In short
How to settle the decision most enquiries are stuck on, in five steps: establish what a rebuild would give you, value what the existing house holds that current rules might not allow again, test the structure honestly, compare the routes side by side, and ask what you actually want. A&A runs fifteen to twenty-one months, reconstruction eighteen to twenty-four, rebuild twenty-one to twenty-eight. The outcome to avoid is a compromised plan at most of the price of a good one.
The question is what the structure will allow
People arrive at this decision through cost and leave through structure. What matters is whether the existing frame lets you move the walls that need to move, put the lift where a lift can go, and open the elevations you need open.
If it does, an A&A is faster and cheaper. If it does not, an A&A buys you a compromised plan at most of the price of a good one.
Work through the five steps below in order. The answer usually becomes obvious by the third.
Step one: establish what a rebuild would give you
Before valuing the house you have, find out what would replace it. A feasibility study tells you the envelope, floor area and layout a new house could achieve on the plot under today's guidelines.
That is the baseline for every comparison that follows. Without it you are comparing your existing house with an imagined one.
Step two: value what the existing house holds
Compare the house against that baseline and list what a rebuild would lose.
- Floor area or footprint that current setbacks would not allow again.
- Walls closer to the boundary than today's rules permit, where they were lawfully built.
- Mature trees and established landscape, particularly any that are protected.
- Site levels and retaining walls already in place.
- Room proportions or ceiling heights you value and would not otherwise get.
If the list is short, the case for an A&A weakens considerably. If it includes meaningful floor area, it may outweigh everything else.
Step three: test the structure honestly
Commission a structural survey before you design anything. You need to know the foundations, the condition of the frame, and whether the loads you want to add can be carried.
This is the step most often skipped and the one that most often reverses the decision. A house built for two storeys and a light roof will not automatically take an attic, a stone floor and a roof terrace. When the cost of strengthening approaches a large share of a new structure, you are paying rebuild money to keep an old frame — and that frame then has to be worth a great deal.
Step four: compare the routes properly
| A&A | Reconstruction | Rebuild | |
|---|---|---|---|
| Time, first meeting to handover | 15–21 months | 18–24 months | 21–28 months |
| Floor area achieved | Limited by the existing structure | Much of the envelope, around what is kept | The full permissible envelope |
| Freedom in the plan | Limited by the grid and floor heights | Substantial | Complete |
| What you keep | Most of the house | Parts of the original structure | Nothing — current guidelines apply |
| Main risk | Unknowns in the existing fabric | Unknowns where old meets new | Ground conditions under a new structure |
The times are indicative and based on typical KAPA projects. Reconstruction sits between the other two and is worth investigating whenever the frame is sound.
Step five: ask what you actually want
The technical comparison narrows the field. The final decision is usually about temperament.
A rebuild gives you the house you designed, with no compromises inherited from someone else's plan. An A&A gives you a house with history, sooner, at the price of working within constraints you did not choose. Sometimes it has nothing to do with either: a family that has outgrown a house it does not want to leave is making a decision about attachment, and that is a legitimate input.
The job is to make sure the compromise is understood rather than discovered.
Key takeaways
- The deciding test is structural and answered by a survey, not by taste.
- A&A: 15–21 months. Reconstruction: 18–24. Rebuild: 21–28.
- Value what the existing house holds before you decide to give it up.
- A compromised plan at most of the cost of a good one is the outcome to avoid.
Questions people ask
An interior transformation improves the inside — layouts, finishes, lighting, carpentry, kitchens and bathrooms — and keeps the structure as it is. An A&A changes selected parts of the house, such as extending, reconfiguring the plan or adding a lift, while keeping most of the structure. A reconstruction substantially upgrades and reconfigures the house while keeping parts of the original structure where permitted. A rebuild demolishes the house and builds a new one from the ground up.
