Ceiling Insulation

[Twigg]

Originally Posted by Rusty

I consider butted and taped to not be unbroken. The issue is the ribs- are you spanning that gap, leaving a void? You are correct in not wanting to loose any headroom unnecessarily.

Ok, I went-out and took a picture of my ceiling. Even if you cut the foam neatly and kerf-cut the back, you will never match the efficiency of a liquid in hugging a contour.

Attachment 16658

Agreed.

Cut the insulation boards on an angle at the edges and they will form an unbroken seal. It would require careful cutting, but I can do that.

The problem with the sprayed in remains ... how to deal with the ribs which form a perfect thermal bridge.

There probably isn't a perfect solution. I can see the advantages of sprayfoam, but it's not a complete fix unless we can find a way to stop those ribs transmitting heat and cold. Plywood has an R-Value of about 1 per inch.

I just read one account of serious condensation issues in a decently insulated bus. In that case five people were breathing in it and propane was being used for heat.

I'm leaning towards minimizing the moisture in the air probably with diesel, blown-air heating (a woodstove would be good for longer stays). Good ventilation even though that does increase the heating costs, and trying to prevent as many cold surfaces as possible.

I'll keep thinking about it

[joeblack5]

Nice post of the van dweller. of course that inner is structural.... but his reasoning is great, follow the money.. why would you put up something with so much effort if it is only cosmetic.
Earlier someone suggested cutting 10" holes at strategic location and pull the old insulation out. Filling the space is where foam is at its best. The structural gain is enormous. Some car A frame pillars are filled with high density foam just for the collision strength.

Contractors are not interested in experimenting and in general will give you poor result. Better get a small kit and do one area your self and see how it goes. Drill small vent holes so that air and foam can escape.

regarding the thermal bridging ,.. now the metal has stayed in place it is very easy to clad the interior with 1/2 or 3/4 foam sheets and butt and tape them. If you take 1" or thicker there even might be tongue and groove insulation sheet out there.

For some people structural strength is important , for others it is not. but it is for sure that they put it in for a reason.


later J

[Tedd]

Originally Posted by Rusty

So many engineers in one place.

True that. And every one of them is passionate about his pet theory concerning insulation.

It would be helpful to find a book by someone with creds in the field ... like Mike Sokol and RV Electrical Safety. But then I've seen threads on this forum where some home-grown experts argued ad nauseum with him about hooking up grounds properly. Hey ... it's the internet.

[dan-fox]

Keep in mind that these are aged buses we are talking about here. "Good enough" will be good enough. I don't have a bus yet, so take what I say with that large grain of salt, but I can't get too bent out of shape at the magnitude of thermal losses of ribs covered in plywood when the rest of the interior surface foamed up level to said plywood strips. Compared to what you had the day you drove it home, it's great!

This ain't the space shuttle, folks. Stop the enormous amount of outside air infiltration and you're 3/4 of the way there. Sure, you could cover your ribs with fiberfrax, but is it worth it for the difference between reducing heat transfer from 5% of what it used to be down to 4% of what it used to be? Besides, neither fiberfrax nor artisanally hand-carved insulation will take screws all that well. And plywood's cheap-to-free.

[Twigg]

Originally Posted by dan-fox

Keep in mind that these are aged buses we are talking about here. "Good enough" will be good enough. I don't have a bus yet, so take what I say with that large grain of salt, but I can't get too bent out of shape at the magnitude of thermal losses of ribs covered in plywood when the rest of the interior surface foamed up level to said plywood strips. Compared to what you had the day you drove it home, it's great!

This ain't the space shuttle, folks. Stop the enormous amount of outside air infiltration and you're 3/4 of the way there. Sure, you could cover your ribs with fiberfrax, but is it worth it for the difference between reducing heat transfer from 5% of what it used to be down to 4% of what it used to be? Besides, neither fiberfrax nor artisanally hand-carved insulation will take screws all that well. And plywood's cheap-to-free.

You make good points.

However, you didn't live in that bus all those years ago.

There are many descriptions, on this site and elsewhere, about condensation issues on converted buses. Moisture will condense on any surface that is colder than the surroundings, hence the desire to eliminate as many thermal bridges as possible.

We can very easily insulate ceilings and walls to R-10, but if you then leave all the ribs with an R-value of 1 or less, you created a condensation issue. This is not about heating and cooling comfort.

This thread has simply been exploring ideas for reducing the moisture in the air, then giving it as few surfaces to condense on as possible.

[dan-fox]

Originally Posted by Twigg

You make good points.

However, you didn't live in that bus all those years ago.

There are many descriptions, on this site and elsewhere, about condensation issues on converted buses. Moisture will condense on any surface that is colder than the surroundings, hence the desire to eliminate as many thermal bridges as possible.

We can very easily insulate ceilings and walls to R-10, but if you then leave all the ribs with an R-value of 1 or less, you created a condensation issue. This is not about heating and cooling comfort.

This thread has simply been exploring ideas for reducing the moisture in the air, then giving it as few surfaces to condense on as possible.

I see. I either hadn't grasped the original intent of the thread, or lost it in the haze and smoke of argument.

Determining whether or not condensing conditions exist at the surface of your ceiling would be empirical in the extreme. So, one question I would ask would be, Is there evidence of anyone who has spray-foamed their bus and finished it out, who is experiencing stripes of condensation on the ceiling? Or the lower walls for that matter? It's intuitively obvious to me that if you've insulated well, stopped unintentional airflows in and out, and heated the bus to where it's comfortable, that you wouldn't have condensation problems barring active showers, hardboiling some eggs, etc.

But you know what happens when you assume, and an ounce of experience is worth a pound of theory, etc. etc.

[Twigg]

Originally Posted by dan-fox

I see. I either hadn't grasped the original intent of the thread, or lost it in the haze and smoke of argument.

Determining whether or not condensing conditions exist at the surface of your ceiling would be empirical in the extreme. So, one question I would ask would be, Is there evidence of anyone who has spray-foamed their bus and finished it out, who is experiencing stripes of condensation on the ceiling? Or the lower walls for that matter? It's intuitively obvious to me that if you've insulated well, stopped unintentional airflows in and out, and heated the bus to where it's comfortable, that you wouldn't have condensation problems barring active showers, hardboiling some eggs, etc.

But you know what happens when you assume, and an ounce of experience is worth a pound of theory, etc. etc.

You can't really eliminate condensation, but you can minimize it. Some of the solutions are counter-intuitive.

Spray foam is an excellent sealer and insulator, but it doesn't solve the problem of the ribs (kinda where this thread began). If the ribs are furred over, or worse, the ceiling screwed straight into them, you bridge the insulation and there will be issues.

Ventilation, and lots of it, will help remove the moist air, but it will also remove the cold or hot air too so it's a balance.

Not creating the moisture will help most. Dry air heating from either diesel or propane ... or woodstove. No exposed propane heaters, cooking outside as much as possible ... etc.

Even some expensive RVs I've slept in have suffered condensation in the bedroom when humidity is high ... all I am seeking to do is reduce the issue, it won't be eliminated.

[dan-fox]

So if I understand you correctly, as long as I don't take a shower, cook, sleep or breathe inside the enclosed space I'll be fine?

So you appear to have "been there, seen that". At least, with s&s RVs. Is this problem exclusive or predominant to either summer, when the interior is being mechanically cooled, or winter, when it's being heated and sealed? I'd think that a heat-scavenging air exchange would be of assistance either way, but more in winter. At a cost in fuel, complexity, and first installed cost.

My fantasy bus will have a Webasto-style furnace in it, and will retain the original radiators or replace them with equivalent functionality. I've been around here long enough to be schooled on the evils of open-flame propane heat wrt water vapor loading. I never did like the the idea of open flame ANYTHING inside a space you're trying NOT to ventilate, anyways.

[Twigg]

Originally Posted by dan-fox

So if I understand you correctly, as long as I don't take a shower, cook, sleep or breathe inside the enclosed space I'll be fine?

Now you understand ... although it's not that simple either.

My garage "sweats" anytime it is colder in there than it is outside ... mostly a summer problem when humidity is close to the dew point. Everything in it gets wet. Here in Oklahoma that's a limited problem, in Nevada, Utah, Arizona, etc, it's almost unheard of as the dry air sucks the moisture out of everything.

When any air gets close to the saturation point for it's temperature, it will condense out on a cooler surface, and it doesn't depend on the time of year. Very warm air can hold a lot of water vapor, and in summer it tends to be warm outside and in, so the problem is diminished. In winter it can be an all-day problem if the interior is warm and the exterior cold.

[Rusty]

I'm going to use Aspen Aerogel to insulate my bus for maximum coefficient of thermodynamicity.

[HazMatt]

Originally Posted by Twigg

Good post Pygmi Yeti.

The problem with "chasing the good weather", is that it will always be either too hot, or too cold for life in a tin can ... except maybe in New Hampshire on June 17th.

So one way or another we do need to insulate ceiling, walls, and floor.

Your point about the structural strength of the shell is well taken, and I doubt many would disagree. The counter-point is simply that even the compromised shell is still vastly superior to an RV, and a school bus has other designed in features that add to the safety aspects, most notably the raised floor. When I drive up behind a school bus in the Taurus, my head is about level with the feet of the kids sitting in the back. If I hit the bus, I am going under it.

Nonetheless, retaining as much strength as possible plays to the reasons we buy the things in the first place, and in a rollover I'd like as much strength in the roof as possible.

So how do we insulate effectively and retain the strength? Both being desirable.

The standard way is to remove the ceiling, spray foam or add rigid panels then fur over the braces before adding a wooden ceiling. The furring provides a thermal break, although not nearly the same R-value as we have in the voids.

One way would be to leave the ceiling in place and use construction adhesive to bond rigid insulation to it, then more adhesive to skin a new ceiling from plywood, or the lumber of your choice. It would cost some ceiling height, but offer a fully insulated roof with zero thermal conduction paths. Add a fresh layer of bus kote and that roof should suffer little in the way of condensation as well as keeping much of the heat outside. With a 78" headroom bus, that would probably be a reasonable solution without a roof-raise.

A ceiling done this way would still provide sufficient support for dividing walls if they were adequately tied to the floor and walls ... and still much better than a Class A motorhome.

The other option would be to add the insulation above the roof, but right now I can't think of how to make that practical.

The current approach to the walls seems to work quite well, especially if attention is paid to how the ribs are furred out.

A fully floating floor, maybe with a little adhesive to prevent is moving up and down, takes care of the floor ...

I dunno ... food for thought.

As a long time resident of the Granite State, I can corroborate Twigg's observation.

As my Gramps, an old VT rock-farmer, told me; "If yew don't like the weather, wait five minutes, she'll change..."

Ayuh.

Taking it for granite that either I'm the only one seeing the obvious mitigation solution to trans-rib thermal migration, or I'm missing something key to unlock this puzzle...

Does anyone have an idea if there'd be any reason NOT to drill a hole large enough to accommodate the spray-foam nozzle high up into the rib's side?

It should be simple enough to calculate the void space inside the rib in order to guesstimate the approximate amount of foam to shoot, after taping over the ceiling's sheet metal screw holes.

Expanding foam will possibly require dusting off some calculus skills, but it's not an insurmountable problem.

With expanding foam, I'd do it in stages: attempt filling from the sub-frame up the walls, coming back after it's achieved maximum expansion, to then top it off to the top.

Thereby avoiding not only excessive waste, but also the amusing mess of an overly long turd being extruded thru the injection port. (Would that be a sh*t stalactite..?)

Condensate forms from the atmosphere, so I'm hypothesizing that; by displacing & forcing the air from the rib's interior, not only will the condensate condition by greatly ameliorated, the thermal draw bridge will be permanently closed to traffic.

Or, if I dare misquote some classic cinema history:

"Bridges..?
"Bridges?!!
"We don't need no steenkin' bridges!"

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[OldWardBus]

You took the words from my mouth! Why not just fill the ribs? I suppose that condensation would form on the face of the ribs either way though... I notice that no one has said much in the way of where does the ever persistent condensation go in a spray foamed situation like ours? If the ribs and other metallic bits sweat, are we depending on normal airflow to keep it from collecting? Part of me thinks it will just stay there and rust. I am from Michigan, and I have fond memories of both driver fans on high aimed at the windshield, with defrosters blasting and windows cracked and there still only being a port-sized window in the condensation for the driver to see through.
Would leaving voids in the ceiling and walls actually be the way to go? I plan(ned) to stud my walls and run conduit and pipes and foam it all in, same with the ceiling. However, all this vapor-talk has me completely doubting the "too good to be true" spray foam/ injected foam approach we all seem to be thinking of taking. What if we did water this down? Instead of filling everything in with shaving cream-esque space-foam, we just isolated the outer barrier from the inner, and let that outer area breathe and stay dry with a sort of intermediate insulating air gap between the cabin and outside of the bus?
I am paying close attention to this, because although I currently reside and am building my bus in Louisiana, I want to fulltime back home in Michigan when that time comes. That means weeks of negative temperatures, brisk wind beating the sides of my bus, cozy nights accompanied by the wood burner, and tons of moisture in the air whenever myself or my woman (whom is no stranger to seeking refuge in the shower) bathe and cook. Year after year. And I have no doubt we can do it, but I'm concerned we are overcomplicating this a little bit!
Anyone here doing this anywhere frosty? Has anyone taken a truly serious approach to insulating their rig, for winter operation, while isolating the inside skin from the outside skin? How did it turn out?

[HazMatt]

OWB,
My thoughts are if we isolate the metal from air exchange, we've eliminated the condensation situation.
If the rib sides are similarly treated, then moisture incursion should be reduced to a statistically insignificant level.
Even if, due to flexing &/or age, some separation from the metal occurs, the quantity of moist air should be marginal.
Running the procedure on a low humidity day might be wise, to avoid trapping some di-hydrous oxide around the foam. Pre-heating lightly before injection could possibly serve to drive out residual moisture.
Chances are fair to middling that the displacement of air in the void should suffice to drive any atmospheric moisture away, tho...

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[Twigg]

Filling the ribs doesn't fix the problem. The thermal energy travels, both ways, through the steel not the airspace inside the rib. The ribs are welded to the roof, and screwed to the ceiling so filling them would have little impact.

This is why water drips from any screws in the ceiling that go straight into a rib.

[Rusty]

Originally Posted by Twigg

Filling the ribs doesn't fix the problem. The thermal energy travels, both ways, through the steel not the airspace inside the rib. The ribs are welded to the roof, and screwed to the ceiling so filling them would have little impact.

This is why water drips from any screws in the ceiling that go straight into a rib.

What if you removed all the ribs and replaced with carbon fiber?

[Twigg]

Originally Posted by Rusty

What if you removed all the ribs and replaced with carbon fiber?

Then at least they wouldn't rust

[Rusty]

Originally Posted by Twigg

Then at least they wouldn't rust

It's ok, I have......

Spare Ribs !!!!

[dan-fox]

Originally Posted by Twigg

Filling the ribs doesn't fix the problem. The thermal energy travels, both ways, through the steel not the airspace inside the rib. The ribs are welded to the roof, and screwed to the ceiling so filling them would have little impact.

This is why water drips from any screws in the ceiling that go straight into a rib.

Or just took out the screws?

Have you seen water dripping from screws that are driven into 3/4" plywood thermal bridging on top of school bus ribs? "" driven into the ribs themselves?

This argument needs some grounding in real world data. When I start this process, you damn betcha I'm going to source a good IR camera somehow!

I still have to think that the folk who are worried about thermal bridging loss on their ceiling ribs while installing Fantastic powered air vents in the ceiling might have their priorities mixed up. Do your due diligence in insulation and especially air infiltration (I'm looking at you, original windows!) and solve the remaining aspect of the problem with brute force BTUs in cold weather. Also, acclimate yourself to a wider range of temps in the summer so as to tolerate keeping your windows open. No delta T or delta RH across the envelope then!

[HazMatt]

I want my baby back
Baby back
Baby back
Baby back


Fly slow.
Stay low below the radar.

[HazMatt]

Originally Posted by Twigg

Filling the ribs doesn't fix the problem. The thermal energy travels, both ways, through the steel not the airspace inside the rib. The ribs are welded to the roof, and screwed to the ceiling so filling them would have little impact.

This is why water drips from any screws in the ceiling that go straight into a rib.

Are we more concerned about the marginal heat loss/cold incursion via ribs that are snugly surrounded by insulation, or condensate collection in an enclosed medium that can encourage the propagation of potentially toxic mold, & metal oxidation?
I frankly don't see more than some minor annoyance condensation from the screw heads. If the interior is heated, the cold will be driven towards the roof as temperatures shift towards equilibrium, effecting negation of the condensation situation.
(I suppose there may be suitable connectors that are less thermally conductive, if dealing with a few drips proves a problem.
(And I'm not acting as an advocate for that condition simply because I can be a drip, too)
The bridge will still be there, however conduction will be isolated to the ribs' walls. Since the open void within no longer acts as thermal variant reservoir, it ought make for a more rapid, and considerably narrower, thermal bridge profile.
While I don't specialize in bio-haz, if mold is a common problem in converted buses, I, for one, prefer facing some minor temperature vagaries over breathing in an enclosed, toxic atmosphere.
An ounce of prevention is worth the pound of cure(d foam).
Just sayin'

===================

Fly slow. Stay low.