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Old 01-06-2009, 10:21 AM   #1
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super insulation retrofit with rigid insulation

Hello, I'm considering re-insulating my 1-1/2 story 1932 house in central Iowa. Currently, it has plaster-lath 2/4 walls, blown cellulose insulation, 15 lb. tar paper, 1 inch polyiso r-board insulation, typar wrap, and vinyl siding. I'm thinking about the following: remove siding, cut 1-1/2 inch out of polyiso at the studs over the wood sheating, fur out with 1-1/2 x 2inch, put 1 inch polyiso over original polyiso between the furred out studs, install another layer polyiso over the furred out studs, 15 lb. tar paper, and then space out the vinyl siding for ventilation. This would make 3 inches of rigid insulation. I'm concerned about condensation in the walls, and also the water drain plane. I did not tape the 1st layer of r-board. My thoughts were to allow any moisture that got in the walls to get out. Also, I furred out my windows and doors. Is there an easier way to install more insulation on the exterior, or a different method? Thanks


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Old 01-06-2009, 11:31 AM   #2
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How is your attic for insulation? It seems to me that tackling this job for the second time is a waste of time / money considering your wall cavities are filled with cellulose and you have rigid foam on the exterior, giving you approx. R-19 insulating value.

The majority of heat loss isn't going to be through your walls. I'd concentrate on sealing bypasses and insulating other areas more prone to heat loss. Just my 2 cents.

Otherwise, have you looked into siding which provides insulating value?


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Old 01-06-2009, 12:00 PM   #3
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Reilley, I realize what your are saying about doing it twice! The attic floor has about 6 inches , some fiberglass and some cellulose. I know that isn't enough. I'm working on some knob and tube issues in the attic floor. Also it is a covered floor used for storage. Several years ago I added 2x4's on all the rafters , kneewalls, and the gable ends. My plan being to superinsulate the attic also. I will get back to this soon. I've heard so much lately about how vinyl siding leaks and I'm really wondering how great my typar wrap is doing. It would have been so easy when my siding was off to fur out the walls. It would'nt take a whole lot more labor as I was doing the whole job anyway. Also, extra insulation would have been about 80 more sheets. Wish I had done it. I cut air infiltration a lot, however. I would go to something else for siding, I think. cw
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Old 01-06-2009, 01:01 PM   #4
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thats alot of space and foam on the outside of that wall your proposeing woul would need a long nail to reach anything solid no matter what siding you install. you lose more heat thru the roof and windows that you will ever lose thru the walls
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Old 01-07-2009, 06:40 AM   #5
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Most heat loss is through windows and attic spaces. Before you start all of this, take a look at what it is costing you to much a month, divided by the sq/ft you are conditioning. I had a guy call me that has a 3000 sq/ft home and was complaining the electric bill was close to $200 a month....well, in the real world, it doesn't get much better then that.
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Old 01-07-2009, 10:23 AM   #6
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I have house of similiar nature,,,in next state 'west' of you. 'Before" I moved here I had Gerkin double pane windows installed,,,replacements,,along with good vinyl siding. before the window replacement was wooden double hung on the rope and pully system,,,they 'rattled' in the wind they were so loose,,,and energy effiecent,,,NOT!!! Now when it was 18 below,,,no freeze up inside, frost or even a percieved 'cold drop' I have had with any other windows,I HAVE had double panes before,,but never this good I guess,,,walls full of blwn fiberglass,,,my heating bill last month was 65 bucks

As soon as I get same issues with wiring above ceilings I will add more insulation there too.

Point being,,,windows should be replaced in those golden oldies FIRST,,then attic addressed,,,what your proposing wont pay off very fast,,,if at all!!

Next project for me is going to 'insulate' the basement block walls since it transfers the cold right thru them!! Plus replace the 2 windows down there that are single pane wooden frame and BAD!!! And put rigid foam in floor joist bay areas.(sealing cracks and left over areas with great stuff.) As well as recaulk ALL of exterior crack between wood and block joint!! Soon as it warms up a bit so caulk can adhere,,,,betting that area of your house needs that too,,,unless you have already done that!!! Are there any hairline cracks in foundation block mortar joints?? IF so that represents a bigger prob than general side walls too!!


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