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Discussion Starter #121 (Edited)
Found 1 possible answer to the unresolved ambiguity with my 1/2" poly. Literally flooded with and overwhelmed by too much information*, in the fine print on one tech sheet of about 50 that I looked at, is the footnote that R Max / R Matte Plus 3 brand Polyiso, in thickness less than 1", is only 16 psi. Even at thicker than 1" it is only 20 psi. So, it moves from the floor to the walls in layers. Scored some very nice green XPS at Lowes. Not really sure what makes it "eco-friendly" other than the color, as XPS has a pretty bad rep for its impact on the environment. But, it has a minimum of 25 psi and easily passed my pinch test.

The down side is I had to bump up to 1" thickness. For the math guys out there, the van has 72" x 144" = 10,368 sq in of floorspace, and a half inch loss in height is a whopping loss of 5,184 cubic inches or 3 cubic feet of interior volume. But the layer went from R 3.2 to 5, so not a complete loss. I can leave 3 cubic feet of sweaters at home. :unsure:

* Okay, figuratively flooded with. But literally overwhelmed. And thanks to everybody for your inputs.

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I too was overwhelmed with insulation info overload. It came down to noise: squeaking.

It was a close call between polyiso and XPS.

I actually bought some XPS first (3M Foamular, pink). And was driving it home in the PM to use. I bought it at the same time as the floor plywood and so on the floor were 3 sheets of Foamular with 3 sheets of plywood on top. Guess what? It squeaked.

Maybe it was because there was a stack of 3 sheets of XPS, one on top of the other, a condition that would not be replicated in the final installation. But as many people know by now, I'm sort of picky when it comes to annoyances and so I bailed on the XPS; immediately turned around and returned it.

I got a deal on some Polyiso (IKO Enerfoil), foil on both sides. Same situation, driving home with 3 sheets of the polyiso with 3 sheets of plywood on top. No squeaks. This was possibly because it was now foil-on-foil rather than XPS-on-XPS (i.e., low friction).

I'm not saying I made the right decision; that's just how it happened (it helped that I got a great deal on the Polyiso due to it showing forklift damage, which I didn't worry about).
 
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@travelvanvan

I believe you are correct & XPS will telegraph squeaking more than Polyiso. That is the only con I believe it has in using it in the floor. I cut mine too tight to the verticle surfaces & had to trim it back once the plywood was down. If the perimeter is trimmed back a bit & the edges filled with “Great Stuff” I do not think it is an issue. I believe the Polyiso “foil faced” will have a tendency to “shape” / deform under weight to the peaks of the metal van floor (Depending on point loading weight). This could rupture the foil face if deformed enough. I believe polyiso would perform well in a van floor, providing it does not absorb water ever. If it does, and is loaded along with road movement I believe it can break down. We DIYers design/builders have to “pick our poison” when choosing materials.

Recently I used some left over XPS to insulate the sliding door cavity over my window area. As I was also using up scrap Polyiso the same day it reminded me of the squeaking sounds while installing & that the XPS had a significant louder squeaking sound when shoving and twisting it into place (I sealed the edges with “Great Stuff” once it was in place & have not heard a peep out of it since.


@keeponvaning

As I agree with your numbers 16 x 1 gross = 2,304 lbs per square foot the 16psi is tested fully supporting both sides of the rigid board & the van floor supports less than 50% of the bottom of the rigid board. Thus the 16psi is a compression strength when fully supported (not tensile, not shear). I had the same concerns as Slather as this rigid insulation has to span the peaks of the metal floor, unless it deforms at the peaks & also has bearing support from the valley area of the floor. I could not find any real world evidence of floor insulation performance on a Promaster van floor (we will only really know this if someone has to rip up their floor after some years use & actually report the condition of their insulation - until then it is just theory). The majority of my build is “loaded” onto my floor.

I think 20 psi or 25 psi (fully supported compression strength), ratings are probably good enough for a PM fan floor. I went high load xps only to get the water permeability rating. The big negative for me using polyiso in the floor is the water absorption & then the disintegration possibility. Otherwise I would have used Polyiso.





One of the greatest attributes of XPS is its ability to retain R-value and compressive strength even when exposed to water.

67901



Note on the chart below - if the foil face is ruptured then I believe the water absorption rate increases huge. Also who seals their floor polyiso butt joints or edges (I suppose great stuff might seal the perimeter edges).
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Discussion Starter #125 (Edited)
Slather, (sic)
You might be overthinking this a bit. 16 lbs per square inch equals 2304 lbs per square foot! What are you planning on carrying?
Yes, I do tend to overanalyze everything. This sometimes becomes an issue when I get stuck planning something and never actually start working on it. And when I do work, I work slow. But for the van, I have specific time goals. I have a Spartan race in Nashville on 2 Oct 2021 - the van needs to be operational by then. With that in mind, I want the floor, roof rack, and 2 x fans installed by the end of 2020. The heated building will help, so I can work year round.

This will address the load bearing aspect only. I can't top RV8R's excellent water retention discussion in the above post. And I am not faulting polyiso in general, maybe the batch I got was not up to spec, but it did appear pretty soft, for lack of a better word. (the squeeze test.) The 1/2" was pretty thin to start with. The problem in my application, IMHO, is not the average 2304 lbs per square foot (static) on the top surface. Any point load is (hopefully) distributed evenly by the plywood layer above the foam.

The problem, for me, is that our sheet metal floors are not flat, they have ribs sticking up. The foam sits across the high spots of the ribs and spans the low spots unsupported. (Unless one fills them.) The ribs are not continuous, there are gaps along the length. All of the tie-down holes are in the low sections. So the load is not evenly distributed along the bottom surface of the foam - probably less than half of the foam is supported from below. Which creates point stresses in the foam and its protective foil layer at each edge of each rib. The rib and the plywood will be doing their own version of the pinch test. Forever. Loads IRL are dynamic, not static. Bouncing up and down over winter potholes in these lousy northern roads, things shift. Makes me curious, in home construction, do they put foam unsupported across spans of floor joists and then plywood on top of that? Or would the plywood go down first?

In full disclosure, I am a Physicist, not an engineer. (So I understand the math, I'm just not going to do it.) IMHO, the goal of engineering since Isaac Newton is to reduce costs by distributing forces efficiently, allowing a design load with minimal expenditure in material. (The joke is anyone can build a bridge capable of carrying 1,000 tons. Only an engineer can build a bridge that can just barely carry 1,000 tons.) The rest of us just overbuild or fail.

My apologies of this got a little philosophical. I am not intending to define right or wrong. For me, the van flooring is the hardest part to get to after the fact, so regular servicing is not really an option. Confidence in its ability to hold up for the long term is high on my list of criteria.
 

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That’s two reasons to use 1" min insulation & 1/2" plywood. I used 1" polyiso & ¾ plywood nothing is going to ever squeak or go thru that. The tie down bolts and cabinets will stop any movement!

I’ve never heard of putting insulation between wooden floor joists and plywood sub-flooring in all my years in construction but that doesn’t mean it’s not done. I certainly wouldn’t recommend it!
 
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Discussion Starter #127 (Edited)
I’ve never heard of putting insulation between wooden floor joists and plywood sub-flooring in all my years in construction but that doesn’t mean it’s not done. I certainly wouldn’t recommend it!
But isn't that exactly what we are doing with our vans? Putting insulation between (metal ribs functioning as) floor joists and plywood sub flooring? Granted, the ribs are closer together than floor joists, so the unsupported span is much shorter.

BTW, this is exactly the strength of the forum... people with different backgrounds and common interests sharing ideas and discussions in a civilized manner. We are stronger than our parts.
 

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Big difference between spanning a 16" o.c. floor joist and nailing plywood down thru it for a floor in a building. You’re correct, the span is only 2" or so and spaced very close together. There really is no reason not to use either underneath a plywood floor in a van plus filling in the spaces is a complete waste of time and money. No reason to glue anything down either. We’re talking a 6‘ wide span 10 to 12 feet long half covered with beds & cabinets, etc. If you use ¼ plywood and ½" insulation it wouldn’t hurt to glue them together, as Gary recommends, but only because of the thinness of both materials.
 

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Discussion Starter #129 (Edited)
Plowing forward, here is my first crack at the flooring plan. (No pun intended). Side view, measurements from the front of step to cab, green XPS on the bottom, purple plywood on top. The goal is to avoid overlapping seams, anywhere near adjoining layers, near the tie-downs (red squares), or near the voids in longitudinal ribs (red hashed areas). I do end up with four seams in each layer instead of three. But I felt that having a seam over the unsupported void would be bad, so it became a necessary evil. Biscuit joining the ply gives some strength to the wood seams. Also, the plan is to put thin wood "spacers" around the tie-downs so snugging the bolts won't crush the foam, since the tie-down nut-holes are in the low portion of the floor and the XPS sits on top of the ribs.

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Yes, I do tend to overanalyze everything. This sometimes becomes an issue when I get stuck planning something and never actually start working on it. And when I do work, I work slow. But for the van, I have specific time goals. I have a Spartan race in Nashville on 2 Oct 2021 - the van needs to be operational by then. With that in mind, I want the floor, roof rack, and 2 x fans installed by the end of 2020. The heated building will help, so I can work year round.

This will address the load bearing aspect only. I can't top RV8R's excellent water retention discussion in the above post. And I am not faulting polyiso in general, maybe the batch I got was not up to spec, but it did appear pretty soft, for lack of a better word. (the squeeze test.) The 1/2" was pretty thin to start with. The problem in my application, IMHO, is not the average 2304 lbs per square foot (static) on the top surface. Any point load is (hopefully) distributed evenly by the plywood layer above the foam.

The problem, for me, is that our sheet metal floors are not flat, they have ribs sticking up. The foam sits across the high spots of the ribs and spans the low spots unsupported. (Unless one fills them.) The ribs are not continuous, there are gaps along the length. All of the tie-down holes are in the low sections. So the load is not evenly distributed along the bottom surface of the foam - probably less than half of the foam is supported from below. Which creates point stresses in the foam and its protective foil layer at each edge of each rib. The rib and the plywood will be doing their own version of the pinch test. Forever. Loads IRL are dynamic, not static. Bouncing up and down over winter potholes in these lousy northern roads, things shift. Makes me curious, in home construction, do they put foam unsupported across spans of floor joists and then plywood on top of that? Or would the plywood go down first?

In full disclosure, I am a Physicist, not an engineer. (So I understand the math, I'm just not going to do it.) IMHO, the goal of engineering since Isaac Newton is to reduce costs by distributing forces efficiently, allowing a design load with minimal expenditure in material. (The joke is anyone can build a bridge capable of carrying 1,000 tons. Only an engineer can build a bridge that can just barely carry 1,000 tons.) The rest of us just overbuild or fail.

My apologies of this got a little philosophical. I am not intending to define right or wrong. For me, the van flooring is the hardest part to get to after the fact, so regular servicing is not really an option. Confidence in its ability to hold up for the long term is high on my list of criteria.
Yup; How I feel Exactly

I will admit there may be areas that I have over built. The problem with DIY Design & Build is pulling solid data from reliable sources. I have been a building science professional & commercial builder since the early 80s. I have my education & decades of work experience to fall back on, but where do I find the manual for “Van Building”?

In 2018 after buying the PM, I did a ton of research on the internet on what DIYers were doing. The conclusion I made was there is tons of information out there & even some of it is correct, but there is a lot of bad information out there. It has to be extreamly diffecult for novices that have zero building or design experience.

You have concerned yourself with the same items I had to think thru before buying my floor insulation.

The only Cons to XPS that I can see is slightly lower R value & possibility of telegraphing squeaks easier than Polyiso
 

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Plowing forward, here is my first crack at the flooring plan. (No pun intended). Side view, measurements from the front of step to cab, green XPS on the bottom, purple plywood on top. The goal is to avoid overlapping seams, anywhere near adjoining layers, near the tie-downs (red squares), or near the voids in longitudinal ribs (red hashed areas). I do end up with four seams in each layer instead of three. But I felt that having a seam over the unsupported void would be bad, so it became a necessary evil. Biscuit joining the ply gives some strength to the wood seams. Also, the plan is to put wood "spacers" around the tie-downs in place of foam, so snugging the bolts won't crush the foam.

View attachment 67911
At first glance this looks good to me (I used a 5’ x 10’ 3/4 BB plywood sheet that was stained & clear coated - kinda looks like a dark stained hardwood floor). The reason for such a big sheet of plywood was so I had no joints in the “living area”.

I don’t know what your plan is for final flooring, but the less joints in the plywood subfloor the better.

My gut says no wood spacers; I think it is better to tighten the bolts up so the plywood is applying some pressure to the XPS insulation.

I used countersunk thru bolts & drilled holes from underneath the van & tightened the bolts so the plywood applied pressure to the XPS rigid insulation. Then cabinets etc are also loading the plywood. All my cabinets are bolted to aluminum angle & the angle is screwed to the 3/4” floor with #12 (or #14 screws).

I did not do this, but I would consider applying Great Stuff around the perimeter to bond the XPS to the perimeter to mitigate any movement (then trim any excess prior to installing the plywood.

Good Luck !!
 

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Discussion Starter #132
I didn't know FedEx Home delivered on Sundays, but my water tanks arrived today. My plumbing schematic has been up for a few days now (post #108), and NOBODY commented that I had all the fittings on the wrong corners. What happened to the collective critical eye? Glad I hadn't cut any tubes for that, yet. :)

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Discussion Starter #133 (Edited)
I don’t know what your plan is for final flooring, but the less joints in the plywood subfloor the better.

My gut says no wood spacers; I think it is better to tighten the bolts up so the plywood is applying some pressure to the XPS insulation.

I did not do this, but I would consider applying Great Stuff around the perimeter to bond the XPS to the perimeter to mitigate any movement (then trim any excess prior to installing the plywood.
Thanks. I tried to hide the plywood seams as much as possible. The aft one is under a support for the bed, the forward one is under the shoe shelf for the swivels. The middle is under cabinets on both sides, so only the middle portion of that seam will be exposed. Will try to keep as close to flush as possible. Very happy with biscuit joinery so far in other projects, should make the butt seam fairly invisible.

There will still be some compression in the XPS from the tie-down bolts. The spacers are just to "fill the gap", since the tie-down nut-holes are in the low portion of the floor and the XPS sits on top of the ribs. I re-did the graphic to better show that. I like your idea of foaming the XPS edges before putting the ply down. I expect I will have to brace the edges down while doing that, to avoid the Great Stuff lifting the XPS panels.
 

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Discussion Starter #134
Re-did the plumbing schematic, which gave me the opportunity to clean it up a bit and fix a few typos. I think I have water shut-offs in correct places to service the pump and heater as needed. Quick question for those of you with experience in plumbing... shouldn't there be one-way valves to stop/prevent backflow/syphoning, and if so where would they best be? Is it a function of the components themselves, or any elevation changes between them?

67936
 

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Re-did the plumbing schematic, which gave me the opportunity to clean it up a bit and fix a few typos. I think I have water shut-offs in correct places to service the pump and heater as needed. Quick question for those of you with experience in plumbing... shouldn't there be one-way valves to stop/prevent backflow/syphoning, and if so where would they best be? Is it a function of the components themselves, or any elevation changes between them?

View attachment 67936
This looks good to me (from what I can understand). My 1st plumbing was “elaborate” with shutoff valves everywhere & I ended up ripping it out after less than a years use when I put in a different HWT. The 1st one I put in had no drain for winterizing. I may replace the 2nd one 120v with a propane fired unit.

My 2nd plumbing was very simple. I will see if I can find pictures to post for you to see the difference.

The pump itself is like a backflow preventer, where else are you looking to place one?

If you are building your waterlines with PEX, one system is a flexible pressure hose after the pump (the supply line from the tank is usually a flexible pressure hose also). This is to reduct pump vibration & noise.

Not sure about the shutoff valve between the accumulator & the HWT?


The original plumbing;
67949



Revised Plumbing (much more basic);
67950


67951
 

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Discussion Starter #136 (Edited)
Thanks for the pictures. Very helpful. I'm a visual guy, seeing something always way better than reading a description. Quick questions - in your second picture you have a HepvO AND a trap? I thought the HepvO replaces a trap. Also, I can't tell from the pictures, do you / recommend crimp or expansion fittings on PEX? I still haven't decided whether to use PEX or flex tubing with barbed connectors.

The pump itself is like a backflow preventer, where else are you looking to place one?
I know nothing about plumbing. I thought, since the sink and shower are higher, water might just drain back downhill when the pump is turned off. Isn't a problem in houses but water pressure is normally always present at taps. Not a problem in van, either?

Not sure about the shutoff valve between the accumulator & the HWT?
Hypothetical worst case scenario contingency planning. Say I am somewhere in the wilderness, really remote, I don't know, let's call it Canada. If the hot water system fails or springs a leak, that cutoff will allow me to continue to use the rest of my fresh water supply through the cold water tap. I know not to run the hot water heater with an empty tank, I would just unplug it when I killed the supply to it. I also thought about adding a shutoff on the cold water side, also just past the tee. In the event of a leak in the cold water side, I could use the hot water side (with the heater off), as redundant supply lines. Limp home mode in the event I couldn't make a proper repair in the field. But, I do overthink stuff. The original plan did not have a shower or hot water. So most of this is an afterthought.
 

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@Sather

You are welcome, visual is the quickest way for me to get the point as well.

Regarding the HepvO - You are correct the HepvO is in place of a P trap. In my case I originally installed a P trap & was not happy with odors coming from my grey tank, so I thought I would try the HepvO & I just have not altered my drain yet to delete the P trap. It works that way & I can still sometimes detect a grey tank smell, so I have not worked thru that issue yet, but I am suspicious of my “cheater valve” (very top of the vent stack).

Regarding PEX; I like the metal band crimp. You only need 1/2”. Just buy the tool.

Regarding Draining Your Pressurized Water Side; What is easy is to have a drain in the lowest spot (mine goes thru my floor, however you could just have a hose connector & open up a door & let the hose lay on the ground. You want a shutoff valve @ that low drain. Pump off / drain valve open with drain hose attached / then you crack open the highest faucet or shower valve you have & let gravity & “syphoning” do its job.

Regarding water draining back; When you turn the pump on it pressurizes the system to 40PSI IIRC. When you open the tap the water flows reducing the pressure & the pump tries to get it back to the 40PSI “shut off” pressure. The accumulator youmare planning to install (I bought one but never installed it) provides a pressure storage tank to say that will assist in the pump operation. You may consider leaving it out of your system. If you put a switch in for your eater pump, you can turn your pump off when you have no need. The pressure should stay charged in the lines until a faucet is used. No not a problem in a house or a van.

Regarding Canada & Wilderness & Really Remote; That is exactly where your hot water system will fail 😜. Yes you could shut down the hot water side 👍. You have a fresh water tank drain & in a pinch you can turn your pump off & harvest water from your tank drain. But the real answer is you don’t need the fresh water in your tank at all, cause you are in The Canadian Wilderness with a broken van water system. You just go down to the local stream, swagger up to and aggressively kick the bears outta the way & take that cold clean stream water like a BOSS. If you figure you need to be armed, see RD about his “Leatherman” field survival courses.

My original plumbing was full of shut off valves & hard plumbed PEX & a dozen of fittings & crimps. For me now simple & pressure hose is the best with as few fitting & joints as possible. HD had a good supply of PEX stuff.

My biggest piece of advice for the plumbing is this; Make your line from the hot water tank to the kitchen faucet of the shower as short as possible. We have a 30gal fresh water tank & the one thing I have learned is to not waste water. Waiting for hot water by running it down the drain is not a good way to conserve the fresh water tank. We only have a kitchen sink - no shower.
 

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This is the most helpful post I’ve read on the forum for awhile. No sheet talk, no insulation talk, only water talk! Drink up, this Molsons on me (to bad it’s made by Coors😝)
 
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