Creating a Thermal Break and Preventing Water Condensation?

[millerhd]

So I'm looking to insulate my 7x14 interstate and want to make sure I do it right the first time. After looking at and reading many of the builds on this forum I am aware that the steel studs in my walls can create huge thermal bridges that need to be prevented, but I'm a little unsure of how exactly to create a thermal break for them.

My general plan is to use 1" foam insulation in the walls, floor, and ceiling. Then I will add 1/2" foam on top of that to mitigate the thermal bridging. My concern is how to securely anchor the wood panelling back onto the studs. Adding wood stripping onto the steel frame would just continue my thermal bridge so I know that is out. Can I just send a long screw through the 1/2" foam? Somehow that doesn't seem right to me. Any help?

I am also aware that I want to prevent water condensation from soaking the foam insulation, but don't really understand how one goes about that. I have seen people using a kind of special sealing tape to prevent this from happening, but don't understand what I'm sealing from what. Any help in this regard is greatly appreciated.

If there are any other concerns that I'm not even aware of in regard to insulation I would certainly welcome any advice.

If it helps at all I am looking to be potentially living in my trailer fairly full time anywhere from western Washington to Montana and Idaho.

[CoventryKid]

I'm not sure I understand your statement: "Adding wood stripping onto the steel frame would just continue my thermal bridge so I know that is out...".

When I insulated my trailer, I added 1" rigid insulation between the ribs. I then screwed a 3" strip of 5/8" plywood over each rib, sides and roof. I then added 1/2" rigid insulation between the strips and sealed all seams with aluminum tape (the kind used for sealing A/C ducting), NOT duct tape.

When I re-attached the plywood walls, I screwed to the wood strips. The strips are my thermal break or in other words, no visible screw on the inside was "attached" to metal ribs.

The other important thing is ventilation. I installed a MaxxAir ceiling fan in the ceiling. When we are towing the trailer, we leave the fan cover open slightly to allow for air movement. When we are in the trailer, especially sleeping, we have the fan running at the 20% setting on the remote. I like the MaxAiir because it has a built-in rain cover, unlike other fans, so we don't have to worry if it rains. Not running the fan at night results in foggy windows in the morning.

We toured BC, Yukon, WA, OR, and northern CA for 6 months last summer/fall with no problems with condensation inside our trailer.

Hope this helps!

[millerhd]

Thank you for the reply. I was trying to describe exactly what you did with adding the plywood to the metal studs. So the wood still works as a thermal break? I guess I figured if wood studs in a wall created a thermal bridge then adding wood to a metal stud would just continue the bridge, but if not then the whole process gets much easier.

Just to make sure I'm not confused, I'm putting the aluminum tape directly on the insulation panel seams, I.E. the seam where the insulation meats the wood stipping, floor, and ceiling?

I have plenty of ventilation with two fantastic fans with rain covers. It gets way too stuffy without them.

Thanks for the help. I'm excited to start the project soon.

[lrrowe]

In my similar application, I used house wrap tape. A lot of it.

[CoventryKid]

In a house wall, there is enough mass in a 2x4 or 2x6 that heat/cold can be transmitted through the wood to the interior, so a thermal break is created by staggering the 2x4s:



But cargo trailers are different.

The screws holding the interior plywood walls in place should not come in contact with the metal frame of the trailer. That's why I installed the plywood strips on all the ribs. The interior plywood walls are screwed to the plywood strips, so there is a "thermal break" i.e. the screw holding the interior wall in place does not touch the rib. If you look closely, you can see the screws holding the plywood are screwed into the plywood.

You can see in this picture how I've taped the seams between the plywood strips and 1/2" rigid insulation. As Bob indicated he used "house wrap tape". That's the red stuff. I used a lot of tape too!



Of course OTTCT will say if you'd bought a CarMate (with wood stud walls) you wouldn't have this problem

Good luck with your project and don't forget - lots of pictures!

Hope this helps.

[hankaye]

CoventryKid, Howdy;

Thanks for the further explanation and the photo.
Question, did you use a wood putty to fill the old screw holes in the walls when you re-positioned
the mounting screws so they would hit just the 5/8X3 strips and not the ribs?

thanks for your insights.

hank

[MtnDon]

There is also the approach I took where all the interior finish plywood (5mm) was glued directly to the foam that was glued into the wall and over the metal wall ribs. Several thousand miles, some on rough roads, and the walls are still in place.

[CoventryKid]

Hi Hank:

The original idea was to wallpaper some of the interior walls with heavy, paintable wallpaper from Home Depot. Following the instructions, I primed the walls with oil-based primer for better adhesion. Long story short, when I rolled on the paint, the wallpaper rolled right off the wall and onto the roller!

So plan B: I trowelled on a skim coat of drywall mud to cover the screw holes as well as the imperfections of the plywood. I even taped the corners knowing that this would not last (and it didn't) - after 4 months of bouncing along, the taped corners were looking a little sad. When we returned home for a short stint, I cut some 1/4" plywood strips (about 1.25" wide) and tacked two of them in each corner. Painted to match the walls, you don't really even notice them as in this picture under the laptop:



Hope this helps.

[hankaye]

CoventryKid, Howdy;

Thanks for the information, very interesting.

hank

[hankaye]

MtnDon, Howdy;

Good to see you again, so-to-speak, I was thinking of some paneling ... maybe, not sure about that at this time,
just tossing it around.
Being as these things are meant to roam, figure I can stay away from the coldest and the hottest by bouncing
between the Borders, or moving West one State and going Up in the Summer and Down in the Winter kinda like
Traunman45 does. After divesting myself of about 1/2 a ton of useless stuff in the Summer of '14 I don't really
have that much left to anchor my furry butt in one spot anymore. Would just have to sell the 5th wheel and POOF!
On the road ...

hank

[OverTheTopCargoTrailer]

Hi Doug

Do you have any actual heating data for your trailer ? I would be very interested to make an actual comparison.......everyone here swears how great their 1/2" of foam works BUT NO ONE....is willing to give any actual numbers to their claim ??


A few nights now I spent at about 19-20F and heated the interior to 75 deg.

Recall I pick up 25 deg over exterior with my body heat and equipment.

So I need an extra 30 deg for heating to 75 and per my formula that's 40 btu " for every one deg F" x 30 deg per hour , or 1,200 btu per hour or about 400 watts.

(( -if it was zero F then I would use 2,000 btu or 600 watts per hour ))

This was the exact result of my real life experience as I used 400 watts per hour to heat my trailer.

Cheers ottct

[CoventryKid]

Hi ottct:
I'd love to share data with you but I don't have any.

Our all-electric trailer means we have to plug in to have any creature comforts. We have a small portable electric heater (900w/1500w) with a fan that we use on cold(er) mornings, just to take the chill out of the air, but that's it.

The majority of our camping so far has been up to northern BC and the Yukon last summer and WA, OR, and northern CA this past fall. So not really climates where a real heater was required.

We are really fair weather campers with the ability, as long as we are plugged in, to cope with cooler temps in a pinch.

[OverTheTopCargoTrailer]

Hi Doug

You do have the data, you just don't know how to analyze it properly.

Let's say it's 50 F outside at night & you never touch your heater. You just use your tv, lights , radio, fridge etc .....you and the wife sleep inside, you have no fans sucking out the warm air - then what is your morning temp ? Mine would would be around 75 deg.

Now if it's 50 outside & 50 F inside, then your insulation is not doing SQUAT ....

Once we have that number , then you can put your elec heater on a small outlet watt meter like I did & see how many watts you used during the night ÷ that by the hours heated and now I can give you a formula of energy use for your trailer.

Cheers ottct


Scroll down the page a little until you see "kill a watt meter"
http://www.treehugger.com/clean-technology/the-power-monitor-top-tools-for-watching-your-home-energy-use.html

[Camp Wags]

..everyone here swears how great their 1/2" of foam works BUT NO ONE....is willing to give any actual numbers to their claim ??

From what I gather he has 1.5" of insulation and did I read some where that you have 3"? I went to your blog but it is difficult to go through it all.

Do you have a photo of your wall insulation and how you did it? I remember seeing other photos before but I can't find them now.

I ask because that is were I am at now, the insulating stage and having the stealth black clocking coating, I need to do it right the first time.

Thanks,

G

[OverTheTopCargoTrailer]

Hi Camp Wags

yes this is the mystical answer I have been waiting for......
Everybody is keeping me in the dark .....and feeding me Sh**t....like a mushroom

Everybody does 1/2" foam to 1" foam and then installs at 12,000 BTU - HEATER and raves about how their world class insulation KICKS BUTT !!!
They all got the worlds best insulation.....some even skip the floor & doors AMAZING !!
One guy promised me the info ....but than back peddled saying he didn't realize we had a "tit for tat" contract

well with a 12,000 - 18,000 Btu gas heater I can keep warm with ZERO insulation at minus -80

I have 3" blue DOW Foam in the walls, 2.5" foam on the interior floor, about 6" Denim in the ceiling , 2" foam on the doors.....
I can only tell you that I pick up 25 deg F over the exterior temp and MOST TRAILERS & RV's ....track the exterior temp EXACTLY...degree for degree....40 outside = 40 inside (( ie..., worthless insulation))

Since no one is willing to tell me how much it takes to heat or cool their trailer.....
my logical theory is that 1" is crap - WORTHLESS !!

I can also tell you my other GA trailer with a metal stud frame and 1" insulation , picks up condensation like Niagara Falls....

NOW I get sick from gas heat , and only have solar - so how much energy I use is a big deal......
If your in an RV park paying $35 a night and got 30 amps - then who cares ??
in my case every watt counts.....

I can cool in 100 F full sun using less then 250 watts - vs 1,500 watts for standard RV solar.....
if you hang out in 50 to 75 F - then skip the insulation.
if you hang out in -40 to 115 F , them more is better