Aluminum Houseboat Insulation

I have a 74 Kingscraft 55' all aluminum houseboat located in Cincinnati on the Ohio River. Previous owned gutted interior and added a heat pump, newer electric and water systems. Since its already opened up I would like to finish for the possibility of liveaboard.


Based on my early research I am planning to insulate with 2" of Extruded polystyrene foam (XPS) [blue board/pink board].

1) Is this a good choice of materials?
2) Do I need to a vapor barrier?
3) If I have a seam between two boards should I seal the seam and if so with what material?
4) Should I have a foil type barrier and if so should it be on the exterior or interior of the wall?
5) Should the boards be cut as precisely as possible to fit in between structural aluminum or do small air gaps matter?
6) should the insulating boards be attached directly to the exterior walls [glued?] or do I need an air gap.

Thanks in advance for your input

 

There should be an air gap between the boards and the aluminum to allow condensation to run down into the bilge. Small gaps between the boards are not a problem.

 

You normally want a vapor barrier to prevent condensation of water vapor from inside the heated space onto the cold wood framing or exterior sheathing. That's not a problem with aluminum, so no barrier should be needed. You'll need to provide channels or a space for the water to run down the aluminum.

 

Ripple, welcome to BoatDesign.net

Speaking from house building experience, extruded polystyrene foam itself is a good vapor barrier. But of course the edges will have to be sealed. The building industry has some very good sealing tapes, such as those produced by 3M or Siga.

http://solutions.3m.com/wps/portal/...lashing-Tape-8067?N=5473971 3293242746&rt=rud

http://solutions.3m.com/wps/portal/...ealing-Tape-4412N?N=5927712 3293241577&rt=rud

https://sigatapes.com/

 

Extruded polystyrene foam is combustible. In some circles best practice for what is basically an incombustible vessel structure (Yes AL will burn, but not readily or easily) would be an incombustible insulation. Also the same for vessels of this size, the same rules of thumb apply.

In the case of a fire incombustible insulation will provide passive fire protection.

 

Rater than using sheet foam, I'd consider a continuous barrier of spray foam. At least as much to form the thermal break and seal the inside of the exterior surfaces. If you want, you can install sheet foam over this. The spray foam will make a vapor barrier and offer some insulation and a break. This foam is available in pressurized cans and is mixed "in the gun" so there's no messing up. It's not cheap, but it is easily the best route, if a true thermal break and vapor barrier are desired. Additional insulation can be placed over it, to save some bucks.

 

Paul,

The problem with spray foams is that it hides issues that slowly arise over time, under the foam, and makes simple repairs when necessary, tricky too.

 

Agreed, though there are ways around maintenance issues. Paint and some wax is the easy way. You still get a continuous thermal break and the insulative value, but it can be pulled down if necessary.

 

What are some examples of typical dangers I will be protecting against? Like a short in electrical wiring?

With so much Foamular type insul used in residential construction I assume its safe. Is there some marine environment issue I should be aware of?

What is this type of incombustible insulation called? What is a brand name for something like this?

 

Incombustible insulation for boats include, fiberglass, mineral wool, ceramics and some foams.

Some foams will burn readily and emit toxic fumes. Look yours up.

For a Houseboat this may not be as important, you're never going to find yourself 300 miles offshore where the benefits of passive fire protection are really appreciated.

Some consider it best practice to use incombustible insulation on steel and aluminum boats and fiberglass over 70-80 ft. Especially in machinery spaces and areas that would be inaccessible.

And I agree with Ad Hoc about spray foams, you never know what's going on behind them