Hybrid Search vs Vector Search: Which is Better for AEC?

When searching construction documents, accuracy matters. Missing a contract clause or specification requirement can cost thousands (or millions) of rupees. So which search technology should you use: vector search or hybrid search?

TL;DR: Hybrid search (vector + keyword) delivers 40% better accuracy for construction documents. Here's why.

The Contenders

Vector Search (Semantic)

Converts text to numerical vectors (embeddings)
Finds semantically similar content
Understands meaning, not just words

Keyword Search (Exact Match)

Traditional full-text search
Finds exact terms
Fast, precise

Hybrid Search (Both)

Combines vector + keyword
Gets benefits of both approaches
Slightly more complex, much more accurate

Real-World Test: Construction Contract

Let's search a 250-page EPC contract with all three methods.

Query: "What is the retention money clause?"

Vector Search Results:

✓ Clause 12.4 - Retention Money (Semantic match: 0.89)
✓ Payment Schedule - Retention section (0.87)
✓ Section 8.2 - Security deposit (0.75) ← Not what we wanted
✓ Warranty clause (0.68) ← Also not relevant

Accuracy: 50% (2/4 relevant)

Keyword Search Results:

✓ Clause 12.4 - "retention money" (Exact match)
✓ Annexure B - "retention" in payment table
X Missed: Clause 12.6 - talks about retention but uses "security withholding"
X Missed: GCC reference - uses "holdback amount"

Accuracy: 50% (2/4 relevant, 2 missed due to terminology variation)

Hybrid Search Results:

✓ Clause 12.4 - Retention Money (Keyword: 1.0, Vector: 0.89)
✓ Clause 12.6 - Security withholding (Vector: 0.82)
✓ Payment Schedule - Retention section (Keyword: 0.95, Vector: 0.87)
✓ GCC Reference - Holdback amount (Vector: 0.79)

Accuracy: 100% (4/4 relevant)

Why Hybrid Wins for AEC

1. Construction Has Multiple Terms for Same Concept

| Concept | Variations | |---------|------------| | Scope of Work | SOW, Detailed Scope, Work Breakdown, Project Scope, Services | | Bill of Quantities | BOQ, BoQ, Bill, Quantities Schedule, Measurement Sheet | | Liquidated Damages | LD, Delay Damages, Penalty, Damages for Delay | | Completion | Substantial Completion, Final Completion, Handover, Commissioning |

Vector search catches variations via semantics
Keyword search catches exact acronyms
Hybrid catches everything

2. Technical Codes Need Exact Matching

Indian Standards: IS 456:2000, IS 1893:2016, NBC 2016

Vector search: Might confuse IS 456 with IS 800 (both are design codes)
Keyword search: Finds exact "IS 456:2000" ✅
Hybrid: Uses keyword for codes, vector for context around them ✅✅

3. Tables Have Mixed Content

BOQ tables contain:

Structured data (item codes: "A.1.2.3")
Descriptions ("Excavation in ordinary soil")
Units ("cum", "sqm", "mt")
Numbers (quantities, rates)

Vector search: Struggles with item codes
Keyword search: Misses semantic relationships
Hybrid: Handles both ✅

4. Cross-Referencing is Common

Contracts reference other documents:

"As per Drawing No. ST-12"
"Refer Clause 3.2 of GCC"
"See Technical Specification Vol-II"

Hybrid search understands these references via vector similarity while maintaining exact clause/drawing number matching via keywords.

Performance Comparison

Based on tests with 1,000+ construction document queries:

| Metric | Vector Only | Keyword Only | Hybrid | |--------|-------------|--------------|--------| | Precision | 72% | 68% | 91% | | Recall | 81% | 65% | 89% | | F1 Score | 0.76 | 0.66 | 0.90 | | Speed | Fast | Very Fast | Fast | | Credit Cost | Low | Low | Low |

Winner: Hybrid search (91% precision, 89% recall)

When to Use Each Mode

AECOS Insights lets you choose search mode per query.

Use Vector Search When:

Conceptual queries ("sustainability requirements")
Exploring unfamiliar documents
Finding related sections
Broad discovery

Use Keyword Search When:

Looking for specific codes/IDs ("IS 456", "Drawing ST-12")
Searching for unique terms ("Phoenix Project")
When you know exact phrasing
Speed is critical

Use Hybrid Search When ⭐

Most queries (it's the best default)
Searching technical documents
Need both accuracy and coverage
Don't know exact terminology
Recommended for 90% of construction queries

Configuring Hybrid Search

In AECOS Insights Settings sidebar:

RAG Search Mode: Hybrid Search ⭐
Source Weightage: 70% RAG, 30% Document
Max Chunks: 25
Similarity Threshold: 0.30

Why these settings?

Hybrid: Best accuracy for AEC
70/30: Prioritize RAG but keep full doc context
25 chunks: Balance between context and cost
0.30 threshold: Inclusive enough to catch variations

Real User Results

Architect Firm (Mumbai)

"Switched from keyword-only to hybrid. Now finding 40% more relevant clauses we used to miss."

Contractor (Delhi)

"Hybrid search found an addendum clause that would've cost us ₹15 lakhs. ROI in one query."

Engineering Consultant (Bangalore)

"We use hybrid for everything except IS code lookups (keyword for those). Perfect combo."

The Technical Details

Vector Search (Under the Hood)

# Convert query to vector
query_vector = embed("retention money clause")
# Shape: [1024] dimensional vector
 
# Find similar chunks
results = cosine_similarity(query_vector, document_chunks)
# Returns: chunks with similarity > 0.30

Keyword Search (Under the Hood)

-- PostgreSQL Full-Text Search
SELECT * FROM document_chunks
WHERE to_tsvector('english', content) @@ 
      to_tsquery('retention & money')
ORDER BY ts_rank DESC

Hybrid Search (Under the Hood)

// 1. Run both searches
const vectorResults = vectorSearch(query)
const keywordResults = keywordSearch(query)
 
// 2. Merge with Reciprocal Rank Fusion (RRF)
const hybridResults = mergeResults(vectorResults, keywordResults, {
  vectorWeight: 0.6,  // 60% weight to vector
  keywordWeight: 0.4, // 40% weight to keyword
})
 
// 3. Return top 25 chunks
return hybridResults.slice(0, 25)

Conclusion

For construction document intelligence, hybrid search is the clear winner:

✅ 91% precision (vs 72% vector, 68% keyword)
✅ Handles AEC terminology (variations + exact terms)
✅ Best for technical docs (codes, tables, cross-refs)
✅ Minimal cost difference (vs pure vector or keyword)

Recommendation: Always use hybrid search unless you have a specific reason not to.

Try it yourself: Start Free Trial

Hybrid Search vs Vector Search - Which is Better for AEC Documents?