A thermal bridge is a location where heat flows out more readily than through neighbouring parts of a construction. The internal surface can consequently be colder in that area.
What does this mean on your roof?
On roofs this can occur around edges, structural components or junctions where insulation is interrupted. It is not the same as an open joint allowing rainwater through.
Moisture at such a location may involve condensation, but the visible mark alone does not establish that explanation or rule out other causes.
An insulation proposal should therefore cover more than thickness at the centre of the roof. Ask how transitions to walls, roof windows and upstands are addressed. A high material rating does not remove the effect of interruptions automatically. Where a junction cannot be improved, record what remains and how that limits the performance of the complete assembly.
Frequently asked questions
Is a thermal bridge always visible?
No. Construction details and conditions may require further investigation.
Does thicker insulation solve every thermal bridge?
Not automatically. Junction design and continuity of the insulation layer also matter.
Consulted 19 September 2026. Check requirements for your own address and selected system.