Replies

1. 
   schrickker | Apr 15, 2014 01:48pm | #1

   Insulating Cathedral Ceilings fom above

   Hi. I am also in Ontario and went through a cathedral ceiling insulation process. Others who contribute on this chat will have better building knowledge than I do and will provide good advice but let me offer a few things for you to consider. I'm assuming that you intend to remove all the deck boards, place batts in the rafter cavities and re-deck the roof. It sounds, from your post, that you are going to do that work yourself. I have insulated cathedral ceilings from inside and outside and it is real tossup as to which one is worse. There is the dust and mess of tearing out the ceilings in the house vs. standing on the roof and rafters while taking off the boards and re-decking. And, you can almost depend on it raining the week that you do it so check to see if the roofers have waterproof tarps to lend or rent to you. The last truly waterproof 50' by 30' tarp I bought last October cost over $2,000 so it is not usually something you want to invest in yourself.

   By rights you should have a vapor barrier but you probably don't have one now so ...  Also, the vapor barrier needs to go on the ceiling side of the rafters which means you would have to remove the plaster and lath. Finally, we ventilated our cathedral ceiling about 10 years ago to try to reduce the incidence of super-size icicles. It helped somewhat although the icicles were now just big rather than super-size. But the house was less comfortable. That's because, without that vapor barrier to help reduce airflow through the rafter area now that they were ventilated, a lot more air was rushing through the rafters and down the inside walls and out every light socket, electrical outlet, and opening it could find. We eventually removed everything down to the inside of the outside walls and spray foamed, which solved many of our problems.

   You may not experience the same problems but these are things you can consider.

1. 
   vicktown | Apr 15, 2014 11:11pm | #2

   Thanks Schrikker. It is good to hear from someone who has been through a similar process. To clarify somethings: I have hired some roofers to do the roofing work but will also have them do the insulation work while they are up there. This is why I have chosen to attack from the outside rather than inside. I will be lending a hand with the work where I can without getting in the way. I am only removing the decking from the roof where it is cathedraled which is about the first 4-6 feet from the roof's edge. I'm not clear about your situation but I do also have an attic. There is maybe 3-4 ft of ceiling that is angled and in direct contact with the rafters. This is the space I am hoping to deal with.

   I do have a few questions regarding your situation and post. Firstly, Im condisering laying down some sort of vapour barrier. Perhaps using poly in the rafter bays on the lathe and plaster, topped with roxul and then with the moore vents and then the decking. There are also more expensive foil backed bubble wrap products out there. Any thoughts on these approaches?

   Im also a bit confused about why you had air coming into your house from the walls. I would think the air would come in through the soffits, through the moore vents, into the attic and out the attic vents. Im not sure where the air would go down into the walls.

   We are also considering blown-in callulose insulation in the balloon framing of the house (which are currently empty). Any experience with this? Ive heard that this type of insulation can absorb moisture and cause issues inside the wall.

1. 
   schrickker | Apr 16, 2014 07:46am | #3

   Insulating Cathedral Ceilings

   Google "Don't used foil faced bubble insulation" and you will find several blogs from Green Building Advisor. I would copy and paste the links but I continue to have trouble copying and pasting anything to this site. Also search for "Can You Add Rigid Foam Insulation on the Inside of a Wall" by Scott Gibson in the search bar of Fine Homebuilding and follow the Green Building link in the article sidebar for further information because there are discussions about cellulose and drying.

   With respect to your idea of adding a vapor barrier inside the bays, a vapor barrier should be continuous otherwise the vapor and air will find its way around the barrier. This means that it would have to be installed on the inside and cover the rafters and bays. If you drape poly vapor barrier from the outside and over the rafters, so that the barrier is on the warm side of the insulation but on the cold side of the rafters then moisture will probably settle on the warm side of the rafters and may not dry out.

   In our case we don't have an attic and we tried ventilating without adding insulation. This was also before I learned that there should be a balance between lower and upper roof vents. Subsequently, the combination of greater venting, no vapor barrier (or, really, air barrier), and poor insulation meant the air didn't escape through the vents but also came through the walls.

   I think the thing I have learned through several renovations is that there are rules to observe but the solutions vary. I hope the articles I have suggested help.

2. 
   schrickker | Apr 16, 2014 10:34am | #4

   Insulating Cathedral Ceilings from Above

   I replied to you earlier this morning but when I chose 'Post' my response disappeared. I must have done something wrong. It might be a day or so before I can recreate that answer. In the meantime Google 'Don't use foil faced bubble insulation' and several artlcles will show up from Green Building Advisor. Also search the Fine Homebuilding site for an article "Can you add rigid-foam insulation on the inside of a wall' by Scott Gibson. Follow the links in that article to Green Building Advisor; there's a blog called 'Beefing up Insulation in a Kitchen Remodel'. You should read all the posts that follow the article for ideas.