Thermal Bridging in Verandas: What It Is and How to Prevent It

Thermal bridging is a term that appears regularly in discussions about building energy performance, but it's less commonly raised in the context of veranda and glass room installations — even though it's directly relevant to anyone having a structure fixed to the outside of their house. Understanding what thermal bridging is, how it affects your home, and what can be done to prevent it is worthwhile knowledge before any structure goes onto your wall.

At Roma Verandas, we consider thermal performance as part of every wall-attached installation. This guide explains the issue clearly and without jargon.

What Thermal Bridging Actually Means

Heat moves from warm areas to cold areas. In winter, the inside of your house is warm and the outside is cold, and heat is always trying to find a path from inside to outside. Your walls, roof, and floors are all designed to slow this movement — that's what insulation does. But wherever there is a material with high thermal conductivity — a material that conducts heat easily — bridging from warm to cold across that material, that insulating effect is compromised. The conducting material becomes a thermal bridge.

Metals are excellent thermal conductors. Aluminium, which is what most veranda and glass room frames are made from, conducts heat approximately 1,000 times better than an insulated cavity wall. When an aluminium bracket or fixing passes through the wall, or when an aluminium frame is bolted flush against the external brickwork, that aluminium provides a direct, highly conductive path for heat to travel from inside the house to outside.

What This Means in Practice

The practical consequence of a thermal bridge at a wall fixing point is that the internal surface of the wall — or the internal face of the fixing itself — becomes cold. In winter, when that cold surface meets the relatively warm, humid air inside the room, condensation forms on it. Over time, persistent condensation on a cold internal surface leads to mould growth.

Homeowners who experience this often notice it first as a damp patch or discolouration on the internal wall adjacent to where the veranda is fixed. Sometimes it appears inside a room that has never had any damp issues before. It's not a roof leak, it's not a rising damp problem, and it's not a fault with the wall itself — it's a thermal bridge created by the fixing method used to attach the veranda.

The frustrating aspect of this is that it's entirely preventable. The solution exists, it costs very little relative to the overall installation, and it simply requires the installer to know about it and care enough to implement it.

The Solution: Thermal Break Materials

A thermal break is a layer of low-conductivity material placed between the aluminium frame or bracket and the wall. Its job is to interrupt the conductive path — the heat trying to travel from inside to outside through the metal fixing has to pass through this low-conductivity layer first, which significantly reduces the rate of transfer.

In practice, thermal break materials for veranda installations are typically rigid insulating pads or strips — made from materials such as polyamide, neoprene, or rigid foam — that sit between the wall plate or bracket and the brickwork. They are mechanically robust enough to carry the structural loads of the fixing while providing meaningful thermal resistance in the through-wall path.

For most veranda wall plate installations, the addition of a thermal break pad adds minimal cost and no significant complication to the installation process. It requires the installer to be aware of the issue and to specify the correct component — which is why it tends to be present in quality installations and absent in budget ones.

Wall Fixings That Pass Through Insulation

In properties with external wall insulation or cavity wall insulation, the situation is slightly more complex. If fixings pass through the insulation layer into the structural wall behind, they create a bridge that bypasses the insulation entirely at that point. The correct approach in these cases is to use fixings specifically designed for insulated wall applications, which minimise the conductive cross-section of the fixing itself, and to ensure that any penetrations through the insulation layer are correctly sealed and that the insulation is reinstated as fully as possible around the fixing.

Where a wall has cavity insulation — blown bead, mineral fibre, or foam — the cavity provides some inherent thermal resistance even where it's not a perfect break. But fixings that pass through both leaves of the cavity wall and the cavity itself should still be considered for their thermal bridging effect, particularly in high-performance installations.

The Relationship With Window and Door Frames

It's worth noting that thermal bridging at veranda fixings is conceptually similar to the cold bridging that occurs at window and door frames in older buildings. A single-glazed window in a timber or aluminium frame without a thermal break will show condensation on the frame in cold weather for the same reason — the frame is conducting cold from outside to the internal surface. Double glazing with thermally broken frames, which became standard in the UK over the past few decades, addresses exactly this issue.

The veranda industry is not yet as consistently rigorous about thermal breaks as the window industry has become — which is partly why it's worth raising as a specific question when you're discussing an installation with a company.

What to Ask Your Installer

Before any veranda or glass room is fixed to your house wall, it's worth asking specifically: how do you handle thermal bridging at the wall fixings, and what thermal break material do you use? If the installer has a clear, confident answer — describing the specific product and how it's installed — that's a good sign. If the question draws a blank or a dismissive response, that's a useful indicator of how carefully the thermal performance of the installation has been considered.

At Roma Verandas, we address thermal bridging as standard practice on wall-attached installations. If you'd like to understand how we'd approach the fixing detail for your specific project, we're happy to discuss it.