About Costi Tiseanu – Structural Insulated Panel (SIP) Construction Specialist
Over 25 Years of Construction Experience
Costi Tiseanu
Company Director
I’m Constantin “Costi” Tiseanu, founder and director of TRJ Construction Ltd.
With over 25 years of hands-on experience in the construction industry, I have dedicated my career to building high-performance, energy-efficient structures that are designed to last — not just look good for a few years.
My journey began as an installer and project manager within the garden building sector, where I developed deep practical knowledge of structural insulated panel systems, foundation methods, and finishing standards.
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) are advanced construction elements made from engineered insulation core with durable structural skins. They provide superior strength, insulation performance, airtightness, and moisture control compared to traditional timber or brick construction. SIPs reduce thermal bridging, improve energy efficiency, and maintain structural integrity in UK weather conditions.
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 ensures every TRJ project meets current building regulations and structural standards.
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.
If you are considering a SIP garden room or granny annexe and want to understand the structural difference before investing, we are always happy to provide honest, technical guidance.
TRJ Construction Ltd
Structural Insulated Panel Specialists
Covering North London & Home Counties
Premium Quality Garden Rooms & Granny Annexes Since 2012
TRJ Construction Ltd is a trusted UK-based construction company specializing in bespoke garden rooms, granny annexes, and home extensions. With over a decade of experience, our expert team designs and builds high-quality, durable, and stylish outdoor living spaces tailored to your unique needs.
From modern garden offices to spacious annexes for independent living, we handle everything from custom design to flawless construction, ensuring superior craftsmanship and attention to detail. Our commitment to quality and customer satisfaction has made us a leading choice for homeowners looking to enhance their property with functional and aesthetically pleasing extensions.
📞 Contact TRJ Construction Ltd today for a free quote and transform your home with expert craftsmanship!
Expert Craftsmanship & Superior Quality
At TRJ Construction Ltd, we take pride in delivering exceptional workmanship in every project. Our skilled craftsmen meticulously plan and execute each build, ensuring durability, style, and long-lasting performance. Whether you're looking for a luxury garden room, a self-contained granny annexe, or a custom home extension, we bring your vision to life with precision and expertise.
✅
High-quality materials & finishes
✅
Custom designs tailored to your needs
✅
Built to last with expert craftsmanship
Affordable, High-Quality Construction Services
We believe that everyone deserves a beautifully designed, high-quality living space, regardless of budget. That’s why TRJ Construction Ltd offers cost-effective solutions without compromising on quality. Our competitively priced services ensure that you get outstanding value while benefiting from our expert craftsmanship.
💰
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!
A garden office company
TRJ Construction Ltd
Registered office
39 Rushleigh Avenue ,Waltham Cross ,EN8 8PP
Contact details
Costi Tiseanu
Business Position
Director
VAT no.
153770309
Contact Number :
+44 79 66800 519
All imagines are property of TRJ Construction Ltd .
Starting 2000 these were our jobs done for different contractors as follow : Gardenlodges ,Hilton, GrannyAnnexe , HomeExtensions Ltd, Gardenspaces UK , Inspired Building Systems ,Studioni Ltd,SuperSips Ltd and more private jobs .
We provided all the labouring for the hole projects and in some occasions technical advise and drawings .
We done installations for our contractors at
NEC Grand Design on 2012,2014,2015 and ExCel London Grand Design on 2013,2014,2015,2016.
During 2012 I was in charge with a project run by Gardenlodges for My Flat Pack Home Tv Show hosted by Amanda Lamb .
