· by Michael Blair, Nashville's Insulation
Radiant barriers reflect radiant heat rather than slowing conduction. That makes them a summer product, and Middle Tennessee has a long enough cooling season for that to matter.
What they do
A reflective foil facing an air space reflects radiant heat from a hot roof deck rather than letting it radiate down onto the insulation and the ceiling below.
They reduce attic temperature meaningfully on a hot day, which reduces the load on ducts and ceilings below.
What they do not
They contribute essentially nothing in winter, because the mechanism is radiant heat from a sun-heated roof. They are not a substitute for insulation.
They also stop working if they get dusty or if they are installed in contact with another surface rather than facing an air gap.
- Summer benefit only, no winter effect
- Must face an air space to work at all
- Not a substitute for insulation depth
- Most useful with ducts in the attic
- Dust reduces effectiveness over time
Where they help most
Houses with ductwork in the attic, which describes many Nashville homes. Reducing the attic temperature around ducts reduces the heat those ducts pick up.
Also houses that already have adequate insulation, where the barrier addresses a different mechanism rather than substituting for depth.
Sequence matters
Air seal and insulate to the right depth first. A radiant barrier over an under-insulated, unsealed attic is addressing the smallest of three problems.
Once the basics are done, it is a reasonable addition in this climate rather than a first move.