Built on experience.
Led by Costi.

Over 25 Years of Construction Experience

Costi Tiseanu

Company Director

I’m Constantin “Costi” Tiseanu, founder and director of TRJ Construction Ltd.

I have worked in construction for over 25 years. My focus is on buildings that last and work well for the people who use them.

I began as an installer and project manager in the garden building sector. That work taught me about SIPs, foundations and finishing a building well.

In 2012, I founded TRJ Construction Ltd with one clear objective:

To build better, stronger and more technically advanced SIP structures than what the market was offering.

Why I Specialise in SIP Construction

What Is a SIP Panel and Why It Matters

Structural Insulated Panels (SIPs) have strong outer faces bonded to an insulated core. The whole building needs careful design. Joints, moisture control, airtightness and structural loads all matter.

Structural Insulated Panels (SIPs) represent the future of low-energy construction.

Unlike traditional timber frame garden rooms, SIP buildings provide:

• Superior thermal performance
• Higher structural strength
• Reduced cold bridging
• Faster installation times
• Long-term durability

At TRJ Construction, we use:

• 150mm SIP panels for roofs and bases
• 125mm structural insulated wall panels
• Professional K-Render exterior finishes
• Fully integrated electrics as standard

Many suppliers reduce thickness to reduce cost.

I focus on increasing structural performance and long-term value.

Commitment to Quality Over Shortcuts

Throughout my career, I have seen how minor compromises in:

• Roof thickness
• Base structure
• Insulation quality
• Exterior finishing

can significantly impact long-term durability.

That is why TRJ Construction is built on a simple principle:

Build it properly once.

Our buildings are designed for real, year-round use — whether as:

• Home offices
• Gyms
• Garden studios
• Granny annexes
• Independent living spaces

Technical Knowledge & Site Experience

Over the years, I have worked directly with:

• Structural engineers
• Building control officers
• Planning departments across Hertfordshire, North London and surrounding counties
• Foundation specialists including screw-pile systems

This experience helps us coordinate the structural design and applicable building-control requirements for each TRJ project.

We do not operate as a sales company.

We operate as a construction specialist delivering engineered living space.

Areas Covered

• TRJ Construction is trusted across Hertfordshire, Buckinghamshire, Essex and North London, including Watford, St Albans, Barnet, Hampstead, Enfield, Borehamwood and surrounding counties.

We specialise in premium SIP garden rooms and high-quality granny annexes built to full structural standards.

A Personal Commitment

As a founder-led company, I remain personally involved in:

• Design consultation
• Technical specification
• Material selection
• On-site quality control

Every project carries my name and reputation.

TRJ Construction – Building the Future Together

Since 2012, TRJ Construction Ltd has delivered bespoke SIP panel buildings designed for durability, efficiency and long-term value.

We do not compete on shortcuts.
We compete on engineering integrity.

Thinking about a SIP garden room or granny annexe? We can explain how the structure works and discuss the choices before you invest.

TRJ Construction Ltd
Structural Insulated Panel Specialists
Covering North London & Home Counties

Premium Quality Garden Rooms & Granny Annexes Since 2012

TRJ Construction Ltd designs and builds garden rooms, granny annexes and home extensions in the UK. We tailor the layout, materials and fit-out to each brief.

We work on garden offices and annexes for independent living. The work can cover design, construction and finishes. We discuss what you need from the space before agreeing the build.

📞 Contact TRJ Construction Ltd today for a free quote and transform your home with expert craftsmanship!

Expert Craftsmanship & Superior Quality

We plan each build around its structure, layout and finish. Our work includes garden rooms, granny annexes and home extensions. You can see examples in our completed projects.

✅ High-quality materials & finishes
✅ Custom designs tailored to your needs
✅ Built to last with expert craftsmanship

Affordable, High-Quality Construction Services

We discuss the budget and scope with you before the build. The quote should make clear which materials, finishes and services are included.

💰 Affordable pricing with no hidden costs
🏡 Custom-built solutions to suit every budget
✔️ High standards of construction & customer satisfaction

Looking to upgrade your home with a garden room, granny annexe, or home extension? Get in touch today for a free consultation and quote!

Hertfordshire Granny Annexe

↗