Attic insulation Q in existing structure. No vapour barrier.

I recently took over a house built in the 1980's during a building boom. The quality of workmanship is poor. I was inspecting a part of the attic which, up to now, was inaccessable. The builder forgot to put in insulation!!! The heat escapes right through the plaster board ceiling and out the house.
The ceiling plasterboards are nailed directly to the ceiling joists with no vapour barrier installed. I'd like to insulate this attic space but can't fathom how to apply a continuous vapour barrier to the existing structure without ripping down all the ceilings involved. I've seen home renovation programs like (Bob Vills'a Home Again and other similar programs) where professionals spray an expanding insulation product, Polyicynene I think, into new construction cavities without first applying a vapour barrier. Is this a good way of getting the existing structure covered in a moisture-proof barrier? Can I follow up the Polyicynene application with a blown loose-fill cellulose or fibreglass batting insulation for greater R-value and not worry about moisture problems like mould?
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My home was built in 1999. The ceiling construction is the very same. Most of the homes in the western US are built this way.
I have cellulose and so have all of my homes in the last 30 years. I am no expert but I would think that the vapor barrier would be important in the walls not the ceiling.
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On Sun, 26 Dec 2004 15:04:06 -0500, "Robert MacKinnon"

I have blown in fiberglass insulation. No vapor barrer. I was concerned so I did some research, there are those for and against vapor barrers when the attic is a free air space like I have. since the attic is a free air space, the idea is that the vapor will migrate slowly upward and out the house. If I had a vapor barrer some say it will cause the ceiling rock to collect water and sag over time.
So, this is what I actually did. I bought cans of BIN and painted my ceilings. Now the rock can't absorb mosture, and I have a vapor barrer.
hth,
tom @ www.WorkAtHomePlans.com
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Sorry, Tom, what is BIN? This is a product i've not heard of before.

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On Sun, 26 Dec 2004 22:45:21 -0500, "Robert MacKinnon"

Here's the product page: http://www.chopurl.com?449
hth,
tom @ www.BookmarkAdmin.com

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That agrees with what I read somewhere, many years ago; that certain types of paint, presumably what are called "Oil paint", can act as something of a vapour barrier. I recall that did not include latex/water soluble/based paints?
In a cool damp climate a vapour barrier IS required in all walls and ceilings; to minimize warmed (and therefore moisture bearing) house air percolating into the roof space and condensing up there. However without a vapour barrier I guess the important point is to make sure that the attic airspace is very thoroughly ventilated?
Roof space venting, in this jurisdiction, for example, is a minimum of three (3) square feet per one thousand (1000) sq. ft. of ceiling area and that it " ... be distributed around the perimeter to ensure cross ventilation and removal of damp air".
To this house we added, under a government sponsored residential energy conservation scheme, some 25 years ago, an additional several inches of blown in insulation, on top of the original six inch glass wool batts; making sure it did block the additional soffit ventilation vents. Then later we covered up some of the 1970s style ceiling tile ceilings from below with plasterboard adding one inch of styrofoam on the warm side of the insulation. (There are guidelines for putting additional insulation 'inside' a vapour barrier, in this climate).
With attention to ventilation winter and summer (30+ years) we appear to not have mildew or other problems in our very low slope roof space. Adding that this fairly windy climate helps; so, while I've considered and even have a suitable fan on hand it has not been necessary to use power ventilation of the roof space.
Terry.
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Sorry, Tom, what is BIN? This is a product i've not heard of before.

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I didn't realize that BIN, which is basically shellac, had vapor barrier properties. Benjamin Moore makes a wallboard primer that is specfically made to be a vapor barrier.
http://www.benjaminmoore.com/tds/1033/TDS260B.pdf
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