Featured Image - How to stop condensation on your boat with insulation

How to reduce or eliminate condensation on your boat

We have been considering replacing our overhead/ceiling in the salon since we bought our boat.  But the job is bigger than that.  It requires thought on how to remove the old, how to insulate, validating any work that needs to be done, etc.

Condensation forming on the roof of the boatLet’s talk about the issues here.  One is the desire to insulate so that the air conditioner (when used) does a better job and can help to keep up with the hot southern sun.  But there is another reason too.  That is when it gets cold, the fiberglass that is not fully exposed to the inside warm and dry air is going to form condensation.  On our boat, when we took the plywood down off the ceiling it looked like raindrops all sitting on the fiberglass surface (the bottom side of the deck surface).

Where the plywood was down and exposed to the salon there was no condensation.

Test 1 condensation test - Insulation not sealed

Test 1 – We left the edge of the Barrier exposed to air and condensation formed

We want to reduce or eliminate this condensation for all the reasons you can imagine.  Reduced rot from moist wood, reducing the chance of bug infestation by not providing a hot, humid and wet place for breeding and lastly the creation of mold in those spots.

We ran a test a year or so ago by removing a section of the overhead and installing 3/4″ closed cell foam between a compressed board (Beadboard) and the fiberglass.  Sadly that was all wet and did nothing to stop the condensation forming on the inside of the fiberglass surface.

Complete seal against the fiberglassThat result made us spend some time exploring what we would do to insulate the boat.  We tried putting a radiant barrier between the foam and the fiberglass, but it still formed condensation.

What we found worked for us was sealing the radiant barrier directly to the surface.  We used aluminum tape to secure every edge directly to the fiberglass.  Once that was completely sealed and covered the entire ceiling, we then added closed cell foam insulation.

We chose 2 layers of 1-inch thick closed cell foam insulation.  It is easy to handle, cut and put in place where we needed it.  We installed the entire 1″ thickness and sealed every opening and edge as well.  Then we installed the 2nd layer and did the same by sealing every single edge.

When we removed the sealed portion, the fiberglass was dry. This would be our path.

We tested our progress by trying this without the radiant barrier sealed and with it sealed.  This test proved that there was condensation that formed when the air was able to get in between the barrier and the fiberglass.

For more details feel free to watch our video this week on Youtube where we covered and showed the details of these test results and how we ultimately removed the ceiling, insulated it and put up the new surface.  We still have work to do in order to get all the trim work up and the ceiling tinted and varnished.

Finished ceiling with radiant barrier and 2 inches of foam

Finished ceiling with radiant barrier and 2 inches of foam

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Video equipment used is: Canon Vixia G40

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See how we go about living aboard and sailing with kids (Grandkids 4 and 12 years of age). We are in the middle of a huge sailboat refit. Our Boat is designed by Bill Garden and built in Taiwan. See how to become a liveaboard whether you stay in a marina or are a cruiser. #boatlife #saillife #SVDreamchaser

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