In terms of the fitting out process windows can be fitted early on the make shell watertight. Do not final fit though as they will need to be removed several times over the course of the fit. Alternatively, fit oversize wooden forms that can be removed after spray insulation has been applied. Use silicon sealant to keep out the weather but remember any residue must be fully removed before any paint finish is applied to the outer shell.
Sealing windows into the cabin side has to be one of the most important jobs. Poorly fitted windows will allow water in and potentially ruin what should be a beautiful interior with water marks.
There are various options when it comes to choosing a suitable waterproof material to act as a gasket between the window frame and the cabin side: Silicone, Mastics such as Butyl or Arboseal and an adhesive closed cell foam tape.
All of these have their own benefits: Silicone comes in various forms , some which can be painted over and others which cannot, butyl which is used extensively within the caravan and motorhome manufacturing process, Arboseal, which is widely used within the building industry and is now also widely used by narrow boat builders because as the fastenings are tightened the Arboseal is compressed and fills any gaps especially if the cabin side is not perfectly flat. The adhesive closed cell foam tape is becoming very popular particularly as one side is adhesive and the other side is a plain foam which, when compressed, forms a seal between frame and cabin side but has the benefit of allowing the window to be easily removed whereas the sealants can make the windows difficult to remove and all old sealant must be taken off and replaced prior to refitting. In many cases, the act of taking a window out will distort the frame which when put back, will not seal and looks unsightly.
Further information on types of windows and portholes found on canal boats can be found in the Integral Parts
section on the website.