Replies

1. 
   Brian Pontolilo|Dec 10, 2018 08:01pm|#1

   RS,

   出于多种原因，在原始壁板上安装泡沫并不理想。想想将在泡沫后面运行的所有空间。空气密封件难以缩短泡沫的有效性。你知道你的房子是否在壁橱后面鞘？

2. 
   RSpatNKY|2018年12月10日08:23 PM|#2

   Thanks for the reply Brian. I haven't removed the existing vinyl siding yet. I have peeled the siding back in a few areas, and can see a layer of very thin foam (about 1/8 inch) sitting on what appears to be some sort of asphalt shingle material. Right below that is the original wood siding. There does not appear to be any sheathing like OSB or plywood.

   Ron

3. Expert Member
   Dana Dorsett|Dec 11, 2018 06:03pm|#3

   In US climate zone 4A northern KY you can install vapor-impermeable insulation on the exterior without risk of excessive moisture build up, as long as the interior side finish is between 1-10 perms (a Class-III vapor retarder), such as standard latex paint on wallboard. Even foil faced polyisocyanurate board is not a problem, as long as the window flashing details and drain plane are attended to.

   Is the original siding shiplap or wideboard plank, with the plank surfaces co-planar, or is it clapboards, overlapping each other with a slight angle? If it's structural and reasonably flat, leave it!

4. 
   RSpatNKY|Dec 11, 2018 06:27pm|#4

   达娜，
   谢谢回复。原始壁板重叠，在外部不平坦。我所遇到的壁板公司建议放置1/4英寸在原始壁板外部的粉丝，以获得光滑的表面，以放置新的壁板。在螺柱腔内的原始壁板和绝缘背面之间会有气隙，因此壁板可以干燥到内部，但如果风扇折叠右相邻，则可能会对外部干燥。但也许不是。这个问题。如果可能的话，我倾向于计划计划最坏情况。再次感谢。

1. Expert Member
   Dana Dorsett|2018年12月12日01:53 PM|#5

   Again, in your climate zone it never needs to dry toward the exterior as long as it can dry toward the interior. You're trying to fix a problem that doesn't really exist, assuming the bulk water(flashing, drain plane, WRB) is being managed reasonably.

   1/4" fan fold won't do much for R-value, but the air gap will provide an additional capillary break and a drying path (and perhaps a thermal bypass of the ~R1 of the fan-fold itself), keeping any liquid water that blows past the new siding from ever reaching the old siding.

   A 2x4 /R13 +R1 fan fold wall does not meet current IRC code minimum for zone 4. (it misses by quite a bit, in fact.) If there is a structural sheathing layer under that old siding the performance of continuous 3/4"-1" polyiso taking up that layer of the stackup would be enough to bring it up to code min, and would keep the sheathing warm enough to never worry about wintertime moisture condensation.

   Another way to bring it up to code performance (on a U-factor basis) without stripping the siding would be to install 1" (R6) polyiso edge strips on the interior side of the framing and install 4.5" of cellulose (R17-ish) instead of 3.5", long-nailing/screwing the wallboard through the 1" foam. With the R-values of the extra layer of siding, additional air-films and the R1 of the fan fold it would duck under U0.060 (=R16.6 "whole assembly").