[Greenbuilding] [BULK] tub/shower and window questions

[George Tremblay]

Thanks much to all who have responded to my inquiry.  Lawrence's analysis
inclines me toward figuring out some movable insulation panels for two
large, south-facing window assemblies, sealing the walls well against air
movement, and worrying less about incremental improvements in R-values.
	George

George Tremblay writes:
>>The builder who will be doing this phase has proposed that I'd be
>better advised to upgrade the windows than go beyond the standard 6"
>wall--that essentially, the windows will be the weakest link in a pretty
>good envelope, at that point.  The new walls will constitute about half
>of
>the exterior surface of the house, with the remainder being the wall
>assembly I described above.  Assuming an R-40 roof, would anyone care to
>offer advice on this?  If the windows are the weak link, what would be a
>reasonable step up?
>
"Lawrence Lile" <LLile at projsolco.com> writes:
>
>Here's my take:  When I built a house, after some analysis, I put in 6"
>walls, filled them with cellulose insulation, and wrapped the whole
>thing in 1.5" of foam insulation plus tyvek. 
>
>Inside, I carefully caulked all the seams in the plywood skin, and then
>carefully sealed all the penetrations in the interior sheetrock.  This
>included caulking around the edges of all the electrical boxes, and
>(before sheetrocking) squirting foam around the backs of the electrical
>boxes and in the holes where romex penetrated the top plates, to seal up
>the swiss cheese that the electricials leave after they get done.  We
>caulked seams in the exterior plywood skin, caulked the top and bottom
>plates to the skin and to the floor, and carefully sealed every
>penetration.  
>
>My take is, spending labor money on caulking and sealing WAY beyond
>normal practice is money better spent than on extra superinsulation.
>You swiftly get into diminishing returns with insulation: If you have an
>uninsulated wall, an inch of foam does a whole lot of good.  If your
>wall is already two feet thick, an inch of foam accomplishes almost
>nothing.  Somewhere in the middle is a balance point where economics
>makes less sense.  
>
>
>Do you want to go to R-38 walls, doubling the normal insulation level?
>Cut your floor area in half, and you've done about as much good.  You'll
>spend twice as much money framing a superinsulated house, because you
>have to build two frames.  It gets expensive fast.  
>
>Your friend is right, that the windows become the Achilles heel very
>quickly.  Earlier on this list I showed that $100 spent on moveable
>interior insulation for windows beats the energy savings from wrapping
>the whole house in 1.5" of foam.  Anything that improves window
>performance makes a great difference in overall energy performance very
>quickly.  
>
>If you do the math, you'll find that 50 to 75 percent of your energy
>flow in a wall is in the window.  Doubling the efficiency of an already
>efficient wall won't affect the whole by very much. 
>
>Now don't get me wrong - the people using superinsulation and Larsen
>trusses are doing a noble thing, and we should be pushing the technology
>in that direction. However, that's not how I chose to spend my limited
>money.  
>
>
>Lawrence Lile, PE, LEED AP
>Project Solutions Engineering
>
>