Tim,
Seems like R- 6.8 closed cell urethane foam would be a better / (over  
all) less expensive option, allowing you to forget the extra expenses  
involved with  wrapping the exterior. If you choose the cellulose &  
exterior wrap option, you probably should also include the expense of  
an interior vapor barrier, which would eliminate air infiltration and  
interior moisture escaping and becoming trapped within the cellulose  
filled cavities.  Just a thought.

Dave Robins

SDR & Associates
131 Cedar Street
East Hampton, NY. 11937
(631) 324-8868
(631) 324-0900 ~ fax

On Mar 10, 2010, at 11:47 PM, Ben Graham <[log in to unmask]>  
wrote:

> Tim,
> Not sure if you have seen the Building Science Corp. method for this  
> deep
> energy retrofit method, but I would check it out, they have it down  
> pretty
> good.  Furring strips are utilized to secure the siding.  I don't  
> think they
> would recommend polyiso or house wrap.  Essentially, if you seal the  
> foam
> well, you don't need the wrap.
>
> Ben Graham
>
>
> On 3/10/10 8:29 PM, "Tim Yandow" <[log in to unmask]> wrote:
>
>> Hello all,
>>
>> On the subject of green building, I am soon beginning renovation  
>> work on a
>> 1960's home in Burlington. We are adding an addition to the south  
>> and west
>> sides of the house. The new envelope will be 2x6 with damp spray
>> cellulose. The existing house is 2x4 with fiberglass and the owners  
>> would
>> like to bottom up the house more, so we are thinking about adding a  
>> layer
>> of insulation to the outside of the house since all the old vinyl  
>> siding
>> is coming down and the windows all replaced (most of them have broken
>> seals). I am trying to figure out the best way to insulate from the
>> outside and make provisions for new corner boards and hardi-plank  
>> siding.
>> With polyisocyanurate, for instance, there is the problem of not  
>> being
>> able to add house wrap and needing to use longer fasteners for  
>> siding and
>> to secure window flanges. Or can strapping be used over that? Then  
>> there
>> is the issue of extension jams either inside or outside...I would  
>> love to
>> know if anyone has worked out a good solid system to do this. What  
>> I have
>> read and seen so far does not satisfy me. Thanks.
>>
>> Tim Yandow
>
> Those who give up freedom for safety, deserve neither.
> Benjamin Franklin
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