channelling underfloor ventilation

[EugeneM]

Hi All,

I have a small extension (office) on the side of the another extension (kitchen). Kitchen has suspended floor with air bricks on all the sides as normal.
Office is supposed to have a floor without any voids so kitchen air bricks as I understand have to be channelled across.

Question is - do I need to remove original air bricks on the side of the kitchen (have 3 there) or can just glue or somehow attach telescopic vents without taking them out? Suspended floor in the office is not an option at this point as concrete slab with membrane is already installed so have no space for proper void.

Thanks!

 

[oldbutnotdead]

You need to maintain airflow to the kitchen subfloor. You need to avoid getting draughts in the wall cavity and you need to avoid getting water in the subfloor.
These telescopic vents you speak of- you planning on going above the new office (won't work) or is there enough space between new office and new kitchen walls (300mm plus) for some effective ventilation?
Those vents are designed to be used with the 'up' bit in the wall cavity. They'll look fuggly outside

 

[EugeneM]

Thank you, I've just realised after checking some old photos that kitchen walls also have telescopic vents installed. I believe it means that airbrick I see on the side of the kitchen wall is just a "faceplate" for telescopic vent.

Basically it means that removing it won't help me a lot as I won't be able to access already installed telescopic vent in the kitchen to duct tape it or glue to the ducting on the office side.

My plan is to have a "shallow" telescopic vent on the office/kitchen wall side and then ducting all the way to the opposite airbrick in the office wall (now external wall).

 

[oldbutnotdead]

You need to maintain a minimum cross section area for your vertical duct extensions. And how are you going to duct horizontally through an already-built concrete slab?

 

[EugeneM]

I've had an idea of just chasing deep enough channel there but it's going to be a nightmare dust and overall efforts wise.
However it seems like I have around 150mm between the slab and top of the unfinished floor. So my plan is to run ducting on the slab, put probably two layers of insulation (1st on slab around ducting and 2nd over) and then put 18-22mm chipboard on top.

 

[oldbutnotdead]

Ok, that could work. Usual floor insulation requirement is 100mm Kingspan or similar so running 110mm waste pipe isn't going to cut it with bco. Flat ducting (look at electrical trunking if you get stuck) would be better in your case, specially if you can grind a 25 or so mm deep groove in the concrete.
Check Approved Documents for the area of vent required for your kitchen subfloor, double it, prepare a scheme & present it to bco. They'll want to maintain the R value of the office floor as well as effective venting of kitchen subfloor.

 

[EugeneM]

Great, thank you - I was thinking about flat ducting as well as it's easier to deal with.

What's the most correct way to deal with the problem in the original question? Should I remove that airbrick on the external kitchen wall and just push telescopic vent in hoping it will connect well with the vent on the other side or just carefully grind around and attach w/o removing it?

 

[JohnD]

I've had an idea of just chasing deep enough channel there but it's going to be a nightmare dust

get a builders canister vac.

you can buy extended hoses and adaptors to fit so you can put it outside the building (they are rather noisy)

this will also prevent the exhaust blowing dust around the room, and will create suction that reduces drift around the house (keep doors and windows closed)

you can also use plastic waste pipe for a neater permanent installation, for example in a workshop.

some power tools have a fitting to attach a vac hose (they are not always very good)

remember your goggles, dust mask, and ear defenders. Ear defenders. I said Ear defenders. EAR DEFENDERS, WHATS THE MATTER, ARE YOU...

oh, sorry.

 

[oldbutnotdead]

If you have sufficient access, I'd advise removing the air bricks (cos they obstruct airflow) and mortaring your ducting or duct adaptors in their place. This has to last the life of the building without allowing ingress of pests or stray water so gaffer tape and silicon won't be the best.