From the perspective of building regulations, replacing a conservatory roof is not a like-for-like change. The replacement of glass, plastic, or any other translucent material to a solid, tiled, or insulated roof is, in the eyes of the law, a change that requires some significant compliance. This is not a problem that can easily be remedied at the point of sale. Once your building becomes uninsurable, it can become problematic with your builder’s insurance, too; it can create serious issues.

When does building regulations apply?

There are conditions under which a conservatory can be exempt from building regulations. A conservatory can be exempt from building regulations if it is single-storey, separated from the main dwelling by quality external walls, doors, or windows, and has a clear or translucent roof. This is why it is vital to understand that the moment you change the roof to a solid structure, the conservatory exemptions fall away. From that point on, the structure ceases to be a conservatory; in the eyes of the law, it becomes an extension, and extensions are not exempt from building regulations, including part A on structural safety and part L on thermal performance.

Some contractors claim that the replacement of solid roofs is considered permitted development and therefore doesn’t need regulation approval. Permitted development and Building Regulations concerns are different. Even if a project is considered permitted development and does not require planning permission, Building Regulations may still apply. They are not the same, and one does not override the other.

What Part L requires for the new roof

Part L of the Building Regulations deals with energy efficiency. If a new solid conservatory roof is considered as an extension, then the thermal performance requirement will apply to the roof. According to Part L, the maximum U-value permitted for roofs in new extensions is 0.15 W/m²K, which is the same as a newly constructed house with pitched roof and good insulation. This is a very demanding target. Some conservatory companies offer an insulated ceiling panel system as a roof conversion, but that will still fall short of the requirement unless it is supplemented with more insulation.

The U-value requirement applies to the roof as a whole, including thermal bridging at the junctions between the new roof and the existing structure. Ask the contractor for the U-value that has been calculated for the specified roof build-up, rather than assuming that the insulation will do it.

The structural loading question most buyers miss

A tiled roof weighs significantly more than polycarbonate or glass. The existing conservatory frame — typically aluminium extrusions designed to support glazing — are not necessarily rated for those loads. A good contractor will perform a structural assessment before detailing the replacement roof. If no assessment is talked about, re-ask. Structural improvement is aesthetic without a roof frame rated to carry the loads.

The wall plate and existing dwarf walls will need to be assessed as well. Older conservatories were often built on inadequate, shallow, and light-glazed structures. This is particularly important for conservatories constructed before 2008, as Building Regulations concerning conservatory foundations were poorly defined.

What is included in a contractor’s specification?

Before signing a contract for a conservatory roof replacement, get in writing whether Building Regulation is needed, and if it is, who takes care of it; the U-value for the specified roof build up; the structural load assessment for the existing frame; the membrane or waterproofing specification for roof structure; and who the Building Regs approved inspector is for the final sign off.

Avoid contractors who can’t or did discourage you from getting Building Regs. It will not fall on the contractor’s shoulders for unresolved approvals; that is the homeowner’s responsibility, and when you sell, the liability for non-compliance sits with you.