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Guide to Glass Roof Extensions: Advice and Inspiration

Glass roof extensions ensure your living space is awash with natural light. They now come with self-cleaning features. They provide excellent insulation. Imagine reading a book under the stars… the list goes on.

With the growing trend of glass roof extensions, our architects have compiled this handy guide. Topics covered include: planning permission, building regulations, costs, effective heating methods… and much more!

We trust you’ll find it beneficial.

Planning permission for glass roof extensions

Deciding whether to opt for Planning Permission or Permitted Development can be complex. Planners treat the structure (the walls) and the roof of glass extensions differently.

The extension structure

Specific types of glass roof extensions can be constructed without planning permission under Permitted Development.

Yet, several criteria must be met for your new glass roof extension:

  • Flats: Permitted Development is applicable only to houses. Flat residents need to seek planning permission.
  • Location: Extensions or other buildings can cover only up to half the area of land around the “original house.”
  • Height: Extensions must not surpass the tallest part of the existing roof or the current eaves in height.
  • Proximity to a boundary: Extensions within two metres of a boundary cannot exceed three metres at the eaves.
  • Siting: Extensions must not be constructed ahead of the ‘principal elevation’ (typically the front of the house) or the ‘side elevation’ (if the house is on a corner).
  • Conservation areas: External cladding is prohibited in conservation areas.
  • Depth: Single-storey rear extensions are restricted to four metres beyond the rear wall of the original house for detached homes and three metres for semi-detached or terraced homes.
  • Height: Single-storey rear extensions cannot exceed four metres in height.

If your glass roof extension doesn’t meet these requirements, planning permission will be necessary. However, this may allow your architect more creative freedom as planning policies tend to be more flexible than Permitted Development rules.

The glass roof

Permitted Development regulations for glass roof extensions are rather vague. The clause regarding allowable external materials states:

“The materials employed in any external work (excluding those used in conservatory construction) must closely resemble those of the existing dwellinghouse exterior.”

Typically, homes feature brick construction with slate or clay tile roofs. Therefore, any extension under Permitted Development should use similar materials.

However, the policy exception, ‘excluding materials for conservatories’, indicates that glass extensions are permissible, as they are common in conservatories.

Certificate of Lawful Development

We highly recommend obtaining a Certificate of Lawful Development from your local planning authority before proceeding with Permitted Development for glass roof extensions. They will issue a certificate confirming that your proposed extension is ‘lawful’ and would not require planning permission.

Building Regulations and Glass Roof Extensions

Great news! If you’ve reached this point, your glass roof extension has been approved!

Yet, some steps remain before construction can begin.

Firstly, your architect’s comprehensive plans must receive approval from Building Control. Energy efficiency standards pose a challenge with large glass areas in your extension, potentially conflicting with building regulations.

Building Regulations Part L

This regulation restricts the proportion of openings or glazed elements in glass roof extensions, including:

  • Windows
  • Roof lights
  • Doors

These elements must not exceed 25 percent of the extension’s floor area. For a modest extension featuring patio doors and a lantern light, this limit can quickly be reached.

Tips for Approving Glass Roofs with Building Control

Increase Thermal Resistance

Enhancing the thermal resistance of other elements like floors, walls, or the roof is one option. If insufficient, upgrading to high-performance glass with superior thermal efficiency might be necessary.

Standard Assessment Procedure (SAP)

Another method involves a Standard Assessment Procedure (SAP) calculation to prove that the CO2 emissions from the extension will not exceed those from a conventional extension of the same size. Solutions might include better loft insulation or more efficient heating systems.

Separate Your Extension

Conservatories can be exempt from Building Regulations if they’re separated from the main house by external-quality doors/windows and have their own heating controls. This option is less feasible for those desiring an open plan.

Pros and Cons of Glass Roofs

Pros of Glass Roof Extensions

  • Stunning appearance
  • Abundant natural light
  • Enhanced sense of space
  • Reduced need for artificial lighting

Cons of Glass Roof Extensions

  • Potential for excessive brightness
  • Can become hot in summer
  • More expensive than traditional roofing methods

Ensuring Privacy with a Glass Roof

The visibility through a glass roof might raise privacy concerns. Various solutions can mitigate this:

  • Electric blinds
  • External louvres
  • Strategic planting

Keeping Glass Roof Extensions Warm

Glass roofed rooms can feel cold in winter. However, numerous heating solutions exist:

Underfloor Heating

Choosing a water-based system over electric is advisable due to lower operational costs and is a must for new extensions.

Perimeter & Trench Heating

Trench heating, integrated into the floor’s perimeter, removes the need for radiators and heats the space via natural convection, visible only by its grille.

Low U-Value

Aiming for the lowest possible U-Value in glass helps retain heat, minimizing heat loss and energy costs. Selecting glass with a low U-Value is crucial for efficiency and cost-saving.

What is the cost of a glass roof?

The typical price for a fully glass roof spans from £1,800 to £2,200 per m2.

Methods to reduce expenses:

  • Plan meticulously: Your glass roof will likely be custom-made. This type of glass is costly and challenging to manipulate. Without thorough planning, any required modifications after installation can become prohibitively expensive.
  • Frame vs. Frameless: Opting for a framed design will generally be cheaper than a frameless option. Frameless designs demand custom specifications and are more intricate to handle, thus increasing the cost.
  • Seek multiple estimates: Based on our experience, the cost estimates for glass roof extensions can differ significantly. With this in mind, ensure you collect various quotes from different producers. Also, verify that you request identical specifications from each to enable accurate comparisons.

Conclusion

Our architects excel in creating innovative and singular extensions. That’s why we believe glass roof extensions are an excellent choice for those wishing to distinguish their homes.

We possess extensive experience in designing glass roof extensions. If you need advice or want to discuss ideas, why not schedule a free 30-minute call with one of our architects?