Planning a conservatory: what to resolve before ordering
Published on 31 July 2026 · Verified on 19 September 2026 · The Mestravaux.lu team
An attractive drawing does not establish whether the room will suit its intended use or whether all work is priced. Document these decisions before ordering. No average cost is assigned to mistakes without comparable local evidence.
The essentials in 30 seconds
- Define a seasonal room or space integrated into the home.
- Assess summer comfort and winter needs together.
- Check the base, junctions and existing ventilation.
- Compare written scope and guarantees rather than a discount.
Mistaking a marketing label for a use specification
Four-season is not a complete performance description. Specify times, season, target temperature and whether the room remains open to the house. Request an explanation of glazing, roof, floor, ventilation and any heating for that use. Do not assume a seasonal space can later become integrated living space without assessment.
| Erreur | Coût de la reprise | Coût évité si anticipé |
|---|---|---|
| Vitrage sans contrôle solaire (surchauffe) | 2 000 – 4 000 € | +15 à 20 % sur le poste vitrage |
| Isolation été plutôt que 4 saisons | 30 – 50 % de surcoût de reprise | Coût intégré dès la conception |
| Travaux sans autorisation de bâtir | Mise en conformité, voire démolition | Quelques centaines d'euros de dossier |
| Évacuation des eaux mal dimensionnée | 1 000 – 3 000 € | Quasi nul si anticipé |
| Chauffage sous-dimensionné | +20 à 40 % sur la facture énergétique | Calcul correct dès le devis |
Montants indicatifs constatés au Luxembourg, hors cas exceptionnels (dégâts structurels importants).
Addressing summer heat only after installation
Klima-Agence recommends reducing solar gains and ventilating when outside air is cooler. Assess orientation, glazed area and external shading before selecting equipment. Consider daylight in the house and practical opening, wind and absence conditions.
Reusing the base without assessment
AQC highlights foundations, slab and connections to the existing building. Have the terrace checked rather than assuming it can support the addition. Identify investigation, excavation, strengthening, finished levels and junctions in the quote. Assign interfaces between groundworks and installer.
Forgetting water and air routes
Plan drainage and accessible inspection points with the professional. Specify roof junctions, thresholds, downpipes and water destination. Check existing house air inlets and outlets that the extension might enclose. Request a ventilation approach rather than simply being told to open a window.
Your project deserves an accurate estimate — it's free.
Request a quoteSelecting heating from a generic area ratio
Assess needs using surfaces, glazing, insulation, temperature and the connection to the house. Appliance output alone does not determine energy consumption; an undersized heater may fail to achieve the required temperature. Do not derive annual bills or consumption increases from watts per square metre.
Ordering with unclear formalities and scope
Guichet directs permitting to the municipality; its page is being updated, so confirm current documents and plot-specific rules. Assume no universal fee or approval period. Separate commercial warranties, responsibilities and actual insurance in the contract. Specify scope, exclusions, handover and defects; do not transpose French insurance obligations to Luxembourg.
Frequently asked questions
Does four-season guarantee year-round living space?
The label is insufficient. Request design and performance for the intended use.
Does solar-control glass replace all external shading?
Assess the whole project for orientation, daylight and use; there is no automatic equivalence.
Does a low quote prove poor quality?
No. Compare scope, specifications and exclusions first.
Does the existing terrace remove the need for foundations?
Not without checking the base and structural solution.
Does a more powerful heater necessarily reduce bills?
No. Building demand, efficiency, controls and use must be considered together.
Take action
Your project deserves an accurate estimate — it's free.
Request a quote