Our Construction Process
This page shows the step-by-step construction process for our most common building projects. Every loft conversion, house extension and renovation follows a structured sequence of stages, each inspected by building control before the next phase begins. Below you can see what each stage looks like on a real LCCL Construction project.
Construction can only begin once the design phase is complete — this includes architectural drawings, planning permission (if required), building regulation approval, structural engineer calculations and party wall agreements. If you have not started the design phase, book a free consultation call to begin the process.
LCCL Construction is a design and build company based in Finchley, North London, with over 20 years of experience delivering loft conversions, house extensions, renovations and new builds across London and Hertfordshire. We have completed hundreds of projects, hold more than 200 verified reviews rated 4.7 out of 5, and were LABC Awards Regional Winners 2024. We are NFB members and LABC Registered Partners.
Below we walk through the construction stages for house extensions and loft conversions. New build projects follow a similar sequence to extensions but are generally more straightforward as there are no existing structures to work around, no load-bearing walls to remove and no existing services to divert.
House Extension Construction Process
Setting out
Setting out is one of the most critical stages of any build. The foundation positions are marked on the ground to ensure the extension is correctly sized, level and aligned with the existing house. On larger projects a surveyor will set out the site using laser equipment to ensure millimetre accuracy. Getting this wrong means everything built on top will be wrong.
Foundations
When the site setting out is completed and fully marked out, the excavation can begin. A digger would dig out a trench usually 1.4 meters deep(depending on specification in your structural drawings) and concrete is poured into the trench
Note: Building inspector has to approve the excavation before pouring the concrete.
Blockwork to DPC
After the concrete has cured (ideally 28 days for full strength), blockwork is built up to damp proof course (DPC) level. A DPC membrane is laid between courses to prevent moisture rising through the walls. The building control inspector will visit to check the work at this stage before construction continues above ground.
Walls and scaffolding
With foundations and DPC complete, the walls are built up to full height. Scaffolding is erected around the perimeter to allow bricklayers to work safely at height. During this stage the cavity walls are constructed with insulation, wall ties and cavity trays installed as required by the building regulation drawings.
Carrier walls installations and restructuring
This is one of the most critical stages of an extension project — connecting the new build to the existing house. Load-bearing walls are removed and structural steels installed to create open-plan living spaces. This work must be carried out in strict accordance with the structural engineer’s drawings and inspected by building control before proceeding.
Waterproofing
Once the walls are up, the roof structure is built, windows are installed and the extension is made watertight. This is a significant milestone — from this point the internal trades can begin working regardless of weather. The building control inspector will check the roof structure, insulation and weatherproofing at this stage.
First and Second Fix
With the building watertight, internal work begins. First fix includes electrical wiring, plumbing pipework, underfloor heating (if specified), stud wall construction, and any structural carpentry. The building control inspector must check all first fix work, insulation and fire stopping before plasterboarding. After plastering, second fix takes place — this includes fitting sockets and switches, hanging doors, installing radiators, fitting kitchens and bathrooms, and completing all joinery.
Paint and decorate
Painters and decorators are typically one of the final trades on site. All walls, ceilings, woodwork and any feature areas are prepared and painted to your chosen specification. Decorating usually takes several days depending on the size of the project and the finish required.
Snagging
A snagging inspection is carried out to identify any minor defects or outstanding items. We typically allow a snagging period of around two months so you have time to identify anything that is not immediately obvious, such as a light fitting that does not work or a door that needs adjusting. The building control inspector will carry out a final inspection and require gas safety certificates, electrical installation certificates and any other relevant documentation before issuing the completion certificate.
Loft Conversion Construction Process
Scaffolding
Full scaffolding with a temporary roof (known as a “tin hat”) is erected over the entire house before any roof work begins. This protects your home from weather throughout the build, allows trades to work continuously regardless of rain, and means you can continue living in the property while the loft conversion is under construction. The temporary roof is one of the most important investments in the quality and programme of your loft conversion.
Roof Strip and Preparation
With the temporary roof in place, the existing roof tiles are removed and the existing timber structure is cut back to make way for the new loft conversion. This preparation work creates the opening and framework for the new construction to begin.
Steel Installation
Structural steels are installed to support the new loft structure. The steel positions and sizes are specified in the structural engineer’s drawings and determine the final head height, room layout and staircase opening. This is a critical stage — the building control inspector must attend site to check and approve the steel installation before any further work continues.
Carcassing (Timber Frame)
Once the steels are approved, the timber frame of the loft conversion is constructed. This includes the new walls, flat roof structure, rafters and floor joists, all built to the dimensions in the structural and building regulation drawings. Quality carcassing is essential for a straight, level finish when the loft is plastered. The building control inspector will check the timber frame before the next stage.
Waterproofing
Once the walls are up, the roof structure is built, windows are installed and the extension is made watertight. This is a significant milestone — from this point the internal trades can begin working regardless of weather. The building control inspector will check the roof structure, insulation and weatherproofing at this stage.
Staircase Installation
The new staircase is supplied and installed, connecting the first floor to the new loft space. This involves cutting an opening in the first floor ceiling and forming the stairwell with fire-rated construction. Staircase installation typically takes one to two days. The stairs must comply with building regulations for width, headroom, pitch and handrail height.
The loft conversion finishing
With the loft watertight and the staircase installed, the internal trades complete the fit-out. First fix electrical wiring and plumbing pipework are installed, followed by insulation and plasterboarding (checked by building control before boarding). After plastering, second fix takes place — tiling in the en-suite or bathroom, installation of sanitaryware, fitting doors, completing electrics and plumbing, and finally painting and decorating. The building control inspector signs off each stage throughout this process and issues the completion certificate once all work is finished and all certificates have been received.
Renovation Construction Process
Home renovations vary widely in scope, from single-room refurbishments to full house renovations. The construction stages will depend on the specific works involved but typically include structural alterations, first and second fix trades, plastering, and decoration. Many renovation projects also include elements of extension or loft conversion work. For more information on our renovation services, visit our home renovation page or book a free consultation call to discuss your project.
Ready to Start Your Construction Project?
Book a free consultation call to discuss your loft conversion, house extension, renovation or new build. Our team will guide you through the entire process from initial design to construction and handover. Call 020 8037 7332, email info@lcclconstruction.co.uk or book online.
Testimonials
LCCL Construction managed the entire build from start to finish. The quality of workmanship was excellent and the team kept us informed throughout every stage. We would highly recommend them.” — Ludovic, Reviews.io
From foundations to final decoration, the LCCL team were professional, tidy and delivered a fantastic result. The project was completed on time and the finish quality exceeded our expectations.” — Parminder, Google
Frequently Asked Questions
Q1: How long does a loft conversion take to build?
A typical loft conversion takes between 8 and 12 weeks from the start of construction on site. The exact duration depends on the type of loft conversion, the complexity of the structural work, and the specification of the internal fit-out. This does not include the design phase (architectural drawings, planning permission, building regulations and structural calculations), which typically takes 8 to 12 weeks before construction can begin.
Q2: How long does a house extension take to build?
A single-storey rear extension typically takes 12 to 16 weeks to build. Larger extensions such as wraparound, side return or two-storey extensions may take 16 to 24 weeks depending on the size and complexity. As with loft conversions, the design phase must be completed before construction can start.
Q3: Can I live in my house during construction?
Yes, in most cases you can continue living in your home during a loft conversion or house extension. For loft conversions, the temporary scaffolding roof protects your home from weather throughout the build. For extensions, the existing house remains largely unaffected until the opening-up stage when the new extension is connected to the existing building. We always plan the construction sequence to minimise disruption to your daily life.
Q4: What building control inspections are required during construction?
Building control inspectors visit at key stages throughout the build to check that the work complies with the approved building regulation drawings. Typical inspection stages include foundation excavation, DPC level, structural steels, first fix (before plasterboarding), insulation, drainage, and final completion. Your project manager coordinates all building control visits so you do not need to arrange these yourself. At the end of the project, building control issues a completion certificate confirming all work has been inspected and approved.
Q5: What happens if something unexpected is found during construction?
Unexpected issues can occasionally arise during construction, particularly in older properties. Common examples include poor ground conditions requiring deeper foundations, hidden structural defects, or asbestos in existing materials. If anything unexpected is discovered, your project manager will inform you immediately, explain the options and provide any revised cost and time implications before proceeding. We recommend maintaining a contingency budget of 10 to 15 percent to cover unforeseen items.