MYGRANNYANNEXE
Meet the team behind your annexe
Legal information, company registration, and contact details for MyGrannyAnnexe — trusted builder of SIP granny annexes and garden rooms across the UK.
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 MyGrannyAnnexe
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 MyGrannyAnnexe 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 MyGrannyAnnexe, 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 MyGrannyAnnexe 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 MyGrannyAnnexe 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
- MyGrannyAnnexe 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.
MyGrannyAnnexe – Building the Future Together
Since 2012, MyGrannyAnnexe 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.
MyGrannyAnnexe Structural Insulated Panel Specialists Covering North London & Home Counties
Premium Quality Garden Rooms & Granny Annexes Since 2012
MyGrannyAnnexe 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 MyGrannyAnnexe today for a free quote and transform your home with expert craftsmanship!
Expert Craftsmanship & Superior Quality
At MyGrannyAnnexe, 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.
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High-quality materials & finishes
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Custom designs tailored to your needs
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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 MyGrannyAnnexe offers cost-effective solutions without compromising on quality. Our competitively priced services ensure that you get outstanding value while benefiting from our expert craftsmanship.
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Affordable pricing with no hidden costs
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Custom-built solutions to suit every budget
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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
Registered office
39 Rushleigh Avenue ,Waltham Cross ,EN8 8PP
Contact details
Business Position
Director
VAT no.
153770309
Contact Number :
+44 79 66800 519
All imagines are property of MyGrannyAnnexe .
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 .
Hertfordshire Granny Annexe
Project gallery
Let’s talk about your garden.
Tell us what you have in mind. We can discuss your space, layout, planning considerations and the next steps.