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Insulation/House Sealing Help Needed

Posted by davidmcd (My Page) on
Mon, Jun 4, 12 at 21:03

We are re-building our house (in upstate NY) after a fire and taking the opportunity to make the house more efficient (they just started re-framing so we are locked in on that front). An obvious starting point is to reduce the amount of heating and cooling energy needed. We did upgrade our windows and are now looking into insulation and sealing of the house.

I have been reading A LOT of opinions on insulation levels - such as 60-40-20 and sealing, but I am trying to get some solid information reference points that I can use to discuss with my builder.

The house will be built with 2x6. The front will be brick and the sides/back will be Hardi plank. We were planning to insulate the attic trusses to help keep the HVAC piping in more of a climate controlled environment. We are looking at spray foam to help with air infiltration, but are not sure if we should use in everywhere (attic, exterior walls, between basement ceiling and 1st floor). We were also going to use 1" foam planks behind the Hardi plank (can/should we put it behind the brick, too?). My build has said that we should be careful to let the house "breathe". I am also trying to find info on why that isn't (or is) a good idea so I can have an educated conversation with my builder.

I am sure there are a lot of things that I am missing, so lots of info would be welcomed! Thank you in advance for any pointers/advice that you may have.

David


Follow-Up Postings:

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RE: Insulation/House Sealing Help Needed

My build[er] has said that we should be careful to let the house "breathe". I am also trying to find info on why that isn't (or is) a good idea so I can have an educated conversation with my builder.

When I hear that phrase I have the choice of running the other way or granting the speaker his/her hackneyed analogy, hoping they mean well.
A house doesn't breathe. Instead, as pre-eminent building scientist Dr. Joe Lstiburek put it in a recent interview, "[B]uilding enclosure is an environmental separator. You want to keep the outside out and the inside in, except when you want to bring the outside in and when you want to have the inside out. That's it and there are certain rules on how to do that.
....It all can be distilled into we need a water controlled barrier, an air controlled barrier, a vapor controlled barrier, and a thermal controlled barrier. Then we need a method of exchanging the inside with the outside based on when we want to."

The insulation levels you decide on are only part of the energy efficiency story on your new home. The percentage of glazing, site placement, overhangs are very important. As is the tightness of the structure, the effective R value of walls as opposed to the R value of insulation in the walls and HVAC choices.

Nevertheless, since you asked, Dr. Lstiburek has been quoted recommending a minimum 10-20-40-60 rule for R Value for any home north of the Mason-Dixon Line. This refers, respectively, to values under the basement floor, basement wall, above-grade walls and attic.

The US Department of Energy provides a Zip Code Calculator that tells you the most economic insulation level for your new or existing home. (Loads slowly.)

The most complete and accurate on-line building science resource in English is free at Building Science Corp.


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RE: Insulation/House Sealing Help Needed

Great post by Worthy. Highly recommend doing the foam if by "planks" you mean exterior sheathing (generally 4x8 sheets). This is being integrated into the building codes right now anyway.

If your ducts are in the attic, then spray foaming the roof deck is probably a good idea. Rarely does it make sense to do the walls.

Most importantly, educate yourself on Blower Door Testing and consider an HRV if you can get it tight enough. From the sounds of your builder though, I doubt you will be getting very tight.


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RE: Insulation/House Sealing Help Needed

Good information. Any detailed information on the sealing aspect? I sent my builder one of the documents from the Building Sciences site, but want to spell it out. He is having me meet with the insulation person, but I feel there is more to do in the sealing of the house.

Is Tyvek good? We would be using that, foam panels, plus other insulation...


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RE: Insulation/House Sealing Help Needed

Here is a link to my asheville home builder site that could be helpful. It has lots of pictures and simplified explanations of the blower door and addressing thermal bridging with foam sheathing.

Tyvek is great but theres not much point in using a high perm housewrap over foam sheathing. A lot of builders will skip the housewrap with foam sheathing but it can still be a good practice to use for water management issues especially on gable walls or those not protected by overhangs.

Here is a link that might be useful: Blower Door Test, stopping thermal bridging with foam sheathing pics from my asheville builders website


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RE: Insulation/House Sealing Help Needed

Good summary of energy conscious info in the site above.

However, if this is all new to your builder, don't expect him to change now. Or consider anything you tell or show him to be of any value. The better way would have been to have had the plans by your designer include all the energy-saving framing, sealing, insulating and HVAC details you desire. That way, it's part of your contract.

Housewrap does next to nothing for air sealing. Its primary function , as springtimeHomes mentions, is water management .

Certainly, there's no point to housewrap over XPS--as long as the foam is the shiplapped variety and all joints are taped. (In fact, considering the consistently improperly installed housewrap that is standard, I wouldn't use it at all when I have the choice.)

Every day I drive by a mansion now being encased in giant pieces of preformed cast stone. Underneath, the structure is wrapped in Typar that has been baking in the sun for more than two years and is so UV deteriorated that it's next to useless. (The maximum uncovered time is six months according to the manufacturer.)


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RE: Insulation/House Sealing Help Needed

If you are following the 10,20,40,60 rule, stud walls with foam sheathing will not get you there, unless of course you are planning on using 4" of XPS exterior foam sheathing. Even then, as Springtime notes, thermal bridging plays into the assembly and reduces the total r value. If you want to hit r40 walls, the cheapest way to do so is with double stud wall construction. Also if you want to hit r60 with spray foam on the roof....get ready to pay dearly. And then pay some more! I prefer to detail the air barrier at the sheathing plain, and the go to product is Huber ZIP sheathing. It creates a good air barrier and eliminates the need for wraps and products such as Tyvek. Caulking is critical at plates, headers, sills, heads, etc to continue the air barrier. Once the house is tight (first priority) then you can insulate. It is next to useless to insulate a loose house. As Worthy states, houses dont breath, at least by means of leaking through the walls. Give it mechanical lungs that allows you to control when it breaths (ERV/HRV for your climate).

While spray foam is a good product, its also a very expensive product. Even though open cell is getting more affordable, its still a lot more expensive then caulk and blown fiberglass/cellulose. It also air seals the stud bays, but fails to address leak prone areas such as top and bototm plate connections. Spray foams place the air barrier at the inside of the sheathing plane. The advantage to placing it on the exterior plane is the sheathing can extend down past the sills, rim joist area, top plates, etc to help prevent leaking in those areas.
You also do not want to use exterior foam AND spay foam on the inside. This creates a moisture trap and prevents drying of your assembly to either direction.

However after you get to around r30, your walls stop controling your biggest loss. your windows and doors will limit the total performance of your assembly. You can have r100 walls surrounding a large expanse simply dual pane glass and it would be all for nothing. Triple glazing windows helps, but sometimes do not always pay off.
My go to wall assembly for most climates is a 2x6 framed wall, blown/dense packed fiberglass or cellulose insulation, air sealing/caulking, Huber zip sheathing, 1-3" of XPS exterior foam (depends on zone), vertical strapping for a drainage plane.


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RE: Insulation/House Sealing Help Needed

I'd recommend using Owens Corning EnergyComplete insulation. It's a very simple installation and unlike some other kinds of insulation it offers top plate sealing as that's where 40% of a home's air loss occurs. That could really help you save on your energy bills while keeping your home at the temperature you want. I included a link to it below, hope this helps.

Here is a link that might be useful: Owens Corning EnergyComplete


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RE: Insulation/House Sealing Help Needed

I can tell you the choices we made....we went with 2x6 construction, closed cell insulation. Closed cell is waterproof, adds structural rigidity, requires no vapor barrier and seals the exterior envelope of the house very well. But it is expensive and you need to be 100% sure of your exterior wall wiring as you won't want to change it after it's foamed.

We live in CT, zone 5. We went with geothermal heating and cooling and use the same duct work for both, as well as use it to circulate the heated air from the wood stove throughout the house when we burn wood. We put all the ductwork below in the finished conditioned basement to minimize heat loss so we did not insulate the attic space. Instead we insulated the attic floor. We put in a fresh air exchange unit to bring in fresh air when we want it and used it to vent the bathrooms as vents are required.

We went with vinyl siding for the low maintenance aspect.


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RE: Insulation/House Sealing Help Needed

Lots of focus on the exterior in the discussion, but the air sealing on the interior is important, too. I assume alexbest27 is a spammer, but there's a good point there (you just don't have to use Owens Corning's proprietary pink foam/caulk to do it).

It's been a while since I looked, but Building Science has lots of info. Doing airtight drywall, sealing all penetrations from above/below, caulking the top/bottom plates, window/door foam, etc are all valuable and easy to do while it's all open.


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RE: Insulation/House Sealing Help Needed

As the walls go up, sill seal or caulking should be
installed to seal the sole plate to the slab.
if you have a second story, the sole plate
on those walls should also be sealed.

use the foam sheathing on exterior of all walls.
tape seams, repair any holes before cladding is installed.

as holes are made, they should be sealed. plumbing
penetrations, electrical penetrations..any hole
should be air sealed.

when sheetrock is installed, use air tight drywall
approach. behind crown moldings the walls should
be sealed to the ceiling, as if no moldings were being
installed.

seal cuts in sheetrock ceilings around bath fans,
supply grills & stove vents.

if you use recessed lights, ICAT cans only.
Insulation Contact Air Tight. cheaper to buy
the right ones now than to retrofit to air tight.

if you chose to put the mechanicals and ducts in
the attic, then you would use foam insulation.
in La. we use open cell. the foam should be level
between rafters without low and high spots. the
faces of the rafters should also be covered to
reduce thermal bridging. the seal from the roof
to the attic floor is critical to seal top plates
and stop leakage at eaves.

shop wisely for foam companies. understand that
1" of open cell foam is R-4 at best, and that
foam has to meet code requirements. don't buy into
1" performs like R-10. code is code for a reason,
it isn't rewritten for different products.

best of luck.


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