Structural & Building Work

Homeowner guides from Wittick Building — North London & Hertfordshire

A loft conversion or home extension is one of the most valuable investments you can make in your property. Done well, it adds usable space, increases the value of your home, and avoids the cost and disruption of moving. But before a single brick is laid or a roof cut open, there's a process that needs to happen — and skipping steps here is where projects go wrong, go over budget, or grind to a halt.

This guide walks you through everything that needs to happen before building work begins, so you know exactly what to expect and why each stage matters.

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Step 1 — Is Your Property Suitable?

• The first question is feasibility. Not every property is suitable for every type of conversion or extension, and it's worth understanding the limitations before spending money on drawings.
• For loft conversions, the key factor is head height. You generally need at least 2.2 metres from the floor joist to the ridge of the roof to create a usable space. A builder or architect can assess this quickly. The pitch and structure of your roof also determines which type of conversion is possible.
• For extensions, the main considerations are plot size, proximity to boundaries, and what your local authority will permit. Some properties — particularly those in conservation areas, listed buildings, or on smaller plots — have more restrictions than others.

Wittick Building Tip: We offer initial feasibility assessments for loft conversions and extensions. It's always worth having someone take a look before you commit to anything.

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Step 2 — Permitted Development or Planning Permission?

Many loft conversions and single-storey rear extensions fall under Permitted Development (PD) rights, which means you don't need to apply for full planning permission. However, PD rights have limits, and not every property has them — particularly flats, properties in conservation areas, or those where PD rights have been removed by the local authority.

Permitted Development typically allows:‍

• Rear extensions up to 3 metres (semi/terraced) or 4 metres (detached) on a single storey
• Loft conversions adding up to 40m³ (terraced) or 50m³ (detached/semi) of space
• Hip-to-gable and rear dormer conversions in many cases

You will likely need full planning permission for:

• Side extensions or two-storey extensions
• Anything that exceeds PD limits
• Properties in conservation areas or with Article 4 directions
• Anything that significantly changes the roofline at the front of the property

Even where PD applies, it's advisable to obtain a Lawful Development Certificate (LDC) from your local council. This is a formal confirmation that your project is lawful — and it's essential when you come to sell the property.

Planning applications typically take 8–12 weeks to be decided. Factor this into your project timeline from the outset.

Step 3 — Appointing an Architect

Once you know your project is feasible and you understand the planning route, you'll need an architect to produce drawings. These are not just for planning — they're the foundation of everything that follows, including structural calculations, building regulations, and your builder's quote.

What your architect will produce:

• Existing drawings — accurate plans and elevations of the property as it stands
• Proposed drawings — showing the new layout, elevations, and key dimensions
• Planning drawings — submitted to the local authority if required
• Building regulations drawings — more detailed technical drawings showing construction methodology, insulation, fire safety, ventilation, and drainage

Architectural fees vary depending on the size and complexity of the project. For a loft conversion, expect to pay between £1,500 and £3,500 for drawings. For a larger extension, fees can be £3,000–£7,000+. Some architects charge a percentage of the build cost.

Wittick Building Tip: Ask your architect whether their fee includes planning AND building regulations drawings — these are two separate packages and not all firms include both in their initial quote.

Step 4 — Structural Engineer Specifications

Once the architect's drawings are in place, a structural engineer produces the calculations and specifications needed to make the build safe and sign-off compliant. This is not optional — building control will require structural engineer approval before and during construction.

For a loft conversion, the structural engineer will typically specify:

• Steel beam sizes and positions (RSJs) for any new openings
• Timber sizes for new floor joists
• Purlin and ridge beam calculations
• Any strengthening required to existing roof members or party walls

For an extension:

• Foundation type and depth (strip, pad, raft — depending on ground conditions)
• Steelwork specifications for any lintels or beams
• Wall construction and load-bearing details

Structural engineer fees are typically £500–£1,500 for a standard loft or extension. The engineer's drawings and calculations are then passed to your builder and to building control.

Step 5 — Party Wall Agreements

• If your project involves work on or near a shared wall with a neighbour — which includes most loft conversions and rear extensions on terraced or semi-detached properties — you are legally required to serve notice under the Party Wall Act 1996.
• Your neighbour then has the right to consent or to appoint a party wall surveyor. If they appoint one, you are responsible for the cost. A party wall award (the formal agreement) must be in place before work begins on the affected structure.

Party wall disputes can delay a project by weeks or months. Serve notice early — ideally at the same time as submitting your planning application.

Step 6 — Building Regulations Approval

• All loft conversions and extensions require Building Regulations approval, regardless of whether planning permission was needed. Building regs cover structural integrity, fire safety, insulation, ventilation, drainage, and more.
• You can submit a Full Plans application (drawings submitted and approved before work starts — recommended) or a Building Notice (work starts and is inspected as it progresses). For anything complex, Full Plans is the safer route.
• A building control inspector will visit at key stages during construction and issue a Completion Certificate when everything is satisfactory. This certificate is essential for selling the property.

Step 7 — Getting an Accurate Cost

• Here's the reality: a builder cannot give you an accurate, fixed price until the architect's drawings and structural engineer's specifications are complete. Anyone quoting a firm price before this point is guessing — and that guess will either be inflated (to cover unknowns) or it will change once the full scope becomes clear.
• Once the full package of drawings and specs is in place, a reputable builder will price from those documents. This means the quote reflects exactly what will be built, to what standard, and with what materials. It's the only basis for a fair, comparable quote.

Wittick Building Tip: At Wittick Building, we work with trusted local architects and structural engineers and can recommend professionals suited to your project. We're happy to advise at every stage, from initial feasibility through to final handover.

Typical Timeline — First Conversation to Breaking Ground

• Initial feasibility check — 1–2 weeks
• Appoint architect, produce drawings — 4–8 weeks
• Planning application (if required) — 8–12 weeks
• Structural engineer specifications — 2–4 weeks (can run alongside planning)
• Party wall notices served and agreed — 2–8 weeks
• Building regulations submission — 2–4 weeks for full plans approval
• Builder quotes and contract agreed — 2–3 weeks
• Work begins

From first conversation to starting on site: allow 4–6 months as a realistic minimum for a project requiring planning permission. Permitted development projects can move faster — sometimes 2–3 months.