Lets break it down.

Typical house extension timelines in Ireland and how stage payments are structured, including sequencing, payment triggers and budget implications.

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:

Labour availability
Cash flow requirements
Temporary accommodation needs
Price certainty

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.

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

Timeline and Stage Payment Structure Breakdown

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.

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

Financial Considerations

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.

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

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:

Overlapping living arrangements

Additional labour cost

Extended site setup costs

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.

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