Typical house extension timelines in Ireland and how stage payments are structured, including sequencing, payment triggers and budget implications.
1. Overview
Understanding project duration and staged payment structure is essential for accurate financial planning.
Most Irish house extensions take between:
10 and 24 weeks of on-site construction
depending on:
- Size
- Complexity
- Weather conditions
- Structural scope
- Planning status
- Contractor scheduling
Timeline influences:
- Cash flow requirements
- Temporary accommodation needs
- Price certainty
- Labour availability
2. Pre-Construction Timeline
Before construction begins, several stages occur.
Typical Pre-Construction Duration
| Stage | Typical Duration |
|---|---|
| Measured survey | 1–2 weeks |
| Design development | 3–6 weeks |
| Planning (if required) | 12–16 weeks |
| Detailed drawings | 3–6 weeks |
| Tendering & contractor selection | 3–5 weeks |
Total pre-construction period:
3 to 6 months
Longer if planning objections or redesigns occur.
3. On-Site Construction Timeline
Single-Storey Extension (30–40m²)
| Stage | Duration |
|---|---|
| Site setup | 1 week |
| Excavation & foundations | 1–2 weeks |
| Structure & walls | 2–3 weeks |
| Roof installation | 1–2 weeks |
| Windows & doors | 1 week |
| First fix services | 1–2 weeks |
| Plastering | 1 week |
| Second fix & finishes | 2–3 weeks |
| Snagging | 1 week |
Typical total:
10–14 weeks
Double-Storey Extension (60–80m²)
| Stage | Duration |
|---|---|
| Foundations | 2–3 weeks |
| Structural build | 4–6 weeks |
| Roofing | 2 weeks |
| Services | 2–3 weeks |
| Internal works | 4–6 weeks |
| Completion & snagging | 1–2 weeks |
Typical total:
14–20 weeks
4. Factors That Extend Timelines
- Planning delays
- Weather conditions
- Steel fabrication lead times
- Window/door manufacturing delays
- Kitchen delivery delays
- Variation orders during construction
- Labour shortages
Supply chain issues can extend timelines by several weeks.
5. Stage Payment Structure in Ireland
Extensions are typically paid in stages tied to construction milestones.
Stage payments reflect:
- Work completed
- Materials delivered
- Cash flow for contractor operations
Example Stage Payment Structure
30m² Extension – €100,000 Construction Cost
| Stage | % | Payment |
|---|---|---|
| Deposit (mobilisation) | 5% | €5,000 |
| Foundations complete | 15% | €15,000 |
| Walls & structure | 20% | €20,000 |
| Roof & watertight | 20% | €20,000 |
| First fix | 15% | €15,000 |
| Second fix | 15% | €15,000 |
| Practical completion | 5% | €5,000 |
| Retention (if agreed) | 5% | €5,000 |
Total: €100,000
6. Retention and Final Payment
Retention is sometimes used to ensure completion of:
- Snagging items
- Minor defects
- Documentation handover
Retention is typically:
2.5% – 5%
Some small residential contracts do not formally use retention.
7. Cash Flow Planning
Cash flow is not linear.
The highest payment points typically occur at:
- Structural completion
- Roof completion
- First fix stage
Example cash flow curve:
Weeks 1–3: moderate
Weeks 4–8: high expenditure
Weeks 9–14: steady
Final weeks: smaller payments
Financial planning should anticipate:
Large mid-project outflows.
8. Delays and Financial Impact
Delays can affect:
- Temporary accommodation costs
- Rental overlaps
- Mortgage drawdowns
- Material price fluctuations
Example:
4-week delay on €120,000 extension
May result in:
- Additional labour cost
- Extended site setup costs
- Overlapping living arrangements
9. Variations During Construction
Variations commonly arise from:
- Changing window specifications
- Increasing glazing size
- Relocating plumbing
- Upgrading finishes
- Structural surprises
Variations can increase total cost by:
5% – 15%
Timeline may also extend.
10. Example Full Timeline & Payment Scenario
40m² Kitchen Extension – €120,000 Construction
| Phase | Weeks | Payment |
|---|---|---|
| Weeks 1–2 | Foundations | €18,000 |
| Weeks 3–6 | Structure | €30,000 |
| Weeks 7–8 | Roof & glazing | €24,000 |
| Weeks 9–10 | First fix | €18,000 |
| Weeks 11–13 | Second fix | €18,000 |
| Week 14 | Completion | €6,000 |
| Retention | Post-completion | €6,000 |
Total duration: 14 weeks.
11. Planning and Timeline Interaction
If planning permission is required:
Add 3–4 months pre-construction.
Appeals can extend project commencement by 6+ months.
This affects:
- Contractor availability
- Build cost inflation exposure
- Material pricing changes
12. Summary
Typical Irish extension timelines:
Single storey: 10–14 weeks
Double storey: 14–20 weeks
Pre-construction can take 3–6 months.
Stage payments are milestone-based and require structured cash flow planning.
Timeline risk and variation risk are major drivers of total project cost.
13. Other Resources:
Extension Cost per Square Metre
Single vs Double Storey Extension Costs
Structural Steel and Foundation Costs