Vapour barrier

[scottybear]

I am going to have to replace the insulation in the attic of a house I bought but my question is about the vapour barrior. I know it's supposed to go under the drywall but in the house there is none on the ceilings. I wanted to know if there is any benefit or if it is even ok to go over the ceilings from above in the attic before I re-insulate. I know this would be lots of work wrapping the joists and am willing to put in the time if there is any benefit. Also, I planned to use batt insulation R40 for replacement, Is that enough? If I can ask another question, any opinions on powered attic fans versus old fashioned venting? My house is in Saskatchewan, Canada.

[Hube]

The best location of a 6 mil Vapor barrier is between the drywall and the studs or ceiling joists. that way the wood is protected too. I have heard of a special type of PAINT that can be applied in the case of no vapor barrier.
It might be worth checking this paint out as it would save you from removing ALL of your ceiling drywall in order to staple on some 6 mil poly in order to apply the vb properly.
I would think that R 40 batts in a attic floor area should be quite efficient. In my area of central Ontario, R32 (minimum) to R 40 does very well. Fiberglas batts or "blow-in" celluloise is very good.
Attic ventilation via "gravity' is all that is needed. If it's done properly, it does the job without spending many $$ on fans, wiring, electricity, etc.
SOFFIT vents and either a continuous RIDGE vent or several high, near the ridge mushroom type vents are required.
Normally, for every 300 sq ft of attic floor area, a MINIMUM of 1 sq ft of vent is required (divided 50/50 between soffit and ridge). In other words ,if the attic floor area was 40 x 30 = 1200 sq ft, you would need a MINIMUM of 4 sq ft of venting.... 2 sq ft for soffit,... 2 sq ft for ridge.
This calculation of a sq ft is based on 144 sq inches of "free" air.
Insect screens are very restrictive, so in order to have a free area of 1 sq. ft., the vent may have to be approx 50 % larger depending on the size of the screens restriction)

[scottybear]

Thanks. Any ideas where i could find info on the paint ? Of course I'm wondering if I insulate properly, will it make a big enough differnce(considering price and work) to go that route?

[Hube]

Scottybear; Try a "color your world" paint store if you have one in your area.
And installing insulation without a vapor barrier on the heated side is bad because without any vapor barrier the insulation will be sbject to moisture and therefore will lose much of its R value.

[scottybear]

Appreciate the help, thanks for taking the time.

[pushkins]

Zinnzer oil base is a vapor barrier, available at Home Depot and Lowe's.