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Community and Q&A

Insulation vs. air flow extra expense

Ani1 | Posted in General Questions on

Hi, I’m going to have a new house built and am confused on where to spend additional money in regards to insulation and air flow.

I have talked with many builders and most offer a “standard” solution involving fiberglass batts in walls for insulation and no air control layer (other than drywall or caulking holes that they find from blower door testing).
If I am interested in anything better it will cost me more money.

I understand that “batt” insulation can be problematic in regards to having it installed correctly.
This would lend me to believe that I should spend additional money on an insulation product that is not in a batt form, a “spray” product.
But, one can argue that no matter what the product is (batt or spray); if it is installed incorrectly it will be a problem.

One can also argue that it is not the type of insulation that is being used that is of importance, but the ability to control air flow in an assembly.
Meaning that if proper controls are put in place to control air flow, it does not matter as much what insulation material is used or if it is installed properly as long as it meets the required R values of the code.

Ideally one would spend additional money for better installed insulation and on proper air flow controls.
But, if additional money is not available for both, what would be best to spend the money on? Better installed insulation like a spray product or better air flow controls?
If better air controls what are some examples? Like a liquid based coating on the outside of the house?

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  1. davidmeiland | | #1

    Well, not a simple question to answer without writing a book (or at least a magazine article), but my vote would be for taped sheathing and dense-pack cellulose insulation in your walls. If you have a concrete slab floor, nothing to worry about there, if you have a framed floor, someone has to air-seal it and you have insulation issues to consider. Hopefully you have an attic and not cathedral ceilings, because an attic is easy to do right with loose-fill cellulose.

    Really, it shouldn't cost much more to do a much better job, but you have to find the people who have already done it at least once. If your builder is saying "what?" about this stuff then you have an uphill battle.

    Exterior foam over the sheathing, sprayed foam, and a few other options are also out there, for more money (although possibly lower total cost over time).

  2. BobHr | | #2

    I think David is on the right track. What you will find is that as you make one change now something else moves to the front of the line to be the next weakness to tackle.

    Air sealing should be at the top of your priority list. I agree with getting rid of batts and using a blown insulation. But once you tackle those 2 steps you find that thermal bridging is a hurdle to over come. Different ways to tackle that issue. Then you should start looking into energy flow through the foundation and basement slab.

    The thing is you have one shot to tackle these issues at a reasonable cost. After the home is built retrofit cost go way up. I like the pretty good house approach that is floated on this site. A search will give you a lot to read.

    The improvements dont have to add greatly to the cost and dont add that much to a new mortgage. In fact you may save more in utilities than the added payment. In the short term you will have lower utility bills. In the long term your house will be worth more. People are becoming more aware of the benefits of energy efficient homes. They are just better to live in.

    Take the longer term view and you wont have to regret your decisions to take short cuts and build a code house.

  3. GBA Editor
    Martin Holladay | | #3

    At first glance, your question appears unanswerable. It sounds a little like, "I can't afford to do everything right. So if I have to do something wrong, what should it be?"

    But if we boil your question down to its essence -- "What's more important, air sealing or R-value?" -- the answer is clear. Air sealing always comes first. So find a contractor who understands the need to pay attention to airtightness.

    Ideally, though, you need to keep looking for a contractor who understands the issues we're talking about, and who cares enough to do a good job.

    If you can't find that person, then none of these discussions matter.

    And if you find that person, you will get a house with very few air leaks, and with insulation that was well installed.

  4. Ani1 | | #4

    Thank you for the helpful answers.

    I will have to do some more research into air sealing and hope to find a builder who cares.

    Most I talk with when I say “air sealing” just refer me to the drywall, or say that is what the Tyvek (building wrap), or vapor barrier is for.
    I like David’s comment:
    “Really, it shouldn’t cost much more to do a much better job”. This may be true, but I have talked with 10 builders so far and all of them say they will do whatever I want, BUT seem to find many excuses and reasons to talk me out of any sort of insulation other than fiberglass batts.
    I just get more depressed at this.
    They all say that they can pass a blower door test.

  5. GBA Editor
    Martin Holladay | | #5

    You wrote, "They all say that they can pass a blower door test."

    Ask a few follow-up questions.

    1. "How many times have you tested one of your new homes with a blower door?"

    2. "What results did you obtain in ach @ 50 pascals?" A result of 1 or less is very good. 1 to 2 is good. More than 3 -- not very impressive.

    3. "Will you guarantee a tightness target? If so, what do you consider 'passing'?"

  6. LucyF | | #6

    Are you going to be directly involved with building the house - meaning are you going to be physically working during the construction? If so, air sealing in most places is easy. I thought it was fun as well because I knew I was solving a problem better than anyone else would have. You could also install insulation yourself. Installing batt insulation is kind of pain, but not really hard physically. Cathedral ceilings, very tall walls make that much more problematic.

    Have you signed a contract with the builder yet? You could require a specific blower door result that the builder must achieve and if he doesn't meet that level, he must go back and find and plug the holes. Much easier and more effective in the framing stage than after the drywall if up. I suggest that you require 2 blower door tests - at the end of framing when windows and doors have been installed, rough-in completed and again after dry wall has been installed. Then you've got a chance to make a difference. If you wait until the house is done you are much more limited in how much you can fix things.

    You could require a meeting with the builder and the major subs to emphasize your energy goals in building the house, emphasize the need for air sealing and your concern that it be done right - offer them a free meal at good restaurant and give them a small stipend to make your point. Put signs up for the subcontractors at the building site - if you put a hole in the building envelope, you must seal around the hole.

    You're going to have to be hands on at some point because this air sealing concept is pretty alien to the average builder in the US. You should probably go to the building site and review the work. We built my brother's small house (1200 sq.ft) with basically 2 carpenters which means that the framing went up over a fairly long period of time so I had time to go by and review their air sealing work. If your builder is a production builder he will have a pretty large framing crew who will have the building framed quickly. You or your contractor will have much less time to intervene with air sealing deficits. In other words, somebody (you or some Air sealing specialist) has to be around to make sure that it is being done properly.

    The two main companies in the US that sell high quality air sealing supplies are Four Seven Five High Performance Building Supply and Small Planet Workshop. They have great information on their websites about air sealing. I've included some links for you to go to.

    Finally, my blog is pretty detail-heavy with air sealing information largely because that's about all I know about energy efficient construction. My blog is Green in Greenville

    I hope this helps you, Ani. Building a house is an adventure, but when you do it right, you will be very happy.

  7. Ani1 | | #7

    Thanks Lucy!
    I have not signed a contract yet with a builder. I'm still in the process of interviewing them.
    I like the idea of 2 or more blower door tests in the contract.
    I will check out your blog.

  8. Expert Member
    Dana Dorsett | | #8

    Air sealing the structural sheathing to the framing is the better location for the primary air barrier, but with fiber insulation you need to attend to air sealing the gypsum carefully too. Don't forget the bead of caulk under the botom plate of the studs, etc. either.

    The air tightness of the sheathing is far less likely to be compromised over time (you're not banging nails into it to hang picutres & mirrors as is commonly done with the drywall side), and has fewer penetrations to seal, since you don't have an electrical outlet every 6'.

    Martin's metrics listed as his #2 question is a pretty good one:

    ""What results did you obtain in ach @ 50 pascals?" A result of 1 or less is very good. 1 to 2 is good. More than 3 -- not very impressive.

    Not very impressive indeed, since over 3 does not actually meet IRC 2012 code for air tightness. Unless the design is some junior architect's framing nightmare of a gazillion bump-outs, set-backs and dormers, if they're paying ANY ATTENTION AT ALL to air sealing issues 3ACH/50 would be a cake walk, more of a stripe painted on the floor than a hurdle to clear. Over 3 is an indication that they're either clueless or careless (which is unfortunately not uncommon.)

    With 4x 8 sheet goods on both sides of a framed wall there's no excuse for performing worse than 3 it's almost idiot proof. And yet... the more idiot proof you make something, the more creative the idiots become. eg: Tract home builders were prone to skipping the interior side gypsum behind tub-surrounds before air leakage standards were enshrined in code- there's lots of ways to build in big holes that don't necessarily show, and some are even more creative than that.

  9. LucyF | | #9

    Creative idiocy - now that's a concept I will be using in the future. Well, I mean that's a term I will be using in the future. I hope not to be exercising the concept, though it will likely happen. Thanks for that, Dana.

  10. davidmeiland | | #10

    Since energy code was mentioned, is there an air leakage standard enforced by the building department where you live? Here, it has been part of the code for ~3 years, and my experience testing shows that most houses will be between 4 and 6 ACH50 if nothing in particular is done for air sealing. Some are a little better, some are a lot worse. If you are in an area with actual enforcement of the 3ACH50 standard, you might not have to do much aside from ensuring that you get an honest test and the inspector signs off. Locally, actual enforcement is just starting (it has been a polite suggestion during the 2009 code phase) and builders are going to be scrambling to meet the standard when they fail their one test at the completion stage.

    You improve your chances with a slab floor instead of framed, attic instead of cathedral ceilings, no ductwork outside the envelope, taped sheathing (possibly something like ZIP), flash/fill spray foam or full-depth foam, dense-pack cellulose walls, a simple shape, good windows (most are), glued drywall, no tongue&groove wood walls/ceilings, air-tight electrical boxes... AND... just ONE GUY on the crew who is a good air-sealer and is present throughout the job. There is a huge difference between someone who has never experienced a blower door test, and someone who has chased and fixed leaks. I would be looking to make sure you have that person as opposed to trying to put wording into a contract to ensure tightness.

  11. Ani1 | | #11

    Thanks David.
    This project will use the 2012 international energy code.

    I will have a full basement and vented attic living in the Midwest (zone 5).

    Funny story about not having the ductwork outside the envelope, I have talked to lots of builders (more than 10) and I always bring this up as something I want to do. They always say the same thing, why would you want to do that? When I express the concern about heat loss and possible ice damming they tell me that never happens because they can now insulate the ductwork and insulate the furnace. When I say why take the chance they think I am questioning their competency and I move on to the next builder. I’m still trying to find a builder who is open to these ideas.

    I am looking at the flash/fill or flash/batt idea, but am worried if not done right condensation could form in between the different insulation layers or at the studs. I’m still not sure if it should be close or open cell spray foam for the exterior walls in a flash and fill/batt solution? I originally wanted to do exterior insulation, but once again builders always try talking me out of this saying too expensive and next to impossible to construct.

    I have been reading Dana’s blog and like the idea of spending the time myself at the construction site with a can of spray foam and trying to plug as much as I can throughout the total building process.

  12. Expert Member
    Dana Dorsett | | #12

    In a flash'n'batt in zone 5 you MUST used closed cell to get away from interior side vapor retarders, and for the assembly to meet code the foam needs be at least 40% of the total center cavity R for roofs, 35% for walls. If you use less foam-R than that, using a smart vapor retarder such as MemBrain would be a good idea, and far safer than using polyethylene. A cheaper second choice would be to use half-perm "vapor barrier latex" under the finish paint but that is somewhat less resilient than a smart vapor retarder.

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