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 12/13/2011 8:21 AM
 

Dear Belinda,

For quite some time Council has used a condition to the effect that any non-recirculating rangehood must exhaust through the roof to the open air - the rationale being that a fire could take hold in the roof space if something caught alight on the top of the stove, and the extra duct and flashing is relatively inexpensive. I understand a lot of other councils see things the same way.

The following is advice being circulated by the HIA suggesting that this is not necessarily the case, and I attach it for interest in case it comes up in other areas also. What do people think about applying this condition - do we have the right to, and is it necessary?

Thank you,

Bob Crawford.

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 12/13/2011 8:22 AM
 

Hello Belinda

In a new place check the basix certificate (I know you would but kris may not) to see what is specified as We received a basix certificate recently and it was the removable filter type due to the raked ceilings in the house ,also it may not be stated in the bca but we had nsw fire inspectors going through the old pubs in town and they spoke about the build up of debris in the ceiling above stoves being a major contributor to loss of houses in a fire situation

Chris Maloney

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 12/13/2011 8:23 AM
 
Bob,
It would appear it does not comply -
Extract from AS1668.2 (Ventilation Code)-
3.7 AIR DISCHARGES
3.7.1 General All exhaust air and spill air shall be discharged to atmosphere in such a manner as not to
cause danger or nuisance to occupants in the building, occupants of neighbouring buildings or members
of the public.
Discharges that are not deemed objectionable shall comply with Clause 3.7.2 and discharges that are
deemed objectionable shall comply with Clause 3.7.3. For the purpose of this Standard, any of the
discharges at the flow rates specified in the table below shall be deemed to be objectionable.
TABLE 3.3
OBJECTIONABLE DISCHARGES
Exhaust-air discharge Flow rate
Type A effluents as defined in Clause 3.3.1 Any flow rate
Toilet exhaust > 1000 L/s
Kitchen exhaust from filtered hoods > 1000 L/s
Tony Hilt
Executive Assessment Officer
(Fire Safety)
North Sydney Council
New Post
 12/13/2011 8:23 AM
 

Bob’

Have a look at the Note after 3.2.1 of AS 1668.2 Which refers to a discretion and

The last sentence in 3.3.1 which refers to domestic purposes the regulatory authority MAY exempt

Paul Riley

Building Surveyor

New Post
 12/13/2011 8:24 AM
 
Morning all,
Just a personal view...........
I am a fan (pardon the pun) of exhausting through to open air if only to ensure no build up of fats and other aerosols into the roof space. One of the "lesser" problems with any venting to roof space or open air (as opposed to re-circulating) is the potential for heat loss from the conditioned space.
Extending the flue through to open air is the best method and I would recommend a self opening and closing storm flap to prevent heat loss when the exhaust is not in use.

In terms of the legal perspective, I would certainly defer to the previous writer's opinion ie kitchen exhaust to the open air.
Cheers, Neil Smith
New Post
 12/13/2011 8:25 AM
 

G’day Bob,

I agree that ventilation of odours/emissions from buildings is an issue that cannot be addressed by simply venting it into the roof cavity space for the following reasons:

  1. Part 2.4.5(c) of the BCA requires that contaminated air must be disposed of in a manner which does not unduly create a nuisance or hazard to people in the building….
  2. An enclosed roof space with inadequate ventilation to the outside will create positive air pressure which will force air to release through any air-interchange access point
  3. Odours derived from rooms provided with mechanical ventilation (including bathrooms and ensuite) venting to the roof space will follow the air flow on the path of least resistance. Bathroom odours to the kitchen and vis-à-vis.
  4. Grease and other particulates are more likely to coat interactive surfaces when not carried with adequate air flow. The build up of this mass could pose a greater fire risk than originally factored into the building design.

Cheers,

Douglas Burke

Director of Environmental Services

Murrumbidgee Shire Council

New Post
 12/14/2011 6:59 AM
 

Bob,

Exhausting through to the open would seem to be the better option, however there are various scenarios for ventilation from kitchens.

If you are dealing with a BASIX affected building, the energy (ventilation) section provides a few options being:-

a) No mechanical ventilation;

b) Individual fan, not ducted; and

c) Individual fan, ducted to façade or roof.

As for b) if a ceiling exhaust fan is being fitted then you need to be aware that a conventional ceiling fan does not have the capacity to be used with a duct as it creates back pressure on the fan and they are not designed to operate with any back pressure. The individual fan not ducted scenarios though will generally be the re-circulating range hoods.

As for c) I believe it could be interpreted to mean ducted to the roof void.

It might be of value if someone had the time to chase the BASIX people and get a determination on this as the builder could easily argue that an installation into the roof void is compliant with the BASIX commitment for the project.

Cheers

Brent Livermore

New Post
 12/14/2011 11:55 AM
 

Hi Bob,

Whilst we don’t have the suite of 1668 standards yet ( hopefully my “contact” at a nearby Council will soon fix that little problem!!!), the advice from the HIA appears to be correct. It was always my understanding that special requirements are contained in AS 1668.2 where exhaust systems serve kitchen hoods installed above appliances as required by AS 1668.2 or where having a heating capacity greater than 8 kw and likely to generate grease vapour. The average domestic cooking stove generates between 2.5 to 3 kw, owing to the fact that even with the oven, griller, and burners going flat out at the same time, they tend to cycle in and out as the thermostat cuts in and out after a certain temp. is reached, even though a normal domestic stove can generate about 5 to 6 kw. However we all know that the people with plenty of money are installing commercial grade stoves in their homes that could quite easily generate 8kw or more heating capacity.

I agree with Neil and Brent too!! What I would do is to either develop a Council Policy that requires the exhausting of non-recirculating rangehood ductwork to the outside air, or do an amendment to your applicable DCP ( assuming you have one for dwellings in urban and rural areas!!!) by inserting a clause to this effect, so that it would mean a report to Council to vary a requirement of the DCP if an Applicant wants the clause to be amended or varied.

Hope this helps mate.

Regards - Ralph Tambasco Director of Development and Environmental Services - Junee Shire Council

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