External Wall in SI Addition

Situation - external wall of an SI building extension, 2 metres to boundary, 80% unprotected wall area allowed. Table 5.3 allows single unprotected areas of 35m2, with at least 2.5 metres between adjacent unprotected areas. Question - do the unprotected area(s) have to be rectangles? Could it be say the top 300mm of a 2.7m wall extending down to include a few windows along the wall length? Hard to explain, and I can’t paste a picture. The end result is that the unprotected area is a multi-sided polygon that extends the length of the building. With fire rated bits in between, so it sort of meets the intent of spreading out the unprotected openings along the length of the wall.

Hi Tim. The use in this situation is incorrect.

The wall was a rated to 2.4 m high, in part.

The designer is trying to claim a 2.7m wall which is unrated above the 2.4m external wall height.

The AS which is the basis of the design requires the 80% at 2m tot eh boundary and 2.5m between the adjacent UPA

the designer wants to claim that the fire rated wall is 2.7m high, which include the unrate wall behind the soffit.

The AS is simple and is base on the external wall being rated 100% and then the openings are put into that rated wall.

The design fails because of the use of the additional non rated section being claimed. The the adjacent UPA is too close ( within the 2.5m distance).

I was at MBIE when we changed the theory and I know I am right in my view based on the fact that I was part of the decision and theory for the AS. If you think about it, it is 180 degrees from the enclosing rectangles method.

Anyway they have been asked to use an alternative method, which may be calculating the exposure to meet the Code.

Give me a call and I will explain, but the design, in my view fails ( and as I know the design, and with my background I pretty sure I am right).

The respondents to this question need to be very aware that 2 CPEng Fire engineers and a very experienced Processing officer have looked at this design.

This is potentially heading for a Determination…

Give me a call and I will be happy to discuss directly.

I guess it is obvious, but the question can not be answered without being in fully aware of the facts and the drawings in this case.

I am involved in this as it is a live application which my company is processing on behalf of a BCA. I am looking at the fire design, done by a non qualified and non CPEng designer.

In our view it does not work and that has been checked with another ( very experienced CPEng Fire Engineer).

It simply doesn’t follow the AS and it can not comply with the enclosing rectangles. It may ( and I mean May) be proven by calculating the exposure on and 1m past the boundary, but as the designer is not CPEng is causes an issue.

They have been invited to a meeting to discuss but they have declined. Umm wonder why?

From the description, the shape is a E, turned 90 degrees. This forms one contiguous area as it is connected along the top, so you don’t have the separation between areas required.
As a more general view, since it is the Building Code that the lawyers will use to hang you with if it goes wrong, or alternatively your get out of trouble card, the answer for any interpretation is to refer to the Building Code.
In this case, since this part of the code has hard numbers and is a simple 10-15 minute calculation for this example, in cases like this, I suggest doing the calculation to be sure of the answer. It may not be issued but having it on file helps to show that you took due care in your interpretation if it goes wrong in the future.

Gentlemen, thanks so much for your help and wisdom.