Natural wool insulation and plaster veneer air barrier
Hey, everybody.
I have a 1904 classic American foursquare in Pittsburgh. Three floors plus basement and attic. Roughly 3,200 square feet. Balloon frame with no fire blocking that I know of. Stone foundation, brick veneer first floor, cedar shingles on second floor and third floor dormers. Hip roof. No insulation. No water issues. Basement is dry. Bathrooms and kitchens don’t have vent fans but hasn’t been an issue because of all the air movement and loss. Renovating the house, starting at the top and working down. Just gutted the third floor to studs (but tongue and groove flooring is still in). Want to improve comfort and energy efficiency along the way. Terrified to do harm to the house by improperly air sealing or insulating. Despite countless hours Googling and listening to the Fine Home Building podcast, I’m still kind of the “houses have to breath” person that everyone makes fun of. Looking for air sealing and insulation that will improve things but keep the house resilient and not require what seems like endless chasing of air gaps.
Wondering what people would think of:
1. Using plaster veneer (blueboard with one or two coats of plaster veneer) as my primary air barrier.
2. Using natural wool insulation–batts or blown-in–for knee walls, exterior walls, hipped ceiling against roof, and attic floor.
3. Not trying to stop stack effect or otherwise air sealing aside from carefully detailed interior walls.
4. Would need to figure out how to air seal and insulate along the whole perimeter between all of the floor joists, so cold air doesn’t come in under the floor and then up through all the floor board gaps. ‘
It’s OK if you want to ignore my question entirely and just tell me what I should do instead.
Thanks in advance.
Ben
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Replies
Ben,
Here's my perspective: One element of your plan -- "Not trying to stop stack effect or otherwise air sealing aside from carefully detailed interior walls" -- doesn't make any sense. Air sealing work is Step One. If you can't control air leakage, all of your other work is for naught.
I'm not trying to make fun of a person like you who describes himself as "still kind of the 'houses have to breathe' person." But my advice needs to be based on science. Studying building science is helpful, because researchers have tested various hypotheses and measured the results.
We shouldn't be remodeling our houses based on beliefs. We should be remodeling our houses based on the findings of scientists.
You absolutely need an air sealing plan that is comprehensive. You need to seal absolutely every air leak you can find. (There will always be a few air leaks that are impossible to seal, especially in a remodeling situation, which is one reason why sealing all of the accessible leaks is so important.) And yes, you need to wage war against the stack effect -- because your stud cavities shouldn't be chimneys.
Martin, how much is air sealing a balloon frame house related to the negative impact that moving air has on the function of insulation (I saw your post about testing R values versus air tightness) or related to preventing moist air from traveling to other parts of the house and potentially condensing?
Similar to the insulation vs airtightness study they did, in a situation where a house uses walls as air barriers and has insulation outboard of those walls and also has air leaks in the exterior envelope, how do those leaks impact performance? I guess part of what I'm trying to understand is the difference between air sealing the interior walls versus exterior envelope. Ideally answer is do both obviously.
Thanks
I would absolutely stay away from wool insulation, but I’m allergic to wool... I would use blown cellulose or mineral wool batts. In a renovation project, I’d use mineral wool batts in the walls in almost all cases, and blown in cellulose in the attic.
You really need to do proper air sealing. Even a relatively small amount of air leakage can negate a large amount of insulation in terms of overall energy loss for a structure. If you’re really worried about the “breathing” of your house, perhaps just change your thinking a little: we talk about “drying” instead of “breathing”. Walls need to be built to dry either inwards or outwards, but if you seal them up completely with vapor barriers on both sides you can have problems. If you start thinking in terms of moisture migration instead of air movement you can seal your house up and still be comfortable with what you’ve done.
Many of us here use exterior foam, which is often a vapor barrier, so our walls are designed to dry inwards. The drywall acts as an air barrier but still permits some vapor diffusion which provides the needed drying ability to the wall. Everything is carefully air sealed, often with multiple redundant layers, but vapor diffusion is carefully mannaged to prevent problems in the wall.
Bill
Ben,
Martin is spot on.
Insulating a balloon framed house without air sealing is wasting your time. Throwing some batts into the walls will not make it more comfortable and would probably only reduce your energy use by only %20.
To get proper air sealing your options are dense pack cellulose or spray foam. From your description I don't think you are a spray foam person.
Dense packing older houses you do have some challenges. You heave to check the quality of your bricks (soft bricks can be a problem) and your wood siding.
With painted wood siding, its good to keep some form of ventilation on the back side otherwise you might end up with peeling paint. Many ways of building this in if your wall is open, probably the easiest is 1x1 strapping in the corner of the stud bays with 3/8 plywood stapled on. This would hold up to dense pack pressure.
If your shakes are unfinished, the ventilation channel is not needed, you can just dense pack the cavity.
Assuming your studs are true 2x4, you would end up with 3" of insulation. Not the most insulated wall but orders of magnitude better then what you have.
There are a lot more details on this form for air sealing and insulating baloon framed house.
Super helpful. Thanks
Akos, the 20% energy reduction number is helpful. Not holding you to it or anything. But one got an old house with lots of stuff that needs done. So I gotta triage. Some thing will have to be better rather than perfect. Other stuff will shoot for perfection. Compared to the 20% reduction, what would I be shooting for with meaningful attempts at air sealing?
Ben,
Throwing some fluffy insulation without fixing the air leaks is asking for trouble.
That "breathing" your house is doing, it is dumping loads of interior moisture into this fluffy sponge you just put it. At best you end up with some soggy insulation, most likely mold in your walls.
If there is one thing to fix, fix the air leaks. Once those are fixed, fix your flashing around your windows/doors, then insulate.
To give you an idea, a 2.5 story balloon framed brick veneer house (~20 ACH, so very leaky) went from a heat load of 52k btu to 20k btu with air sealing and insulation. Most of that was from air sealing.
If your walls are open, fixing the air leaks is easy. Going back to try and fix it afterwards when you have a moldy mess on your hands is going to be way more expensive.
Compared to all the work you need to make a house livable, this is not hard work. You will end up with a home that is not only much more energy efficient but way more comfortable.
Because you're tearing out the inside, I would add horizontal furring or a layer of foam for more insulation.
Adding air tightness and insulation does mean there is way less energy transfer through the walls. That means on the exterior side if rain water is being mismanaged, stuff wont dry fast anymore and it will rot. Akos idea for an air gap is very smart.
Ben, I too agree with a little bit of air movement within a house is a good thing. A too tight house can have its problems also. I like opening my windows in the winter occasionally to change the air. If the interior is sealed, air movement in the exterior is not a bad thing. As a former and occasionally still plasterer, plaster makes a good air sealer and vapor barrier that can get into all the nooks and crannies that drywall may miss. You can literally throw water at a plaster wall and it will bead off. There was a time when it cost more to plaster, then plasterers had to adjust once drywall came into vogue and now it may cost a little more but the advantages are well worth it. Obviously it's an older house so going with conventional batt insulation should suffice and any air leakage will be from the outside and hopefully find its way out elsewhere before it enters through your now completely sealed walls. After all, look how long the house has lasted in the condition it is in now. Sealing things up completely may cause unforeseen problems.
Tom -
When a house gets "too tight" you introduce whole-house ventilation; it's all about control or management. When you open a window for fresh air, you are controlling how much fresh air you introduce.
"Sealing things up completely" causes problems when we don't manage energy and moisture equally. If you manage energy better you need to manage moisture better. It's not just a good idea; it's physics.
Peter
If you think about it energy use and moisture go hand in hand, if you want to talk physics, or thermodynamics actually. If your house is cooler or a small delta T, at a lower pressure, in the winter, then the air will be drier. Same goes for summer, if you use AC then the bigger the temperature difference the more your house acts like a big refrigerator except it doesn't have one of those moister level dial / slide things. So basically the less energy you use in the form of heating and cooling will more than likely manage your moisture better.