It is essential to provide sufficient ventilation. But how to avoid cold draughts? Low level ventilation is best achieved through pipes from higher up.



Good insulation avoids condensation but wherever cold steel is exposed drips will form. (If you use gas to heat or cook there will be huge amounts of moisture in the air.) It is possible to take advantage of this to make a DIY dehumidifier - condensing water out of the air on an area of cold metal connected to the hull, collecting and removing it.



There is some great information about boat insulation materials on the website:

Their conclusion is that a spray foam is the best option as it has very good insulation properties, is easy to install, is vapour impermeable and bonds directly to the hull, so avoiding the risk of condensation and rusting.

correct heating insulation with spray foam

well most boats have 20mm of spray foam in some places it is 5-10mm over the metal ribs this causes cold spots that the heat escapes from, especially made worse by glue and screwing the wood battons directly on the metal with grip fill, in 90% of boats this is WRONG DO NOT PUT WOOD IN CONTACT WITH METAL. instead spray foam all the metal and do not peel back, screw the battons to the spray foam covered metal using tap and die set so that there is a foam sandwich, then spray foam over these battons then screw your tung and grove or ply plasic linning to these covered battons sink the screw heads and spray over them so that the heat has to travel through the spray foam. I put 100mm minimum on my boats that I build, that way body heat and low power under 200-500 watts from under floor heating powered by solar water or heat pump is enough for a whole boat, seal all drafts and vents put in a heat exchange vent to remove condensation. Put 100mm under the floor go 150mm on the water line if you can. You never need a stove and the boat is dry. limit windows to port holes or double/ triple glaze with laminated glass to get an A rating. I never light my wood burner and my new boats do not even have them. Macks

Boat Insulation and Fit Out

Hello Macks

Do you have a website or contact details?

Many thanks




Boat insulation

Sounds like I ought to have a chat with you, Macks! I'm looking at fitting out a boat, and have decided I'd like under-floor heating, combined with good insulation and ventilation - any chance you could contact me?

boat insulation

I used alububble, 25mm kingspan then alububble again, then 9mm ply liner. This works well for conducted heat and radiated heat. Especially important to use thick kingspan under the sidedeck. The alububble fits snugly against the hull.
15mm kingspan can be bent with care to fit a curved roof, then kept in place with 4mm ply.

I found this warm in winter, and very importantly- cool in summer.

I used open shelving, and this allows air to circulate instead of being trapped in horrible little damp cupboards.

home made dehumidifier

having lived on board my boat through winter I cured this problem by filling a box with biodegradable cat litter and passing air through it with a computer fan unit this will run on 12v and if you use the recycled paper type cat litter is eco freildly as well it can just be emptied on to a black metal tray and left to dry in the sun to speed up the process cover with glass or clingfilm but leave some ventilation or it wont dry. happy boating the funkey monkey

Sheep's wool insulation on boats....

Hi Does anyone have experience of using sheep's wool as insulation? I've sourced some local fleeces, currently untreated and would like to use them instead of more conventional insulation. From what I've gathered so far, thorough washing and then treating with Borax seems to be the best preparation. Does anyone have any other/additional suggestions? Sheep's wool is naturally fire retardent according to what I've read on the web and has good insulating properties. Any comments/experiences/further reading links would be appreciated. Thanks

Damp Wool


I've read that damp wool heats up and can combust.  Not sure why but you might like to check into that before you go any further.  Sorry to be the bearer of gloom!