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re: insulation techniques on new home
18 aug 2000
ramman wrote:
>i am shooting for r-19 for my outside walls on a new construction in sc.
>this theoretically would call for using 2"x6" wall studding and 5 1/2"
>batting between them.
that's a bit less than r19, with r1x5.5" studs on 2' centers and a plate
and sill that occupy 0.208 ft^2 of each 2'x8' wall section, which put a
0.0379 btu/h-f conductor in parallel with 0.831 for the batting, a total
of 0.869 for 16 ft^2, ie 16ft^2/u0.869 = r18.4. the sheathing and drywall
further reduce the overall r-value by acting as heat-gathering fins for
the studs.
>...a different and better approach was to use std. 2"x4" [on 2' centers?]
>with 3 1/2" batting insulation and then on the inside wall lay high
>density 2' x8' or 4' x 8' foam board horizontally. 11/2" pink board
>has an r rating of 7.5. this would add to the r-11 of the 3 1/2" batting.
sounds like r7.5 in series with the parallel combination of 0.208ft^2/r3.5
studs + 15.792ft^2/r11 batting = 1.495 btu/h-f for 16 ft^2 of wall, ie
r10.7 + r7.5 = r18.2, with almost no fin-effect for the indoor sheathing.
>...i have further been told that on the room side of the foam board
>i should place 1/2" plywood thus setting up what has been called a
>thermos bottle effect with the outer wall being the sheathing and
>vapor barrier and the inner wall of the bottle being the plywood.
maybe the plywood is useful as an interior finish and vapor barrier in
your warm climate, vs increasing the wall's r-value...
nick
nicholson l. pine system design and consulting
pine associates, ltd. (610) 489-1475/0545
821 collegeville road fax: (610) 489-7057
collegeville, pa 19426 email: nick@ece.vill.edu
computer simulation and modeling. high performance, low cost, solar heating
and cogeneration system design. bsee, msee. senior member, ieee. registered
us patent agent. web site: http://www.ece.vill.edu/~nick
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