regardless of the choice of architect or interior designer you'll need to have a clear idea of you and your familys' likes and needs (otherwise there's a risk that the renovation becomes about the professional's preferences not yours) and this is where your HOUZZ ideas book will be a big help and, if you post specfic questions about the problems with the existing home HOUZZERS will offer a wealth of suggestions to help you decide

Hi gemma_truman, in making this decision, it might be helpful to understand more fully the role that each of these professionals plays in the design / renovation process. I think you will find this article contains information that is helpful:

Architect v building designer v interior designer: learning to navigate Australia’s design landscape

All the best. Jo

Hi gemma_truman, you may use either or both, but it will depend on the interior designer's qualifications and experience, whether they will be able to undertake the whole project. An architect would be my recommendation (i am an architect - trying not to be too biassed!), as they are the only professionals who have extensive training in all aspects of building design, including advice on efficient structural systems, co-ordination of electrical and hydraulic services, as well as the design of all the visible elements, finishes and aesthetic considerations. They will look at your house as a whole, including the outdoor landscape, and consider how spaces relate to one another, the best orientation and energy efficiency considerations, use over time, durability and maintenance of materials, amongst many other things. It sounds like you are planning major structural work, which will require building approval drawings to be submitted to a certifier, which an interior designer may not be qualified to provide.

Good luck with your project!

Wendy

Depends on how major the layout/wall etc changes are. If significant, definitely go for an architect, but check out their past work before you engage them.