How does Bob get the mysterious 1/2" of air in walls?

[breeze]

Osmosis, foam, balsa wood, ...?

Unless something has structural integrity, I do not see how it will keep from being deformed with insulation, etc...

All I see is hundreds of references and not a single explanation or a pic.

 

[GeorgiePorgie]

I am totally incompetent when it comes to building things, but I have often wondered about this question too.

 

[waldenbound]

Well, I'll tell you what I did.
Get some pcv pipe, with a small diameter, but sort of thick walls.
Get a pvc cutter and cut 1/2 inch rings of the pvc pipe.
Get some 3M spray adhesive, and stick the pvc "ringlets" onto the van's walls. There's your air barrier.
Apply the Reflectix.

My pvc ringlets have been in place a year now. During summer, we managed to get over 90 and the van never got over 100 degrees in back. That's being closed up, with no windows or vents open.

 

[Almost There]

I used the thickest bubble wrap I could find. It was just shy of 1/2" thick but I also was able to add some space by attaching the reflectix to the ribs, not the walls themselves.

After cutting the reflectix panels to fit the area I was working on I laid the reflectix on a work table, outside side up, sprayed it with 3M 77 adhesive and applied the bubble wrap, then cut it to match. The combined panel was then applied to the van wall with metal tape, sealing it all the way around.

So far, it's been great.

 

[user 13531]

Why not use wood as a furring strip? You could also use Tyvek rigid foam board insulation, you can even wrap the foam board with Tyvek house wrap for a water tight insulation barrier.

 

[Potter15]

I used the thickest bubble wrap I could find. It was just shy of 1/2" thick but I also was able to add some space by attaching the reflectix to the ribs, not the walls themselves.

After cutting the reflectix panels to fit the area I was working on I laid the reflectix on a work table, outside side up, sprayed it with 3M 77 adhesive and applied the bubble wrap, then cut it to match. The combined panel was then applied to the van wall with metal tape, sealing it all the way around.
So far, it's been great.

Almost There, when you write reflectix panels, are you saying that your reflectix did not come in rolls but panels? Or are you saying that you glued reflectix onto panels and then attached the panels to the ribs. That's what I am planning to do. I just got a Chevy Express van and am starting to set it up for camping trips first (baby steps so to speak). Because I live in deep south Texas, half an hour to Mexico and 45 min from S. Padre Island and don't plan on traveling in winter, heat is what I am most concerned about. I have watched Bob's video on insulation and found out that he advises against insulating your vehicle when containing heat is the goal. So, I figured I would glue reflectix that comes in rolls onto plastic white paneling that I am going to paint beige (maybe ) and attach to the ribs of my van. There will be lots of space between the panels and the van's walls, I hope. Should I be concerned about the paneling touching the ribs? Any input would be highly appreciated.

 

[Almost There]

I cut the panels out of the rolls. It's available as a 48" wide and in either 50' or 100' foot rolls. Sometimes you  have to special order the large rolls.

48" wide is the perfect height for my GMC Savana to go from the top rib to the floor. I used aluminum tape to secure the panels to the ribs.

Actually, take a look through my build thread (in my signature line) and you can see exactly what and how I did it.

 

[user 423]

Any guesses how much R-factor is added by the 1/2" air space?

 

[Almost There]

Any guesses how much R-factor is added by the 1/2" air space?

There is no R factor involved in providing the dead air space.

Reflectix is a radiant heat barrier NOT a form of insulation. It's purpose is entirely different than insulation.

The dead air space is an absolute necessity if the reflectix is to do it's job of reflecting heat. If the reflectix is tight against the metal wall of the van it will simply allow the radiant heat to pass through it in to the interior of the van.

The dead air space allows the reflectix to do it's job properly.

 

[user 423]

There is no R factor involved in providing the dead air space.

Thermal windows use air space to increase R-value. I know they are sealed up and maybe there's a vacuum but if you use a vapor barrier on an RV, that seems like it would work in a similar way.

 

[Almost There]

Yes, thermal windows use a hermetically sealed space between the glass but it's not just air in there.

Here's a Q & A that helps explain how thermal windows work.

https://www.doityourself.com/stry/thermal-pane-window-frequently-asked-questions

It's not something that anyone doing a DIY of a van interior can accomplish. Hence there is virtually no R factor involved in the installation of reflectix.

 

[John61CT]

Any guesses how much R-factor is added by the 1/2" air space?

about R-1 but only if the seal is 100%

 

[tnvangirl]

Could you just attach the reflectix to the ribs without the bubble wrap? Or does the area between the van and the reflectix need to be sealed?

 

[John61CT]

Reflectix **is** bubble wrap, plus shiny.

You can buy the shiny (mylar sheeting) without the bubble wrap.

Or vice versa.

None of the above provides any actual insulation.

 

[Almost There]

Could you just attach the reflectix to the ribs without the bubble wrap? Or does the area between the van and the reflectix need to be sealed?

Adding the bubble wrap ensures that you are leaving the dead air gap there. Trying to get the reflectix (it's pretty bendy ) to actually stay at least a 1/2" from the wall of the van while you're trying to hold the panel in place and tape it with pieces of aluminum tape to the ribs while peeling the paper off the tape would be an exercise in futility for starters.

Then once the panel was in place you have no way of ensuring that it stays where you put it. If it's not creating a dead air space, it's not going to do it's job properly.

There are some places where it's okay to cut corners but putting the radiant heat barrier in place properly isn't one of them IMO.

When I put my panels in place I started with a couple of pre-cut strips of tape, picked open the corner so I could peel the tape off with one hand, put the panel in place, used the small strips to secure it to the ribs and then went back around the panel. Remember that the tape doesn't curve so every time you hit a bend anywhere you have to use shorter pieces of tape and overlap them.

And yes, the panel needs to be sealed all the way around with the tape. The bubbles themselves in the bubble wrap act as dead air space as well as acting like a spacer. They also give the reflectix some more rigidity which  helps when you're putting the panel in place.

 

[tnvangirl]

OK - Thanks for explaining!

 

[future_vandweller]

Any guesses how much R-factor is added by the 1/2" air space?

R value is defined as:

R = L/lambda
where L is the thickness of the insulation in metres (1/2" = 0.0125 m)
lambda is the thermal conductivity in Watts/m-K, which for air is 0.025 W/m-K.

So, for 1/2" of air, the R value is 0.0125/0.025 or 0.5.

 

[user 423]

^
Better than 0.0 then...LOL. I wonder if it would be more if the gap was between two foam boards? And the Reflectix glued to one or the other.

 

[John61CT]

The shiny only has a significant contribution facing out to prevent entry of sun's radiant energy.

With the air gap outside that, then the outermost skin, not behind insulation.

The effectiveness of the air gap depends on how complete the seal is, aka vapor barrier, usually plain 6mil plastic.

With the very limited wall thickness in a van, best is to just fill it all with foam, again as complete a sealing of the envelope as possible.

 

[Almost There]

.

With the very limited wall thickness in a van, best is to just fill it all with foam, again as complete a sealing of the envelope as possible.

That depends entirely on what the van owner hopes to achieve.

If you're filling it with foam, then no 'sealing of the envelope is needed' at all. As a matter of fact, you could be trapping moisture in there, particularly in the form of condensation. No great gaps are needed to eliminate the condensation but no great attempt at sealing the cavity should be put in place either.

I, for example, didn't want or need insulation as such. I travel with the seasons and utilize ventilation and a heater to finely tune the inside van temperature as needed. What I did need was a radiant heat barrier to assist with keeping the inside temperature from being too high when the van is parked in higher temperatures. So that's what I installed.

Each vandweller has specific needs in mind, one size does not fit all....please don't generalize like that. You give the impression that there is only one correct way to do something, which is not true at all.