Finishing the frame – bad news from the CFA January 2011

We finished the kitchen frame and hearth yesterday. It was very exciting and, as soon as I’ve solved some technical issues, I hope to post pictures and video.

Today the CFA inspected the property for the fire permit for next weekend. It is a condition of the permit that we not light a fire in the kitchen building. We CAN light a fire in the firepit.  This is disappointing.

One of the things the CFA passed onto astemudfoot is that the entire building needs to be clad in “non-combustible” materials in order for us to use it as a kitchen in the fire season.  Based on my research below, I think he’s wrong.

Here’s my revised research on what’s involved in making the thing legal. It was nice to note that when I started researching the requirements I realised that I had already read most of them as part of the design process. However there have been some changes since Black Saturday.

BUILDING CODE COMPLIANCE

The building is classified as a class 10a structure under the BCA. Class 10a — a non-habitable building being a private garage, carport, shed, or the like.

The fireplace has to comply with the following (from the Building Code of Australia):

3.7.3.2  Open fireplace construction
An open fireplace must be constructed as follows (also see Figure 3.7.3.1):
(a)  All masonry must be constructed in accordance with Part 3.3.
(b)  The front hearth must be constructed of stone, concrete, masonry or similar material so that—

(i)  it extends not less than 300 mm beyond the front of the fireplace opening and not less than 150 mm beyond each side of that opening; and
(ii)  its upper surface does not slope away from the back hearth.
(c)  The base of the back hearth must be constructed of stone, concrete, masonry or similar material and any combustible flooring or framing members must be situated not less than 150 mm from its upper surface.

(d) The fireplace rear and side walls up to a height of 300 mm above the underside of the arch or lintel—

(i)  must be constructed in 2 separate leaves of solid masonry with an overall thickness not less than 180 mm thick, excluding any cavity; and
(ii)  must not consist of concrete block masonry in the construction of the inner leaf; and
(iii)  must be constructed of masonry units with a net volume, excluding cored and similar holes, not less than 75% of their gross volume, measured on the overall rectangular shape of the units, and with an actual thickness of not less than 100 mm.
(e)  The fireplace must be constructed on footings complying with 3.2.5.5.

3.2.5.5  Footings for fireplaces on Class A and S sites
(a)    Fireplaces must be supported on a pad footing—

(i)    150 mm thick for single storey (one trafficable floor and a wall height not more than 4.2 m) construction; and
(ii)    200 mm thick for 2 storey (two trafficable floors and a wall height not more than 8 m) construction; and
(iii)    reinforced top and bottom with SL72 mesh; and
(iv)    extending 300 mm past the edges of the masonry except for any edge flush with the outer wall.
(b)    The pad footing may form an integral part of the slab.

BUSHFIRE RESISTANCE
Australia has a new classification system for determining the risk associated with bushfire.  The summary is here.   We don’t have to comply because the building is a non-habitable building.  However, it does refer to “naturally bushfire resistant timbers”.  With a bit of digging, these are timbers with a density of at least 650kg/m3.

Information from here says that the density of the Monteray Cypress we have used is 540kg/m3.

SUMMARY
With some minor changes we can make the kitchen fireplace comply with the BCA.  We need to line the inglenook with 10mm of cement sheet.   We could build some sort of construction to reduce the size of the fireplace slightly and increase the distance of the official fire place to greater than 150mm from the wall timbers – the boiling structure?  Alternatively, we could remove 150mm of the hearth from each wall.

I like to think that if we can show the CFA that the fireplace complies with the requirements of the BCA, then we should be allowed to light a fire in it.  This might be easiest with a report from a building surveyor.

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