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Conservatory Roof Replacement: The Options

Conservatory Roof Replacement
Thames Valley Window Company (Image credit: Thames Valley Window Company)

A conservatory roof replacement can transform an existing conservatory into a more comfortable space that will last for many years to come. 

The main benefits of a conservatory roof replacement are:

  • It will change the appearance giving it a new modern look that will complement your home
  • You can incorporate spotlights and rooflights for added light from above
  • A new conservatory roof is likely to make it more thermally efficient, not to mention warmer
  • If done properly, it will also add value to your home by providing more space and a habitable room.

When to Consider a Conservatory Roof Replacement

Many old conservatories have a lightweight plastic roof with no proper foundations. As a result, many have proved to be short-lived structures that:

  • Leak rainwater from poorly weathered joints
  • Crack from ground movement
  • Are perforated by hailstorms.

Conservatory Roof Replacement

(Image credit: Getty Images)

Those conservatories that do survive for any length of time are often abandoned for much of the year, as they are too hot in the summer months and too cold in winter. 

Not surprisingly, many owners are keen to replace or upgrade them. A recent trend is to replace the roof with a lightweight solid composite roof.

Something that is both adequately insulated and solid, rather than translucent or transparent, will block out the sun’s rays and keep the heat in. However, there are some issues to overcome on the way.

Replacing a Conservatory Roof with a Solid Roof

Replacing a conservatory roof structure with a solid roof is defined as material alteration work, which means that it is covered by Building Regulations

You will have to submit a building control application and a building inspector will check the work meets Building Regulation requirements. If it does, you would then be issued a completion certificate.

Some of the national conservatory roof conversion companies have partnered with building control bodies to ensure they have a nationally-approved design they can follow wherever they are working.

Conservatory Roof Replacement

Conservatories from Thames Valley Window Company start from £1,800 per square metre (Image credit: Thames Valley Window Company)

There are four main options:

1. Add stronger I-shaped profiles to strengthen the structure

The existing roof of polycarbonate or glass is usually only supported by the windows from thin glazing beads.

These are unlikely to be suitable to act as rafters supporting the new solid roof.

Replacing the beads with stronger I-shaped profiles that have a wide top flange capable of supporting the new roof is the first element of the project.

2. Consider using timber rafters for added support

You could install something more substantial, such as timber rafters, alongside the existing beads. Timber is strong, but there are a few things to consider:

  • As a live material, it is prone to twist and warp as it dries out and so it needs bracing and fixing in place
  • It also needs support at the end bearings. It can’t be screwed alongside the existing glazing beads for support
  • At the eaves, support might be absent if the walls are all windows and it could need an arrangement of lintels and posts

For many years, the designers of sunrooms and garden rooms, where traditional heavy tiled roofs sit over windowed walls, have been built this way. 

The beams over the windows bear on the corner posts that frame them and transfer the roof weight down to the walls or foundations beneath.

(MORE: Creating a Garden Room)

3. Add a lightweight solid roof

Some conservatory roof conversions use lightweight solid roofs of either moulded resin sheets with the appearance of tiles or composite lightweight slates. The insulation is usually provided by the PUR sheets (a Polyurethane rigid foam) creating a warm roof without a cold void that needs ventilating.

As lightweight as these individual elements are, the weight adds up and a ceiling finish will be needed. The weight is greater than a polycarbonate roof but perhaps equal to one double or triple glazed in toughened glass.

This means that the windows that supported the roof before are now being asked to carry a heavier load:

  • If they are PVCu windows, the frame’s profile will need to include steel reinforcing inside. Some discreet pilot-hole investigation or magnet testing may be necessary to confirm this
  • Without a steel core reinforcement, changing from a polycarbonate sheet roof to a solid one will require replacement windows or a new supporting framework.

4. Revamp or replace the structure

By itself, this project will not create a habitable extension that can be made open plan to the home; work to the roof alone is not enough. You may decide to revamp the structure or replace it entirely.

Conservatory Roof Replacement

(Image credit: Getty Images)

Will a Conservatory Roof Replacement Help with Heat Loss?

With most heat lost up through roofs, the alterations will help, but the roof is only one element of the conservatory. 

As the remaining structure will still be considered lightweight and possibly over-glazed with windows (more than 25% of floor area) the accepted approach is for them to remain thermally separated from the main house with insulated doors and windows.

Effectively you will end up with a completion certificate for a replacement conservatory roof. This is the same as if you had replaced the roof of an exempt front porch, for example.

(MORE: Oak Frame Conservatories)

Michael is HB&R’s Head of Content and Product Development. Michael is also, Chair of the National Custom and Self Build Association (NaCSBA), presenter of multiple property TV shows and author of Renovating for Profit (Ebury). Michael is a regular in the seminar theatres and Advice Centre at the Homebuilding & Renovating Show.