Thermal bridging???

[Booyah45828]

My favorite is when they stack the wood in the space around the stove. As if that could never create a problem. It's a good spot to dry the wood out

and people wonder why insurance can be a hassle........

[turf]

hey -
i just am catching up here.....
but this is my opinion and experience on thermal bridging.

my bus has 2" spray foam and the original ceiling (FRP?)
by any standard, its a well insulated bus.

yes, thermal bridging occurs.

its kind of a neat.... see how hot that screw is?... trick of the bus.

in my opinion, it doesnt affect the heating or cooling of the bus much more than opening up a cooler inside the bus affects the inside temperature.

much ado about nothing. how much would i spend to fix..... your call.

[LargeMargeInBaja]

Originally Posted by dzl_

...skepticism is a reasonable baseline...

.
Going on my new business cards.

[Rucker]

Originally Posted by turf

hey -
i just am catching up here.....
but this is my opinion and experience on thermal bridging.

my bus has 2" spray foam and the original ceiling (FRP?)
by any standard, its a well insulated bus.

yes, thermal bridging occurs.

its kind of a neat.... see how hot that screw is?... trick of the bus.

in my opinion, it doesnt affect the heating or cooling of the bus much more than opening up a cooler inside the bus affects the inside temperature.

much ado about nothing. how much would i spend to fix..... your call.

In a well-insulated bus you're right, thermal bridging will not influence the air temperature much.

It will, however, contribute to condensation and mildew issues to the degree that the inside temp and the outside temp dance around the dew point.

Much like rust, condensation never sleeps.

[o1marc]

Originally Posted by Rucker

In a well-insulated bus you're right, thermal bridging will not influence the air temperature much.

It will, however, contribute to condensation and mildew issues to the degree that the inside temp and the outside temp dance around the dew point.

Much like rust, condensation never sleeps.

I always questioned the concern of, not room heat difference, but raining from the screw heads. Rust never stops, but condensation dries up.

[turf]

i've never had a condensation or mold issue.

on a summer day when i have the AC running, the metal strips that hold my frp ceiling in place are blazing hot. don't touch. (its amazingly hot)

on a winter day when im heating, the steel ribs are visible on the oustdie skin thru the snow or frost.

im not aware of having a condensation problem, not saying it doesnt happen, just not with my level of insulation/bus/situation. heating or ventilation inside has always dealt with excessive moisture, ime.

again, i see thermal bridging as a feature and not a problem.

[Rucker]

Originally Posted by turf

i've never had a condensation or mold issue.

on a summer day when i have the AC running, the metal strips that hold my frp ceiling in place are blazing hot. don't touch. (its amazingly hot)

on a winter day when im heating, the steel ribs are visible on the oustdie skin thru the snow or frost.

im not aware of having a condensation problem, not saying it doesnt happen, just not with my level of insulation/bus/situation. heating or ventilation inside has always dealt with excessive moisture, ime.

again, i see thermal bridging as a feature and not a problem.

Your experience is probably the norm for insulated buses with good heating and cooling systems that move air around. Also, condensation is not as much an issue in climates where it is either very warm, or very cold and the interior ambient air temperature and the exterior temps don't cross each other on the way up and down, or hover at dew point.

We've had some folks from PNW whose climate wreaks havoc with everything. They have had serious condensation issues because surfaces that separate the warm and cool air are more frequently at or near the dew point.

Another example of the relentlessness same kind of thing, just to a more extreme degree, are van lifer videos where they flip up their mattress and show the moldy underside. Warm and humid on top, cool on the bottom (because the bed is built on top of an unheated 'garage'), and over time that dampness becomes a perfect home for little spores.

I think when folks read these discussions they'll be able to judge whether it's something they need to take into consideration.

Thanks again for the dialogue.

[Booyah45828]

Originally Posted by Rucker

We've had some folks from PNW whose climate wreaks havoc with everything. They have had serious condensation issues because surfaces that separate the warm and cool air are more frequently at or near the dew point.

I think that's the big thing. Location, climate, and humidity

Condensation from thermal bridging won't be an issue with low or controlled humidity. Neither will mold or mildew. So if your location is high humidity, like the PNW, then you need to make accommodations to bring that humidity in check.

[turf]

there is no moisture between the bus skin and the sprayfoam, to my knowledge that is completely sealed off to air and moisture.

a lesser bonding insulator may cause issues with moisture.

here is a picture of my bus insulation. yes, those stainless steel bands that hold the roof up get hot.

moisture hasnt not been a problem for me. yes, the metal bands should condensate, but i've never noticed it. i think i heat enough that it pushes the condensate outside the bus and not inside. idk, just guessing

[Rucker]

Originally Posted by turf

there is no moisture between the bus skin and the sprayfoam, to my knowledge that is completely sealed off to air and moisture.

a lesser bonding insulator may cause issues with moisture.

Agreed. As has been said in this forum several times the goal is to keep the dew point somewhere within the insulation, or all the way on the outside of the bus.

I don't have the math skills (or maybe the computer skills) to calculate the flow of heat through surfaces but I betcha you can get condensation on the inside of foam under the right circumstances. Granted, probably not circumstances we experience on this planet, but yeah.

Point is that all we're doing is slowing the exchange of heat, and never stopping it completely; and a good understanding of how dew point changes with vapor pressure and temperature, and how different materials conduct heat differently, will help us design the best rig possible.

[WilboVIBC]

Originally Posted by gbww

So I get the basic idea if thermal bridging. With all the info I'm reading, I'm wondering if it makes sense to put a barrier between the furring strips and the metal?

I was thinking a Dynamat, Noico kind of layer.

Not sure if this is a bad idea or just ridiculous overkill?

Any thoughts?

Thanks
Dan
@rollingossuary

Reducing the thermal bridging isn't overkill. 5% of the area can account for 50% of your heat loss if it's a highly conductive bridge.

I used a detail that I was pretty keen on.

The main objective for me is to avoid metal to metal continuity to the interior, and use a highly insulative layer for the thermal break. Ended up with 1/2" of spray foam.

Woodblock attached to hat channel, furring strips attached to the blocks, and spray foam thermally breaking the hat channel from the interior.

Works great, just wish I had enough money to do it to the whole bus. We have an insulated sleeping compartment that we use for cold weather camping.

[dzl_]

^ This is a cool and fairly simple solution