We have a 1986 SIP home that is currently undergoing some major construction due to a previous owner putting on a traditional roof over half the house creating massive localized condensation issues. The only issues I see on the side with the original SIPs are in the master bath over the shower, where a light fixture allows moisture to penetrate the panel. The bathroom has a fan but it is mounted in the wall a good bit below the peak of the vaulted ceiling, so moist air stays trapped in the recessed skylights and the peak. I am planning to replace the light fixture over the shower with a fan/light directly over the shower to pull out the moisture at the source. Does anyone have a recommendation for a fan that can be mounted in the SIP and vent directly out the roof? This is not a lot of space to work in, as it is only the thickness of the SIP. Also concerned about it being a hole for cold air to pour directly into the shower in the winter months (northern OH). The house does not have any other major source of ventilation, which I've noticed seems to be the trend nowadays with SIP construction. A fan that is reliable enough to be run on a timer on a regular basis would be great too. Thanks in advance for the advice!

Hard to visualize from the description but here goes. I would definitely lose the light fixture over the shower but not necessarily replace with a fan/light combo. First step I think is to look at replacing existing fan with a bigger unit. Use this site http://www.todayshomeowner.com/bathroom-vent-fan-cfm-calculator to calculate CFM requirements and maybe go up a size to be sure. I am a big fan of the Panasonic Whisper line. Mine are wired to a wall timer and have worked trouble free.

Without knowing your SIP thickness it may be possible to find a fan that would be thin enough to fit (if I understand the problem/configuration), but I know of no fan that exhausts in such a way that would not require gouging out SIP foam to run fittings/duct; plus you now have another roof penetration. I suppose one could rough in a space below the SIP to accommodate, but... Better to remove exsiting set-up, fix the SIP over the shower, beef up existing fan to handle your moisture load, and modify lighting at shower area in another way. Lots of options for the lighting.

Thanks for the response, I will check into the Panasonic units.

One of the complicating factors is deeply inset skylights, one of which is directly adjacent to the shower. As a result all the warm moist air from the shower rises into this space and avoids the existing wall-mounted fan which is lower than the skylight on the wall, several feet away. The water condenses all over the skylight and surrounding wood in the winter leading to mold. I don't think any normally sized vent fan would create enough turbulence to pull the air down and out of this skylight.

Yeah, I can imagine the skylight issue on a cold Ohio morn. How deep are the SIPS?

A possible approach in addition to a properly sized fan could be sliding covers for the skylights. They make units that might mitigate the amount of moist air entering the skylight well in the first place. Not sure how tall your ceilings are but Mom has these covers on her skylights that are ~14-16' high that she is able to open and close with a provided collapsible wand thingie. Not the most elegant solution but I don't see any easy answers for this problem.

Besides you could close it during the start of winter and leave it closed all season. You won't be missing any of the light as your skylight is covered with snow anyway .

Once the hot air/water vapor rises to that area, no lower exhaust fan is going to move it.

Maybe a 3' ceiling fan mounted under the skylight and blowing upwards would move enough air to dilute/mix the water vapor and warm/dry the surfaces. Or some infrared bulbs in the recessed skylight would keep the surfaces warm enough that condensation doesn't occur (ie, warmer than the dew-point of the surrounding air/water vapor mix).

But I use a fan in the shower stall itself (attempting to remove the moisture before it escapes to the room). Some always leaks out.

skip the fan, do an ERV or Hrv

Going with a low profile Panasonic in the shower itself, only 5-5/8" thick, so hopefully will leave some SIP above it for insulation. We will see how it improves the situation.

ERV or HRV would be great, but is that simple to retrofit into existing construction?