Reflectix

What are trying to insulate , walls, ceiling , floors

all of the above. Its completely gutted to be renovated

Put your insulation in and then staple the Reflectix over everything. Forget about trying to achieve that required air space method. The Reflectix folks state to have the air space so that they can tout higher R-values. Unfortunately, that space needs to be perfectly sealed, an unattainable goal.

My original thoughts were to put the Reflectix up against the outer shell, then the fiberglass, then cover it all with 6 mil poly, THEN the paneling.

eddie-kimberly wrote:
My original thoughts were to put the Reflectix up against the outer shell, then the fiberglass, then cover it all with 6 mil poly, THEN the paneling.

Dunno, I've never seen that method. It may work great but it seems like you would have two vapor barriers and that may trap moisture in the cavities. Of course, that is my scientific estimation and that has been proven wrong on occasion. ;)

I would also want to put the reflex on the outside layer, where it can reflect the most heat, then if you have extra space, the fiberglass inside the wall. But if you don't have extra space, a second layer ofReflex will help. I think it is 4.7 R value without a air gap, and 6.0 with a air gap. But a double layer is not automatically 9.4, it is actually only about 7.0 Rvalue.

A double layer, with Reflectix on the outside, a 2" gap, and reflectix on the inside would give you about R-10. There is no need to have the 6 mil plastic, the Reflectix has all the qualities of the 6 mil plastic, and not allow wind or rain through it. Just tape it with aluminum tape and you will have a wind and water tight seal.

Reflectix tests wall panels in their lab, with a heat lamp, and measuring how quickly the heat goes through the walls in the lab. You can see some video's in their website.

Fred.

Just remember that not all heat transfer is influenced by radiant transfer. In a wall, there is also convection and conduction.

I don't think you ever want two layers of moisture barrier. It traps moisture between them. Your moisture barrier should always be on the warm side of your wall, i.e., the inside.

Would the gains with Reflectix over poly in a camper justify the extra cost?

Golden_HVAC wrote:
I would also want to put the reflex on the outside layer, where it can reflect the most heat, then if you have extra space, the fiberglass inside the wall. But if you don't have extra space, a second layer ofReflex will help. I think it is 4.7 R value without a air gap, and 6.0 with a air gap. But a double layer is not automatically 9.4, it is actually only about 7.0 Rvalue.

A double layer, with Reflectix on the outside, a 2" gap, and reflectix on the inside would give you about R-10. There is no need to have the 6 mil plastic, the Reflectix has all the qualities of the 6 mil plastic, and not allow wind or rain through it. Just tape it with aluminum tape and you will have a wind and water tight seal.

Reflectix tests wall panels in their lab, with a heat lamp, and measuring how quickly the heat goes through the walls in the lab. You can see some video's in their website.

Fred.

Learned a lesson some time ago. Reflective barriers have a DIFFERENT effective R-value when used in walls than when used in a ceiling. Essentially, the RADIANT heat gain/loss is inhibited in the direction of the barrier.

Much (most?) reflective heat loss/gain is vertical via the ceiling/roof. In such a case, reflectix can be quite effective, but in a wall may have little effect- unless you have a radiant heat source that is aimed at that wall.

This is the 'dirty little secret' of the radiant barrier reflective insulation market. Read a good explanation and testing when evaluating the blow-in foil pieces for the attic a few years back and lining the roof with reflectix style bubble wrap, etc.

It can be quite effective, but is not a substitute for real insulation when building.