Direct answer: on Algarve figures in 2026, a new Passive House modular home beats renovating an old house on almost every financial criterion. An old T3 100 m² house at €400,000 + a serious renovation of €250,000 = €650,000 to reach Class C, in 18-24 months and with 30-40% surprises. A new modular T3 of 180 m² Passive House Class A = €315,000 + €60,000 land = €375,000, in 12-14 months, with a fixed price. Renovation only pays off when the location is unrepeatable or the heritage value of the existing structure is part of the project.
Many Algarve buyers start with the hypothesis "I buy a cheap old house and renovate". This article runs the numbers honestly for a T3 on the coastal Algarve, with real 2026 market costs, timelines, typical surprises and resale value.
Typical scenario: T3 on the coastal Algarve
We compare two options for a family of 3-4 people who want to live in a typical coastal Algarve zone (Silves, Lagoa, Loulé Quarteira periphery, Tavira):
- Option A: buy a T3 house of 100 m² built in 1970-1980 and renovate in depth.
- Option B: buy a 600 m² urban plot and build a new Ecoimport Passive House modular T3 of 180 m².
Option A — Renovation (realistic figures)
| Item | Cost |
|---|---|
| Purchase of 1970s T3 100 m² coastal house | €350,000 |
| IMT (7-8% for second homes) | €26,000 |
| Stamp Duty 0.8% | €2,800 |
| Notary + registration | €1,500 |
| Architect + engineering + licensing | €15,000 |
| Partial demolition and clearance | €8,000 |
| Reinforcing/rebuilding foundations (30% surprise) | €18,000 |
| Rebuild roof (waterproofing, insulation, tiles) | €28,000 |
| Full re-plumbing and drainage | €14,000 |
| Full new electrical installation + board | €12,000 |
| ETICS 12 cm + render + façade paint | €22,000 |
| High-performance triple PVC/aluminium windows | €16,000 |
| Flooring, false ceilings, interior doors | €18,000 |
| Kitchen, bathrooms, tiling | €28,000 |
| MVHR + heat pump DHW + AC split | €18,000 |
| Solar thermal or 3 kWp photovoltaics | €7,500 |
| Interior painting, finishes, ironmongery | €8,000 |
| Alternative rental 15 months × €1,100 | €16,500 |
| Renovation subtotal | €259,300 |
| Reserve for surprises 25% | €65,000 |
| Option A total | ~€715,000 |
Result: renovated T3 of 100 m² Class B or C (rarely A), structure retained, layout with the limitations of the original, 18-24 months until habitable, and a 25% surprise reserve that in practice gets spent.
Option B — New Passive House modular home
| Item | Cost |
|---|---|
| Purchase of 500-700 m² urban plot | €60,000 |
| IMT on land (5-6%) | €3,600 |
| Stamp Duty 0.8% | €480 |
| Notary + land registration | €800 |
| PIP + certificates | €800 |
| Topographic + geotechnical survey | €1,500 |
| Turnkey T3 180 m² Passive House modular home | €315,000 |
| Utility connections (electricity, water, sewerage) | €4,000 |
| Perimetre walls and gate (300 linear m) | €18,000 |
| Basic garden, landscaping | €4,500 |
| Alternative rental 8 months × €1,100 (only at the end) | €8,800 |
| Option B total | ~€417,500 |
Result: new Passive House T3 Class A guaranteed, 180 m² usable (80% more area than the renovated), 12-14 months total, Ecoimport fixed price with no revision clauses, 10-year warranty.
Difference: €297,500 and twice the quality
Option B costs €297,500 less and delivers 80 m² additional, Class A, a 10-year guarantee, a fixed timeline and no hidden risks. In practical terms, this means:
- Usable area nearly doubles (180 m² vs. 100 m²).
- Annual energy consumption 60-75% lower (Passive House vs. Class B/C renovation).
- Annual maintenance 3-5× lower.
- Resale value per m² 8-15% higher (INE/OE, 2024 market).
- No cost overrun risk (fixed Ecoimport contract with late-delivery penalty).
Typical surprises in deep renovation
Renovating a 1960s-1980s house in the Algarve has four major categories of surprise typically underestimated:
- Foundations: old houses had foundations sized for solid stone or single-brick walls. Adding loads (new flooring, roof) requires reinforcement with micro-piles or a new perimetre footing. Cost €12,000-30,000 that does not appear in the initial budget.
- Roof and roof void: 1970s-1980s roofs have timber trusses infected by termites or fungi in 40-60% of cases. Full replacement costs €20,000-45,000 depending on area and complexity.
- Plumbing and drainage: PVC before 1990 has hidden leaks at joints. The building's plumbing usually needs full replacement (not always by choice — by necessity). Cost €10,000-18,000 for a T3.
- Electrical installation: electrical boards before 2005 rarely comply with the RTIEBT in force. Meter connections require redoing the board, earthing, RCDs and sometimes cabling. €8,000-15,000.
Each of these surprises is only identified once the works have started, when there is no going back. A serious renovation assumes a 20-30% reserve on the base budget.
Energy efficiency: where renovation ends
A Passive House reaches Class A or A+ through integrated design: continuous envelope insulated to 200-300 mm, blower door airtightness ≤0.6 h⁻¹ at 50 Pa, MVHR, no thermal bridges, optimised orientation, passive shading. Real measured consumption 15-25 kWh/m²/year.
A renovated old house, even with good technical choices, typically reaches:
- Class D→C: if you only change windows, add 8 cm ETICS and install AC (~120-160 kWh/m²/year).
- Class C→B: ETICS 12 cm + triple windows + MVHR + heat pump (~80-100 kWh/m²/year).
- Class B→A: requires intervention close to demolition+rebuild; rarely economically real.
Stone or solid-brick structure has massive thermal bridges (pillars, lintels, slabs) that only full encapsulation resolves. And encapsulating internally reduces usable area by 5-8%.
Timeline: how long it takes
| Phase | Deep renovation | New modular home |
|---|---|---|
| Purchase / land | 1-2 months | 1-2 months |
| Design and licensing | 3-6 months | 3-5 months |
| Works | 12-18 months (with surprises) | 6-7 months |
| Inspection and occupancy licence | 1-3 months | 1 month |
| Realistic total | 17-29 months | 11-15 months |
Resale value
According to INE data and market observatories (Confidencial Imobiliário, OM/ERA, Idealista), a new Class A house in the Algarve has an 8-15% premium over a renovated Class B/C house at an equivalent location. Over a 10-year horizon:
- Renovated 100 m² Class C house valued at €4,500/m² resale: €450,000.
- New modular 180 m² Class A house valued at €5,100/m² resale: €918,000.
In addition to doubling the area, Class A carries a value premium. This is the structural reason why the new house, despite costing 30% less than renovation, is worth more on resale.
When it makes sense to renovate
Renovation makes sense in three specific scenarios:
- Unrepeatable historic location: house in an old core (Tavira centre, historic Lagos, Silves castle), consolidated ARU, privileged view, plot in a street that is fully built up.
- Heritage or emotional value: family home, building with unique architectural features (Algarve chimneys, original tiles, local stone masonry), traditional rural villa.
- Urban restriction: PDM prevents demolition+rebuild or reduces usable area if proceeding as new construction. Common cases in historic cores and ARU.
Outside these scenarios, the maths favour a new Passive House modular in almost 90% of cases.
Comparative summary table
| Criterion | Renovation | Modular Passive House |
|---|---|---|
| Total cost (T3 coastal zone) | ~€715,000 | ~€417,500 |
| Usable area | 100 m² | 180 m² |
| Energy class | Typical B/C | A guaranteed |
| Timeline | 17-29 months | 11-15 months |
| Fixed price? | No (25-40% surprises) | Yes (Ecoimport contract) |
| Structural warranty | Legal 5 years | Legal 5 + contractual 10 years |
| Annual operating costs | €1,800-2,800 | €350-700 |
| Resale premium | Base | +8-15% |
"The question 'shall I buy old and renovate?' is emotionally attractive. On Algarve figures in 2026, the new modular home wins almost every time."
Conclusion
Renovating an old house in the Algarve in 2026 rarely pays off on the figures — it costs 30-50% more, takes 50-100% longer, reaches Class B/C instead of A, and carries 25-40% cost-overrun risk. Only in scenarios of unrepeatable location, heritage value or urban restriction is it worthwhile. A turnkey Ecoimport Passive House modular T3 of 180 m² for €315,000 + land is faster, more efficient, more valuable on resale and free of contractual surprises.
Market values, timelines and typical surprises are 2026 estimates and vary by location, condition of the house, client choices and municipal by-laws. Contact us for a tailored comparative analysis.
→ Ask us for a comparative analysis (renovate vs new) for your case (48h) or see the investment page.