Making a frog energy efficient

amazinglady2348August 10, 2012

I am converting the bonus room over my detached garage into an apartment. Extended dormers are being added on the east and west sides.

I've read that this apartment has the potential for huge utility bills if it is not insulated and sealed properly.

I've asked the builder to air-seal the room as well as use a radiant barrier. I can see that the contractor is using thermoshield for the roofing but doesn't appear to be using it for the walls. Should I request a radiant barrier be added to the walls?

I'm considering asking for spray foam insulation instead of fiberglass but have been told that it is 3 times the cost of fiberglass.

Is there a compromise that perhaps a combination of spray foam and fiberglass could minimize my utility bills without costing an arm and a leg? For example, a 1 inch layer of foam AND fiberglass batting or foam for the garage and apartment ceiling and fiberglass for the walls?

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BTW, we are located in Texas and our biggest concern is the cooling cost.

    Bookmark   August 11, 2012 at 12:07AM
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I've never came across a foam company that did flash &
batt. why make minimal $ for a 1" install when
they can move on to next customer and sell full job?
they may do it for production builders...but not
the average homeowner.

you know the frog is going to be expensive to
heat and either pay upfront or
for as long as you use this room. in the
long run..the foam will pay back because utility
costs never go down.

are the walls shared with attic space?
foam insulation will cover all the issues
of heat gain, air movement & R-value.

install open cell foam to meet code requirements.
this would not be the 'average' 2-3" but full rafter
depth, and covering the faces of rafters.
the whole 2-3" performs as R-30 is bs.

foam should cover roof area to eaves. an airtight
seal would include foam extending onto attic floor.

you could RB the roof, but then you would have to
RB the walls shared with attic also. foil/foam sheathing
boards installed from top plate to sole plate & extending
to ceiling of garage below. taped, caulked and made air tight. conventional insulation in stud bays.

lots of labor and high chances of it not being done
correctly. the foil facing into attic space works
as RB to keep heat gain out of walls. 4x8"
sheets provide air barrier..when correctly done.

foam is an easy out. labor to install foil/foam sheathing
vs cost vs frustration. this is one of the
things foam does..covers thermal/air infiltration errors.

here in La. we have the same concerns. cooling climate
high humidity, too much a/c to overcome heat gain.

shop around for foam companies, and a/c companies that
will understand install of foam, a/c and that 400
sq ft per ton is a wag..not proper sizing.

personally I have a RB I installed myself. no
ductwork or mechanicals in attic. air barrier
between attic and living space is near perfect.
but I'm a diy..and have tested enough homes
and solved enough homeowner issues to know
what I'm doing. lots of sweat equity!

best of luck.

    Bookmark   August 12, 2012 at 12:26PM
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Ok, you've convinced me of the benefits of foam insulation. You said open cell instead of closed. Is that what's best for humid and hot region? Closed cell not appropriate?

Also, my contractor says that the framer company air seals the places where walls meet floors and ceilings because of code. Is this the type of air sealing necessary for a frog? If not, foam insulation will seal it sufficiently correct?

One more question, you said the foam should be on the roof deck, the attic floor and where they join?

Thank you so much for your help! It's so hard to know how proactive to be - kind of like working with the medical community.

    Bookmark   August 12, 2012 at 3:49PM
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your humidity may not be as big of an issue in Texas
as it is here in La. @ 10 am it is 91 degrees and 74% RH
we had rain yesterday and last night so it is like a sauna
outside. of course inside..74 degrees & 52%RH. RH is dropping already, usually 50% RH is the norm.

here is a link to my pics online of foam installs
some existing homes some new. you can navigate through
all the should allow you to do so.

framers frame, builders don't always tell the truth.
while framing the carpenter is loaded down with tools
usually not caulking gun. I wouldn't rely on the air sealing
they provide unless I went behind them & checked.
been there, done that.

yes, where the roof deck connects to the attic floor
eaves, soffits..whatever it is called by your builder
should be a solid foam seal.

why open cell vs closed cell?
oc lets water exit
cc traps water..roof decking rots over time.
and sooner or later the roof will leak.
better to have visible indication of leakage..oc letting
water exit water stains on ceilings would quickly
let you know that there is a roof leak.
with closed cell replace decking, shingles
and cc.

and make sure that ducts/plenums & plenum to equipment
are mastic sealed. paint on mastic or hardcast brand 1402
mastic tape.

manual j for sizing hvac, also manuals for duct sizing
and design. these are important for the efficiency and
comfort of the house you will be living in.
unlike hvac co who will install and move on.
you are installing recessed lights?
purchase ICAT insulation contact air tight
cost is a little higher to buy in bulk.
IC insulation contact are cheaper, but to
retrofit to AT is about $15 PER light.

best of luck.

best of luck.

    Bookmark   August 13, 2012 at 11:24AM
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Thank you so much for the information!

One problem with foam insulation in the attic is that the roof deck is that techshield with the radiant barrier foil on the underside. I'm told that radiant barriers are not effective unless without an air pocket/flow. I could still do foam on the attic floor, garage ceiling and walls, though.

How do you handle that situation when there is a radiant barrier on the roof deck?

    Bookmark   August 13, 2012 at 3:42PM
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Seeing design concepts reduced to contractor jargon like FROG saddens me for some reason. Probably time to retire and criticize the government full time.

    Bookmark   August 18, 2012 at 10:04AM
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in a frog (sorry renovator 8) I'd sacrifice the
rb for the foamed roofline. these rooms are
hard to condition.

I'm a try different things to see how they work
kind of gal. over the years we have done the rb
thing, rb with foam on attic floor, kneewalls ect,foam on rooflines and many many variations.

once we even installed baffles over the entire
techshield roof and foamed against that.
worked well. but the labor to install the baffles
to keep the rb pretty much offset the install.

so based on my experiences, encapsulate the frog
with open cell. if the ductwork will be in the
attic area..all the more reason to foam seal this space.
rb's have their place, I have one, but my ductwork
and equipment are within the living space.

the acronym frog is kinda offputting, but explains room over garage. I find a lot of
folks have never heard frog, so I seldom use it personally.

best of luck.

    Bookmark   August 18, 2012 at 9:49PM
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Also consider more simple things, such as thermal window with shades. These make a difference on reducing the solar gain. East and West windows do add the most to a cooling load.

Have you considered for the HVAC to use a minisplit heat pump like a Daikin? These have some advantages. One is that you don' t need to worry about the duct size being too small, a classic way that corners are cut at build time on those rooms over the garage. Secondly they offer a very high SEER. Thirdly they wold be an independent system from the house proper, allowing more local temperature control of the space.

    Bookmark   August 19, 2012 at 8:46AM
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