insulation questions for our new home

soonercrewAugust 12, 2014

currently about to start our new home construction... about the only thing we're trying to nail down is the attic insulation. we live in ne oklahoma for those interested in our climate. we are doing 2x6 walls (where most homes here are still built using 2x4). we have already decided not to incure the cost of foam in the walls. but our wall dilemma is whether to bat the walls or blow? and thats not as discouraging as myself trying to decide on the attic! if we blow the attic we will be doing r50 and our roof decking will be backed with a radiant barrier. but im thrown as to whether it would be worth spending the extra $3500 to foam the roof instead? we already have our hvac set up for high efficiency, so we wont incure any upgrade costs there (will be running 2 16seer condensers outside and 2 2-stage 96% furnace units in the attic. the home is a single story (which makes me think the additional cost for foam may not be worthy) that is 3000sqft... any help, comments and opinions will be greatly appreciated!!!
btw... we also plan to have a caulk party and seal every possible opening we can as well...

This post was edited by soonercrew on Tue, Aug 12, 14 at 18:57

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I'd trade off the radiant barrier for a foam sealed attic
radiant barrier will save you a bit in hot times of
the year, but not as benefit year round as an
unvented attic.
I'm amazed that it is only $3500 to foam the roofline.
either you have a low roof pitch, or the foam company
is telling you the old "3" performs like R-xxx".
understand that R-value is R-value, "performs like",
"quanitive values" & the like are bs.
attic insulation has to meet minimum code requirements
for your R-values.

closed cell is about R-7 per inch, open cell about R-5.
multiply inches by R-value to understand what is needed.

if your ductwork & hvac equipment is in the attic, you'll
benefit by keeping attic semi conditioned. any leakage
between living space & attic is not as big of an issue
as it would be with a vented attic.
by moving air & thermal barrier from attic floor to
roofline, the many penetrations in the ceilings will no
longer 'suck' from attic into living space.

I agree to not put spray foam in walls.

visit southface inst & search for air sealing pdf's.
they have some excellent non biased info...with great
illustrations for air sealing details.

check into foam price & post back with more details
of what is proposed.

good for you asking before you spend!

best of luck.

    Bookmark   August 12, 2014 at 11:03PM
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Northeast Oklahoma is Climate Zone 3A, bordering on 4. See International Energy Conservation Code 2012 requirements in table below. (The state prescribes IECC 2003 at present.)

Radiant barriers are most effective in hot climates, so the barrier may not yield much value in your climate.

It's not clear if this is a vented or unvented attic. If it's vented, there's no point adding insulation under the roof deck. In vented attics, for 30 years, I've only used blown cellulose in our cold climate. There are simply too many areas for error in installing batts. I haven't switched over to blown or netted in walls but really should consider it for the same reason. Instead, I've sheathed with XPS and used fg batts.

IECC 2012

This post was edited by worthy on Wed, Aug 13, 14 at 0:31

    Bookmark   August 13, 2014 at 12:18AM
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If the furnaces are in the attic you should insulate the roof and create a conditioned attic. You can do that with spray foam and avoid vents or use dense pack cellulose and add soffit vents, vent baffles and a ridge vent. In some jurisdictions the vents are allowed to be omitted with dense pack cellulose but I'm not buying it yet.

    Bookmark   August 13, 2014 at 4:10PM
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If putting HVAC in attic, I agree with insulating roof line to the 2012 IECC levels and not what the insulation company recommends if lower.

To meet insulation minimums more affordably, redesign to get the HVAC out of the attic and do loose fill insulation on the attic floor paying attention to raised truss heel above exterior walls.

Most importantly, ensure your home passes code for the blower door test minimum. I feel it might be more cost-effective to get to 1.5 ACH50 before adding the insulation.

    Bookmark   August 14, 2014 at 9:12PM
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I don't understand why you would need two HAVC units with a single story. You could use one unit zoned. Gas fluctuates quite a bit, how much is your kw in your area? Might be feasible to use elect HVAC and that would give you heat/ac. Have you looked at GEO?

Have you looked into ICF? Might be even less(probably) than 2x6 and it includes all exterior insulation.

    Bookmark   August 14, 2014 at 11:26PM
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well... we made our decision today after 24hrs of research, talking with friends, speaking to contractors and our builder. we're going to fully encapsulate the house (envelope it). the roofline will be sprayed at a depth of 7-8" and walls at 4". now we're just waiting on our hvac contractor to do his calculations. he's going to run a manual j for each room and match equipment using what i believe he called a manual s. I'm 99% sure we'll be using bryant equipment. the way I'm calculating it we'll be using a single 4 ton unit (condenser outside) and the furnace in the attic. with the furnace in the attic we will be spraying foam with fire barrier.

    Bookmark   August 14, 2014 at 11:30PM
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Congratulations on doing some good research and going with a proper load calc. Have to point out that 7.5" of Open Cell foam is R27. This puts you at a little over half of the international energy code required minimum for zone 4.

I guess you are technically in the R38 zone 3 both locally and internationally. So you are R11 below minimum building codes.

    Bookmark   August 14, 2014 at 11:50PM
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don't quote me, but i believe we are adding blown in on top of the ceiling to achieve the minimum. i've been told that adding a little blown in on the ceiling will also take some of the echo effect away from the rooms as well.

    Bookmark   August 15, 2014 at 12:08AM
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you are spending your money unwisely.

greatest heat gain/loss is from attic.
putting equipment and ducts in an attic
with extreme temps surrounding it is a
bad idea.
at best duct insulation is R-8, in summer
attic temps reach 140 degrees.
in winter...well your winters are colder
than in my area...but attic temps
will still be extreme.

R-8 isn't much, consiter the fact that
ambient walls are at minimum R-13, and
the sun only hits one wall at a time.
roof gets sun all day, every day.

by putting the foam on the roofline,
you create an unvented, semi conditioned
attic. temps in this attic will be within 10 degrees
of conditioned space.
this allows temps leaving the unit to be the same
when exiting from supply box.
this is your money saver.

the other part is downsizing hvac system.
lesser equip costs, lower operation costs,
longer life of equipment.

spray foam in walls drives up the amount
of time it takes before the investment pays itself
off. air tight walls (foam sheathing, conv insulation
and air tight drwall approach) is an excellent trade
off with faster payback than foam sprayed walls.

most foam companies put just a couple of inches
of foam in walls, leaving voids between insulation
and sheetrock.

I'd re-think the decision. you'll never have the ease
of doing it right like you do now.

visit & read about the
best wall construction for all climates.

also read Joe's list of stupid things we do
in hot and cold climates.

this is completely untrue :
"adding a little blown in on the ceiling will also take some of the echo effect away from the rooms as well. "
the foam absorbs the sound, blown insulation on top
of foam doesn't effect sound absorption as that all takes
place within the foam itself.

best of luck.

    Bookmark   August 15, 2014 at 8:38AM
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i guess i should have done a little more research before reaching this point. unfortunately it's too late now to make a change. our foam contractor is well known and has done a few homes of friends. ive looked at their work prior to drywall going up. the contract reads 4-5" in walls, minimum 8" on roof. they also come out right after framing and energy seal the house in this manner:
Apply caulking to the junction of the base plate and concrete slab
Apply caulking between double and triple studs
Apply caulking to exterior door and window header junctions
Apply low pressure foam insulation to exterior wall penetrations
Apply low pressure foam insulation to top plate penetrations
Apply low pressure foam between the exterior door and window jams and the wall framing
Apply low pressure foam in HVAC wall penetrations

im thinking we'll end up with evolution variable speed equipment from bryant. but not positive yet...

    Bookmark   August 15, 2014 at 10:53AM
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Even if he is currently spraying it shouldnt be difficult to have them add another 3" to get you to the poorest performance allowed by law in your roof deck.

Agree that foam for walls is most effective as foam sheathing on the outside of framing. OC foam is generally the same price as blown cellulose/FG in our area. They really should be filling the entire cavity especially with no foam sheathing.

    Bookmark   August 15, 2014 at 11:15AM
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"Apply low pressure foam in HVAC wall penetrations "

at penetrations for supply boxes?
foam isn't an acca approved hvac sealant.
I'd much rather mastic tape to seal supply

usually caulking sole plate to slab is done
during framing, before wall is stood in place
& anchor bolts tightened a double bead
of caulk is applied. some builders use
products like Sill Seal. good stuff.

the rest of the stuff is just the detail work
of air sealing.

best of luck.

    Bookmark   August 15, 2014 at 11:00PM
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The OP never refers to open cell foam, so there will be no problem in exceeding IECC 2012 with medium or high density foam, which is not required yet in his jurisdiction.

This should be a very comfortable and energy miserly home. Enjoy!

    Bookmark   August 16, 2014 at 12:34AM
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I must know that its Open Cell from my superior intuitiveness.. OC or light density foam at 3.6R per inch yields a Total of R27 with an average 7.5" thickness. That's roughly 30% below what should be locally enforced. Its barely over half of what it should be for the 2012 IECC in zone 4.

Sounds like you could be on track for a comfortable home. As for energy miserly, that would depend on what youre comparing it to. There are other envelope variables, namely the airtightness as verified with a blower door test and the fenestration details. Compared to code intended roof performance, you will have considerable making up to do in comparison with baseline envelope energy performance.

    Bookmark   August 16, 2014 at 2:50PM
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