winter insulation

Living aboard in areas with hard winters is tricky, especially if your boat is not insulated. Condensation in lockers can damage wood, and cause rot and mold. A boat that isn't insulated will also cost more to heat. To keep the interior dry, it's necessary to get rid of the moisture generated by cooking and breathing. To dry the space out you need to allow air from outside into the cabin, and then heat it. The heat won't stay if your boat isn't insulated, but winter isn't the time to add insulation, it's better to wait for a drier, warmer season. If you try to use adhesives in cold weather, materials won't bond to the hull.

When we cook, we crack open a hatch to allow the steam to escape. We don't have room for a fan so this is our best option.

Hull. As stated above, a good winter setup requires both insulation and ventilation in the cabin. Insulation keeps the inside of the boat warm when it is cold out, and ventilation helps to eliminate condensation. Condensation forms because of the difference in temperature and the ambient humidity. There is no miracle solution to eliminating condensation, the only thing to do is to keep the air flowing. Add vents to every locker, every space. If the air moves, moisture won't be an issue.

If you spend a lot of time in very, very cold weather, you will probably want to insulate thicker than 1” to get more R-value.

Closed-cell spray foam. R-value per inch of R-7. A good way to insulate a hull is polyurethane closed-cell spray foam. Closed-cell foams tend to be water-resistant due to the closed nature of the cells that make up the foam. The more small and compact these cells are, the more resistant to water the material will be. This is how people insulate narrowboats. Closed cell foam is designed to expand to about 1″ of thickness when sprayed. The closed cell also acts as a vapor barrier, so water and moisture won't come through. While insulating, it also provides extra wall strength and buoyancy. The foam is sprayed directly onto the inside of the hull and adheres well to most surfaces. The foam can be trimmed, and sanded. Any foam that is cut loose its waterproof properties, and ought to be sealed. Generally, the foam is covered up with panelling for a nicer, cleaner finish.

Polyisocyanurate foam board. Polyiso has a R-value per inch of R-6. Sold as rigid sheets, these are bonded to the bare hull using a strong adhesive, or spray foam (helps to close gaps). Insulation of this type must be sealed, and well-secured to the backing surface with no air gaps.

Extruded Polystyrene (XPS) Foam Board. A rigid foam board with a R-value of R-5. They are typically blue, or pink(Foamular). Like polyiso, it doesn't retain water but performs better in cold weather. XPS is more bendable than polyiso if you have really curvy walls. XPS manufacturers use HFCs, making this not the greenest option. (This is what we chose, due to availability/price/r value.)

Note: EPS is not the same material as XPS, avoid this if you can, the air gaps make it weak to water.

For other types, see insulation.

Bilge and floor. For the bilge area, keep it dry and cover the floors with carpet as insulation.

carpet, your feet will thank you

Windows: The windows on our boat are another source of heat sink. We made curtains for each window, and plan to add a thin layer of bubble wrap in between it and the window in winter.

Ceilings: If you can remove panels on your ceiling, install polyiso or XPS foam boards. Like the hull, these panels ought to be glued using spray foam or a high strength spray adhesive. Fill any gaps with spray foam.

Is there such a thing as green winter insulation? The greenest option is no insulation(ha!). Wool batting is green, yes, but tricky if you espouse non-speciest values. As they say, pick your poison.