From the first tap of the hammer to the handover of the keys, a renovation project goes through phases whose duration and cost vary depending on the order in which they are carried out. Understanding where budget and schedule overruns are most likely to occur helps you plan each stage before signing a single quote.
Renovation costs and timelines by type of work: where the differences arise
Most guides list the stages in chronological order without quantifying their relative share of the overall budget. The table below brings together the main work categories in a typical renovation project and compares their financial and time impact.
| Type of work | Indicative share of the overall budget | Average observed timeline | Main risk of overruns |
|---|---|---|---|
| Structural work (roofing, structure, foundations) | Highest | Several weeks to several months | Discovery of hidden defects (roof framing, damp) |
| Insulation and waterproofing | Significant, depending on the area | A few weeks | Thermal bridges not properly addressed, changes to the energy-efficiency plan |
| Plumbing and electrical work | Medium | Two to four weeks | Unexpected upgrades to bring an old system up to code |
| Joinery (windows, doors) | Medium | Made-to-measure manufacturing lead time | Supplier delivery delays |
| Finishing work (painting, flooring, fittings) | Lowest individually, but the total is sometimes underestimated | A few days to several weeks | Late material choices, cosmetic rework |
Structural work takes up the largest share of the budget and carries the greatest risk of cost overruns. Finishing work may seem minor when considered individually, but taken together, it often adds up to an amount comparable to plumbing or electrical work when renovating an entire home.
For a broader methodological overview of each work category, the Habitat Guides renovation guide explains the sequence of work and the key points to watch for with each trade.
Energy audits and the order of work: the pitfall of insulating in isolation
An energy audit does more than assign a rating to a home. It proposes renovation plans, either in stages or as a single project, which can sometimes radically change the order in which work should be carried out. An audit can change the order of work, not just its cost.
Replacing windows before insulating the walls may seem logical for immediate comfort. An audit often reveals that this sequence creates thermal bridges where the walls meet the window frames, requiring the finishes to be redone once the insulation is installed. The cost of this rework cancels out some of the expected savings.
Phased plan or whole-home renovation
The choice between these two approaches depends on the available budget and regulatory deadlines. For a landlord, the timeline is fixed: homes rated G have been banned from the rental market since January 2025, with the ban set to apply to F-rated homes in 2028 and then E-rated homes in 2034.
A phased plan spreads out the expense, but each stage must be designed so it does not compromise the next one. For example, insulating the attic without planning for adequate ventilation can cause condensation problems that damage the roof structure addressed in the previous stage.
RGE-qualified contractors and access to renovation grants
Choosing a contractor is about more than comparing three quotes. For energy-efficiency work, some grants require a contractor with RGE certification that specifically covers the planned work. Seeing “RGE” on a quote is not enough: the certification must cover the exact type of work involved (wall insulation, heat pump installation, windows and doors, etc.).
- Before signing, check the contractor’s RGE certification in the official directory, including the area of expertise and expiry date.
- Do not base your budget on a grant you assume you will receive: MaPrimeRénov’ rules may change while your application is being prepared.
- Contact France Rénov’ or Anah to confirm that your work is eligible and check the conditions that apply to your circumstances before making any commitment.
A contractor may be RGE-certified for attic insulation but not for external wall insulation. Hiring a contractor with the wrong certification means losing the corresponding grant, with no possibility of correcting the issue afterwards.
Project handover and snagging: checks that protect your budget
Handover is the legal act that transfers responsibility for the project from the contractor to the client. Any defect not recorded at handover is difficult to have corrected.
On handover day, every room and every type of work should be inspected methodically:
- Check that all opening elements work properly (windows, doors, shutters), and inspect the airtightness and hardware.
- Check that the electrical and plumbing installations match the signed quote (number of outlets, location of water points, type of taps and fittings).
- Inspect the finishes: joints, paintwork, flooring, tile alignment.
- Test the installed heating or ventilation system, noting the set temperature and airflow rate.
Snags must be recorded in writing in the handover report. The contractor then has an agreed period to address each one. Until all snags have been resolved, the final payment remains withheld, giving the client their main source of leverage.
Warranties after handover
The one-year defects liability warranty covers defects reported within the year following handover. The ten-year structural warranty applies to damage that compromises the building’s structural integrity or makes it unfit for its intended use. Checking that the contractor has a valid ten-year liability insurance certificate before work begins can help avoid costly disputes if structural damage occurs.
A renovation project should be managed one work category at a time, from the initial assessment through to the resolution of all snags. The budget is protected upfront by the energy audit and at the end by a joint handover inspection. In between, verifying contractors’ qualifications and planning a coherent sequence of work remain the two factors the client can control.
