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Old 04-28-2015, 02:29 PM   #1
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Need advise on my plan

So here is my current setup:
Live in ca half way between sf and Sacramento, hot in the summer cool in the winter (rarely gets to freezing).
I have a ventilated crawl space with 12" minimum clearance, zero insulation and dirt/rock ground. I have attic with maybe 5" blow in fiberglass insulation and ducting in attic. One central return at the furnace. Energy bills are through the roof and energy analysis with blower door test recommended insulation below and above, envelope sealing and duct replacement.

Here's what I planned on doing...
In attic: remove all contaminated insulation, seal all cracks, replace duct work in a better lay out with r8 ducting and seal properly (current ducting has duct tape not silver tape). Replace fiberglass blown in with the greener blow in material to an r30 or 38 value. Also considering a radiant barrier against attic ceiling, like the reflectix bubble material.

In crawl space: seal under floor cracks and gaps, insulate with r19 faced fiberglass batts between joists, then a radiant barrier like the reflectix on the underside of the joists to seal in the batts and prevent them from falling as well as adding the radiant and r value benefit.

I am not really looking to enclose and encapsulate the crawl space as it is cost prohibitive to have a company do it and doing myself seems an impossible task (especially with having to have the area sealed and conditioned). I'm also concerned if the reflectix is even beneficial or if having it next to the batts (on the ground side) would cause more harm to the batts in regards to condensation/moisture and rotting.

I appreciate any thoughts on my plan or advise. Thank you!
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Old 04-29-2015, 07:18 AM   #2
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Sounds good on the top side.

Not sure about the crawl. If you want to leave it vented and insulate the floor so be it. You will need to check the floors and make sure that you don't create a vapor sandwich with the VB if you run that across the floor joists.
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Old 04-30-2015, 06:42 PM   #3
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If using RB on the rafter bottoms, don't spend extra money on bubbled for the insulating value. Think about what the bubbles are insulating; the air space with outside ventilation removing the radiant heat reflected from the foil---- or the attic air; high above your thermal barrier (attic floor). A mute point, if so, IMHO. The RB should be open at top/bottom to let attic air in/out.

"Seal all cracks"; not just cracks but all ceiling/wall drywall joints to stop air/moisture movement through the paper tape in the corners;

In the crawl, add rigid foam board with a foil facer; Fig. 7;

Otherwise, without the foam the FG would receive heat from the vented crawlspace through the foil/bubbles by convection. May as well use a housewrap (vapor permeable) if not rigid. Foil (RB) would disconnect the joists from the earths temp, but how warm/cold are they in your mild climate?

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Last edited by Gary in WA; 04-30-2015 at 06:44 PM.
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Old 05-01-2015, 01:10 PM   #4
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Thank you both for the insights and Gary for the links to further detailed information. I will certainly consider the foil faced boards to seal in fiberglass batts. My biggest concern there is the amount space I have to work with. I only have 12" max between ground and bottom of joists. Pretty tight fit.
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