Quantity Surveying

🏗️ Curtain Wall Systems – Types & Key Insights
A curtain wall is a non-structural external façade that protects a building from weather while enhancing aesthetics and allowing natural light. It transfers only its own weight and wind loads to the structure.
🔹 Main Types of Curtain Wall Systems

1️⃣ Stick System
• Installed piece-by-piece on site (mullions, transoms, glass)
• Flexible and suitable for complex shapes
• Lower material cost but higher site labor & time
👉 Best for low to mid-rise projects

2️⃣ Unitized System
• Pre-fabricated panels assembled in factory
• Delivered as large glazed units for quick installation
• High quality control & faster construction
👉 Ideal for high-rise buildings

3️⃣ Semi-Unitized System
• Hybrid of stick + unitized systems
• Partially pre-assembled off-site, finalized on-site
• Balanced solution for speed, flexibility & cost
👉 Widely used in modern commercial projects

🔹 Other Advanced Curtain Wall Types
✔️ Structural Glazing – seamless glass appearance
✔️ Point-Supported System – minimal framing, modern aesthetics
✔️ Double Skin Façade – energy efficiency & thermal performance
✔️ Cable Net System – lightweight and transparent design

🔹 Key Selection Factors
✔️ Building height
✔️ Project budget
✔️ Installation time
✔️ Quality control requirements
✔️ Architectural complexity

💡 Conclusion

Choosing the right curtain wall system is a balance between cost, performance, speed, and design intent. From traditional stick systems to high-performance unitized façades, each solution plays a critical role in modern construction.

Retention Money in Construction Contracts – With Reference to FIDIC Red Book 1999 🏗️📑
Retention money is a financial mechanism used in construction contracts to ensure that the contractor completes the works in accordance with the contract requirements and rectifies any defects during the defects liability period.
Under the **** (Conditions of Contract for Construction), retention is addressed under Sub-Clause 14.3 – Application for Interim Payment Certificates and Sub-Clause 14.9 – Payment of Retention Money.
What is Retention Money?
Retention money is a percentage deducted from each interim payment certificate (IPC) issued to the contractor. This amount is held by the employer as security for the contractor’s proper performance of the works.
Typical Retention Structure (Common Practice):
• Retention rate: 5% – 10% of each interim payment
• Maximum retention limit: usually 5% of the Accepted Contract Amount
Example (Based on FIDIC Practice):
Assume:
Contract Price = AED 10,000,000
Retention = 10% of each IPC
Maximum retention = 5% of Contract Price
Step 1 – Interim Payment
Contractor submits an IPC for AED 1,000,000
Retention deduction = 10% × 1,000,000 = AED 100,000
Amount paid to contractor = AED 900,000
This continues until the retained amount reaches the limit:
Maximum retention = 5% × 10,000,000 = AED 500,000
Once this limit is reached, no further retention deductions are made.
Release of Retention (Under FIDIC Red Book 1999):
1️⃣ First Half Release
Paid when the Taking-Over Certificate is issued for the works.
2️⃣ Second Half Release
Paid after the Defects Notification Period (DNP) ends and the Performance Certificate is issued.
Why Retention Money Matters
For the Employer:
✔ Provides security against defective work
✔ Ensures contractor obligations are fulfilled
For the Contractor:
✔ Encourages quality completion
✔ However, it impacts cash flow and working capital
Modern Practice
Many projects now allow contractors to replace retention with a Retention Bond or Bank Guarantee, improving cash flow while maintaining security for the employer.
Retention money remains one of the most important financial controls in construction contracts, and understanding its application is essential for Quantity Surveyors, Contract Administrators, and Project Managers.

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