Choosing Wall Insulation for New Build
Zone 4A Exterior Wall Insulation / Contractor disagreement
So I know from reading the blogs that the ideal time to have done my diligence and planned the insulation was at the design phase. But like many, I am well past that. I live on Long Island, Climate zone 4A, and my two story house is now framed and sheathed with plywood. This is going to be our family’s forever home. I need to make a decision now on insulation. I want to do it right but I am not looking to spend money unnecessarily. While I want my house to be efficient I am not looking to have a passive house by any means. My contractor wants to do closed cell spray foam and blueskin WRB. That’s what he did in his home and that’s what he’s done in his homes.
I work in the renewable energy industry and have folks in the energy efficiency space and build science recommending I do differently. They’ve suggested, like has been brought up in other comments, to do an exterior rigid board insulation and a dense pack cellulose stud cavity insulation. I had another friend who is also knowledgeable say that in the new build, to go with open cell spray foam for exterior walls. They both unequivocally were against closed cell, which I’ve gathered from folks here would be their opinion as well.
So now I am trying to figure out with all of the options, what do I do. One of the challenges is that I don’t have a great perspective in the cost differences between the options. Again, I am looking to achieve the desired goals without spending more than I have to. From my research and assessment, I am thinking about a 1” Rigid foam EPS or GPS exterior insulation (R-5) with open cell spray foam or blown cellulose for exterior wall cavity. A few related questions:
Should I have a Tyvek house wrap under the rigid insulation or is that not necessary if the rigid foam board is taped properly?
Can Hardie lap siding be nailed directly over the rigid insulation board? Someone suggesting furring strips but my contractor has concerns of having any more off the house that would cause more work on window jams, etc. and he said he’s done the Hardie directly over with just longer nails.
Is GPS (Neopor) worth it?
I have some concerns about dense packed cellulose, as it relates to settling, water damage in the wall, and general installation. My contractor flat out told me he’s never done a house with dense packed cellulose and doesn’t know who would even do it. (To be clear I like my contractor but believe he’s not bought into the house science part of the industry).
I appreciate all of your comments and thoughts.
– JK
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Replies
Good luck. It's never easy coming to terms with a contractor who like to do things their way.
FWIW I've done a structure (in Westchester btw) with 100% Open cell and it's tight as a drum. I believe we used Tyvek...this was a while ago.
Recently I did one in CT with Closed Cell in the roof and band joists with Rockwool in the walls. Again, very comfortable. Think we got 2 ACH on the blower door test.
The next building I'm doing all the GC's were concerned with the ZipR creating a problem for trimming the windows, eaves etc. Everybody always wants to do CC: it's easy, effective and makes their jobs easy too. Right now the GC is on board with ZipR and Rockwool with CC in the roofs (this is an old building) but I know he would prefer CC everywhere. I'm going to try to hold firm on this.
Check with Hardie to see if your GC's approach meets their install standards.
FWIW my last GC didn't like me sticking my nose in his business. That's exactly why he didn't get the next job. This new one is happy to talk with me.
The additional cost of exterior insulation is mostly about the additional labor, the material cost is pretty much noise. The issue is if you are in an area where it is not code and dealing with trades that are not used to exterior insulation, in that case the upgrade cost will probably never pay.
In terms of the insulation inside the walls, spray foam is the last thing you want. If you already have a peel and stick WRB, the walls are pretty air tight, there is no extra air sealing benefit from the spray foam. Once you do the math on the R value of the whole assembly including the thermal bridging of the studs and the fact the CC SPF can't be a full cavity fill, the assembly R value difference between the different insulation options is pretty much noise. There is a significant cost as well as non-zero risk of a bad install with spray foam, so it is something best avoided.
If your GC is not familiar with exterior rigid, I would not push it and spec either high density batts (fiberglass or mineral wool, both work just as well) or even better, dense pack the walls.
If not too late, you can use the exterior insulation/SPF budget to get better windows.
I would absolutely NOT use spray foam in walls, either open or closed cell. You just don't gain much going that route over more traditional methods that are usually much cheaper. My preference is usually mineral wool batts in the walls and exterior rigid foam (usually polyiso), but dense pack can work too. Fiberglass batts can also work. Just be sure to do a good job air sealing the "old fashioned way" with caulk and canned foam on the exterior sheathing and interior drywall as you put things together.
Exterior rigid foam usually isn't a big deal up until you get up to 2"+ where it complicates some exterior trim details. If you're under 2" (or at 2" most of the time), it's not that bad to work with IF your crew takes some care to do it right. I would go with foil faced polyiso here, for a bit more R per inch, but EPS and GPS would work too. I would avoid XPS here (least green, and it gains you nothing in this application compared with GPS or polyiso).
Be sure to follow the tables about the appropriate amount of rigid foam for your climate zone. Note that the tables are ratiometric, meaning that the important thing is the ratio of interior to exterior R value, NOT just thickness of anything. You need a certain percentage of the total overall R value of the wall to be in the exterior rigid foam to avoid moisture issues in your climate zone. As you go further North, into colder climate zones, more of the total R value needs to be in the rigid foam instead of the batts in the wall.
Bill
The way I look at it any flavor of spray foam is always the least green option possible and the most expensive possible option! Given that I have to assume anyone suggesting spray foam has zero regard for planet or my wallet and their credibility is now very questionable.
There are a few times when spray foam is the only real option but they are rare and mostly due to failure to make a better plan in short laziness in new construction.
Walta
Thanks for the response. After going back and forth, the likely conclusion will be:
Exterior:
Tyvek house WRB
1” EPS rigid insulation with Neopor (aka GPS)
Hardie lap siding
Interior:
Rockwool confortbatt R-23
Deleted
I would stick with a peel and stick air barrier or detail out another system (tape plywood, etc). I do think exterior at this point in the game without planning may be problematic detailing it. Just make sure you have good strategies and draw it out before starting.
Consider getting a quote for damp spray cellulose insulation. It is likely to cost much less and fill the gaps much better.
I am not a Tyvek fan in the weeks between when it gets poorly installed and siding covers it the wind rips it up to the point of being useless as an air and water barrier ask for a quote for zip sheeting but skip the plusR option.
Did you say their would be a gap / rain screen behind the Hardie plank?
Walta
Most on here do not like spray foam (open or closed) due to environmental concerns. Contractors like it because it makes it easier to get a tight house.
I went with damp applied cellulose in the walls, and am pleased with how it turned out. It is VERY dusty, but I'd rather that dust than fiberglass or rockwool dust, and once the house is done there is no dust issue. I have open cell with a vapor diffusion port on part of my roof, so before they sprayed the damp applied cellulose, while they were in the house spraying open cell, my contractor had them go around and shoot open cell in some very difficult to access areas/tricky connections, including behind the tubs. When they did the damp cellulose they overshot it and came behind with a long straight edge and "trimmed" using the face of the stud as their guide. Consequently the ENTIRE stud cavities are filled with cellulose.
I would never do dense pack cellulose - I had that applied at two short interior walls for sound abatement (they could not do damp applied because they were interior walls and my contractor did not want to hang a few pieces of gyp in advance...and the damp needs a hard surface on which it is applied...). The dense pack has a net on both sides but makes the installation of gyp MUCH more difficult, and it settles. They did not apply the gyp in my house for 2 weeks after the damp cellulose, in order to give it plenty of time to dry out. By the time they applied the gyp there was at least a 3-4" gap at the top of the interior wall with the dense pack cellulose. Not a big deal since it is only for sound, but would be a big deal on an exterior wall where it is for insulation. The GC forgot to sound insulate another wall, so they came back and did that with rockwool. I realized the quality of the job you get with rockwool depends entirely on how much your installers care about doing a good job, and these installers did not care too much. All that to say I think you would be much better off with damp applied cellulose and it should also be less expensive than your spray foam.
Since you already had blueskin budgeted, stay with that, because that is a terrific air barrier. With the money you are saving on the spray applied foam, install the appropriate thickness of exterior insulation, and require your contractor to install either a rainscreen or furring strips. The strips don't need to be thick - 1/4" material will do. Once you are doing exterior foam, your contractor needs to think about the window bucks, and an extra 1/4" of furring won't make any difference.
If you are doing exterior foam, think about the longer fasteners you will need for the Hardi.
One of the downsides of closed cell foam that isn't talked about much is how hard it is to remove. It needs to be chiseled out or cut out with power tools. If there are pipes or wires buried in the foam it's hard to see if they're there and it's hard to remove the foam around wires without damaging them.
During the finishing stages of building a house you'll have guys constantly making holes for all the things that get added at the end. And they'll just drill into the foam, and they'll break things.