Ceiling service void size for domestic sprinkler system

[MattD]

We're in Wales, meaning all new builds must have a sprinkler system. We're designing a two-bed timber framed cottage with one-and-a-half floors (bedrooms in the attic space). Sprinklers are required in bedrooms, meaning we will need to allow for the sprinkler pipes in the ceiling service void. Since the bedrooms are in the attic (roof space), service void space is limited.

 

I was under the impression that a ceiling service void is typically 25-75mm: 25 if you only plan on running cables, and 50 or even 75 if you plan on running water pipes too. Just to be on the safe side, I thought I'd contact the sprinkler company we're thinking of using to ask them how much space they need. They said 120mm (as a minimum!) Does this sound right? Can anyone else who has built for a domestic sprinkler system confirm if this much space is really necessary? If we make our ceiling service void that large we would effectively need to box in the entire timber frame, which would be a real shame. I'm not entirely convinced that the sprinkler company really understood what I was asking about, but thought it worth asking here in case anyone else has had experience with this. They said the sprinkler heads require 120mm.

[Stratman]

Hi There

 

Looks like you didn't get any responses to your query.  Did you get it resolved in the end?  We will have vaulted ceilings upstairs and I just came across similar advice from the sprinkler company - actually 130mm void. Also in Wales by the way.

 

The TF supplier is installing only 25mm service battens below the VCL to the underside of the roof joists.

 

Does anyone out there have any experience or suggestions?

[Nickfromwales]

19 minutes ago, Stratman said:

Hi There

 

Looks like you didn't get any responses to your query.  Did you get it resolved in the end?  We will have vaulted ceilings upstairs and I just came across similar advice from the sprinkler company - actually 130mm void. Also in Wales by the way.

 

The TF supplier is installing only 25mm service battens below the VCL to the underside of the roof joists.

 

Does anyone out there have any experience or suggestions?

Yup. Done a few with both types (sprinklers and mist) of automatic fire suppression systems.

 

This was what I did on an MBC PH TF client project. I made top hats out of membrane and tape, using an off cut of the 125mm duct (or something round etc) and then set them in to give the required depth. 
 

Did the same downstairs when I did the prep for the cinema room speakers to go in (Dolby Atmos ones in the same type of ceiling, under the balcony).

 

Easy enough to sort without adding more battens, if you know beforehand what’s going in etc. 

 

 

I got MBC to specify holes in glulam and steel beams to allow services to get about the superstructure with ease. Makes 1st fix a breeze!  

[Nickfromwales]

@Stratman, have you asked if you can go for a mist system instead? 

[Stratman]

50 minutes ago, Nickfromwales said:

I made top hats out of membrane and tape, using an off cut of the 125mm duct

Fantastic - thank you!  And I see the pipes are just tucked over the battens below the VCL.

[Nickfromwales]

Just now, Stratman said:

Fantastic - thank you!  And I see the pipes are just tucked over the battens below the VCL.

Yup.  

 

51 minutes ago, Nickfromwales said:

have you asked if you can go for a mist system instead? 

A robot in cyberspace says:

 

Yes, you can fit a water mist system instead of a traditional sprinkler system in Wales, as the regulations require an "automatic fire suppression system" (AFSS) rather than explicitly demanding a traditional sprinkler. However, this alternative must meet specific, strict standards to be accepted by Building Control. 

Here are the key details regarding the use of mist systems as an alternative to sprinklers in Wales:

 

1. Regulatory Compliance (Approved Document B - Wales)

• Mandatory Requirement: Since 2016, all new residential buildings, care homes, and high-rise student accommodation in Wales must have an automatic fire suppression system.
• Approval Standards: Water mist systems must be designed and tested to recognised standards, typically BS 8458:2015 (Residential and domestic water mist systems).
• Case-by-Case Assessment: Because mist systems are sometimes considered "engineered solutions" rather than standard prescriptive solutions, they must be validated by a Building Control Body to ensure they are fit for their intended purpose. 

 

2. Benefits of Mist Systems over Sprinklers

Mist systems are often chosen as a "direct replacement" because they offer several advantages, especially in retrofits: 

• Less Water Damage: Mist systems use up to 90% less water than traditional sprinklers, reducing post-fire damage.
• Installation Ease: They can often connect to the existing potable water mains rather than needing a dedicated water tank, making them much easier to retrofit in homes or apartments.
• Flexibility: They can be used to achieve compliance for open-plan living, loft conversions, and open-plan staircase layouts. 

 

3. Considerations

• No "Off-the-Shelf" Approval: Unlike standard sprinklers, not all mist systems are suitable for every situation. You must ensure the chosen system has valid third-party certification (e.g., LPCB, IFC).
• Early Consultation: It is highly recommended to consult with your local Building Control Body in Wales before installation to ensure the system will be approved.
• System Type: The system must provide full building protection, not just localised, spot-protection. 

In summary, a properly specified and installed water mist system is a viable and often preferred, compliant alternative to sprinklers in Wales, offering similar safety standards with fewer installation constraints. 

[Nickfromwales]

@Stratman

 

Mist system saves a load of money on tanks / pumps / bigger incoming cold mains, and only runs for a set 45 mins iirc. The equivalent of you filling a bath and tipping it over, and that's the sum of the water damage vs a sprinkler which will devastate the property by flowing continuously until discovered.

[Stratman]

Thank this is really useful. I will ask BCO about mist system as at the moment the sprinkler company is concerned that water pressure will be inadequate so will need a pump set and tank to the tune of several more grand cost.

[JohnMo]

On 26/11/2023 at 20:26, MattD said:

Sprinklers are required in bedrooms,

That would wake you up.

 

Water mist, you could get back in to bed and finish your nights sleep.

 

If my memory is correct sprinklers cool the flames, water mist essentially smoothers the fire, ok in electric switch rooms etc and delicate environments such as a house.

[Mr Punter]

21 minutes ago, Stratman said:

I will ask BCO about mist system

 

I have had quotes for this before and they were very expensive to cover the whole house, but can be handy for smaller areas.

 

Get a flow rate / pressure check.  You can request a very meaty supply from the water co. just for fire sprinkler purposes.  Have it separate from your main supply.