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Complicity in Stupidity

Greetings Everyone,
I just left a very disheartening situation where a homeowner has faithfully sought the advice of "putative professionals" to solve her problem with high bills and overwhelming discomfort. I say putative because in every case, the "professional" who visited her home seemed more intent on selling their product and/or service than diagnosing and solving her problems.

The list is voluminous from a meaningless blower door test, foam encapsulated attic where an 80% gas furnace resides, closed crawl space, new Pella windows, air sealing including plugging the combustion air supply in two furnace closets adding insulation and air barrier via foam board on the back of knee walls as well as increasing the insulation levels on the floor of the attic. Yes, the attic is also encapsulated with foam. Supposedly the bills went up and their comfort has suffered.

After seeing that no adults seemed to be present during sales pitches, I simply told the homeowner that someone needed to call a time out on the "let's try this" plan and put some diagnostic scholarship in its place.

Contrary to the implication of events, the homeowner is extremely intelligent, which I absolutely love. I just think she trusted to wrong people.

One issue I am trying to get my head around that I know will require explanation is why the attic is still substantially hotter in the summer than they expected. To review, spray foam was applied to the underside of the roof deck at about R-19. BUT they left the R-19 or so of rock wool on the attic floor. After feeling they weren't getting the full benefit of the spray foam, the owner took the advice of another insulation contractor who installed even more insulation on the attic floor using R-19 fiberglass batts.

I realize the attic space temp is now going to be somewhere between the outdoor and indoor temperatures (Plus a few degrees for radiant) ---- with the % of R-value determining which side of 50/50 it will fall. And to be honest, I am not really interested in explaining energy balance equations. Moreover, I don't want to measure the roof surface area to do them.

I dont see this set up being a determinitve energy penalty. But it does present the perception that the foam ain't working. Then I had a second thought. Since the attic will be hotter in the summer, how are duct loads affected? I am musing its a moot point. But at this stage, I am throwing the question to you folks because I am too lazy to think about. it.

Any ideas?


  • North Carolina, right? Excuse the WTF, but who in their freaking mind thinks R19 sprayed against the roof deck is adequate besides Liennyne. Yes it will help keep heat out but it isn't near enough (For Alabama I went with 4" of CC while a few I knew said 3").

    Is it open or closed - my gut says they probably sprayed open in there which is known to also have huge humidity swings which guess what that means... Along those lines because they have insulation in the bottom you have added a thermal sponge which is going to help hold that heat in the attic. Are the bottom of the trusses / rafters encapsulated with at least 2" of closed or 4-6 of open? Roof color also does play a part.

    Energy penalty inside with all that insulation, I don't see a penalty. The attic can be hot as it wants as long as you have enough insulation between it & the living space. As for humidity issues, etc... that could pose an issue especially if things are not well sealed

    As for ducts, insulated or not - if not then that will impact them more than insulated. How much I cant say, maybe David or someone has a rule of thumb or something. A lot also has to do with leakage. As I recall in Az (uninsulated) when they looked at it - at 10 or 15% it essentially cut the performance of the equipment in half.
  • Danny GoughDanny Gough Posts: 185
    The roof deck is all open cell. Its probably more than R-19. But I didnt give it much thought when I wrote the post. My guess is an average of 7.5 to 8.5 inches. I did not see the rafters, which are likely 2x8's. So my gut tells me it averages about 1 inch over the 2x8. I think it is Bayer .5 lb/ft3. Their ESR shows about R-28. The floor is more like R19 in some spots and R-19 plus R-19 batt over top in other spots.
  • David ButlerDavid Butler Posts: 3,889
    @Sean, when I used to work in Charlotte, Icynene advocated R-21 under the roof deck, but that was 12 years ago. At that time, prescriptive code was R30 for ceilings under vented attics. They would issue compliance letters in cases where the code official wouldn't pass the house.

    Although I would never recommend R-21 today, there is rationale for putting less insulation on the roof deck than on the ceiling under a vented attic. In fact, the commercial code prescribes less R-value in this configuration. There are a couple of reasons you need more insulation on the ceiling than in the walls -- (a) the delta-t is much larger, and (b) typical fiberglass ceiling insulation loses a significant amount of its R-value due to convective currents since it's not enclosed on six sides, and can even be subject to wind washing. Today the min R-value for ceilings in Charlotte (and in central NC where Danny is) increased to R-38, so R28 would be an appropriate for the roof deck in an unvented attic. (In my projects with encapsulated attics, I usually spit the difference between the wall R-value and the ceiling R-value if attic were vented.)

    @Danny, as Sean said, the added ceiling insulation is not likely the culprit for high energy bills. By isolating the the attic from conditioned space, the attic temp would move further from the house temperature, but the ceiling would see less heat flux. On the other hand, if you remove the insulation, the the bills will increase, but the attic will move closer to the house temperature. All of that said, with ducts in the attic, there's no way to know the net effect. It depends on how well the ducts are insulated and sealed and the relative surface areas, etc.

    Then reason you don't want to insulate the ceiling is to protect against winter condensation.

    You mentioned an 80% furnace in the encapsulated attic. How is it vented? You also mentioned two furnaces in closets where combustion air source was sealed. Are those also the 80% variety? If so, how are they vented now? If any of these furnaces are not vented (or weren't replaced with sealed combustion models), then nothing else you describe matters until that situation is rectified.

    You may recall I had a client in Tulsa who contacted me about mold & comfort issues. His house was foamed, including roof deck, but then the mech contractor cut eight holes in the roof to accommodate four 80% furnaces (high/low vent pipes as required by code). Sigh. On top of that, he installed 12 tons of cooling against a load of less than 6 tons. To the builder's credit, he admitted he and his mech sub didn't understand foam insulation and agreed to replace all four systems including my fee, repair the roof, and remediate the mold.
  • Danny GoughDanny Gough Posts: 185
    David, There is a lone 80% gas furnace in the attic. The others are 90% single pipe down in the basement. The foam contractor had someone install a 6 inch round duct through the roof deck and connect it to the vesitbule of the furnace for combustion air. But I am fairily well convinced there is communication at the eaves between the attic and the yard. I was asked to come back and investigate that further.
  • Are there can-lights or other metal penetrations in the home?