Airtightness for Flush Mounted Consumer Unit

[MortarThePoint]

I've agreed with the sparky that I am going to have a satellite consumer unit (CU) for an attic conversion. That way, I have a single feed to the attic and then dedicated isolator, RCBOs etc for the attic sockets, fans and lights etc. I am planning to put a flush mounted consumer unit into a stud wall that has an airtightness requirement. I'm not expecting to achieve airtightness with the CU itself[1], so am thinking I'll create an OSB box behind the plasterboard that is lined with Passive Purple (air tight paint) and has sealed entries for the cables. The airtightness membrane of the wall would then get tape sealed to this OSB box. Is that how airtightness is normally done for flush mounted consumer units?

 

I like the look of the flush mounted consumer unit below. I know Hager also make a good one, but I feel it's a bit industrial looking for being visible on a wall in living space. Hopefully this one doesn't actually have the logo on it, but if it does a pit of paint could easily solve that. Has anyone used a Live brand consumer unit? 

 

[1] I know Wiska do airtight cable grommets you can get from TLC, but attaching the membrane to the CU housing sounds tricky.

 

https://www.electrical4less.co.uk/product/live-electrical-fmc16-16-module-flush-mounted-metal-enclosure/

https://www.liveelectrical.co.uk/product-detail/fmc16_72

https://www.liveelectrical.co.uk/storage/documents/datasheets/1720044797__LSMC &FMC DATASHEET.pdf

[Nickfromwales]

On 12/06/2026 at 15:26, MortarThePoint said:

I'm not expecting to achieve airtightness with the CU itself[1], so am thinking I'll create an OSB box behind the plasterboard that is lined with Passive Purple (air tight paint) and has sealed entries for the cables. The airtightness membrane of the wall would then get tape sealed to this OSB box. Is that how airtightness is normally done for flush mounted consumer units?

The wall behind the CU is where your AT layer should be? So you'd just airtight the wall from floor to ceiling and then neither the CU or the cabling / grommets are outside / breaching the AT layer. What is the wall construction?

[MortarThePoint]

17 hours ago, Nickfromwales said:

The wall behind the CU is where your AT layer should be? So you'd just airtight the wall from floor to ceiling and then neither the CU or the cabling / grommets are outside / breaching the AT layer. What is the wall construction?

 

That makes sense when it's a surface mounted consumer unit, but when it's a flush mounted one it extends behind the plasterboard. The wall construction is 4x2 studs with plasterboard, VLC (300ga polyethylene), Knaug Omnifit insulation slabs between the studs and behind. I was thinking I could build a box in between a couple of studs and then airtight that and have the VLC taped to it. That would effectively create the 'bump' in the airtightness layer needed to accommodate the rear part of the flush mounted consumer unit.

[Russell griffiths]

Just build a box like you say, like you would a shower niche, except airtight instead of water tight. 

[Nickfromwales]

12 minutes ago, Russell griffiths said:

Just build a box like you say, like you would a shower niche, except airtight instead of water tight. 

Yes, but take the box all the way to meet the AT layer at the ceiling, so all the cables can go up in an AT riser. Requires zero GAF for the electricians then.