Adding R'BULL to conventional insulation

Complement does not mean replacement

Thin reflective insulation does not take the place of mineral wool laid in a loft. The two act on different mechanisms, and adding them together makes sense only if each works where it is effective, with the air gap the second one requires.

Where the complement makes sense

On a ceiling already insulated but whose surface stays cold, or above a new stretch ceiling, where adding thickness is impossible. The reflector then deals with the radiant share that the wool does not.

Where it does not

Pressed against wool, with no void in front of it, it reflects nothing useful. That is the most frequent mistake and it cancels the entire expected benefit, while giving the impression the situation has been improved.

The single rule to remember

A reflector needs a void in front of its bright face, and that void must be closed around its edges to stay still. That rule holds whatever the nature of the insulation already in place.

What the complement brings beyond heat

Continuity. Wool laid between joists has joints through which air moves. A continuous membrane fitted below closes those passages, and that gain in airtightness often weighs more than the thermal gain itself.

How to check it at home

By touching the finished ceiling on a cold day. If the surface is clearly cooler than the walls, the radiant share is not being dealt with, and that is precisely the situation where the complement is justified.

The comparison is developed on the thick and thin insulation page, and the fitting on the execution page.