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Old 10-11-2009, 06:50 AM   #1
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Insulation question


I want to add additional insulation to the basement perimeter (joists sitting on top of cinder block).

Currently, there is fiberglass roll type faced with kraft paper (facing basement). The local home store has been running specials on kraft paper faced product.

I have read regarding adding faced insulation to an already insulated attic, that one should cut slits in the facing of the added insulation.

Should the same technique be used in the basement? Specificaly, should the original (up against the plate) insulation have its facing slit, and then add the new insulation with facing to basement?

Thanks.

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Old 10-11-2009, 07:59 AM   #2
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Do not cut slits. You cut to fit & place in between the joists, with the Kraft facing away from the Sill. I used R-13 around my basement, but could have gone with R-19, which would have been overkill. You also do not use Kraft faced in the attic, you used unfaced. Only time you would use Kraft faced, would be to place the Kraft against the Gypsum for a heated space that may be the wall going up the stairs, but not to place along the rafters.

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Old 10-11-2009, 08:26 AM   #3
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Originally Posted by gregzoll View Post
Do not cut slits. You cut to fit & place in between the joists, with the Kraft facing away from the Sill. I used R-13 around my basement, but could have gone with R-19, which would have been overkill. You also do not use Kraft faced in the attic, you used unfaced. Only time you would use Kraft faced, would be to place the Kraft against the Gypsum for a heated space that may be the wall going up the stairs, but not to place along the rafters.
O.K., perhaps I wasn't clear. I want to ADD insulation to the existing (kraft faced toward basement) insulation; I do not want to replace the existing (kraft faced) insulation. My question regarding slits, in this case, was that only the original facing would be in play.

With regard to my comment on attic insulation. It also involves adding to the existing insulation, where there is a kraft facing against the ceiling (heated surface) and not have 2 facings in play.

The reason for using kraft faced insulation in this case, is a matter of economics (great sale).

V
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Old 10-11-2009, 09:47 AM   #4
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Insulation question


I thought the Kraft was supposed to work as a vapor barrier? Not quite as good as plastic though.
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Old 10-11-2009, 10:19 AM   #5
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Insulation question


You may want to consider removing the fiberglass entirely and replacing with styrofoam blocks (that is what I used), or expanding foam directly againsts the rim joist. Styrofoam is about R-5 per inch, so a four inch block gives you R-20, whereas fiberglass is perhaps R-3 at best, so you would need about 7 inches of fiberglass to get the same result. Polyisocyanate foam is quoted at R-7 per inch, better yet than styrofoam.
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Old 10-11-2009, 03:41 PM   #6
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Insulation question


It is the vapor barrier.
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Old 10-11-2009, 03:45 PM   #7
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You where clear, just that you cannot do it with Kraft faced insulation. Only way is to replace with R-19, or do as Dan stated, and use either block styro, or Poly, but will ned a contractor to do the latter. Why are you looking at adding more downstairs, having problems with a cold basement? Usually with a cold basement, it is because of air leaks, or poorly insulated walls. Since I reglazed my windows downstairs, and added low density expanding foam above to stop air leaks, my basement is staying the same temp as the upstairs. We keep our thermostat at 67, and so far both spaces are staying dead even.

Now, come later in the Winter season when the winds are blowing, and Wind chill gets down to -15, I will find out if I did it right to help cut costs down.
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Old 10-11-2009, 05:04 PM   #8
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Insulation question


The basement will never see the -15F because there is no wind below grade and the entire soil mass outside the basement in all directions since the soil for many feet away and down will have to be cooled off also. Don't get this confused with the frost depth because that is the maximum depth the most frost susceptible soil frost can freeze in 100 years or so. If you have a snow cover, the practical depth is at most half of the code number and often much less depending on the orientation and exposure.

In northern Minnesota in late February, about three months after the lakes froze and 2 weeks of -20F nights (and a few -40F ones) I was out in the woods looking for a survey monument. I knew where it was within a foot or so and scrapped off the snow and probed. I found the monument under the snow and the frost was only a few inches into the topsoil. - Mother Nature and mass are great moderators of climate.

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Old 10-11-2009, 08:48 PM   #9
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The soil mass does not reach as high as you believe. There is a 2' space between the ground & the top of the concrete block for my home. The house is over 70 years, and does not have any insulation in the walls. Being that they are double Gypsum with a Plaster coat, the house is very air tight, and maintains the heat very well, and cool in the summer. As for the basement, last year before we did the windows, the temp would be at 58 if the temp outside was like it is now, and in the summer at least 80. This year since doing the windows, like I stated before, the temp is staying the same as the main floor (67).

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