a house can be made tight enough to require fresh air by other means than

just spray foam insulation.

just fyi.

OP, what is your location?

will heating system/ahu be in the attic? ductwork in attic?

can't give you an answer with out more info.

best of luck

My husband is the one posting so I will let him answer most of this but the quick answer- according to that map we are green, 4-5 we are in Rockland county. The heating is in the attic and in the basement- variable speed forced air. Ductwork in attic and basement (insulated). Our house is coated in enviro dry waterproofing which I heard seals it.

If your house will be coated with Tremco's liquid-applied Enviro-Dri Weather-Resistant Barrier, then it will be as air-tight as a house can get and it would not matter what kind of insulation you used if the R-value is the same so foam would offer little advantage over fiberglass.

You will definitely need a ventilation system to reduce the amount of pollutants in the air from building materials and furnishings.

I suggested that you to consider the design of the entire building envelope instead of just the insulation and now that you have done that the insulation issue is no longer an important issue. You will find this principle applies to all aspects of a house design.

Liquid housewraps are rare in residential use. In our cold climate, the preferred method, combining air tightness and insulation, is exterior foam sheathing. A bit surprised to see that the builder who used such a premium product didn't treat the attic as conditioned space in light of HVAC ducts (and furnace?) located in it.

I had planned to make the same point that Worthy did but probably not as succinctly.

After the air barrier and insulation issues have been resolved the next area of concern should be the design of the HVAC system. The most important rule is to keep ducts and equipment out of a cold attic. If the attic were to be conditioned, ducts would still need insulation to prevent condensation.

OP, here is how is it supposed to work

built tight ventilate right.

erv, hrv, ventilating dehumidifier, simple duct with barometric damper..

these are all ways to ventilate the house.

I don't know code requirements in your location, but many

counties now require blower door testing to determine

the actual amount of air tightness of the house.

this is the right way to do it, measuring how tight the

house is & then calculating the amount of fresh air required.

with blower door numbers & calculated amount of fresh air

required, then one chooses the way they want to ventilate.

(or perhaps code dictates method of ventilation)

it all goes back to ASHRAE 62.2 ventilation strategy.

you can't depend upon the hvac company to be up to date.

you should educate yourself & then share your info with

hvac company.

in a lot of my client's homes we do simpler method of

fresh air.

filter back grill (with filter) located in soffit, under porch or

patio. duct with barometric damper (damper set to

cubic feet per minute (cfm) required for your specific home)

duct to return air, where fresh air is conditioned before

entering living space.

clean, measured (dehumidified) fresh air for home.

this is the best wall construction for all climates:
http://buildingscience.com/documents/insights/bsi-001-the-perfect-wall

air tight from exterior, walls air sealed, studs thermally broken.

any type of insulation...fb, cellulose, rice hulls...doesn't matter

as long as air is not moving through the insulation.

from the interior you continue the air sealing of the walls

with air tight drywall approach.

then, you use the spray foam insulation on the roofline.

the benefits for the ductwork are huge, but the foam solves

a lot of issues that otherwise are left unaddressed.

air leakage between attic & living space is number

one.

the holes cut into the ceiling...for bath fans, recessed lights,

supply boxes, etc are no longer an issue when attic is

unvented because the attic air isn't being pulled into the house,

for you to pay to condition. indoor air quality is better, hvac sizing

decreases, because the system doesn't have building failures to

overcome.

changes in ceiling heights create kneewalls in the attic.

these thermal bypasses allow attic temps to transfer into the

house.

foam solves these issues, that are not addressed by trades.

you are getting a lot of info here. hopefully in time to make

a difference in your build. so many people wait to the 11th

hour to make decisions. efficiency & performance require

planning & are not last minute add ons.

best of luck

and btw...lot of threads here where homeowners foamed walls &

put conventional insulation (not foam) in attic.

this is backwards, like bundling up for a snow storm & not wearing

a hat. heat escapes the conditioned space via the leaky ceiling

into the attic.

capping off the house with foam in the roofline is a huge thing.

30% of heat produced escapes into the attic.

give it some thought before choosing otherwise.

Thank you all for responses. It is becoming clearer.

JDS & Worthy, our builder has his methods and we are stuck with the current situation. Framing and roof is already complete. Enviro-dri has been applied. The HVAC is already installed in the roof and basement (There are two forced air systems). Siding is going on starting tomorrow and we need to decide on insulation as soon as possible.

We have two quotes that our builder says we can use for insulation, one for fiberglass and one for the open cell spray foam. That's it. Anything else is beyond our builder's experience and then we have to figure this out on our own. Something we lack experience and time on.

It's not an ideal situation but we are trying our best to do the best method based on our situation.

energy-rater, I do agree that spray foaming the attic is ideal, but that is the main expense. Spray foam of the walls vs fiberglass insulation of walls is similar in price It is spraying the attic that is real additional expense. So, based on the situation, I see it as spray everything or fiberglass everything.

What do you advise based on this? (and no, I can not get another builder)

So true energy rater. Walls only account for 15-30% of the building envelope's energy concerns. Staying balanced with air leakage, foundation, windows and roof is needed for any one component's upgrade.

I agree with JDS that a liquid applied flashing like enviro-dri will improve performance, but just like with spray foam, it doesn't equate to better blower door test results. Walls are relatively easy to make airtight. Its transitions and penentrations that have the most opportunity for improvement and vented attics need extra special attention with typical industry standard practices.

Adding to sis33's traditional chimney concerns, expect substantially more air leakage without advanced dampers and increased indoor-air quality problems.

I've used open cell once on the basement rims and would never use it again. It pulled back all along the perimeters. Maybe too cold, maybe a poorly trained applicator. After that, I have only used cc foam, even doing all the basement walls and rims instead of fiddling with XPS sheets. Given the OP's two choices, I'd sigh and use fg. If they're lucky, there will be a building inspector who catches the worst installer fails.

Thank you for responding to my question about the chimney, Springtime. It seems the OP does have this problem too so I hope my further question does not hijack her thread. In our current home (Florida) the fireplace is LP gas logs and by code the chimney damper has to be locked permanently open. We plan to have an open gas logs fireplace in our new build, is there any solution to the damper and indoor air quality issues?

FYI we have no chimney- I just read what my husband wrote earlier and he was mistaken. We have a direct vent gas fireplace. Also, our framer also works as a building inspector (in a neighboring county)- not sure if that helps but he seems knowledgeable on things.

Given your situation I would use fiberglass in the walls (assuming it is cheaper than foam), closed cell foam between the rafters and no insulation in the attic floor. Even if that is more costly, the break even time should be short and the house more comfortable. If you add a heat recovery ventilation system the house environment would also be more healthy. By the time you sell the weather barrier and attic design is likely to be the what buyers are looking for.

Your DH needs his own name.

Hi JDS,

The cost difference of open cell spray foam for the walls compared to using fiberglass is minimal. Its about $1,500 more for open cell spray foam vs fiberglass for exterior walls (and this is for a 4,000 sq ft home). Because the costs are similar I am leaning towards spraying, but would appreciate your opinion and insight.

So to use fiberglass everywhere will cost approximately $9,600.

To use open cell spray foam exterior walls and attic is $18,000 and another $2,000 to insulate basement ceiling with fiberglass - so it will cost $20,000 altogether.

To use open cell spray foam in attic as you describe and fiberglass everywhere else (including basement ceiling) will be $18,500.

I do not have a quote for closed cell spray foam. I only have open cell as I have been told closed cell will be close to double the cost. Is this true? If so, I can not afford this higher cost. Please advise.

Your design conditions have been presented in bits and pieces so its not entirely clear to me even after rereading the thread. When you describe insulation in the attic is it in the attic floor or between the rafters? What is the roof/ceiling design R value? Is there currently a forced air furnace in an unconditioned attic or just the ducts? Is the roof framed with rafters or with trusses?

OP, I would never suggest that you change builders. I try really hard to keep my recommendations based on what happens

in the real world.I wouldn't change my recommendation, and have tried to educate

you as to why foam sealing the attic is a good investment.

if you do decide to foam, understand that foam, like every other

insulation has the industry accepted R-value.

the R-value of the install, has to meet code requirements for

your climate.

best of luck.

Hi JDS,

As it is a 4,000 sq ft home our HVAC contractor put in two split system in the home. One furnace is in the basement and a second is in the attic. The ductwork is also in the attic for this and is insulated. It is already installed. The attic is framed rafters. In the hope of being clearer attached are my two proposal. One is open cell spray foam and the second is for fiberglass. Hopefully this is clearer.

This fiberglass quote is for $9,600.

Energy rater - so you believe that we should use the open cell spray for the attic - correct? What about the exteriors walls. The price is similar to fiberglass (there is a small saving using fiberglass).

I am going to assume the fiberglass is in the attic floor and the foam is in the walls so the two proposals are part of one with no alternate proposals.

I am also going to assume the attic and basement are both thermally separated from the main living spaces and are unconditioned and each contains a furnace and ductwork.

I know this is a lot to understand at this late date but for maximum thermal conservation the attic and basement should be insulated at their exterior surfaces and conditioned (i.e. partially heated which is helped by normal leakage from the ducts) instead of being thermally separated from the house.

http://buildingscience.com/documents/information-sheets/basement-insulation

http://energy.gov/sites/prod/files/2014/01/f6/1_1c_ba_innov_unventedconditionedattics_011713.pdf

The walls can be filled with fiberglass (or foam) because they are already unusually well sealed. Foam would be prefferred in the attic floor to seal it and prevent warm air from being drawn into the unconditioned vented attic (at least seal it with a layer of foam and then install fiberglass). Alternatively, to make the attic conditioned and conserve even more energy, the insulation could be moved to the rafter bays and be either fiberglass with a vented air space above it (and perhaps a radiant barrier below it) or spray foam tight to the roof sheathing without any venting (sealed conditioned attic).

Is the heating system hydro-air (i.e. two air-handlers served by one hot-water boiler) or are there two forced-air furnaces?

Is the unit in the attic in an insulated enclosure? If its a high-efficiency condensing furnace, is the condensate trap and drain protected from freezing?

Hi JDS,

Thank you for the thorough response, your initial assumptions are correct, although I'm still a little confused.

To answer your
questions, these are variable speed forced air systems. Not
Hydroair. The ductwork is insulated, but the actual system will not
be in an enclosure (at least to my knowledge).

So are you saying the following: We
should do either:

A) Fill walls with fiberglass or foam
and then use foam in the attic floor. Basically making the attic unconditioned space.

or

B) Fill the attic walls and rafter with
insulation and make the attic part of the conditioned space.

If that is the case, I have a few
questions.

1. For scenario A, do we still use
fiberglass to insulate the rafters or are we basically saying the
attic will be completely unconditioned? Also, we only received a quote for spray foaming the rafters, should we get a quote to spray foam the attic floor?

2. For scenario B do you recommend
spray or fiberglass? Is there a big difference here in which we use
as the cost is significantly more expensive for spray.

3. The walls will cost an additional
$1,500 to spray vs fiberglass (which is not much compared to the
difference in cost of the attic). Is it worth the extra money to
spray because we used envio-dri we should just use fiberglass as
there really won't be a difference.

Lastly, now based on everything you know, what do you do?

I really appreciate all your help on this, as it's not an ideal situation and I'm trying to make the best of it.

The information from your contractor that you added to your previous post seems to contradict my assumptions in the later post about what is in your contract but the wording of the specification is oddly cryptic and unspecific so I will summarize it and see if it is true.

Here is what it appears to mean to me:

Attic roof decks [the underside of the sloping roof sheathing between the rafters] R38 open cell [open-cell sprayed foam] inc. gables [including stud walls of gable fronts at about R20].

If my interpretation is accurate, the insulation is not in the attic floor but at the sloping roof deck and the attic is therefore sealed and conditioned which is what we have all been recommending. I don't know why we thought it was an unconditioned

Interior walls inc. basement framed walls, rims joists, & Garage int. wall R31 [probably intended to be R21]

You can put anything you want in the walls because the weather barrier is so superior to house wrap it won't matter assuming the R value is the same.

Basement ceiling and stairwell to be insulated by others. [It appears the GC doesn't think this insulation is necessary]

If the basement foundation walls are well insulated and there is insulation under the slab, I don't see any reason to insulate the ceiling of the basement but if you did insulate it that would allow the basement to be cool and possibly less dry and that would be ok if condensation did not occur. Leakage from the ducts and the furnace might take care of that issue. But if you intend to heat the basement, insulation in the ceiling would serve no purpose unless it is for sound reduction which will not be very effective. For effective sound reduction use resilient channels above the drywall ceiling.

Is there any habitable space above the garage?

Kudos for JDS's patience and perfect explanation of the OP's choices. (Though my choice will always be closed cell foam!)

What I don't understand is the builder's locating HVAC in the attic when there is a perfectly good and unfinished basement for it. The HVAC in attic scenario is usually when the house is on a slab.

Thanks, I also prefer closed-cell foam; have never actually seen open cell foam. I think putting the HVAC in the attic saves duct runs to the second floor and uses an otherwise unused attic. I've done that but I always use a hydro-air system for better control and zoning and it keeps a gas fired appliance out of the attic. I suspect hydro-air might even be cheaper than two furnaces since a shared boiler is small enough to be hung on a basement wall.

The basement must be heated because there will be insulation under the slab. Perhaps that is just for condensation in a cold basement. Its a confusing project.

Hi JDS and Worthy,

That is exactly why we have a furnace in the attic. The furnace in the attic is for the 2nd floor only while the furnace in the basement is for the first floor only.

We don't plan on using the basement and are not heating/cooling it. Same for attic.

There is a bonus room over the attic. It won't be used initially, but we plan to use it one day.

I too really like the idea of closed cell, but the price is just too beyond our budget.

I really appreciate all the info and my options are becoming clearer but I'm still not sure what you are recommending to do. Do I use the fiberglass quote? Do I go with the the spray foam quote? Is it a mix of both?

Thanks.

FWIW, we did open cell in both the old part of our house and my workshop/barn three years ago now. It's been great so far, no issues of pullback or cracking. The stuff sticks like crazy to whatever surfaces it touches. A thick application of open foam seems to provide adequate barrier to moisture transmission even though it is not impervious.

Maybe I'm just not paying enough attention but it would help me if you would confirm whether the R38 insulation is in the roof rafters or the attic floor and where the R31 insulation is located and what kind it is.

The disadvantages of open cell foam in a roof (not a floor) is 1) it will need to be almost 11" thick and that can be an issue for the installer since the foam can gets hot but maybe he can control it with multiple passes 2) open cell foam is not a vapor retarder so condensation can occur against the cold roof sheathing if humidity is not controlled in the attic but that can be dealt with by a good contractor.

Closed cell foam would only need to be a little more than half as thick as open cell foam so installation is faster and easier and it is a vapor retarder. To compare prices for thee materials you need to see prices for the complete installation rather than each board foot of material. Did you get a quote for closed cell installed or did the contractor just say it is twice as expensive?

I suspect the insulation your contractor has quoted is just fine; I just haven't been able to understand it.

Hi JDS,

For the open cell spray foam quote the R-38 insulation is on the attic slope in the rafter. The R-31 is apparently an error - it's actually R-21. Sorry about that. The R-21 (not 31) is open cell spray foam as well and will put in all exterior walls.

Our contractor has told us it would cost about double if using closed cell. I don't think he is lying. While we don't have a quote, the sub-contractor implied this as well...and again, it is then out of price even with some wiggle room.

There is a lot of conflicting info out there on closed vs open cell. My builder in Florida will only use open cell. Yes it has to be thicker to achieve the same R value, but he says that if there is a roof leak, he'd want to know about it vs have the roof sheathing rot. YMMV

"There is a bonus room over the attic. It won't be used initially, but we plan to use it one day."

all the more reason to foam seal the attic. otherwise the room

will always be uncomfortable.

fwiw, I always thought the question was for unvented foam sealed attic

(foam at roofline) vs blown fg on attic floor.

your hvac systems are heat pumps?

it is confusing when you say furnace, one thinks of gas furnaces.

one of the bad things about foam being a last minute add on, is

that the sizing of the hvac system changes.

Keywest, we use open cell here too for the reason you state.

best of luck OP

OK, I think it is now clear that the attic is included in the conditioned space of the house and is sealed with open-cell spray foam rather than being vented.

The original question was about whether or not the increased air tightness of spray foam in the walls would necessitate an ERV. The answer is that for your house, foam instead of fiberglass in the walls will not increase the air tightness much since you have an exterior liquid applied weather/air barrier that is far superior to a conventional membrane house wrap. Therefore, the more important issue for air leakage is the windows and yours are apparently very tight. So, because of the windows and the weather/air barrier and because interior materials continue to add more pollutants to houses, I recommend installing an ERV. The choice of insulation shouldn't be a factor.

For your second question, I doubt that open cell foam in the walls would decrease your heating costs compared to fiberglass of the same R value since the house is well sealed from the outside. However, the insulation at the attic roof must be spray foam if the attic is to be sealed and unvented. I would use closed-cell because it is half the thickness and few manufacturers have tested their product at a thickness of 11" and I am careful to not approve anything that doesn't meet the building code since I am held to a much higher standard of responsibility than builders and installers. That thickness is often allowed but be sure the inspector has approved it and does not require the addition of a thermal barrier or intumescent coating.

Interesting read on the topic: It’s OK to Skimp On Insulation

(open cell foam manufacturer argues that due to superior air-tightness of product, that you don't need the same R-value as "traditional" types of insulation)

DH is handling the hvac and insulation so he is the one responding on this thread (and finally made his own account now as R Stevens) but to chime in quick, they are starting siding/trim/soffits next week. I believe they said if we do fiberglass (for everything) we need vented soffits. If we do the foam it will be unvented soffits. I can't answer most of these other questions but I think with the basement we have the option of either insulating the ceiling between the basement and the main living area, or increasing the insulation in the basement walls and then not insulating the basement ceiling. The basement will be unfinished for now and, as a note, it is a walkout with a number of windows which makes it less insulted than if it were solid walls. You are all SO helpful we can't thank you enough.

Please be specific about the options; if you used fiberglass would it be put between the rafters or in the attic floor?

great article keywest. I'm having the R-value battle right now on a new construction home. new company ripping off people in my backyard. can't have that now!

Hi JDS,

I wanted to check with our contractor before answering you, and I have yet to get a response, but I'm pretty sure of the following:

The spray foam is just on the rafters and the attic is part of the envelop.

The fiberglass would have insulation on both the attic floor (R30) and on the cross batts (R11).

I take the foam description to mean the attic is inside the conditioned envelope which is the proper place for HVAC equipment so that's great.

I don't understand the reference to "cross batts" but If all or most of the insulation of the fiberglass option is in the attic floor, the attic space will be unconditioned and will need to be vented. That will require thermal protection of the HVAC equipment and careful sealing of the duct joints and since that is so difficult to do the cost of heating and cooling will increase.

The currently installed equipment might not be adequate for the additional heating and cooling load of a vented (unconditioned) attic. Even if the equipment was sized for the greater load, you should avoid the additional cost of operation.

So don't give up the conditioned attic option without the opinion of a qualified HVAC designer that you trust.

Hi JDS,

Finally heard from the insulation contractor and the HVAC contractor.

The fiberglass insulation would be in the attic floor only and the attic would be unconditioned.

The open cell spray foam will be on attic slope and keep the attic as part of the conditioned space.

My HVAC guy personal preference is to use spray foam, but fiberglass is ok. He said if we use fiberglass he would recommend building an insulated enclosure for the furnace. A lot of homes in our development had done this.

It sounds like the answer is to go with spray foam, but now that I have hopefully answered all questions you can give your recommendation as it sounds like you are obviously much more knowledgeable.

Thanks

If you can afford it use spray foam in the rafter bays. Your house will be more comfortable and cheaper to heat and cool. Insulation in the walls can be anything that provides the needed R value since it is already so well air-sealed.

just make sure you get full depth of spray foam installed.

foam has to meet R-value for your climate.

the two most important things about foam install are

depth of foam

air seal of roof at soffit to attic floor.

glad to see you chose this option.

best of luck.

I think we will go ahead with the open spray foam. I will definitely make sure to verify we get full depth and I will speak with the contractor about the best methodology to avoid any peeling due to the thickness of the spray.

Two quick question for my own curiosity:

1. Wouldn't it be cheaper to heat and cool the home if we insulate the attic floor rather than the rafters? The building envelope is now smaller so I would think heating and cooling it would cost less. (Yes, I know fiberglass has more leaks...but still, I would think a smaller envelope would have significant benefits). I guess my question is, what is the benefit of making the envelope bigger?

2. After we spray foam the attic rafters, does it then make sense to fiberglass the attic floors? In my mind it double insulates the ceiling of the actual living space of the home while also insulating the attic. Or is just a waste of money?

Thank you all again. This forum has definitely been the best help for figuring this out.

To clarify my comment on problems with very thick foam, it is closed cell foam that must be installed in layers to prevent overheating not open cell foam so that should not be a concern

It is definitely beneficial to make the envelope bigger! Insulating the attic floor instead of the roof rafters would be a large net loss in energy efficiency for all the reasons stated repeatedly in this thread by many knowledgeable people. It is not a matter of building envelope size but rather the multiple penetrations of the attic floor assembly (ducts, exhausts, recessed lights, etc) that cannot be effective sealed and the energy loss from equipment and ducts that cannot be adequately sealed and insulated. If that is not clear enough please read this article from the Building Science Corporation.

It would definitely not be beneficial to insulate the attic floor in addition to the rafters. After reaching an R value of 38 additional insulation in the floor would save little money and reduce the substantial benefit of a warm and dry attic.

best option to insulate roofline.

insulation on attic floor of foam sealed attic

does nothing.

installer should know temp of foam mix has to be

right & temp of roof decking factors into the temp.

any savings from only insulating attic floor would

quickly be lost to inefficiency of ducts inside vented

attic space.

plus then you might actually have to seal some of

the holes in the ceilings.

I've run these numbers many times to be able to

share the info with you.

best of luck.

"plus then you might actually have to seal some of the holes in the ceilings."

Wouldn't you do this anyway? You foam the roof deck/rafters, do nothing to the ceiling for insulation, why would you not seal all the plumbing/lighting etc holes that go up into attic?

Great thread (bookmarked) giving me lots of info when i build in 3 years in coastal ga.

OK. So here is what I will be doing.

Open Cell spray foam on rafters in attic.

Walls can be either foam or fiberglass, doesn't make a difference. Its a minimal cost difference so I will probably do spray foam.

What about the basement ceiling? The basement will be unfinished, but there is a furnace in there as well. Should I use fiberglass in the basement ceiling? As we have a walkout basement, some of the basement is framed and other parts are poured concrete. The frame basement walls will be insulated, while the poured concrete (mostly under ground) will not be. Do we want to fiberglass the basement ceiling then?

Thank you again so very much!

The basement walls below grade should be insulated on the outside. If not, they must be insulated on the inside.

Since you will have insulated basement walls and apparently plan to even insulate under the floor slab and an HVAC system and its ducts are located in the basement (leaking air and penetrating the floor above), it will already be conditioned so insulation at the ceiling would serve little purpose.

The days of steam and hot water boilers in cold damp basement are gone; modern forced air systems in tight fully insulated houses should be in conditioned spaces where trapped moisture can be controlled.

My builder recommends fiberglass batt insulation in all interior walls and floors for noise insulation (which I'm skeptical of). But it's his standard practice so I'll play along.

Using insulation to reduce sound transfer between habitable spaces has no effect on energy conservation. And there would be no reason to use sound insulation between a habitable space and an uninhabitable attic or basement. Therefore it is wise to design insulation for sound abatement and energy conservation separately.

"madpebs87

"plus then you might actually have to seal some of the holes in the ceilings."

Wouldn't you do this anyway? You foam the roof deck/rafters, do
nothing to the ceiling for insulation, why would you not seal all the
plumbing/lighting etc holes that go up into attic?

Great thread (bookmarked) giving me lots of info when i build in 3 years in coastal ga."

been out of town so just getting to answer this.

when the attic is vented, you absolutely want to seal all openings

between living & attic space.

when the attic is unvented & foam sealed, then you want

air exchange between living & attic space.

you can get this exchange from not sealing the openings

that trades make & never seal, or seal it up tight

and dedicate an exchange air pathway.

problem is...seldom does anyone seal these openings,

so adding a dedicated pathway is redundant.

people think they built tighter than they actually did in my

experience. but it is all just a guess until you blower door

test to see what leakage actually exists.

build tight, ventilate right, and TEST to find out what

performance actually is.

OP, I have to defer to folks in climates with basements,

as we have too high of a water table in La. for basements.

I have no hands on experience with basements,

best of luck.

The building code requires the holes for plumbing and wiring to be sealed between floors and at the attic floor.

I would highly recommend that you consider injection foam for your walls it is non-toxic has no VOC off gasing, remains soft and plisble in your walls. Easier and cleaner to have installed than sprayfoam. It fills all nooks and cranies around wires and plumbing.