Single Storey Extensions Plans

At AC Design Solution, our loft conversion drawings typically cost between £550 and £2,500, depending on several factors:

What affects the cost of loft conversion drawings?

• Project complexity: The size and complexity of your loft conversion will influence the level of detail required in the drawings, Also the level of detail in your property some properties may take longer to draft due details in the elevation which can increase the price
• Type of service: The package level taken out, simple Basic planning drawings cost less than comprehensive packages that include detailed construction drawings, structural calculations, and building regulations compliance and party wall awards.
• Location: While we strive to keep our pricing consistent, certain areas may have different requirements that affect overall costs.

What’s included in our loft conversion standard package?

Our standard loft conversion drawing package includes:

• Initial consultation and site survey with a 3d scanner
• Existing and proposed floor plans, elevations, and one section
• Planning application drawings (if required)

What included in your higher loft conversion package

• Building regulations compliance drawings
• Structural calculations (may be an additional cost for complex projects)

Why professional drawings are essential

Investing in professional loft conversion drawings is crucial as they:

• Ensure your project complies with current building regulations
• Provide clear instructions for your builder, reducing the risk of costly mistakes
• Are required for planning permission applications (where applicable)
• Help accurately estimate material costs and project timeline
• Can identify potential issues before construction begins

Do I need planning permission for a loft conversion?

Many loft conversions fall under Permitted Development rights, eliminating the need for formal planning permission more information can be find on the government website (Permitted development rights for householders: technical guidance). Based on our 15+ years of experience designing over 500 loft conversions across London and surrounding areas, we’ve found that approximately 70% of standard loft projects can proceed without planning permission when they meet these specific criteria:

• Volume limitations for loft spaces: Your loft extension cannot exceed 40 cubic metres of additional roof space for terraced houses or 50 cubic metres for detached and semi-detached properties (measured externally and including any existing roof extensions), we will do the calculation on cubic metre for you to assist in making sure you’re compliant.
• Roof height restrictions: The highest part of your loft conversion must not be higher than the highest part of your existing roof, and dormer windows must be set back from the eaves. This is where many homeowners get caught out with internal heights – you must take into consideration the size of the new joists (whether they are 8×2 or 6×2) plus the complete roof makeup (usually OSB board, firrings, insulation meeting new regulations requiring a minimum of 150mm, another layer of OSB, and waterproof roof covering). These layers can significantly reduce usable height, so your existing loft should have a minimum height of 2.7m to achieve a reasonable finished ceiling height after conversion.
• Front elevation design constraints: No dormers or roof extensions are permitted on the front elevation only flush roof lights that don’t protrude more than 150mm

Roof materials and appearance: The roof covering of any dormer must match or be similar in appearance to the existing house roof covering, including tiles, slate, or other roofing materials. This is another critical area where homeowners can encounter serious planning issues. Through our extensive experience with planning appeals and enforcement challenges, we’ve successfully represented clients who deviated from approved materials. In one case, a client received an enforcement order after changing from the approved tiles to rendered walls. Our team navigated the complex planning process and secured approval on the first attempt by carefully analyzing:

• Local planning policies and material guidance specific to the area
• Streetscape and neighborhood character assessment
• Visual impact analysis from multiple viewing angles
• Presence of screening vegetation or existing similar precedents
• Technical justification for the material change
• When material changes are unavoidable, our in-depth knowledge of planning appeal processes and success in previous cases significantly increases approval chances. We recommend consulting with our team before making any material changes to avoid costly enforcement proceedings.
• Roof edge setbacks: All roof extensions (except hip-to-gable) must be set back at least 20cm from the original eaves, and side-facing dormers must be at least 50cm from party walls
• Protected sight lines: No part of the loft conversion can be within 2 meters of a boundary line that projects above a 45-degree plane from a rear window in a habitable room
• Window and opening requirements: Any side-facing windows must be obscure-glazed with opening parts at least 1.7m above internal floor level to prevent overlooking neighboring properties

Our CIAT-qualified architectural technologists can confirm if your project meets these criteria during our comprehensive property assessment.

When planning permission is definitely required:

Based on our experience working with 20+ London boroughs and numerous local authorities planning permission is typically necessary when:

• Your property is in a Conservation Area, where Article 4 Directions often remove Permitted Development rights
• Your home is a listed building (Grade I, II* or II), requiring Listed Building Consent alongside planning permission
• Previous extensions have used up your permitted development rights
• Your design includes dormers facing the highway or substantial alterations to the roof profile
• You’re planning a more extensive conversion that exceeds permitted development limits

Even when planning permission isn’t needed, all loft conversions require Building Regulations approval to ensure compliance with the latest UK standards for structural integrity, fire safety, thermal efficiency, and ventilation. Our building regulation drawings have achieved a 95% first-time approval rate with building control authorities across Greater London.

For a free planning assessment of your specific property and expert guidance on navigating the planning process for your loft conversion, contact our technical team today.

There are few different types of loft conversion which suit different shaped properties, understanding the difference will help you choose the correct option or the only option

Roof Light Conversion (Simple Room Conversion)

What it is: The simplest and most affordable type of loft conversion. We add roof windows (like Velux windows) to your existing roof slope without changing the external roof structure. However, you still require steel beams and new floor joists. It is a common misconception that you can use the timber which is there now – this is not the case. The timber that is there is for your ceiling joists and not designed for floor loads. We are able to assist you with matters relating to structural engineering for loft conversions.

Best for: Homes that already have sufficient head height in the loft (at least 2.3m at the highest point) and where budget is a priority.

Appearance: From the outside, only flat windows will be visible in your roof – no change to the roof shape itself.

Cost range: £15,000-£25,000, making it the most economical option.

Pros: Minimal disruption, usually falls under permitted development, most cost-effective option, quickest to complete.

Cons: Limited additional headroom, less usable floor space than other conversion types.

Dormer Loft Conversion

What it is: The most popular loft conversion type in the UK. We extend your roof outward with a flat-roofed “box” structure that creates vertical walls and flat ceiling sections, maximizing usable floor space and headroom. Usually on a normal semi-detached property it will require three steel beams and a ridge beam. If you have a chimney in the way where the steel will be positioned, an additional steel beam connecting to both beams is required and a post to carry the ridge beam.

Best for: Most UK home types, especially terraced and semi-detached houses with pitched roofs.

Appearance: From the outside, you’ll see a box-like extension protruding from the rear or side of your roof, typically with windows.

Cost range: £30,000-£45,000 for a standard rear dormer.

Pros: Creates maximum usable floor space, good value for money, suitable for most properties, usually falls under permitted development if at the rear of the property.

Cons: Can change the external appearance of your home, especially if visible from the street.

Hip-to-Gable Loft Conversion

What it is: We convert the sloping side of your roof (the “hip”) into a vertical wall (the “gable”), creating additional headroom and floor space at the edges of your loft.

Best for: Semi-detached and end-of-terrace houses with a hip roof (where the roof slopes down on three or more sides).

Appearance: The sloping side of your roof becomes a straight, with either a timber vertical wall or block or brickwork wall extends to the peak, significantly changing that side of your roof profile.

Cost range: £35,000-£50,000.

Pros: Creates substantial additional space, particularly effective when combined with a rear dormer for maximum space gain. It will allow you to create an additional ensuite and will allow the stairs to flow correctly without awkward riser heights. The stairs can be positioned right next to the exterior wall, making the room upstairs bigger.

Cons: Only suitable for certain property types, more visible external change to your home’s appearance.

Mansard Loft Conversion

What it is: The most dramatic and comprehensive loft transformation. We change the entire roof structure to create a nearly vertical wall (typically at 72 degrees) with a flat roof on top, almost adding an entire new floor to your home.

Best for: Properties where maximum space is needed, common in London boroughs, especially for terraced houses.

Appearance: Creates a flat roof with very steep sloping sides and usually includes dormer windows. It substantially changes your roof’s appearance.

Cost range: £45,000-£70,000, making it the most expensive option.

Pros: Creates the maximum possible space, can completely transform a small attic into a spacious living area with excellent headroom throughout.

Cons: Almost always requires planning permission, most expensive and disruptive option, not suitable for all property types, longer construction time.

Which type is right for you?

The best loft conversion for your home depends on several factors:

• Available budget: Roof light conversions are most affordable, while mansard conversions are most expensive
• Property type: Hip-to-gable only works for end-of-terrace or semi-detached homes
• Existing roof height: Lower roofs may require dormer or mansard conversions to create usable space
• Planning constraints: If you’re in a conservation area, roof light conversions are often easiest to get approved
• Space requirements: For a master bedroom with ensuite, dormers or mansards provide more usable floor area

Our design team provides free initial assessments to determine which loft conversion type would work best for your specific property and requirements. Contact us to arrange a property evaluation and discover the potential in your roof space.

Staircase placement is one of the most critical decisions in your loft conversion project, significantly impacting both the usability of your new space and the existing rooms below. Building Regulations mandate specific requirements for loft conversion stairs, and finding the optimal location requires careful consideration of several factors:

Building Regulations requirements for loft stairs

Your loft conversion stairs must comply with strict regulations:

• Minimum width of 800mm (though we recommend 900mm for comfort)
• Maximum rise (height) of each step: 220mm
• Minimum going (depth) of each step: 220mm
• Minimum headroom of 2m throughout the staircase
• Maximum pitch (steepness) of 42 degrees
• Handrail required on at least one side
• Protective balustrading with gaps no larger than 100mm

Spiral staircases or space-saving alternating tread stairs can sometimes be used for loft conversions but are subject to additional restrictions and are generally only permitted for conversions used as a single room.

Optimal staircase positioning

The most common and practical staircase locations include:

1. Above the existing staircase

• Creates a natural continuation of your home’s circulation
• Minimizes impact on existing rooms
• Often requires removing part of the landing and reconfiguring bannisters
• Can present headroom challenges that need careful design solutions

2. In line with the existing staircase

• Works well in properties with straight staircases
• Creates an intuitive flow through the home
• May require sacrificing part of a bedroom or bathroom below
• Often provides better headroom than other options

3. Perpendicular to existing stairs

• Effective solution for many semi-detached and terraced houses
• Can utilize otherwise awkward corner spaces
• May require reconfiguring a bedroom or bathroom layout
• Need careful planning to ensure adequate headroom

4. From a box room or small bedroom

• Practical when a small third bedroom is less valuable than new loft space
• Allows for a more centrally positioned staircase in the loft
• Creates opportunity for a more generous staircase design
• Minimizes disruption to main living spaces and larger bedrooms

Our approach to staircase design

Our detailed 3D scanning technology allows us to analyze multiple staircase options within your specific property, identifying the solution that:

• Maximizes usable space in your new loft conversion
• Minimizes impact on existing rooms
• Ensures full Building Regulations compliance
• Creates a natural flow through your home
• Considers future needs and flexibility

We present you with visual representations of different staircase options during the design phase, helping you understand the implications of each position before making this crucial decision. Many clients are surprised by how creative solutions can transform what initially seemed like problematic layouts into highly functional designs.

For a personalized assessment of the optimal staircase position for your specific property, contact our design team to arrange a consultation.

As with any loft conversion steel beams will be inserted into a wall which you may share with your neighbour this goes for semi detached and terraced properties, your loft conversion will likely require a Party Wall Agreement under the Party Wall etc. Act 1996. A lot of people shy away from the party wall award however it protects both you and your neighbors during construction work that might affect shared structures.

When is a Party Wall Agreement required for loft conversions?

A Party Wall Agreement is typically necessary when your loft conversion involves:

1. Work directly to the party wall – This includes:
   • Cutting into the party wall to insert beams or padstones even though this is on your side.
   • Removing chimney breasts attached to the party wall.
   • Raising, underpinning, or thickening the party wall
   • Increasing the height of the party wall (as with some hip-to-gable conversions)
2. Work to the party wall structure – Including:
   • Installing flashings that bridge the boundary
   • Weather-proofing the junction between your new structure and the party wall
   • Removing, replacing or adapting roof structures connected to the party wall.

Common loft conversion scenarios requiring Party Wall Agreements

For terraced houses:

• Both adjoining neighbors (on either side) will require Party Wall Notices and potential Agreements
• Roof structure modifications often affect both party walls
• Beam positions typically require support from party walls. You will need a set of structural engineering General arrangement plans and architectural plans Aswell, if your neighbours have converted the loft, surveyors will need to see how you plan to enclose the gap between the existing structure to avoid water penetration in gaps that cannot be services. Weathering details will need to be shown preferable scale 1:20

The Party Wall process explained

1. Initial assessment – Our team evaluates your loft design to determine party wall implications
2. Party Wall Notice – At least two months before work begins, formal written notice must be served to all affected neighbors (known as “adjoining owners”)
3. Neighbor’s response – Your neighbors have 14 days to respond, with three possible outcomes:
• They consent to the works (no Party Wall Award needed)
• They dissent or fail to respond within 14 days (Party Wall Award required)
• They can request additional information or modifications
4. Appointment of surveyors – If your neighbor dissents or doesn’t respond:
• You and your neighbor can each appoint a surveyor
• Both parties can agree to use a single impartial surveyor (typically more cost-effective)
• If your neighbor fails to appoint a surveyor, you can appoint one on their behalf after 10 days
5. Party Wall Award – The surveyor(s) prepare a legally binding document that:
• Details the work to be carried out
• Specifies working times and methods
• Records the condition of the neighbor’s property before work begins
• Includes provisions for compensation if damage occurs
• Outlines the responsibilities of both parties
6. Construction phase – Work proceeds according to the terms of the Award
7. Post-construction – The surveyor may conduct a final inspection to identify any damage requiring compensation

What happens if I proceed without a required Party Wall Agreement?

Proceeding without the necessary Party Wall Agreement carries significant risks:

• Your neighbor can seek an injunction to stop work immediately
• You may face legal proceedings and substantial costs
• Retrospective Party Wall Agreements typically cost more
• Your property sale could be complicated as solicitors usually check for Party Wall compliance
• Your building insurance may be invalidated for any damage related to the works