Our Guide to Installing
Modular Extensions
Your Step-by-Step Guide to Building a Modular Extension
Homeowners across Newport, Cardiff, and wider South Wales are choosing modular extensions from Morgan Garden Studios for their speed, exceptional insulation, and long-term durability. Every structure we build is constructed using SIPs panels (Structural Insulated Panels) for superior thermal performance and structural strength.
Pre-Build - Pull Test and Utility Identification
A Pull Test (for ground screws) assesses the suitability of your soil for ground screw foundations. Ground screws are steel piles driven deep into the ground to hold the modular extension securely.
The Pull Test evaluates: Soil stability, load-bearing capacity, required screw depth and ground resistance values. This is essential in areas like Cardiff, Newport, and other parts of South Wales, which feature a mix of clay, shale, reclaimed ground, and uneven terrain.
Why a Pull Test Matters
The results are sent to a structural engineer, who determines: number of screws required, the type and size of screws, layout, structural calculations for your SIPs extension.
Utility Identification
We will also undertake a full site-survey to identify any underground pipes for gas, electricity and drainage. A drainage company will visit your property to map out underground water-pipes and drains. Nothing is left to chance.
Day 1 - Onsite Survey, Marking Out & Clearance
The build team marks out the footprint of the SIPs extension using:
Laser-levelled measurements
Boundary and access checks
Confirmation of the planned service routes
Minor ground clearing if necessary
This step is especially important in tight garden spaces in Cardiff and Bristol, and on Newport’s varied ground levels.
Day 2 - Ground Screws Foundation Installed
Guided by the earlier pull test, the team installs precisely positioned ground screws and structural base plates or brackets for a fully levelled foundation grid. Ground screws pair perfectly with SIPs structures, providing a solid base that avoids the mess and curing time of concrete.
Day 3 - Structural Assembly - SIPs Floor & Walls
Extension Floor: The build team marks out the footprint of the SIPs extension using laser-levelled measurements, access checks, confirmation of planned service routes and ground clearing. This step is especially important in tight garden spaces in Cardiff and Bristol, and on Newport’s varied ground levels.
Walls: SIPs wall panels and internal studwork go up as well as fixings and sheathing, vapour control membranes and service void.
Day 3 (cont) - Roof Cutting
The roof is cut with timber rafters precisely calculated by a structural engineer, so your build is strong and durable. We create flat roofs with a clean, modern finish or pitched roofs to match the existing tiles or slates of your property.
Your chosen external finish — including EPDM rubber roofing, tiles or slate — is fitted to UK standards for complete weatherproofing. The result is a strong, attractive and thermally efficient roof that enhances your modular extension. By the end of Day 3, your SIPs structure is clearly defined.
Day 4 - Windows, Doors & Exterior Envelope
External walls are wrapped in breathable felt, counter-battened and membraned. High-performance aluminium or uPVC windows and doors are installed precisely into the SIPs openings.
The team completes weatherproof sealing, flashings and insulation checks. Your SIPs extension is now secure and fully enclosed.
Day 5 - Roof Insulation & Completion
Timbers are insulated (between rafters, plus an underlayer of insulation); and foil taped to create a vapour layer. Roofing complete, the extension is now water-tight against the elements. Internal works begin.
Pitched Roof: Pitched roof rafters are overlaid with breathable felt and counter-battened. (Tile or slate is applied to finish.)
Flat Roof: Topped with an OSB (Oriented Strand Board), for strength and water resistance. (EPDM rubber applied to finish.)
Day 6 - First-Fix Electrics, Internal Insulation & SIPs Boarding
Inside the extension, the following are completed:
Electrical cable routing & Network/data cabling
Heater or panel radiator feeds
Additional internal insulation
Vapour control layers
Plasterboard installation on the SIPs walls
Day 7 - Plastering, Jointing & Internal Preparation
Your SIPs rooms are now prepared for finishing:
Full plaster skim to walls and ceilings
Interior left clean, ready for your own decorators and flooring installers
We ensure a perfect base for you to complete the interior in your chosen style.
Day 8 - External Cladding
This is where the exterior begins to match your vision. Options include:
Composite cladding for a durable modern look
Cement board for contemporary styling
Brick slips ideal for matching your home
Render for a clean crisp finish
Morgan Garden Studios can design your SIPs modular extension to match your existing house (useful in Cardiff and Newport estates), or complement it using contrasting colours and materials.
Day 9 - Second Fix Electrics & Handover
The final day of your modular extension build includes:
Fitting sockets, switches and lighting
Testing electrics and issuing certification
Completing external cladding and trims
Final waterproofing and sealing
Full quality inspection
Customer walkthrough
Your SIPs modular extension is now complete—ready for flooring, painting and furnishing.