You need to ensure that the conversion will be totally insulated, airconditioned, roof space extractor fan/whirly bird, windows that can be opened to circulate air. Hot air rises, and any upper storey, be it brand new, or a conversion will get hot. The last 5 days in Perth have been extremely hot and humid. I wouldn't like to be in a roof space this week, without all the above installed.

But before all of that, what is the height of the internal roof space that you are wishing to convert.

Is it legal height for a conversion??

Thanks dreamer. Definitely things we'd need to take into consideration. I guess my question is is it possible for all of those things to be enough to make it comfortable?

Height still TBC, I'm aware of the 2.2m (I think? I've also seen 2.4) for 60% of floor area requirement. I'm just not sure actual void height or how much is lost in the fitout. By my geometry calculations of pitch and total width, it *should* be just short of 3m at the centreline before any fitout.

We did an attic conversion in our Federation Brick and Tile house in Sydney some years ago, we ended up with 2 bedrooms with QB's and robes plus a study the width of both bedrooms which the stairs opened into. It was airconditioned and all 3 rooms had large rectangle pivoting Velux skylights ((above the bed head on the lower external walls and again above the long desk in the study. First thing we did was check out internal roof space and where to fit the staircase to suit both floors. We had a great builder, you could employ a local draft person to do this for you. Also on the East coast there are people who specialise in Attic conversions

I'm east cost and am regularly in a property with a loft. It's hotter than hell up there despite being airconditioned. Insulation, whirly bids etc help to a degree. But I suspect the reason why your builders are suggesting an entire second story is simply to increase the volume on the second level. Think of your car, it's small interior volume can reach an incredible temperature within minutes. Small air volumes that receive the rising heat from the downstairs living space are going to get hot. In perths climate? It's not a good idea. A roof space conversion is going to have a lot of low head height area because of the slope of the roof = low internal volume.

You may be better off doing a 2nd story extension out the back where the existing tall roofline will hide it from street view. Their reluctance to touch your 1917 roof may also be because it's unlikely to meet modern building code and converting it to a living space may require the entire roof being rebuilt anyway.

I can't speak for anyone else's attic conversions but after planning and consultation with our very experienced builder for insulation and ventilation needs it was a fabulous success, The whole house was airconditioned into 3 zones with the attic having it's own zone. Hot air does rise hence the importance of windows for it to pass out through.

Perth, Adelaide, Melbourne and Sydney can all get very hot, Sydney and above can also be humid, so good cross ventilation and aircon deal with this. From my experience I can highly recommend attics conversions when done with careful consideration and experienced builders. The drawing from memory with no dimensions, There was a door at the bottom of the stairs back into the family room and next to that a door out to a small verandah

Thanks, I think it's worth at least continuing to explore as an option then.

I don't the a 2 storey extension is the worst idea, I just don't want a big box on the back of the house. And in all honesty, was/am hoping the cost of an attic conversion will be cheaper, but I need to talk to builder/designer and actually check the space properly. Thanks all.

At about the same time another builder friend with a young family who's federation house didn't have as much workable roof space as ours, built the space as open plan and only filling the walls at around 50cm so as to make a kids space with a couple of desks etc, it had an open staircase up to a wide opening and again Velux roof windows, it had a lot of use. yIt is cost effective if you have the space otherwise by posting a plan as OKL has suggested you could consider other options.

And I have seen those roof conversions with a Box banged on top and they look terrible, unless it's an Architect designed one

Thanks @oklouise, @siriuskey.

I know I really really need to get up in the roof (or more likely get someone else to get up there, it's a small access hole and a long way off the ground and I'm not great at either of those things with a ladder). If I'm right about a max ~3m height in existing roof space we could fit ~3-3.5m wide room essentially above the hallway of original house and meet minimum heights (I think....). And then hopefully a little wider under an extended roofline to the back, without it being a full/boxy second storey extension.

Here is a super rough sketch of the current layout of the house. The dotted orange lines are drawing over existing roofline when I overlay a screenshot from google maps, so not 100%. I don't have a proper house plan, will need to get something drawn up.

It pretty much fills the block width (~0.5m from wall to fence each side), but we have heaps of backyard to extend into (`18m from current back of house to back fence), but do plan to eventually add a separate garage accessed from back lane and want to keep a big backyard. No important view to chase, but looking directly south is over green space/park, every other direction is pretty suburban.

If the roof conversion is possible, I think I want to convert the small bedroom 3 into a family bathroom, kitchen into a 3rd bedroom, split the dining in half and make that into a study off the lounge. Then push the whole back wall out probably 2.5-3ish metres and in that open space, fit a powder room, staircase, laundry/mudroom with external access, living/dining/kitchen. Possibly fit a scullery into the other half of the current dining? And put a covered deck off the back.

This is the real design dilemma I guess, where exactly do the stairs go (against wall shared with lounge?), and if no roof conversion, then it's either raise up full storey (still need to work out where stairs go) or work out how to add a master suite to single storey extension. I'm really struggling with getting that to work.

looking at the original plans it appears that the high part of the roof space is ónly over the central hallway and there might be enough space for a modest attic room but to access that space you would need to raise the roof over the whole living area and have the stairs along the south wall of the living area to arrive in the centre of the upstairs rooms but an oblong alfresco and verandah would be more useful than a 3m extension across the full width of the house ... the upstairs is about 55sqm and a similar space would be much cheaper as a single level extension (or consider a two storey extension with slab on ground that could fit below the roofline from the front) but you need to have a detailed floor plan of the original house including wall thickness and precise shape of the roof to be able to be more specific.. but maybe something like this with two ideas for a master suite and upstairs plan includes the outline of downstairs

We live in Perth also. Our last house had a complete Reno including the second story upstairs.
You really need to consider insulting the walls as the roof.
We lived on the coast and the breezes came in every night but during the day I really didn’t go upstairs as it was hot.
We now have moved and built using SIP walls. (Super insulated panels) plus double glazed windows, insulated ceilings and that works.
Same area, same beach and we now live upstairs.