New C/AS2 Query to MBIE

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Hi All

On reading the new C/AS2 there were a couple of items in particular that seemed awry, so we sent a query to them, You can make your own conclusions.

Our query and response for your edification:

HI Dave and Saskia

Thanks for the messages re the new C/AS2 AS.

We haven’t had a chance to review it completely however 2 changes in particular are going to make a significant impact and we believe that these may be unintended by yourselves.

Firstly the issue of Intermediate Floors within household units

In the current C/AS2 for Residential the definition of intermediate floor includes a comment:

Intermediate floor Any upper floor within
a firecell which because of its configuration
provides an opening allowing smoke or fire
to spread from a lower to an upper level
within the firecell.
Comment:

  1. Upper floors within household units need not meet
    the specific fire safety requirements which apply
    to intermediate floors in all other situations.
  2. An intermediate floor may be open to the firecell
    or enclosed with non-fire rated construction. If enclosed
    with fire rated walls another firecell is created.

This has, in the past, been taken to mean that the escape route length within household units need not be multiplied if there is an upper level.

During consultation the draft removed all comments, but the paragraph dealing with the multiplier had the additional paragraph added to ensure that the allowance of comment 1 was continued.

Intermediate floors
3.4.3 On intermediate floors (see Figure
3.7), the open path length, shall be taken as
1.5 times the measured length in accordance
with Paragraph 3.4.2 c). However, the
measured length may be used where
the intermediate floor is a smokecell and
an escape route is available from the
intermediate floor without passing through
any lower space in the same firecell.

The extension of travel distances on
intermediate floors within household units
does not apply.

In the published version both of the above have been deleted and now have to multiply the upper level escape route length by 1.5.

Intermediate floors
3.4.3 On intermediate floors (see Figure 3.8),
the open path length shall be taken as 1.5
times the measured length in accordance
with Paragraph 3.4.2 c). However, the
measured length may be used where
the intermediate floor is a smokecell and
an escape route is available from the
intermediate floor without passing through
any lower space in the same firecell.

This will have a significant impact on the apartments and townhouses that we are designing in significantly greater numbers meaning that the cost of these will increase as we will have to specify smoke detection where this is not currently required or even sprinklers in order to allow the internal travel distance.

Secondly, the new document has made a subtle but significant change to the scope of Risk Group WB:

Storage activities now states:

Storage activities such as: Buildings or parts of buildings capable of storage no
more than 5.0 m in height). Warehouses and storage buildings (other than those listed
above), capable of storage no more than 5.0 m in height, with a height to the apex no
greater than 8.0 m and total foor area of no more than 4200 m2. Temperature
controlled storage with a capable height of storage of less than 3.0 m, other than
some limited areas in processing areas, or up to a maximum area of 500 m2 with a
maximum capable of storage height of 5.0 m.

Whereas currently, and in the consultation document, it was:

Current:
other storage buildings capable of <5.0 m storage height
(except some limited areas <8.0 m to the apex), light aircraft
hangars

Consultation:
Storage activities such as: Warehouses and storage buildings (other than
those listed above), with storage of no more than 5.0 m or a height to the
apex no greater than 8.0 m and total foor area of no more than 4200 m2.
Temperature controlled storage with a storage height of less than 3.0 m,
other than some limited areas in processing areas.

The OR in the consultation document has been changed to a comma - changing the requirement to be:

The building has to be capable of storage of less than 5m AND have an apex no greater than 8m nor an area of greater than 4200 sqm.

Thus negating the allowance for small warehouse buildings that happen to be taller than 6m apex.

As stated above we believe these are unintended in nature and there is no intent to increase the requirements in the Acceptable Solution in these particular areas.

If so can you advise soonest that is the case and that the status quo can continue until an errata is published.

Thanks

MBIE Response:

Hi Nick

Thanks for bringing this to our attention. We will look to update the text in these sections for a future amendment in the June 2020 bi-annual building code system update cycle. The previous C/AS2-7 Amend 4 2017 documents remain in effect until 31 October 2019 and can be used to demonstrate compliance until that time.

Regards

1 Like
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Hi Nick,
Unfortunately this is not the limit of the errors. The drawings are still incorrect in respect of the wording. Eg the instruction to start 1m from the furthest point and follow the wall at 1m away to the exit (is roughly the wording)…then the revised picture is actually worse than previously drawn. It now shows an egress route across the middle of a floor, and you and I know what that does for right hand or left handed searches and egress…

I don’t see how this document is going to help at all. it will bring additional confusion to an already confused area and add more stupidity to a relatively easy set of basic rules. Best just do specific designs and not rely on this broken document.

:slight_smile:

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The definition of limited storage is particularly significant. We do a lot of fire reports for warehouses that, until 31/10 will qualify as risk group WB, but from 1/11/19 until June 2020(?!) will have to be WS! I’m wondering if the TA’s will accept an argument that there’s effectively a typo in C/AS2?!

1 Like
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Hi Rob,
There are a lot of discrepancies in the C/AS2 and C/VM2 documents. It would be nice to assume that they’re all typo’s and ignore them but unfortunately as a deemed to comply document there is no scope for interpretation.
C/AS2 is quite clear on storage over 5 m now being outside scope. It was always a bit odd that this was allowed in the first place, particularly where the 20TJ limit of C3.8 is exceeded.

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just thinking about the storage problem that we will all face…the Act still allows “alternative” designs to the Code and supports the reliance on “in service history”. therefore I would design/review to the Code using the current documents if needed…problem solved until MBIE sort this out.

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Hi Nick,
Ive found the same thing with an apartment fire design I’m currently writing. C/AS2 para 4.13.8 removes the floor area limit normally imposed on AS mezzanines, and also removes the requirement to fire rate the underside of the floor and stairs. However; there is no likewise exemption from factoring escape route lengths in Risk Group SM upper floors. Reading without the benefit of commentary notes and MBIE companion guidance material, an upper floor mezzanine within a Risk Group SM apartment firecell is open to the same factoring that would apply if it was a commercial mezzanine with up to 100 people on it.

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Problem with that is that the building code is in many ways inadequate to support desirable outcomes. It is intrinsically tied to the VM such that neither is adequate in isolation. the acceptable solutions are another problem as they have a very tenuous link to the current building code. divert from the acceptable solution and the building code is more often than not an adequate back up. its easy to throw around the we can do alternative solutions and sure in service history is a valid methodology but you still have to be able to tie the proposed building work to a building act obligation and most in the C space are holistic, ie they apply an obligation to the building, not building elements. Fine if your designing a new building but fraught with issues when your altering existing buildings.

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make that building code obligation, ie a performance criteria