Rmax btwn drywall & rafter any impact?
Our kitchen has a cathedral ceiling (2×12 rafters) with two velux skylights. Because of condensation issues on the skylights during past winters, I am re-doing the drywall in the “well” that goes from the finished ceiling level up the face of the 2×12 to the recessed skylight.
I had a thought while demo’ing that to help insulate the drywall from the rafter it might be useful to put a 1/2″ or 3/4″ layer of Rmax between the rafter and drywall. I don’t have room for anything thicker than 3/4″. Is this too thin to have any impact, or has anyone done something similar?
This is in addition to doing a better job of insulating around the inside rough opening of the skylight than was previously done. I will also be making a kind of storm window at the base of the “well”, even with the surrounding level of the finished ceiling to keep the warm air from getting trapped in the cooler skylight “well”.
I am hoping that these steps will remedy the problem of the condensation running down the skylight “well” and following the slope of the cathedral ceiling to the wall. Any ideas or thoughts?
Replies
What kind of ventilation do you have in the kitchen?
Is the condensation occurring on the skylight or on the walls of the well?
Insulating the well better may help some, but controling the amount of moisture laden air the reaches the skylight would be better.
An exhuast hood tied to an HRV would be something to look into.
Dave
I can't help much with answers on your plan except to tell you about a situation in a condo unit I manage. The condo owner was having water condense on his skylight and drip down into his great room. He installed a piece of Plexiglass as a storm window at the bottom of the well, even with ceiling. He didn't make it air tight. That created a colder well, the moist warm air entered, and as he put it created a downpour instead of a sprinkle. We checked out the skylight and found only a single layer. Don't know how that happened, but we installed a new bubble and every thing was fine. He removed the storm window, so I don't know if it would be a problem with a good skylight. This happened in 1991 and same owner is still there and has never had any further problem.
Edited 11/8/2006 11:06 am ET by condoone
What do you mean by a single layer, was it missing one of those exterior bubbles some skylights have? Is the bubble you added on the exterior? These skylights open and didn't come with an exterior bubble. ALthough maybe I could get one to install for the winter.Thanks for the tip, I will make sure the storm window is airtight. I plan on mounting a frame of trimwork on the inside of the well and then attaching the storm window to the frame. That way I will be able to remove the storm window and have a decent looking frame that can remain in place the rest of the year. I can use weatherstripping between the frame and storm window to make it airtight.
I don't know what you call the clear skylight material, but it resembled a bubble and was supposed to be a double layer. We think someone broke the top layer and never replaced it. I just edited my first reply to say I don't know if the storm window would work with a good skylight because the owner removed it.We do find minor condensation problems in many of our skylight wells and upon invetigation (luckily most have attics)we find they are not insulated.
Just reporting back in case others encounter this same issue....
So far so good on resolving the condensation issue in the kitchen cathedral ceiling skylights. I decided to put the 1/2 Rmax behind the drywall and made a couple of storm windows with 1/4" plexiglas and Azek. Used some self stick foam weatherstripping between the storm window and the moulding on the inside of the ceiling well where the storm windows are fastened to. Had to wait a while for it to get good and cold to test it out, it has been a very warm winter for us so far.
There has only been a tiny amount of fog (vs the heavy, dripping water droplets we were used to on the entire skylight) on the perimeter of the glass of the skylight. Not enough to drip anywhere, just enough to fog about 1/2" of the edge of the skylight glass. This has happened on only the coldest two or three nights (about 15 - 20 degF) so far.
I'm not sure if the storm windows alone would have had the same success or not. But since I already had the drywall off the rafters, it made it an easy decision to do the Rmax also.
As was suggested regarding humidity levels, this is in a kitchen so there is plenty of moisture in the air from the sink, dishwasher & lp stove. Even when the dishwasher is in the dry cycle throing out a lot of steamy air, there has been no problem. Since it is a cathedral ceiling we keep the ceiling fan running on low as we always have to help circulate the warm air.
The repainting of the ceiling has yet to be done, that is why the two shades of white can be seen. SWMBO is still deciding on the extent of the double oven, cooktop remodel yet to be done & the colr scheme. I also want to use a thin piece of trim around the edge of the storm window to clean up the uneven reveal between the storm window and ceiling well.