AOVs omitted from top floors of domestic blocks

witsd · Post by **witsd** » Fri Feb 28, 2020 11:47 am

Trying to get my head around the logic (if there is any) of this:

5 storeys, domestic, Scotland. Main shared stairwell providing access into a lift / flat door access lobby (2 flats per floor).

The main stairwell is fitted with normal windows on all floors. These can be manually opened part way.

Each lobby has a single window, which on floors Ground → 4th have automatic openers, linked to smoke detectors which are in all areas. The fifth floor however just has a normal, manually operated window, and I'm told that this is a common set-up.

I'm assuming that this is something to do with likely direction of travel, with far less people having to pass through or past this area, than, say, on the first floor (with all persons on floors 2–5 having to pass by), but it still doesn't quite add up. The smoke is going to generally rise to the 5th floor – surely an AOV there is going to be the most effective of all?!

I'm looking through the Technical Handbook now, but thought I'd see if I'm missing anything painfully obvious via you guys.

Ta,

R

Messy · Post by **Messy** » Fri Feb 28, 2020 5:13 pm

I agree it sounds counterintuitive as the smoke is always worse on the upper floors . Of course you may need AOVs at lower levels for cool air input, but to miss the top floors seems odd. Is it a new build?

I am not massively familiar with Scottish Building Regs but the Building Standard Technical Handbook 2019 (link below) states that where a building is between 7.5m and 18m tall, it should have lobby approach and those lobbies should be vented. It also says:

Fire-fighting lobbies - ventilation should also be provided in every fire-fighting lobby ....... by:
a ventilator of at least 1m2 at each storey on an external wall, or ‘Smoke shafts protecting fire-fighting shafts: their performance and design’ (BRE, 2002).

A ventilator is defined as: means a window, rooflight, grille or similar building component (and in the case of a dwelling includes a door) capable of being opened to provide ventilation.

So although this doesn't necessary answer your question re why the omission of AOVs on the top floor, it seems there is no requirement for AOVs anywhere so this situation appears acceptable but not logical

https://www.gov.scot/publications/build ... acilities/

witsd · Post by **witsd** » Mon Mar 02, 2020 11:02 am

Cheers Messy.

Yes, my understanding is that it was built, or at least substantially upgraded in 2007. This isn't intended to be an FRA, just an advice request for a specific issue, so I've not delved further than what I've been told.

These lobbies can't be (as far as I can remember) specified as firefighting lobbies, as they include flat door entrances, which could potentially compromise the space as soon as a flat containing a fire was accessed. I might be fudging that though...?

The Scottish Tech handbook states this:

"The building should be designed to inhibit fire and smoke spread into the escape route. Where occupants have only one means of escape from the building, automatic smoke ventilation is normally provided to help remove any smoke and heat that may enter the escape route." (emphasis mine).

https://www.gov.scot/publications/build ... -9-escape/

So for me, although the top floor has a window that is capable of being opened, by the STH it should really either be a fixed-open vent, or a window with an AOV attached.

witsd · Post by **witsd** » Tue Mar 10, 2020 10:16 am

In case anyone would appreciate a conclusion to this, it turns out that the STH that was in place in 2007 specifically omits top floor protected lobbies from requiring automatic ventilation. It doesn't explain its reasoning and it is no longer the case, but there you go.