Blown-in insulation in cathedral ceiling?
lesjones
| Posted in General Questions on
Attached is a photo of a cathedral ceiling in a hallway in a 50 year old house we moved into recently. Rafters are 2″ x 6″. I know it won’t have much R value, but it’s better than 0, which it is currently. The simplest thing to do would be to blow in cellulose or fiberglass. Anything else would be very difficult to do because of a lack of workspace. Are there any potential issues with this since it won’t allow any airflow?
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Another option to consider depending on the life left on your roof would be to re-sheath when you roof - opening up the bays so you can spray foam them (that's going to give you the best r-value per inch). If you live somewhere cold and snowy - spraying any eave overhangs too will help prevent ice dams.
Yeah, I will probably do that, but it will hopefully be a long time before I replace my roof!
lesjones,
Unfortunately you can't add permeable insulation to unvented empty rafter cavities.
There are two types of roofs: vented and unvented. If you want to use permeable insulation (batts or blown), you need a vent cavity (or in climate zones 1, 2 and 3 a vapour diffusion port). Without those you will have moisture issues. If you don't have room or it isn't possible, you need to use impermeable insulation. This article shows options that work. https://www.greenbuildingadvisor.com/article/five-cathedral-ceilings-that-work
I stand corrected and deleted the erroneous comments I made above. Thanks for steering me straight Malcom Taylor.
@lesjones - this article covers why you can't use permeable insulation in an unvented space. https://www.greenbuildingadvisor.com/article/can-cellulose-be-used-in-an-unvented-roof
Deleted
Thanks for the input. I'm attaching a side profile to help you get a clearer picture of what I'm dealing with. I just threw it together so the measurements aren't very good (the hallway is 4 feet wide and the storage area is more like 10 feet) but you get the picture. As you can see, it's a single slope roof and I'm trying to deal with the yellow area and then maybe the red area. Both of them had fiberglass batt insulation at one point, but it is in bad shape and probably wasn't very effective to begin with. These areas are difficult to deal with since I can't easily remove the ceiling or roof. I had the idea of cutting strips of 4" polyiso but sealing the sides wouldn't be easy but might be do-able with a 4 foot spray foam trigger. What do you think about that idea?