Where should you insulate? Inside or outside?
It's a tough decision with significant aesthetic and building-science implications.
At the 28th International Passive House Conference in Essen, Germany, Emily Ong and James York presented Civic House, the conversion of an industrial building into a sort of flexible community centre, on a tight budget. It is an interesting demonstration of a perennial question: if you are going to insulate a building, do you put in on the inside (the innie) or the outside? (The outie)
The reason that this question is so fraught is that for many reasons, it makes far more sense to insulate on the outside. It’s easier, it’s cheaper, it eliminates thermal bridge and moisture problems, it makes so much sense just to wrap a big blanket around everything. Building science expert John Straube has written about this often:
“From a building perspective, exterior insulation retrofits offers the easiest, largest, and lowest risk approach to improving enclosure thermal resistance, airtightness, and rain penetration resistance. At the same time, exterior enclosure retrofits enhance the durability of the existing wall more than any other approach (by maintaining it at a constant temperature and eliminating all sources of wetting) and ensure the continuity of all control layers.”
Except who wants to turn all of our existing buildings into bland styrofoam and stucco boxes? I have never been a fan of outies; we treasure the warmth of the brick, the historic appearance, the details and the craftsmanship. It is what we love about these buildings. But innies can be a technical nightmare; as Straube notes,
“Renovating any wall can disrupt the moisture balance and there are examples in practice where this disruption has resulted in damage or performance problems. The damage mechanisms of concern are primarily freeze-thaw and salt subfluorescence. The addition of insulation to the interior of a load-bearing masonry wall will lower the temperature gradient across the masonry and reduce the difference in temperature between the masonry and the exterior air. Both of these changes reduce the drying capacity of the masonry.”
I remember years ago a lecture by a very smart climate scientist who proudly described how he insulated his 150-year-old Ontario farmhouse with seven inches of polyurethane foam inside the old brick. The architect next to me whispered, “he just destroyed that building,” because in our cold climate, if the brick gets wet it will never dry out, and will deteriorate quickly.
Innies are also expensive and difficult and can eat up usable space, but outies are often boring or ugly. In this case it is not unattractive, it is not just a stucco box, and I like the integrated graphics.
Here, the interior mattered more; it is all exposed brick and wood trusses and has real character. This is what people relate to, not the exterior, and it is pretty wonderful.
James York and Emily Ong are covering all of their bases and going high-tech as well, with heat pumps, solar power and smart energy monitoring. The heat-pump and solar panels route is favoured by the Fabric Fifth crowd these days, but here it plays second fiddle to the fabric improvements, as I believe it should.
Michael Ingui is the king of the innies; he takes fabulous old New York buildings and homes, restores the exteriors and does Passivhaus renovations to the interiors, which usually involves a complete gut.
Here, he showed a renovation of a fire hall where they took everything of value that was inside and preserved it, insulated and sealed everything from the inside, and then put most of it back, reconstructing the stairs and the architectural features inside the new improved envelope.
Nobody is going to cover up this exterior, but doing work like this is a time-consuming and incredibly expensive process. Admire it all here.
Sometimes, it is difficult to do either an innie or an outie. My own house was built in 1918 with a brick exterior and interior walls lined with wood panelling and plaster. I wouldn’t think of gutting the interior and losing all that character, but I don’t have the nerve that James York did to wrap the exterior with insulation and stucco or other materials. It’s not a matter of money; I just don’t want to do an innie or an outie and lose the charm of either side of the wall.
And so I do almost nothing- some caulking, insulating the basement and wherever I can pack some into gaps and spaces. This isn’t good enough in the face of the climate crisis.
Some in the Fabric Fifth crowd say I shouldn’t worry about this anymore; we are in a new high-tech world with heat pumps and solar panels, where you can decarbonize without having to do a gut job or an Energiesprong wrap. I am not sure this is good enough either, especially in the dead of winter when everyone’s heat pump is running flat out. In my first post of the year I tried to address this problem, and concluded that the best solution may be a good pair of long underwear.
Or I could do what Harold Orr suggested, “You have to tackle the big hunks, and the big hunks are air leakage and uninsulated basement.” Insulate the roof and the basement, seal all the leaks, cut heat loss as much as I can, and then make up the difference with a heat pump and a pair of Glerups.
If you can’t do an innie or an outie, it might be the next best thing.
It’s May Day in most of the world, and Loyalty Day in the USA! Read my history here. “May Day was so much more fun before it got political. In honour of how it used to be, get outside today. Maybe do a leape and daunce or two. Enjoy the day and hug a tree. Or a socialist, whatever.”
Happy May Day, which used to be green instead of red
Many of my old Treehugger posts have been deleted, but I found this on the Wayback Machine and reconstructed it here. I think it’s from about 2015.
I've done a fair amount of both!
As to the deterioration of brick - there are tests that can be done to see the resistance of the brick to freeze-thaw damage. Also, some of the bearing wall brick buildings I have been involved with in retrofits have been unheated for many years - either that was commensurate with their historic use, or they were abandoned for some time. I've worked on a number of New England mills. One in West Peterborough NH hadn't been occupied in years, there were no intact windows. Those walls had no internal heat to drive moisture to the exterior yet evidenced no spalling. Good brick, so no big worries about innies. It's really important to notice any failed detailing on the exterior that handled water and now is gone. On one building of several stories, a gutter downspout was gone, and below the place where the gutter dropped water into the once-present downspout the entire vertical line of mortar was gone in 4-6" wide strip! Everywhere else, perfectly intact.
Many parapets had stone coping that allowed water to get into failed mortar joints. In one four story 72,000 sf VT building one could push sections of parapets over by hand. Solution is repair (or removal sometimes) and a metal cap.
So many thoughts! I am outie all the way. I did my own house as an outie. I don't disagree with any of the arguments you're making here , it's just that they seem lopsided. On one side you have increased energy efficiency, carbon reduction, comfort, etc, etc, Etc. On the other side you have.... aesthetics? Sure, aesthetics are important but they don't come close to the amount of stuff that's on the other side of that teeter totter. As a Nova Scotian living in Toronto I personally detest the sameness of all the brick here. I've told people that in Halifax you can stumble home in the middle of the night three sheets to the wind and have no problem finding your home. Here in Toronto I still have to pay attention when I'm going to visit a friend so that I don't drive by their house! Not saying we should get rid of all the brick but there are tons and tons of entirely unexceptional brick houses in this city. Mine is one of them. Or was! Not only did I insulate from the outside but I actually removed the 150 year old bricks so that I could pile on more insulation without increasing the size of the house. And I sold the bricks for a dollar a piece so they are not cluttering up a landfill and they are being reinstalled in Heritage homes around the city. Why not take this approach with a substantial amount of the totally meh brick houses and use the bricks on the exceptional brick buildings. And one does not have to cover their insulation with stucco. In my case I used vertical wood siding and it looks terrific. Let's not aesthetic ourselves into 5° of warming, eh!