Can you post a google view of your property and Climate with aspect.,

I can't post a google view, but north is to the front where the deck is pictured.

Can you show position of house on your block plus size and materials house is built with, a google maps shot is easy to get.

It is brick veneer with a colourbond roof.

To have no columns I would expect you will need to reroof the whole of the new room. Prob with a gable extending to the south centred on new great room

Do you mean including the kitchen area Kate, or just the dining/ living area? The original house (which includes the kitchen) has a truss roof that we can't tamper with (original house is the rectangle with the blue line through the middle, existing extension is the small rectangle forming the l-shape).

A flat roof over the new room will be the cheapest. It will need a slight fall and may be able to tuck under the existing gutters.

Depends on how you can support the existing roof. It will be held up, and down, on supporting posts/walls and foundations. You are taking out two walls that provide this support. You can run beams to transfer the load but not sure in both directions. Will need a structural engineer to assess and design

Kate and OKL have good points. What is your kitchen design? I think you’re going to have to have a support post in the corner where the original exterior corner was. Hopefully it can be incorporated into the kitchen design.

Thank you so much for the suggestions everyone. To answer the questions:

@oklouise - The kitchen is staying in essentially the same place as in the diagrams. The laundry is in the existing part of the house that isn't being touched so is not part of our considerations. We need the 5m wide opening to allow a galley kitchen running north to south along the eastern wall of the area labelled kitchen.

@bigreader- Why would it need an additional support post to span a 5m width, instead of using a larger beam for the span? We can't have a flat roof due to heavy rains and lots of leaf litter from trees, so we need to consider other options.

@kate - we weren't expecting to keep the existing roof on the living room that relies on the two removed walls. We want to expand the width of that part of the room (living/dining in new plan), but I'm interested in the most cost-effective way of doing that even though I assume it will involve a new roof over the whole space.

Let me know if any of that doesn't make sense.

Many thanks!

a new roof over the whole space is not the cheapest option but is probably the best option

Why can’t you have a truss roof on the new extension. I assume the new beam, which I have circled, will be supporting the existing truss roof. If your kitchen is running south to north, then incorporate an extra pillar support at the end of the island bench.

Thanks dreamer. If that is the most cost-effective way, then there is absolutely no reason why we can't have a truss roof on the new extension. That is what I'm asking for help with though, is that the most cost-effective way to do this type of extension (that isn't a flat roof). Why would the post be necessary though if we put in the beam? The post in that position would be in the middle of the seating area of the kitchen island.

With your extension you could consider extending the kitchen as it is quite small, which would mean using more of the eastern wall

The pillar may be required for additional weight bearing of roof. But if not required, wonderful.

And as you haven’t given the kitchen layout, I was assuming that the pillar would be at the end of the island, not in seating area.

@siriuskey Yes, definitely. Extending the kitchen and putting in a decent island bench is the main reason for the extension, and the dining area doesn't need to be the full length of the extended section.

I notice that the garage is on the western side, are you on a large block

No @sirius, it's a single carport through that door as that's all that will fit there.

Kitchen layout, as requested.

Here is what I think we need to do, from the feedback everyone has given. @kate you suggested a structural engineer to assess, and I imagine they would tell us if the beam is sufficient across kitchen ceiling instead of a post. Do I arrange that myself or ask the building designer?

You are going to need Engineers plans to get your Council etc permits so use whoever is organising that paperwork for you.

Thanks @bigreader. I will discuss with designer and arrange to get an engineer involved. It is possible that if it is too expensive to approach it in the way we want to, we could possibly achieve what we need with a couple of small bump outs (in purple) that allow us to keep the existing roof and just follow the roof line down. It isn't ideal but might be more affordable and it leaves more room for a larger covered outdoor area.

Thats good, how deep are your eaves would that be enough space

@siriuskey The existing house has no eaves on that side, but we do need to replace the roof of the whole house anyway, so I think at that point we could get them to cantilever an extension of the roof framing out by the extra 70-80cm to extend the roof over the pop outs.

Sounds like a good plan, this will also give you a better kitchen. You already have another living space so what you will have should be plenty

I would add a servery window in the kitchen with stools on the deck

@sirius Great idea, I wondered if we would have room for that, it would be lovely!

I'am sure you do

I’m not sure what your budget is but you will be looking at about $30k just for the plans, permits and reports (engineering) before you begin construction. Using the size beam your after and rebuilding a whole section of roof to tie in with an existing roof is one of the more expensive ways to do things.

@bigreader I think whatever we do we will be paying for plans, permits, engineering reports. What do you suggest would be a cheaper way to achieve more space here?

I like your last idea and will save a lot without the need to remove external walls, I would have a large sliding door from the living out to the deck, I would also make it open from the left next to the kitchen

With you bump out plans you have lost storage. And there is virtually none in W area and only a small linen for this size house. With the family bump out you haven’t left wall space for a tv. Is the window seat really needed. I would prob get a bigger ensuite and add storage to dining area But otherwise like this more modest plan

Working with your drawing the passageway between bed 2 & 3 can be used for Robe space. Don't think it's wide enough for linen storage going by the dimension shown. The Laundry and Bathroom access from your new deck and alfresco area will be great for entertaining and possible for future pool

@siriuskey Yes, that's my bad diagram. That end of the passageway has built-in robes facing into each of those bedrooms. There is also an existing storage cupboard across from the WC (it carves off part of the shower space). Ideally we would have a lot more storage, but I'm not sure that it's worth a $400-$500K renovation if we can solve the other issues more affordably! We can put a secure batten door across the carport to securitise it and put a weatherproof storage cupboard in there for camping gear etc. I agree, I like having the separate WC accessible off the alfresco and the laundry tub will be good for drinks!

Sorry I missed that in your first plan posted, it would be ideal to have outdoor storage for camping gear etc, even a small shed. The living room looks quite large, so you may be able to work some storage into that. As it is I think you need all the space you have for the kitchen dining family, you could forget the the bump out in the family for TV and Heater plus it will save you money.

You could pump out in dining and ensuite for extra space there instead

Thanks @kate, the carport is on that wall so can't bump out the dining, and we're fine with the size of the ensuite, it's small but functional. If I could only change one thing in our house it would be to fit an island in the kitchen. Second priority would be to able to have a u-shape of lounge seating in the family room (hence the inclusion of the bump-out window seat to gain the extra side of seating.