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Kingspan narrowboat insulation

We are considering having a new bespoke narrow boat built and have visited nine potential builders after visiting Crick last year. Perhaps not surprisingly, we have received various opinions on virtually ever aspect of boat build and design including insulation of the shell.
Most builders seem to use spray foam. But one builder, who we are particularly interested in, uses a Kingspan-sourced ridged foam board which, while giving a consistent thickness would seem to have limitations in insulating hard-to-reach areas. I wondered what your opinion is regarding the merits or otherwise of the two systems?
Trevor Hogg.

Asked by: Andrew Denny  | 3.58pm, Monday 13 February

WW says:

The key element with insulation is to avoid condensation which can manifest itself over time in the form of stains on the cabin lining. Providing a vapour barrier between the warm moist air and the cold steel surface will stop condensation.
Sprayed foam insulation is applied directly to the inside of the steel shell. Rigid sheet insulation such as Kingspan requires careful cutting to fit and fixing with any gaps sealed with metalised tape. Sprayfoam needs to be carefully applied to give a uniform thickness without any thin patches and thick enough for the required insulation factor. Sheet insulation is usually fitted to completely fill the gap between the shell and the lining, reducing any air movement; sprayed foam often does not fill this void to avoid having to cut away any excess.
Potentially a higher insulation factor can be achieved with rigid boards but it does need to be fitted well. Both systems have their merits but sprayed foam is the most expensive.

Rupert Smedley  | 8.49PM, Monday 13 February

An advantage to using board-type materials is that they can be removed fairly easily should repairs or inspection of the steel shell ever be required- and if any welding needs to be done, scraping back- then reapplying spray foam, can be a challenge.
Some of the boarding materials have much better thermal and fire resistant properties than spray foam, though as you point out, they can be difficult to reach harder areas such as bearers (though these can be covered in 3M's Thinsulate, for example).
Some spray foams can react with other polymers, notably PVC cabling, though if the correct material is chosen, this should not be an an issue. If spray foam is badly or unevenly applied, it can lead to voids where corrosion can take place; conversely any gaps left with boarding materials can lead to pockets of condensation as Rupert suggests, with localised corrosion as a possibility.
In the end, the choice between the two wouldn't be a deal-breaker for me in choosing a builder... high quality fitout, care with use of materials and especially good ventilation are far more important! And for you to enjoy the finished product :)

Mark Langley  | 11.04PM, Monday 13 February

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