Expert: Dave Johnson - 4/16/2009

Question
QUESTION: I am building a lake cabin in North Dakota and am in the process of insulating with standard batts and covering with 4 mil plastic...have some left over 1/4 inch fanfold (from the exterior)...was wondering if the left over fanfold could be used on the interior (over the batts)...would attach the fanfold to the studs, tape the seams, and cover with 4 mil plastic...would like to do this only on the North side...

ANSWER: Hi Bill,
I normally would tell you to NOT use the poly, but if you're only using it on one side, go for it. And, the fan fold is ok, too.
If poly is used on all walls, there is too much chance of condensation/moisture unless air exchangers are used.
Best of luck, and if you need more, mail me again,

Dave

---------- FOLLOW-UP ----------

QUESTION: Thanks for your response and time...the cabin is 18 x 24 with 10ft walls and a 12x12 pitch...from outside to inside are 1/2 logs, fanfold, Tyvek, 2x4 studs, batts, fanfold (north side only), and 4 mil plastic...the roof is steel on 1/2 inch plywood with R19 insulation...eventually we will cover the walls with knotty pine...There is a loft on each end... we are about 80% done with the insulating...We use the cabin year round, do not have an air conditioner but do have electric heat...are we going to have condensation problems? Where would we put the air exchangers?  

Answer
Hi Bill,
With all that I think the poly is overkill. The tyvek, fanfold(x2)
etc, will be tight enough.
If there is no poly, an air to air exchanger isn't needed.
You should not be bothered with condensatiobn.

I'm in Central Maine and also have a camp in the "north woods". Great to "get away" isn't it?

Best of luck,

Dave