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Community and Q&A

Adding insulation

Crush8633 | Posted in GBA Pro Help on

My wood frame Wisconsin home was built in 1894. Over the years I have been making improvements.
When I take down a plaster and lath wall, I’ve been putting in insulation and 4-6 mil plastic to tighten things up prior to drywall. I found that upstairs, where the roof meets the outer walls there exists an opening directly to the outside. I assume it’s designed that way to circulate air. Is it OK to be sealing that up like I have been doing? Should I be putting in ventilation panels in those spots up to the attic space?

In the upstairs areas I have insulated the angled part of the wall/roof, I clearly see a difference in the amount of frost on the roof shingles winter. Is that OK? I’m worried I’m trapping moisture. I’m worried the shingles could be effected negatively. If it’s ok to do so…I would be excited to know I can get myself in the attic to fill the spaces between the inner roof framing.

Some expert advise would be very appreciated. I’ve trying to research this online all these years without a satisfactory answer to these questions. I love my old home. I’d hate myself if I did something to damage it.

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  1. GBA Editor
    Martin Holladay | | #1

    It sounds like the area you are talking about is a sloped ceiling on your second floor. This type of insulated sloped ceiling can't be insulated the same way as a wall.

    If you are insulating a sloped ceiling with an air-permeable insulation like fiberglass, you must include a ventilation channel between the top of the insulation and the underside of the roof sheathing. This ventilation channel must have openings at the bottom to allow outdoor air to enter the channels. The channels need to connect with a vented attic or a ridge vent (that allows the air to escape).

    You still need an air barrier to keep your warm, heated indoor air where it belongs -- indoors -- and to limit movement of this indoor air into the ventilation channel.

    If you don't want to create a vented roof assembly, you can create an unvented roof assembly. This approach will usually require the use of spray polyurethane foam.

    If all of this is new to you, you may want to read articles on the topic here on GBA. Here are some links to get you started:

    How to Build an Insulated Cathedral Ceiling

    Site-Built Ventilation Baffles for Roofs

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