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Spacious loft conversion on a suburban home

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What Drawings Do I Need for a Loft Conversion?

Understand which drawings are needed at each stage of your loft conversion, from exploring the design to obtaining approvals and preparing for construction.

A loft conversion usually requires more than one set of drawings.

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The plans needed to explore the layout are not necessarily the same as the drawings required for a planning application, a Lawful Development Certificate or the technical construction stage.

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A homeowner may begin with a simple idea:

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  • create an additional bedroom;

  • add an en-suite bathroom;

  • form a rear dormer;

  • convert the hip to a gable;

  • install rooflights;

  • extend over the rear addition; or

  • explore a mansard conversion.

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However, before a builder starts work, the project normally needs to be developed through several stages.

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The exact drawing package will depend on the property, the type of loft conversion and the planning route.

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The Practical Answer

 

Stage   / Drawings or information normally needed

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Exploring the options

Measured survey, existing plans, initial layouts and sections

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Planning application or Lawful Development Certificate

Existing and proposed plans, roof plans, elevations, sections and supporting information

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Building Regulations

Detailed technical drawings, specifications and coordinated construction notes

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Structural design

Structural calculations, beam positions and construction details

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Builder quotations

A coordinated design and technical package so contractors price the same scope of work

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Construction

Approved drawings, technical plans, structural information and any revisions agreed during the build

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Start With a Proper Measured Survey

 

The drawing process should normally begin with a measured survey of the existing house.

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This records the property accurately before the design work starts.

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The survey may include:

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  • the existing floor plans;

  • roof-space dimensions;

  • ridge height;

  • eaves levels;

  • ceiling heights;

  • staircase positions;

  • chimney breasts;

  • windows;

  • external walls;

  • party walls;

  • roof slopes;

  • rear additions;

  • drainage positions where relevant; and

  • the relationship with neighbouring roofs.

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Photographs are also useful.

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A loft may appear spacious when viewed through the loft hatch, but the true usable area can reduce once the new floor structure, insulation, staircase and sloping roof are taken into account.

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Accurate survey information allows the designer to assess the possibilities realistically.

Existing Drawings


Existing drawings show the house as it currently stands.
 

These usually include:
 

  • floor plans;

  • elevations;

  • roof plans; and

  • sections.
     

The level of detail depends on the project.
 

For a straightforward loft conversion, the existing plans should explain the current layout and roof form clearly enough for the designer, planning authority and technical team to understand what is being altered.
 

A section through the roof is particularly useful because it shows:
 

  • the existing ridge height;

  • the roof pitch;

  • the eaves;

  • the current ceiling;

  • the available headroom; and

  • the relationship between the loft and the floors below.

     

Proposed Design Drawings


The proposed drawings show what the loft conversion could become.
 

They may include:
 

  • the new loft floor plan;

  • the staircase;

  • bedrooms;

  • bathrooms;

  • storage;

  • dormers;

  • rooflights;

  • hip-to-gable alterations;

  • mansard slopes;

  • gable windows;

  • roof terraces where proposed;

  • elevations; and

  • sections.
     

These drawings help the homeowner understand the design before the project moves into the approvals stage.
 

The staircase should be resolved early.
 

It affects both the new loft layout and the existing floor below.
 

Where possible, the new staircase should usually rise above the existing stair. This often creates a more natural route through the house and avoids taking unnecessary space from an existing bedroom.

 

Planning Drawings


A planning application requires a clear set of drawings showing how the proposed loft conversion affects the appearance of the property.
 

The required package may include:
 

  • a site location plan;

  • existing floor plans;

  • proposed floor plans;

  • existing roof plans;

  • proposed roof plans;

  • existing elevations;

  • proposed elevations;

  • sections through the roof;

  • dormer details;

  • window positions;

  • external materials; and

  • contextual photographs where useful.
     

The planning authority will consider the proposal in relation to the house and the surrounding area.
 

The drawings should explain the design properly.
 

A planning application for a front dormer, mansard or roof terrace may need more contextual information than a modest rear dormer.
 

Where neighbouring roof extensions are relevant, photographs or additional drawings can help explain the established roofscape.

 

Drawings for a Lawful Development Certificate


A Lawful Development Certificate, often abbreviated to LDC, is different from a planning application.
 

It is commonly used where the proposed loft conversion is intended to fall within permitted-development rights.
 

The drawings still need to be accurate.
 

The application may include:
 

  • a site location plan;

  • existing plans;

  • proposed plans;

  • existing and proposed roof plans;

  • existing and proposed elevations;

  • sections;

  • window details;

  • external material notes; and

  • volume calculations where relevant.
     

The drawings should make it clear that the proposed work complies with the relevant permitted-development rules.
 

This may involve showing:
 

  • the relationship with the existing ridge;

  • the dormer setback;

  • the retained eaves;

  • the position of side-facing windows;

  • the external materials;

  • the size of the roof enlargement; and

  • any previous roof extensions.
     

An LDC relates to the specific design submitted.
 

If the loft conversion is changed materially during construction, the certificate may no longer confirm the lawfulness of the revised scheme.

TOP TIP

Do not treat the staircase as an afterthought. Resolve its position before the proposed layout is finalised. A poorly positioned stair can reduce the usefulness of an existing bedroom, create awkward circulation and compromise the loft floor before the technical design has even begun.

Building Regulations Drawings


Planning drawings are not construction drawings.
 

They may show the shape of the dormer, the position of the staircase and the new room layout, but they do not necessarily explain how the conversion should be built safely.
 

A habitable loft conversion will normally require a proper Building Regulations package.
 

The technical drawings may include:
 

  • floor construction;

  • steel-beam positions;

  • joist sizes and directions;

  • trimming around the staircase;

  • trimming around rooflights;

  • dormer construction;

  • roof buildup;

  • wall buildup;

  • insulation specifications;

  • ventilation;

  • fire-protection notes;

  • staircase details;

  • headroom;

  • smoke-alarm requirements;

  • drainage;

  • bathroom ventilation;

  • sound insulation;

  • window information;

  • structural references; and

  • notes for the Building Control body and contractor.
     

The drawings should be coordinated with the structural calculations.
 

This gives the builder a clearer basis for pricing and construction.

 

Structural Calculations and Structural Drawings


Most loft conversions require input from a structural engineer.
 

The engineer assesses how the new loads can be carried safely through the existing building.
 

The structural package may include:
 

  • beam calculations;

  • beam positions;

  • floor-joist design;

  • padstones;

  • posts;

  • connections;

  • dormer supports;

  • roof supports;

  • trimming details;

  • chimney-related details where relevant;

  • load paths; and

  • strengthening to the existing structure where required.
     

The engineer may also need to consider the existing walls and foundations.
 

This is particularly important where:
 

  • walls have previously been removed;

  • the ground floor is open plan;

  • large openings already exist;

  • chimney breasts have been altered;

  • the property has been extended;

  • the roof structure is unusual; or

  • the proposed loft conversion is substantial.
     

The structural calculations should not be treated as a separate document prepared in isolation.

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They need to be coordinated with the architectural and Building Regulations drawings.

IMPORTANT POINT

The original loft floor is often only a ceiling. Do not assume that the existing ceiling joists are suitable for bedrooms, bathrooms, furniture and people. A properly designed new structural floor will normally be required before the loft can become habitable space.

Why Planning Drawings Alone Are Not Enough for Builder Quotations


A builder may be able to provide an early budget estimate from planning drawings.
 

However, that estimate may contain assumptions.
 

The price can change once the technical details are developed.
 

For example, the contractor may not yet know:
 

  • the steel-beam sizes;

  • the floor-joist arrangement;

  • whether posts are required;

  • how the staircase is trimmed;

  • whether the existing walls need strengthening;

  • how the dormer should be insulated;

  • what fire-protection work is required;

  • whether existing doors need upgrading;

  • how the bathroom drainage will run;

  • whether the boiler or electrics need upgrading; or

  • whether additional work is required on the floors below.
     

For a more reliable comparison, contractors should ideally price from the same coordinated Building Regulations and structural package.
 

This reduces assumptions and makes it easier to compare like with like.

 

Drawings for Different Types of Loft Conversion


The level of detail depends partly on the conversion type.

 

Velux or Rooflight Loft Conversion


A rooflight conversion may involve fewer external alterations.
 

However, the drawings still need to address:
 

  • the new floor;

  • the staircase;

  • structural trimming around rooflights;

  • insulation;

  • ventilation;

  • fire safety; and

  • internal room layouts.

     

Rear Dormer Loft Conversion


A rear dormer package may need to show:
 

  • the dormer size;

  • external cladding;

  • roof buildup;

  • window positions;

  • eaves detail;

  • steelwork;

  • dormer supports;

  • insulation; and

  • fire-protection requirements.

     

Hip-to-Gable Loft Conversion


A hip-to-gable package should also explain:
 

  • the new gable wall;

  • the relationship with the existing roof;

  • structural supports;

  • the combined volume of any rear dormer;

  • external materials; and

  • side-facing windows where proposed.

     

Mansard Loft Conversion


A mansard package is likely to require more detailed drawings showing:
 

  • raised party walls;

  • parapets;

  • the steep rear roof slope;

  • dormer windows;

  • roof buildup;

  • structural supports;

  • neighbouring roofs;

  • external materials; and

  • the relationship with the original building.

     

Loft Conversion With a Roof Terrace


A roof-terrace scheme may also need:
 

  • terrace dimensions;

  • doors;

  • balustrades;

  • parapets;

  • privacy screening;

  • drainage;

  • structural loading;

  • waterproofing; and

  • contextual information showing nearby windows and gardens.

Drawings for Fire Safety


Fire safety is a major part of the technical design.
 

The drawings may need to show:
 

  • the protected staircase route;

  • fire-resistant doors;

  • fire-resistant walls and partitions;

  • smoke alarms;

  • protection to structural steelwork;

  • separation between floors;

  • the final exit;

  • open-plan ground-floor arrangements; and

  • any additional measures agreed with the Building Control body.
     

The required work may extend beyond the loft itself.
 

For example, an open-plan ground floor can complicate the escape route from the new loft floor.
 

This should be reviewed during the design stage rather than left until construction is nearly complete.

 

Bathroom and Drainage Drawings


Where the loft includes an en-suite bathroom, the design should consider:
 

  • the soil pipe;

  • drainage routes;

  • water supplies;

  • falls;

  • ventilation;

  • waterproofing;

  • electrical safety;

  • structural loading;

  • sound insulation; and

  • the position of sanitaryware.

The bathroom should ideally be positioned with the existing services in mind.
 

A bathroom located close to the existing drainage route may be more straightforward and economical than one positioned at the opposite side of the house.

 

Party Wall Drawings


Party Wall procedures may apply where a loft conversion involves work to shared walls.
 

This is particularly common on terraced and semi-detached houses.
 

The work may include:
 

  • inserting structural beams into a party wall;

  • raising a party wall;

  • altering a parapet;

  • rebuilding part of a shared wall;

  • working around chimney structures; or

  • carrying out other structural alterations.
     

The drawings and structural information help explain the proposed work clearly.
 

Where notices are required, they should be served before construction begins.
 

Party Wall matters are separate from planning permission and separate from Building Regulations approval.

 

Drawings During Construction


Changes sometimes arise once work starts.
 

For example:
 

  • the existing structure may differ from the assumptions;

  • a beam position may need adjustment;

  • drainage routes may need to move;

  • a staircase detail may need refinement;

  • a chimney may require additional work; or

  • the homeowner may request a design change.
     

Any significant change should be reviewed properly.
 

The designer, structural engineer and Building Control body may need to update or approve revised information.
 

The contractor should not make substantial changes casually on site.

 

Keep the Final Drawing Package


At the end of the project, retain the paperwork.
 

This may include:
 

  • survey drawings;

  • design drawings;

  • planning drawings;

  • planning approval or the Lawful Development Certificate;

  • Building Regulations drawings;

  • structural calculations;

  • revised drawings;

  • Building Control correspondence;

  • inspection records;

  • the completion certificate;

  • electrical certificates;

  • window certificates where relevant;

  • Party Wall documents; and

  • photographs of structural work before it was covered up.
     

These records may be valuable when the property is sold or refinanced.

 

A Sensible Drawing Sequence


The precise route depends on the property, but a practical sequence is usually:
 

  1. measure the existing house and roof;

  2. prepare the existing drawings;

  3. explore the layout and staircase position;

  4. agree the proposed design;

  5. prepare the planning or LDC drawing package;

  6. obtain the relevant planning confirmation;

  7. prepare the Building Regulations drawings;

  8. coordinate the structural calculations;

  9. review Party Wall requirements;

  10. issue a coordinated package for builder quotations;

  11. update the drawings where necessary during construction; and

  12. retain the final documents after completion.
     

This approach gives the homeowner, contractor and approval bodies a much clearer basis for progressing the project.

 

Tell Us About Your Loft Conversion


Every property is different.
 

The drawings you need will depend on the roof shape, the proposed loft type, the planning route, the staircase position and the technical work required.
 

Tell us a little about your home and the space you hope to create. You can also select the services you need help with, including design plans, a planning application or Lawful Development Certificate, Building Regulations drawings, structural calculations, a Registered Building Control Approver, Party Wall advice and loft-conversion contractors.

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