Replies

1. 
   Gabe | Mar 25, 2002 10:23pm | #1

   Donna,

   In your climate I wouldn't worry about thermal bridging of wood joists or components. Overspraying with foam will take care of those trouble areas.

   Everything is fine, enjoy your new home.

   Gabe

1. 
   TNDonna | Mar 26, 2002 05:40pm | #2

   Thanks much for the reassurance, Gabe. One more question: if you were in my shoes would you spray only 5 1/2" under the roof deck as recommended by Icynene for our region, or would you add more in certain areas to compensate for the framing (ie, next to double studs etc)? Wasn't sure if that's what you meant when you wrote "overspraying with foam will take care of those trouble areas".

   Of course, the Icynene contractor would be happy to fill up the rafter bays if I want him to, but if the additional 4" would be overkill I'd rather not spend the extra dollars on it.

   Donna

1. 
   CloudHidden | Mar 26, 2002 06:15pm | #3

   All insulation has a cost/benefit ratio. For the type of houses I work with, for example, we've discovered that more than 4" of foam is wasted money. Not in the sense that it doesn't help. More insulation can almost always help. But the cost of the extra foam is a capital cost whose value cannot be made up for by reductions in utility costs. Your house will also have it's break-even point at some thickness, which may very well be the recommended 5.5--I dunno.) Also, adding more next to a trouble spot won't help reduce the losses from the trouble spot.

   [That's just a comment on filling bays with more and more foam, and not a comment on overspraying double-joists.]

1. 
   TNDonna | Mar 26, 2002 09:59pm | #4

   Good points about cost vs.benefits; thanks. However, I think I may need clarification from someone on what is meant by overspraying, as I originally interpreted it to mean beefing up the thickness next to those rafters. Does it mean instead that foam is sprayed UNDER the doubled rafters so they're enclosed by foam on the bottom as well as sides? Guess that would not be an option on cathedral ceilings but would work where there won't be drywall installed, ie, attic areas. Right? Or am I still misinterpreting the recommendation?

   I realize someone at Icynene would probably be able to answer this, but do appreciate the chance to gather the objective, experienced-based advice of others before making a decision. (Hard lesson learned!)

1. 
   CloudHidden | Mar 26, 2002 10:09pm | #5

   >Does it mean instead that foam is sprayed UNDER the doubled rafters

   That's how I read it, but was hesitant to interpert another person's post. Continuous foam is a great way to stop air infiltration where you don't want it.

2. 
   Don | Mar 31, 2002 09:42pm | #7

   Cloud:  I live in Nawth Jawja, not too far from you in Nawth Ca'lihna, so my insulation problems are similar.

   I am reaching the point that I must make some decisions on how to insulate.  I first have to convince my county's chief inspector, who is a very reasonable man, that a sealed attic is the best way to go.  I think it can be done - he appears to be looking for a rationale to support me, based on some preliminary discussions.

   I talked to my insulation subcontractor last JULY about getting cellulose blown into the space between the rafters.  They had just recently begun doing wet cels insulation, and were quite high on it.  There were few of us down here who knew what it was and were true believers.  Called and talked to them last week, getting them prepared for the real thing, when the woman who does their quoting mentioned Icycene (?) and the fact that they had just started doing that. 

   Question - is Icycene (?) better than wet cels?   Is it a lot more expensive?  I have 2X8's on 16" centers for rafters.  Are you saying I shouldn't have a full 7 1/2 inches of insulation blown in?  Any other advice for me at this juncture, when I am about to make a decision and have an open mind?  (That's open, as opposed to full of holes.)  The woman is going to call me this next week and we are going to make a selection.  I'd like to be prepared before I hear a sales pitch so I can find the steer in the feed lot paving.

   My guess from reading the rest of this thread is that you have a coating of insulation blown over the rafters to keep them from conducting heat directly into the enclosed space through the blown insulation in the space between them.  I've seen that done on steel buildings, but never thought of having it done on wooden rafters. 

   Thanks.

   Don

3. 
   CloudHidden | Mar 31, 2002 10:43pm | #8

   Don, so y'awlz a fer bit nawth of Elanna? My ol' lady's brudder lives der.

   My house is not especially instructive here. I have a thin-shelled concrete dome which involves spraying polyurethane foam against an airform and then rebar and shotcrete. Follow my profile for more info if interested. No framing. The advantages are instructive--continuous waterproof membrane, continuous insulation with no gaps anywhere, and monolithic concrete and rebar--but the techniques aren't that instructive for frame-house construction. For that, I'll need to defer to others here who have vastly more expertise w/ frame houses...

4. 
   donpapenburg | Apr 01, 2002 06:23am | #9

   I used Icynene in my house N C Illinois . My installer did not want to put in more than 6" Though some spots puffed up to over 11 1/2" .

   I think that you could fill the joist with cells and be cost effective ,where the icynene would be too expensive to make a cost /return.

5. 
   Gabe | Mar 26, 2002 10:43pm | #6

   Donna,

   Cloud has already done a good job of filling in the gaps and I concur with his comments.

   There is a point where it's no longer recoverable to add insulation.

   Enjoy your home, you will be comfortable.

   Gabe