Easy RV Underbelly Insulation in 5 Steps

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Last Updated on August 23, 2024 by Paul Clayton

Easy RV Underbelly Insulation in 5 Steps

Being on the road throughout the year sounds fun, but your adventure can turn dreadful if your RV underbelly isn’t insulated enough. An exposed underbelly means a cold floor, broken plumbing lines, and corroded wiring. Not to mention higher propane or electricity bills for heating your RV.

However, you don’t have to let the cold weather damage your recreational vehicle or stop you from enjoying camping. You can insulate the RV’s underbelly to prevent all these problems and have a comfortable space.

Check out this guide to learn how to insulate your rig underbelly for enjoyable RV living!

How to Insulate RV Underbelly

Insulating your RV’s underside is not a complicated procedure. You only need to pay attention to the underbelly details and choose a reliable insulation material.

Here is a quick guide for insulating an RV underbelly with foam panels or rolled fiberglass:

Step 1: Prepare the RV’s Underbelly

The first thing you need to do is to get under your RV and examine its condition. If your RV is a large motorhome, you’ll easily access the underside without lifting it.

However, if your RV sits low, you will want to jack it to work on the underside.

Once you can access the underbelly, look for any accumulated road debris and remove it. You should also check for cracks or loose seals, expected due to road vibrations.

To seal the cracks, use silicone caulking, but before you apply it, consider cleaning the surface properly to achieve a tight seal.

Closing these openings will keep your rig’s underside intact and prevent bugs and little crawling critters from entering your vehicle.

Before lying underneath your motorhome, you may want to put clean cardboard on the ground to keep your shirt or work apron clean.

Step 2: Remove the Coroplast

Most RVs feature a plastic sheet, called coroplast, designed to protect the components underneath. If your RV has this sheet, you’ll want to loosen the screws and remove them to insulate the underbelly.

Before you proceed to the next step, you can take a photo and see what the underbelly looks like. This will prevent confusion and make it easier to assemble everything back when you finish installing the insulation.

Step 3: Disconnect the Wires and Pipes

When installing the insulation, you’ll realize that the various underside components will inevitably get in your way. So, detaching them helps to ensure a conducive working space.

If the underbelly components are a bit complicated, mark all the wires and pipes with wire labels or masking tape before removing them. This may be time-consuming, but it’s necessary for peace of mind when fixing back the parts. You don’t want to mount things incorrectly.

Step 4: Measure the Underbelly

Next, grab your measuring tape and measure the RV’s underbelly to know the appropriate insulation material size.

Remember, you’ll be installing your insulation in the open spaces between the underside joists, so you need to measure the size of those openings correctly for a secure fit.

If you plan to use foam boards, you’ll want to measure the underbelly size accurately to ensure you cut panels that fit perfectly. You can note the entire length and then measure different patches for installing the insulation material.

Step 5: Install the Insulation

Once you get the correct measurements, cut the appropriate foam panel sizes or rolled fiberglass to fit them to the openings. Then use coarse-threaded screws, wires, metal bandings, or any adhesive suitable to attach the insulation to the rig’s floor framing.

You may think securing the insulation with nails is okay, but it’s not. Nails are ideal for house construction projects but not for RVs, as they loosen with time as you move around due to road vibrations.

Step 6: Put Everything Back Together

Once the foam panels are in place, it’s time to set everything back on the underbelly. You can check the pictures you took to ensure that you reinstall all the parts correctly.

Re-installation should be a breeze if you label the different underbelly wires and pipes when dissembling.  

Insulate the plumbing tubes with RV pipe insulation to prevent water from freezing in low temperatures. Then wrap the pipe insulation with a zip tie for a secure fit.

If you have any exposed or bare wires, cover them with pop-on sheaths to prevent corrosion.

Before you cover the underbelly with the protective plastic sheet, you can seal the insulation edges with silicone caulking to improve the barrier and ensure everything stays in place.

Step 7: Reinstall the Underside Coroplast

Lastly, if your RV has an underside plastic sheet, you’ll want to reinstall it. Ensure everything is set and adequately secure before sealing your new insulation to avoid unnecessary inconveniences.

Insulating Your RV Underbelly with Spray Foam

The process is much easier and faster if you prefer spray form to foam panels or rolled fiberglass. You may not need to dissemble the wires and pipes, but you’ll want to protect them before spraying.

When applying spray foam insulation on your RV underbelly, it’s vital to remember that the foam expands rapidly. If you aren’t sure how it works, do several tests before applying it to the entire RV subflooring.

You can apply spray foam insulation on your RV underbelly using these instructions:

• Remove the coroplast and inspect the underside. If there are any cracks, clean the surface and seal them using silicone.
• Protect the critical components like wires and water lines using a wood frame to prevent them from contacting the spray foam.
• Spray the foam insulation on the appropriate areas and give it time to expand.
• Clean up the areas sprayed accidentally before the foam hardens.
• Confirm that all the wires and plumbing are properly secured and in good condition.
• Reinstall the coroplast.

Can You Insulate Your RV Underbelly Temporarily?

Yes. You can insulate your RV underbelly temporarily.

The above procedures are ideal for permanent RV insulation, but if you want something temporary, you may not need to go through all the steps involved. Instead, you can quickly install your insulation outside the plastic sheet underneath the rig.

Then use S hooks to ensure a tight mount depending on your preferred insulation material. This is only a short-term solution convenient for RVs that don’t move around often.

Another incredible option for temporary insulation is RV skirting. This method involves installing sheet metal, decorative panels, insulation foam board, or rigid plywood around the RV base to prevent heat loss when parked up. It protects the underside from outdoor elements like water, wind, mud, and other contaminants.

The downside of skirting is that you need to disassemble the setup to move your RV around. You’ll also need to design a convenient space to store your skirting boards unless you plan to discard them when it’s time to hit the road again.

If you move your RV often, consider removing the coroplast and attaching the insulation directly to the rig’s underside frame.

Spray Foam Insulation vs Foam Panels: Which is Better for RV Underbelly Insulation?

Both spray foam and foam panels are great insulation options that provide excellent insulation for RV undercarriage with advantages and disadvantages. They have effective moisture resistance and reliable R-values to keep your RV warm in cold weather.

Let’s discuss the strengths and weaknesses of each option to help you decide what’s best for your RV underbelly:

Spray Foam Insulation

Many RVers prefer spray foam insulation since it’s highly effective and safe. You can quickly apply it to your RV underbelly without detaching the wires and tubes.

When applied correctly, spray foam sticks tightly to the RV floor framing, creating a solid barrier that blocks cold air and moisture from the surface. This ensures reliable insulation even in adversely low temperatures.

Its snug attachment to the frame and subflooring also means you don’t have to worry about loose insulation parts that may fall off while traveling, especially if your RV lacks a coroplast.

The disadvantages of spray foam insulation are that it’s a bit expensive, especially the closed-cell option, and doesn’t perform well in extremely high temperatures. Spray foam can shrink, crack, and smell when exposed to scorching conditions.

Rigid Foam Boards

Rigid foam boards are more affordable than spray foam insulation. They come in different thicknesses, and you can easily cut them into varying sizes to suit other parts of your RV underbelly.

Installing foam panels requires more work than spray foam as you must take measurements, cut the appropriate board sizes, and remove wires and tubes. But this shouldn’t be a problem, especially if you have someone to offer extra hands for the work.

The downside of using rigid foam boards is that it’s easy to end up with a loose fitting if you don’t measure the size accurately to cut the appropriate panel sizes. If this happens, you’ll have unreliable insulation and risk losing some parts on the road.

Overall, spray foam is the best option if you want quick and easy insulation and don’t mind paying the extra dollars. Rigid foam boards take time and more work to install, but they are a perfect solution for four-season RVers who want affordable insulation for their RV’s underbelly.

This video was inserted for its explanation of the subject matter. Thanks to:The Lost Texan

FAQs

Q: How Do I Keep My RV Underbelly Warm?

A: Insulating your RV underbelly is the most effective and cheap way to keep it warm. You can spray foam or install foam boards to prevent cold air from hitting your RV floor framing.

If you worry that spraying foam insulation will prevent you from accessing essential wires and plumbing lines when needed, you can complement it with foam panels. You can install foam panels on areas you need to access often and then apply spray foam insulation on other parts.

Q: What is the Material on the RV Underbelly?

A: The material featured on the underbelly of an RV is coroplast, a sheet made of corrugated plastic. However, some RV models have a fabric underbelly.

The work of an RV underbelly coroplast or fabric is to protect the tanks, wires, and plumbing lines underneath an RV. It also keeps critters at bay and prevents debris from accumulating on your vehicle’s underbelly as you travel. 

Q: What Kind of Insulation Do You Use for an RV Underbelly?

A: You can apply spray foam insulation or install foam panels to block cold air from your RV underbelly.

The best method for you will depend on your budget and how much work you are willing to do. If you have a tight budget, foam panels are cheap and readily available in stores that sell building materials.

Spray foam insulation can be expensive, depending on where you buy it, but it’s worth the price, given its safety and effectiveness. Furthermore, it’s quick and easy to spray foam insulation underneath your camper, and it works very well as long as you don’t mess with the wiring and plumbing lines.

Q: How Do You Insulate an RV Underbelly for Winter?

A: To insulate your RV underbelly for winter, you have several options, including spray foam insulation, foam panels, and rolls of fiberglass.

If you intend to use foam panels or fiberglass, you need to remove the plastic sheet featured underneath and detach the wires before installing your insulation. This can seem challenging due to the wiring complexity, but you can take photos and mark the wires and tubes before removing them for easy and accurate reattachment.

The spray foam insulation is an easier and faster option, as it does not require you to remove the wires and tubes before application. You only need to shield the sensitive components with a board during application.

When camping in frigid weather, you must cover the plumbing lines with foam wrap insulation to prevent the water from freezing and breaking the pipes.

You may also wonder whether skirting will keep your RV warm during the winter. The good news is that it can! You can put a skirting around the base of your RV to block cold wind and air from the RV’s underbelly.

However, skirting works only when parked up, and don’t plan to move around often.

Q: Can You Insulate Your RV with Fiberglass?

A: Yes. You can insulate your RV with fiberglass for constant temperature regulation. Fiberglass has a higher R-value, offering the best temperature maintenance, especially for RV walls in hot and cold climates.

The good thing about fiberglass is that it’s an affordable insulation material readily available in many hardware stores.

Q: How Do You Insulate RV Water Lines?

A: You can wrap heat tape on the water lines to protect them against freezing temperatures. Heat tape keeps the pipes warm in low temperatures and automatically cuts power off when the temperature goes up.

Covering the pipes with foam wrap and installing skirting around your RVs outsides is also a perfect way to protect your water lines in low temperatures.

Conclusion

Insulating your RV is an effective way to stay warm and comfortable in cold weather. It protects you from issues like cold feet, high propane or electric bills, and constant repairs to broken pipes and wastewater tanks.

Hopefully, this guide will help you insulate your RV underbelly and enjoy camping in winter. Along with excellent insulation, you’ll also appreciate reduced road noise and won’t have to deal with pest infestation!