my employment, the clients had waited months for this muppet to get his thumb out of his (overpaid btw) ass.

 

 

[Gus Potter]

28 minutes ago, Jammy5 said:

Gus,

 

I paid for an architect, they don't even respond to my messages or calls anymore so I'm kind of stuck. If you have advice on how this should be working and if I should be pursuing legal action for their lack of involvement then let me know?

 

Yes you're right I don't have a clue! I thought these forums were for people to help? If not then I apologise.

 

I'm unsure what drawings would you like me to post?

 

I'm going to use the insulated cavity closers as per the recognised construction details. My question was, do they have to be fire rated or not. I was simply just asking @ETC what he was meaning in his reply so I could understand better.

 

I'll try and obtain confirmation from my designer, I doubt I'll get a response but even if I do, what if he won't admit it's not required even though reading Part B it's not applicable around doors/windows in my situation?

 

Thanks, and like I said I'm trying to learn and understand. I appreciate everyone's help on here. I'm certainly not trying to wing it, I'm trying to understand the difference between how it's written and how these can be reasonably applied. It's sometimes not straight forward 

 

Thanks,

 

Jamie

Hello Jamie.

 

My last post was intended to see if you were serious, bit of tough love!

29 minutes ago, Jammy5 said:

Yes you're right I don't have a clue!

Ok now you are among lots of kindred spirits on BH. Everyone has to start from somewhere, don't whatever you do feel embarrased! What you are doing is not easy! The hard part is the interfaces. These ccan take lots of time and expense to sort out.

 

32 minutes ago, Jammy5 said:

I'm unsure what drawings would you like me to post?

This is very much up to you.

 

I do this as a day job..there are other folk like me but also lots of folk that have forgotten more than I know! On BH there are contractors, glazing specialists, Architects @ETC for example..that are all chipping in with their professional knowledge and practical construction advice. 

 

This is up to you but the best thing to do would be to get all the info and drawings you have., bundle that up.

 

Remove any personal details and identifying marks an post the whole lot on BH!

 

I'll, when have the time chip in.. but the other members will really give you an insight and help.

 

It's kind of a come to "Jesus" moment.. you post the lot and get lots of expert advice..straight off the batt.

 

Some suggestions you get will be off the wall, some not viable as we don't really know what you want to do. But that is part of the desing process.. which is often about ruling out the things you DON'T want to do.. I'm a big advocate of this! Story for another day. 

 

I'll give you mine as an SE / Desinger but I can't spend time playing detective with you, if you hold back. Some sugestions you get will not be applicable but will help just generally inform you. BH members really do what it says on the tin! There is the odd wanker but the Mods sort them out quickly. 

 

To finish Jamie..

 

It's ok to not have a clue! I didn't when I first started out! Welcome to the club! Main thing is to enjoy the design and learning process. Remember it's your money so every pound is a prisoner! 

 

 

[Nickfromwales]

Just now, Jammy5 said:

I'll give them one last go before I do that bud. I'm really peeved off with the situation I've been left in, it's been the steepest learning curve of my life!

It's what happens, unfortunately, when unscrupulous companies see their client as subordinates.

 

I've instantly dismissed more than 80% of the architects I've been asked to work with, based on easily demonstrable incompetence (and worse, over-charging).

[Nickfromwales]

4 minutes ago, Jammy5 said:

I'll give them one last go before I do that bud. I'm really peeved off with the situation I've been left in, it's been the steepest learning curve of my life!

I've not long got off a Teams meeting, with my new clients and the newly-appointed AT. It was a great meeting, ideas shared, bad ones guffawed at, and a high-value next step for the clients self-build adventure. At NO point, none whatsoever, should this be so fecking difficult!!

[Jammy5]

4 minutes ago, Gus Potter said:

Hello Jamie.

 

My last post was intended to see if you were serious, bit of tough love!

Ok now you are among lots of kindred spirits on BH. Everyone has to start from somewhere, don't whatever you do feel embarrased! What you are doing is not easy! The hard part is the interfaces. These ccan take lots of time and expense to sort out.

 

This is very much up to you.

 

I do this as a day job..there are other folk like me but also lots of folk that have forgotten more than I know! On BH there are contractors, glazing specialists, Architects @ETC for example..that are all chipping in with their professional knowledge and practical construction advice. 

 

This is up to you but the best thing to do would be to get all the info and drawings you have., bundle that up.

 

Remove any personal details and identifying marks an post the whole lot on BH!

 

I'll, when have the time chip in.. but the other members will really give you an insight and help.

 

It's kind of a come to "Jesus" moment.. you post the lot and get lots of expert advice..straight off the batt.

 

Some suggestions you get will be off the wall, some not viable as we don't really know what you want to do. But that is part of the desing process.. which is often about ruling out the things you DON'T want to do.. I'm a big advocate of this! Story for another day. 

 

I'll give you mine as an SE / Desinger but I can't spend time playing detective with you, if you hold back. Some sugestions you get will not be applicable but will help just generally inform you. BH members really do what it says on the tin! There is the odd wanker but the Mods sort them out quickly. 

 

To finish Jamie..

 

It's ok to not have a clue! I didn't when I first started out! Welcome to the club! Main thing is to enjoy the design and learning process. Remember it's your money so every pound is a prisoner! 

 

 

Thanks for the understanding. I'll grab the details tomorrow and post them on here with any personal details removed. Do I just post them in this chat? Or the introductions section?