Insights on insulating the Underbelly

[geo]

Doing just a quick Search will lead you to my posts on insulating the underbelly of the Alpine and installing tank heaters.

But what I would like to share is what I learned on a recent tour of the DRV Suites manufacturing facility. DRV chooses to use unfaced rock wool batt in the underbelly as this material does not have any residual Formaldehyde and does not cause the skin irratation by micro-cuts. Using unfaced Fiberglass batt is OK if you take precaution to "air it out before installation", wear a breathing mask, and protect exposed skin.

If you insulate the underbelly, do not totally fill the underbelly with insulation. I previously addressed protecting the slide rams and toothed rails. But just a R-19 layer of insulation laying on the coroplast will make a huge difference. You want to leave an air space above the insulation and below the sub-floor. This means you will probably be able to shine a light in an opening in the I-beams and see the top of the insulation and the bottom of the sub-floor. According to DRV, it is this air gap that keeps the humidity and moisture from building up in the insulation! Luckily, I got lazy when insulating the underbelly of my Alpine, so I did leave the recommended air gap! Nice to be lucky and lazy sometime!

If you have any questions, please let me know.

Ron

[RVUSA]

I recently added heat tape to the water lines in the underbelly of my montana. the bottom of the frame had a layer of the silver foil bubble wrap stuff and then the corplast.

When I put it all back on I taped all the edges of the bubble wrap to the frame and the seams where the bubble wrap over lapped. The thought was it wouldnt let near as much air flow as not using the tape.

That said, the sides of the frames are still tall and still metal which conduct heat very well, and the frames also have some rather large holes in them for the slide out arms and what not. While the bubble wrap, and in your case the layer of insulation seem to have a "it helps" feeling to them I have to wonder really just how much do they help considering the heat loss thru the frames metal and airflow thru the holes in the frame.

Any thoughts on the heat loss via the frames themselves?

[geo]

RVUSA -

The aluminum coated bubble wrap is Keystone's all-round answer to insulation. The problem is that the bubble wrap part offers very little insulation, and the aluminum does better at reflecting heat than the bubble wrap does at insulating. Try getting some of that bubble wrap at HD, wrap it around you, and then go outside when it is just freezing - 32F/0C - and see how warm it keeps you. Let your loved ones stay inside - you won't be out long!

The steel I-beams offer no insulating qualities. Steel is an excellent conductor of heat and electricity. Ever put your tongue on a flagpole when it was freezing outside? OK, you will have to find an old flagpole that is steel, but aluminum is basically the same. The heat that is lost into the underbelly is quickly absorbed by the steel I-beams and the aluminum on the bubble wrap (and through the coroplast) and transferred outside. I discussed all of this in my postings about installing tank heaters and insulation in the Mods section.

As discussed in the thread about the Arctic/Polar/Glacier tank package, there is just basically no insulation in the Keystone underbelly and tank area. If you install tank heaters, it will help keep the tanks and valves defrosted. But to keep the inside warmer and lower in humidity, one needs to install insulation. In North Texas, rock wool batts are impossible to find, so I chose Fiberglass. There was plenty discussion about this, but I do feel I did make the correct decision. My laziness proved to be correct also! Since I did not fill the underbelly, but left an airspace above the Fiberglass was the correct thing to do! If I had packed the underbelly full of insulation, as was my original plan, I would have done the wrong thing! I would have had an underbelly full of moisture! But as it is, I did good!

When I reattached the coroplast and aluminum-coated bubble wrap, I sealed the edge of the coroplast with silicon roof sealant. That way I prevent any road moisture from being thrown by the tires up into the underbelly. The holes in the I-beam provide ventilation above the Fiberglass to keep moisture minimized but blocking the massive area of the flat of the underbelly and up along the bottom of the I-beams makes a huge difference in the temperature of the fiver and moisture of the living area.

Ron

[Htfiremedic]

I'm going to add some this year. Maybe during the winter. About how many rolls did it take. My Fuzion is 35' so I'm just wondering.

[nuskovich]

So you salvaged all your original Coroplast? I'm guessing a razor knife to cut old silicone sealant?

Htfiremedic....about 280 sq ft should do it, faced or unfaced. If faced put paper to Coroplast with fiberglas to living space.

[geo]

Nuskovich - Because of the differences between the climate of Alaska and North Carolina, I would highly not recommend the use of faced insulation in the lower 48. The problem is that the treated paper facing will cause the insulation to retain any moisture, and as that moisture builds, the insulation will become heavier, lose insulating qualities, and the paper will start to mold and mildew. I can think of several other reasons, but just will say, I would hesitate to even use faced insulation even in central Alberta. I will pass on making such statements about Alaska as my experience is limited to only one week one January in past time.

Htfiremedic - If you are considering going to all the trouble to insulate the underbelly, I would encourage you to consider also adding heat pads to the waste and fresh water tanks. One of our members, Wolfwalker, is a dealer for UltraHeat. You can also find UltraHeat on the Web and purchase directly from them. The plus is that the insulation will "work with" the tank heaters to allow one to camp (live) in colder weather. Here are the primary posts on installing the tank heaters themselves and about insulating the underbelly of the Alpine:

http://www.keystonerv.org/forums/showthread.php?t=4829
http://www.keystonerv.org/forums/showthread.php?t=5843
http://www.keystonerv.org/forums/showthread.php?t=5842
http://www.keystonerv.org/forums/showthread.php?t=5841

Note, I left out the posts describing the Control Panel installation. If you click on my id on this post, you can go to my Profile Page, then click on the Statistics tab, and then click "Find all threads started by Geo". You will find posts about the control panel there and also posts from past discussions on Keystone insulation (or lack thereof) of the underbelly.

The Alpine was 39' long. I only used unfaced Fiberglass purchased from HD. I used one large roll of R-30, one package of R-13 batts, and six packages of R-19 batts. And one pair of shears to cut the insulation to fit. I also used four sheets of R-5 pink foam board insulation to insulate under the heat ducts under the utility basement (slid the foam board under the ducts above the coroplast to save space and not bind the flexible heat ducts). Some of this foam was used to insulate the ceiling of the storage compartment and also the front storage compartment above the generator. I also sealed the major openings above the generator compartment into the bedroom with non-expanding foam above the foam board. (There was a post on this process also.)

In general, what I found is that the Keystone Alpine has some impressive insulation in the floor, wall, and ceiling. But very little insulation in the slide walls (that part of the slide that is extended, not the outside wall). I also found that the RV was fraught with openings to the outside - around the slides, around the insulated floor, under the bed (not only an opening directly to unheated space above the front storage compartment but also almost directly above the generator exhaust!). I found that the construction of the Alpine relied upon "getting a component and attaching the ends". In my posts, I found the flexible heating ducts looped, intertwined, "horse-shoed", and kinked because they were not cut to fit, rather fit and crammed.

Also remember, insulation works both ways - keeping the inside warm in the winter and cool in the summer. Except in summer months, with the AC going, the colder air is "heavier", so it will flow downward through the basement, into the underbelly, and out. Yes, one can cool the great out-of-doors! I also found that once I installed the insulation, the "humidity level" of the inside of the Alpine dropped drastically. When the Alpine was in storage, any season, I would check on it on weekends and find the Eva-Dry dehumidifier's tank full and it shut off. Once the insulation was in place, it would take a month before the Eva-Dry's tank would fill to hit the shut-off.

It's all documented in the above posts and in other postings. As with this post, I tend to be verbose and know it. I would be more than happy to answer additional questions either in a posting or by PM.

Good luck on your project!

Ron

[dm1401]

I think I would like to tackle this project to help our TT keep warm in the shoulder seasons. I still find my air flow thru the vents OK but that's about it. So this will also possibly address that issue. A question I have is has any one tried to use rigid ducting wear possible. A friend of mine runs a manufacturing plant and he says that you loose a large amount of efficiency from flex ducting VS rigid ducting. I don't even know if I can purchase the correct dia.
Any thoughts or experience with this idea?

[JRTJH]

dm1401 said, "A friend of mine runs a manufacturing plant and he says that you loose a large amount of efficiency from flex ducting VS rigid ducting"

Your friend is correct in stating that you lose a large amount of the "velocity" of air movement from flex ducting, but you really don't lose any BTU's of heat. It's simply "expended" in the underbelly rather than forced through the duct and back into the cabin. If you think about it, there is only a 2" flex duct to "heat the underbelly" in most trailers. That 2" duct won't deliver much heat, but the "uninsulated flex ducting" that runs through the underbelly as it "meanders" through the space will leave behind a significant amount of the heat that is produced by the furnace. It's true that heat isn't keeping you warm, but it is contributing to keeping the tanks and plumbing from freezing, so it's not "inefficient" use of the heat, rather it's "redistributed" use of the available heat. It does serve a purpose and it does keep your RV functional even though it doesn't deliver all the heat produced by the furnace "through the registers" to keep your cabin warm.

Insulation in the underbelly will help, dual pane (or plastic film on the windows) will help significantly. I'd suppose that if you completely insulated some rigid ducting to replace all the flex duct in your underbelly, your RV tanks and plumbing would freeze much faster than it currently does.

I'll agree, it's a very inefficient use of the limited BTU's, but it's not totally "wasted" because of the flex ducting.

[geo]

Originally Posted by dm1401

I think I would like to tackle this project to help our TT keep warm in the shoulder seasons. I still find my air flow thru the vents OK but that's about it. So this will also possibly address that issue. A question I have is has any one tried to use rigid ducting wear possible. A friend of mine runs a manufacturing plant and he says that you loose a large amount of efficiency from flex ducting VS rigid ducting. I don't even know if I can purchase the correct dia.
Any thoughts or experience with this idea?

Dm1401 -

While your friend is correct, the application of rigid ducting in your Cougar might be difficult. The flexible ducting directly connects the furnace to the vent. And, if you look inside the underbelly, you will see that there is no "easy" path between the two. Even if you could "get around" the fresh water tank (if it is installed the same way it was on my Alpine), the multiple turns and elbows you would need to install to route around tanks, through cross-members between the I-beams, etc., would cause as much turbulent airflow as a flexible ducting method. The additional problem would be this rigid ducting coming apart at some point as the RV is towed down the road.

Now, it is true that there are some brands of RVs out that use rigid ducting. However, most all of this rigid ducting is incorporated inside of the floor build as rectangular ducts connected to the furnace by short runs of flexible ducting.

If you look inside the underbelly by removing say three or so screws and dropping the coroplast a little, you will see what I am trying to describe. Actually, you may get a bigger gain on warming by just installing insulation in the underbelly and making sure that the insulation separates the ducting from the coroplast and outside, like I did in the Alpine.

Ron

[dm1401]

Thanks for the responses everyone, I really do appreciate it. The loss of efficiency I was referring to would be the loss in air flow, and I didn't even think of the heat loss, but I would think it would be the same as flex ducting maybe even worse now that I really think of it. As for insulating the under body I am going on the experience of this form and the recommendation of putting a single layer down that would sit on the chloroplast, and I'll be sure to keep it out of the slide mech, (Thanks for the heads up on that). My TT has double pain windows already, so I figure this can only help if done carefully and correctly. I will re post when I do the mod. Thanks again to all.

[BulletOwner1]

GEO,
I have read a number of your posts and you truly have gone the extra mile to achieve a more cozy RV. Did you ever research installing a skirt? I've often thought that it would go a long way in winterizing. Understand that it would probably be more expensive, but in some applications would work better. Any thoughts?

DM1401,
While I didn't change out my flex tubing for rigid I did drop the coroplast and found that the flex was installed, let us say, poorly. In one case it entered a void between sections, did a complete 360 and then continued to the outlet. I basically went in and removed excess tubing and routed it better. Before I did that there was very poor flow in the bedroom. After, much better.

Richard

[geo]

Originally Posted by BulletOwner1

GEO,
I have read a number of your posts and you truly have gone the extra mile to achieve a more cozy RV. Did you ever research installing a skirt? I've often thought that it would go a long way in winterizing. Understand that it would probably be more expensive, but in some applications would work better. Any thoughts?

Richard

Richard -

No, I never really considered skirting because DW and I wanted a mobile RV. Proper skirting does an excellent job of helping to hold in heat. However, it does take time to deploy/pick up and occupies a good deal of space in transport. If one is going to be in a location overnight, a couple of days, or even a week - is it worth the work that skirting involves? I thought "no", so I opted to insulate the underbelly, protect the Pex plumbing, and install tank heaters. I think, overall, skirting would be cheaper and easier. What I did was very labor intensive though relatively lower cost. One person could easily install skirting in a day or two. I spent most weekends (one to two afternoons) over some two months.

If you are wintering in one location, skirting would be the way to go. If one wants to relocate several times, or if in a particularly frigid location (insulation and skirting), then insulating the underbelly is better.
Ron

[sjturbo]

Good discussion! I have a question that someone may be able to help me with. Since my Laredo 316RL has a raised front bedroom and bathroom with basement storage below would it not be a better idea to insulate with R Panel, (foam board) below the bedroom floor, than insulate below the basement floor, (Above the coroplast)?

[Festus2]

If I were you I'd insulate the ceiling of the lower storage compartment with rigid insulation. This should help keep the floor of the 5th wheel bedroom warmer. While insulating the rest of it - the "underbelly" will still be a good idea, any insulation you apply there won't do much for the upper bedroom area in a 5th wheel.

[sjturbo]

Thanks Festus! I thought I was on the right track. Regarding the remainder of the under belly, since we live in the southwest should I be worried about condensation in the under belly? Are most people using batting with no facing?

[BulletOwner1]

sjturbo,

One question - in the area under the bedroom heated? If so then I would think insulating the underbelly would help more. I don't know about your particular RV but I think there are some 5er's out there with heat vented to the storage area, probably ones that have exposed plumbing. Just a thought.

[sjturbo]

Thanks for the question BulletOwner1. My unit is a 2010 Laredo and I don't believe that Keystone was doing any type of storage area heating, other than the dryer vent style un-insulated ducting or insulation, at least not on mine. There is a "small" section of fiberglass that serves as "for show only" insulation in the underbelly. I believe that my best bet is to use R Panel under the bed/bath floor and bat insulation in the remaining underbelly. Of course I will need to add some coroplast in areas where Keystone determined it would be easier/cheaper to cut back the coroplast than shape to fit. But I understand, it's a business.

[geo]

In our Alpine, the storage basement did have a limited amount of heating along with the 2.5" duct to "heat the tank valves". I chose to use a double thickness of R-5 pink foam board cut and wedged between the aluminum rafters to insulate the ceiling of the storage area. I did notice an immediate difference (it was August in Texas) in that the bedroom was cooler! After all the insulation, etc., of the underbelly, I returned to the very front of the Alpine inside the compartment that holds the generator and storage. (This is one of my last posts linked in the Mods sticky.) This front compartment is open at the sides to the "outside" on each side. This is also the area where the hydraulics and power lines are fed through an open hole in the deck under the bed. Basically, this means that there is an open hole under the bed that has direct access to the outdoors - above the generator, immediately in front of the generator exhaust, right next to the front landing gear and a perfect run for mice, etc. to under the bed! As you can read in the sticky link, I cut foam board to create channels for the power and hydraulic lines, then put a second layer of foam board beneath the first. I used a low-expansion foam to seal the channels at each end, then finished installing the lower, second sheet, of foam board beneath the first. By this time, it was February in Texas, and the bedroom as immediately warmer! The front closet was no longer cold!

So, yes, as I mentioned to SteveS, I did use a combination of foam board the unfaced Fiberglass insulation. And yes, I noticed that with the addition of the Fiberglass insulation on the coroplast, the humidity of the inside of the Alpine was reduced.

Ron

[sjturbo]

Geo, has the duct tape holding the fiberglass batts really passed the test of time?

[geo]

Originally Posted by sjturbo

Geo, has the duct tape holding the fiberglass batts really passed the test of time?

Sjturbo - I used the duct tape only to hold the Fiberglass batts in place during installation and putting the coroplast back in place. I'm positive that the duct tape has released long time ago. Duct tape is cheap and held well for a couple of days . . . that's all I wanted.

Ron