Lets break it down.
Why house extension quotes vary in Ireland, including scope differences, provisional sums, structural assumptions, VAT treatment and pricing risk factors.
It is common for homeowners to receive extension quotes that differ by: €10,000 – €40,000 for what appears to be the same project.
In reality, quotes rarely price the exact same scope.
In reality, quotes rarely price the exact same scope.
Variations arise from:
- Different assumptions
- Specification differences
- Structural allowances
- VAT treatment
- Risk pricing
- Contractor overhead structures
Understanding these differences is essential before comparing figures.
Risk Pricing
Contractors price risk differently.
Higher-risk elements include:
- Ground uncertainty
- Structural complexity
- Tight access sites
- Unknown drainage
- Integration with existing house
Some contractors price conservatively.
Others price optimistically.
This can create 10–20% variation.
Scope Differences – Total difference could exceed €20,000 without either builder being “more expensive.”
The most common reason quotes vary is scope.
Two contractors may price:
- One including kitchen installation
- One excluding kitchen supply
- One including flooring
- One excluding finishes
- One including drainage relocation
- One assuming none required
Unless scope is documented identically, price comparison is unreliable.
Example Scope Difference
| Item | Builder A | Builder B |
|---|---|---|
| Kitchen supply | Included | Excluded |
| Floor finishes | Included | Excluded |
| Drainage relocation | Allowed | Not allowed |
| Steel beam size | Engineered | Assumed |
| VAT | Included | Excluded |
Provisional Sums and Prime Cost Allowances
Many residential quotes include allowances.
Provisional Sum (PS)
Estimated cost for work not fully defined.
Prime Cost (PC)
Allowance for supply of items (e.g. kitchen, tiles).
If allowances are unrealistically low, final cost increases during construction.
| Item | Allowance in Quote | Actual Cost | Variation |
|---|---|---|---|
| Kitchen | €8,000 | €14,000 | +€6,000 |
| Tiles | €25/m² | €45/m² | +€2,000 |
| Drainage | €1,000 | €4,000 | +€3,000 |
Quote initially appears lower, but final cost rises.
Pitfalls to watch out for
Programme Differences
Timeline affects cost.
A shorter build programme may:
- Increase labour intensity
- Increase subcontractor coordination
- Increase overhead cost
A longer programme may reduce immediate labour cost but extend disruption.
Programme assumptions influence pricing.
Structural Assumptions, VAT Treatment Differences & Contractor Overheads and Business Model
Structural pricing differences can be substantial.
Variables include:
- Steel beam sizing
- Number of beams
- Foundation depth assumptions
- Drainage diversion risk
- Load redistribution
Builder A may price conservative structural allowances.
Builder B may price minimal structural scope.
Difference can exceed €10,000.
One quote may:
- Include VAT
Another may: - Be exclusive of VAT
Example:
€120,000 incl VAT
vs
€110,000 excl VAT
The second quote becomes:
€124,850 incl VAT
Apparent difference disappears.
Not all contractors operate at the same overhead level.
Cost differences may reflect:
- Insurance levels
- Warranty provisions
- Staffing structure
- Certification roles
- Project management involvement
- Business scale
Lower quote does not automatically equal better value.
Example Quote Comparison Scenario
35m² Rear Kitchen Extension
| Category | Builder A | Builder B |
|---|---|---|
| Construction (ex VAT) | €105,000 | €95,000 |
| VAT | Included | Excluded |
| Structural allowance | €8,000 | €4,000 |
| Kitchen included | Yes | No |
| Drainage allowance | €3,000 | €1,000 |
| Total realistic cost | €119,000 | €122,000 |
The lower initial quote becomes more expensive after scope alignment.
Tendering with Detailed Drawings Reduces Variance
Quote variation reduces significantly when:
- Detailed construction drawings are provided
- Structural calculations are completed
- Specifications are written clearly
- Allowances are minimised
- Scope is standardised
Without documentation, contractors must make assumptions.
Assumptions create variance.
When a Lower Quote Is Legitimate
Lower pricing may be legitimate when:
- Simpler business structure
- Lower overhead
- Efficient labour scheduling
- Strong supplier pricing
- Clear documentation reduces risk
Price difference alone does not indicate poor quality.
Scope clarity is the determining factor.
Typical Variation Range
For standard Irish extensions:
Quote differences of:
8% – 20%
are common.
Differences exceeding 25% usually indicate scope mismatch.
For most Irish households in 2026:
Summary: Extension quotes vary due to the following.
- Scope differences
- Allowance structures
- Structural assumptions
- VAT inclusion
- Risk pricing
- Business overheads
Comparing headline totals without aligning scope is unreliable.
Detailed documentation significantly reduces price variance.
Other resources:
Extension Cost per Square Metre
Single vs Double Storey Extension Costs
Structural Steel and Foundation Costs
Timeline & Staged Payments Breakdown