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please help with insulation questions

Posted by Karen.1288 (My Page) on
Thu, Jul 19, 12 at 15:40

I was hoping that someone could give me some advice about the insulation on our new build. We have not started construction yet so anything goes. We are in the northeast so the winters get pretty cold.
Our specs give us 12" R-38 for the ceilings, 6" R-9 with poly vapor barrier for the exterior walls, 4" R-11 for the foundation walls. All that I know is that this is fiberglass insulation. Should we be looking for anything else?

Thanks...


Follow-Up Postings:

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RE: please help with insulation questions

Depending on how much $$ you want to spend, I would suggest you investigate closed cell or at least open cell spray foam insulation. Closed cell is the most expensive, but you save on not needing a vapor barrier with it. It adds structural rigidity to the house and our house is also very quiet as a result.

When we were looking into building green, all of the advice we got said put your money into your insulation as, regardless of how you generate a BTU, the longer you hang onto it, the more you save.

We live in the northeast as well.


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RE: please help with insulation questions

there are less expensive ways to make walls perform.
payback for foam in walls is very long, and
we can build walls air tight fairly easily.

your best savings would be to clad the house
on exterior with foam sheathing, tape all seams
and insulate walls with whatever type of insulation
you please.
if you put the foam to the exterior it minimizes
thermal bridging, seals the walls air tight.
seal sole plates to slabs.
install air tight drwyall to interior and you have
a high performance wall.
just a little more attention to detail for
air sealing is needed.

relying on foam for structrual integrety
of walls is a sales tactic.

visit buidingscience.com and read building
a perfect wall article.

if you use foam, use it to create an unvented
attic. then things like recessed lights, oversized
cuts at bath fans, stove vents etc won't be
an issue. trades people make lots of holes in
ceilings and few seal the holes.

here in the south we use open cell, but if closed
cell is your choice
you need to understand a few things about foam
insulation.

R-value for your area still has to be met.
if your R-value is R-38 then that is 5.5 inches
of closed cell. not 3 or 4".
rafters should not show after install. faces
of rafters are covered to minimize thermal
bridging.
moisture content of decking should be measured
and not installe if moisture content is high
as it will trap moisture in decking.
temp of roof is a consideration when installing
foam. if it is winter time & roof deck is 30 degrees
then the mix temp has to be adjusted.

foams shrink. they are installed in wrong places
if installer doesn't understand the placement of the
thermal barrier.

here is an fairly comprehensive article on the
pitfalls of foam insulation.
its a good read, comments are also good.

http://www.energyvanguard.com/blog-building-science-HERS-BPI/bid/25546/4-Pitfalls-of-Spray-Foam-Insulation

educate yourself and make informed decisions. you'll
only have one shot to get this right as easily as now.

best of luck.


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RE: please help with insulation questions

thanks for the advice.

energy rater what do you mean by "R-value for your area still has to be met.
if your R-value is R-38 then that is 5.5 inches
of closed cell. not 3 or 4". "

Thanks


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RE: please help with insulation questions

you have to have enough foam to meet code requirements.

if your code requires R-38, then the inches of foam
have to total R-38.
closed cell foam is usually about R-6.7 per inch.
so you have to have enough inches to meet code.

the 'average' 3-4" of foam that 'performs' like R-38
doesn't meet code.

R-value and air tightness are two different things.
there are no 'quanitive values' accepted by code.
it either meets code or it doesn't.

foam companies can't invent their own values
and expect them to be accepted because they say so.

best of luck.


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RE: please help with insulation questions

I design insulated and super insulated structures all the time. Trust me, do not waste your money on spray foams. As ER said, there are far better ways to achieve a tight shell. With the right materials and fairly simple methods, you can get a tighter shell, higher r value, and guess what, it will cost less then foam.

What ER is meaning is a lot of foam guys will claim that, since spray foams perform better then fiberglass batts (meaning, they are more air tight) then therefore you do not NEED to put in as much thickness as code requires. This is not true. They know they have an expensive product, so they are trying to be more competative in pricing.
With that being said, air sealing trumps r value. You can high as much insulation in the walls as you want, but if you have air moving through it is it next to useless.
I am not sure what zone you are in, but I would guess 5, maybe 4.
A good, solid wall system to consider would be as follows:
gyp board, NO vapor barrier, 2x6 studs spaced 24" oc, blown insulation (either dense back cellulose or fiberglass), Huber ZIP sheathing with seams taped (caulk to rim joist plates and top framing plates) 1.5-2" of XPS foam sheathing, seams foams and taped, vertical rain screen strapping screwed through the foam into the studs, siding of your choice. FOr the ceiling consider bumping up in r value to r 50 or better. Air seal the ceiling plane. Use air tight insulated cans with the gyp caulked to them (or better yet, dont use cans at all!). Foam or caulk ALL penetrations through the ceiling including wires, cables, plumbing, etc. Keep all ductwork within the air sealed and insulated space. Avoid putting them in the attic.
The list can go on, but increasing the shell and taking time to make it as tight as possible first, and then increasing r value both within the walls and outside of the walls (reduce thermal bridging of the framing) will keep your house warm and healthy for many years. Also put in good windows. Explore glass options and tune the glass to the appropriate exposure of the house. Not all glass is the same. Read about different glass tpyes such as 180, 270, and 366. I personally recommend fiberglass products, such as Inline windows. Casements will give you the tightest seal over double hungs. And finally, install an ERV or HRV to supply fresh air.


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RE: please help with insulation questions

Your proposed insulation levels would not meet code here in the warm South, much less in the cold north. At a minimum, you need to be looking at 2x6 construction to get the code mandated minimums. And a heck of a lot more attic insulation.


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RE: please help with insulation questions

The problem with these other methods is they are very dependent on the diligence of the installer vs. spray foam which covers all openings and places where materials come together without a lot of effort. But with spray foam, be prepared for a chemical smell which will take time to dissipate.


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RE: please help with insulation questions

lzearc - do you think zip sheathing with foam taped on top is a bit of overkill?

And in a lot of the NE, with a decent southern glazing, wouldn't an HRV not be cost effective. I'm sure it depends on your heating fuel, but getting that tight and then ventilating is obviously ideal, but may not be a reasonable ROI.

If someone is really concerned about costs, HRVs are expensive. What you are telling the OP to do is spend $7k on the walls and then $3k on the HRV. Sure they will save $500 a year and be more comfortable but few people stay in their houses 20 years. Obviously the numbers are fictitious and maybe $1000 is a more realistic savings but you get my point.


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RE: please help with insulation questions

Annie- what does spray foams do to address thermal bridging? what does spray foams do to address leak prone areas at top and bottom plates?
Spray foam places the air barrier inside the walls, my recommendations (and many building scientists) place the air barrier on the exterior of the wall. While there is some diligence required by installers, by using sheathing from top plate to basement sill plate, you now have a continuous exterior air barrier.


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RE: please help with insulation questions

David
as I mentioned above, I like to detail and exterior air barrier. Having a solid, rigid nailed continuous barrier is what I prefer as I am more confident it will last longer. Foams can move, shrink and pull apart opening up cracks for air movement. I use foam as a thermal bridge reducer, never as my air barrier plane. (and IECC in our area requires it for framed commercial walls, soon for residential)
On the cost of ZIP, from the projects I have done, it has been a wash with the contractors compared to properly installed Tyvek and typical 1/2" OSB sheathing. Infact most prefer using ZIP after they have used it. We all know how easily Tyvek can get ripped or snagged and is flapping in the wind. A contractor can lean a ladder against it and rips a big hole in it. They rarely return to patch and tape it... It is next to useless at this point.
SO no, ZIP + foam sheathing is not overkill IMO especially since we really are not seeing an increase in cost for contractors who have used it before. (I will say I am not sold on the roofing ZIP and that does cost more then a 5/8" deck with synthetic felt).
The HRV recommendation was not to save energy, but to provide the mechanical ventilation a tight home requires, assuming of course there is a blower door test completed and it tests out below 2 ACH@50 pac. My project specs are typically 1.5 or below, averaging closer to 1. It could be an ERV as well assuming zone 4 or 5.
Again, some of my findings could also be more localized as far as costs, but then again very few residential contractors use or have used foam sheathing either in my area, but I have yet to have a single one refuse. Most are very open to it, are sceptical at first, but when its done they admit it was much easier then they thought.


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RE: please help with insulation questions

Except who uses tyvex when you have foam sheathing?

And how much air is coming through 2 layers of staggered foam taped and then OSB? I understand that air sneaks in thru very small paths but when there are panels where seams don't line up, it is hard to imagine the air movement.

My last build, I told my builder to use Zipwall if it was less than $1000 (2100 sqft) and we went with Tyvex (no foam sheathing).


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RE: please help with insulation questions

no one uses Tyvek over foam sheathing that I know of. Nor did I say to use it over foam. I said I did not trust a foam layer to be my air barrier and hold up over the years compared to a rigid nailed sheathing layer.
If you apply 2 layers of overlapping foam with joints foamed and taped...yes, you can get it very tight. However the labor costs do increase with this method as well.
One can also air seal standard osb sheathing if they prime the joints and then tape it off. Then use Tyvek over top and you will achieve about the same thing as ZIP sheathing.


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RE: please help with insulation questions

You probably meant r19 for walls and foundation insulation would be foam But to advise you about insulation I would need to know what town and how the walls would be constructed. There are too many ways to build and insulate a house.


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RE: please help with insulation questions

Investigate flash and batt.

A thinner layer of spray foam is used to seal ad provide the outer layer of insulation, and then batts are used to achieve the balance of the R-value at less cost than foam alone.


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RE: please help with insulation questions

note that all my comments are on common practices
and materials I see in my 10+ years in the
efficiency business.
this is not to say one product is superior over
another, just itrw here in La.

concerning flash & batt:
I've never seen anyone do flash and batt.
to get the foam company to apply such a small
amount turns companies statewide off. instead
they talk the homeowner into full depth..or
close approximation in 2x4 walls.

also note that I've never recommended foam sprayed
walls, and if they go that route..foam has to completely
fill the stud bay..overfill with open cell & shave flat with
stud faces.

never seen flash and batt on attic side of
ceilings either.
If you could get a company to flash & batt walls
it would entail a second trip to do again a minimal
cost job to do attic floor.

here we don't do fiberous insulations against rooflines
so flash & BIBS wouldn't be installed.

I wonder why would a foam company make multiple trips
to the same site where they are making mininal dollars?
even if they did foam & batts or blown..it is usually
different crews. so you would have multiple trips
and tie up two crews.

now if it was for a bulider with several projects
a year..that would work.
but for a homeowner with one house at most every
several years..just don't see it happening.
maybe in Austin Texas.

I try to be that bridge that brings homeowners and
trades people together. so that is my pov in all this.
people in my trade are unbiased and only sell efficiency
so although we don't have a material dog in the fight
its the efficiency that we fight for.

Davd cary & lzerarc
Yes builders do use tyvek & foam sheathing.
because they don't understand clearly what the
end goal is. if a builder has upgraded from felt
to housewrap..that to them is a big step.
and now you want them to skip the housewrap??
land of mercy!! you tryin to put them out of business?
LOL!

here we have hurricanes. solid sheated walls with osb
& cdx is the norm. putting 1" polyisocyanurate foam sheathing over the solid sheated walls and taping all the
seams..tape has to adhere to CLEAN and DRY surfaces..
sealing any holes mades by trades people before then installing cladding has been our most cost effective
wall to date. follow with conventional insulation
on interiorr of walls and air tight drywall. you've
got high performance wall. R-7 foam sheathing..R-13
to R-15 insulation..not bad for a 2x4 wall.
of course air sealing also includes sealing sole plates
to slabs or subfloors, proper flashing & sealing of windows
and doors. Air sealing ceilings..that is a whole other
post. we do walls well..but ceilings!
recessed lights that aren't ICAT holes for supply boxes
returns..bath vent fans..stove vents.. speakers..
and wire and plumbing penetrations.
the air sealing is in the details. but it pays back
in comfort, smaller tonnage hvac, better indoor air
quality.
another post would be fresh air requirements & how
exactly do do it.

here is a link to my utility co-op's energy efficiency
design for new homes. while it isn't as comprehensive
as I pushed for it does show lots of good information.

pay special attention to the exterior wall composition.
you'll see that since so many builders INSIST on housewraps
that they specify that it be next to studs and sheathing over tyvek.

in general:
designers/architects really let us down in that they
don't design with hvac & ductwraps in the conditioned space.
or incorperate accurate load calcs into the house when it
is in design stages.
maybe some do..but I've had several architects incorperate
my spec sheet word for word onto thier plans. MY spec sheets. hell, they went to college for years, IMO they
should have a clue...but just my angst there!

trades people should seal holes they make as they make them.
hvac should be comperhensively sized..not just rule of thumb. insulators should learn where to put the foam and educate themselves in thermal boundry locations.

in a perfect world.

continuing education for everyone! LOL!

best of luck.


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RE: please help with insulation questions

lezarc - what I heard was you arguing that zipwall doesn't cost more than tyvex. Right? But when you are using foam sheathing, you don't use tyvex. So of course, zipwall costs more.

I see your argument about durability, I am just not sure I agree. Of course a second layer is better than one. I just don't see if you glue and nail the foam to OSB and the seams don't line up that there is much air movement at all there. And if there isn't much air movement, then the cost of a zipwall is wasted.

We can agree to disagree and given a good argument, I would change my mind. I've really come around to your double wall in a cold climate so you never know.


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RE: please help with insulation questions

tyvek, with a k ;)
What I was arguing was, from my experience and local area, zip wall does not cost more then osb and tyvek from people who have used zip wall before. I thought you were meaning Tyvek over foam. So yes, zip wall plus foam would cost more then osb plus foam if you do not put tyvek over the osb. Like I said, foam moves. it shrinks, shifts, etc. the wood walls are shifting, shrinking and the foam doesnt always go with it. I just dont trust it, and that is based on experience of seeing foam opening up. But even if it were 500-1k more...and it helps insure a better air barrier for a longer period of time...why would it not be worth it? on a 250k+ home? that is half a percent of the total cost.
The OP asked what people recommended, and I am sharing what I have found to work great. Its not always the cheapest option. People do not batt an eye at dropping 20-40k on custom cabinets when Ikea are arguably just as good for under 10k. Everyone has their areas to spend the money on...most times things you dont see are not as important in the budget unfortunately.
but since you brought it up....I have found the double stud wall to be cheaper then thicker foam walls, details are easier, etc. However you do lose some square footage, and very few people jump at the higher r wall option mainly due to that. The couple double stud wall projects I have done cost the same as a 2x6 wall with 2" of XPS with close to 2x the insulation and nearly 100% thermally broken. If designed right, one can completely eliminate a ducted furnace system instead using a single mini split. Mitsubishi hyper heat units can product 75% of their heating output at -13, and 100% at 5. Most mean temps in zone 6 are above 5 degrees in the winter, with design temps pushing -10 to -17, however they last for a very short amount of time. A tight, highly insulated structure can ride out the dips in temps easily for several hours with only a few degrees lost.
Obviously many are very skeptical of this method and are sold on over designed, multistage ducted hvac systems bc that is what hvac guys are pushing these days in order to obtain comfort. A tight, highly insulated home does not have temp differences from room to room. So your insulation and shell increases by a few k, but you cut the hvac and ducting, so you drop 10k or more depending.

So yes, i think the double stud is the best for zone 5 and above. However I typically do not go there first since its a hard sell. Hell getting people to upgrade from batts to a blown product is hard enough sell sometimes!


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