GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

How do you super insulate a brick bungalow?!

GBA Editor | Posted in Energy Efficiency and Durability on

Super insulating to Passive House (R-40 / R-60) standards has been well documented in these forums for existing or new frame homes, but no one with experience has discussed existing, 100 year old, 12 – 18″ thick walled, brick masonry homes that are prevalent here in the greater Chicago area and in other areas throughout the country.
If you spray foam against the exterior walls will they deteriorate from the inside? Or does open cell allow enough vapor transmission that it will dissipate at a rate acceptable to the wall.
Do you use spacers upon which hard foam board is fastened to create an air barrier and then surface to which you can then spray against? But doesn’t this cause vapor issues because of the foam board?
How do you do it?
Please inform those of us trying to bring the fortresses of the 20th century up to tomorrow’s energy standards and beyond.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. chris | | #1

    the european answer is EIFS-type systems on the exterior. this works doubly, as the brick can be utilized for thermal mass, provided there is no insulation on the interior of said masonry.

    you could also insulate w/ rigid insulation interior of the masonry, but lose valuable NFA.

    the brooklyn passivhaus went w/ closed-cell soy-based foam interior of masonry, but i recently heard there were severe failures with this curling off the brick wall.

  2. wjrobinson | | #2

    My open cell subcontractor says the closed cell not so good against concrete... because it seals moisture... and then things go bad. He uses open cell for concrete. By the way he has both open and closed cell foam and could use either.

    R-60 over 18" thick walls... call Building Science Corporation... do one and let us know the results. I am sure besides me... many are interested.

  3. Riversong | | #3

    The simple answer is "you don't".

    A 3-wythe brick building offers excellent diurnal heat lag and time decrement, dramatically reducing daily temperature fluctuations and offsetting them by about 12 hours for optimum comfort and efficiency. They typically have durable and attractive exterior facades with good drainage from sloped sills, etc.

    Insulating them on the outside destroys their aesthetic integrity and insulating them on the inside destroys their drying ability and durability.

    The best approach for these classics is to replace doors and windows and air seal the entire envelope, with particular attention to top and bottom planes. Add controlled ventilation, perhaps with heat or energy recovery. Make sure interior moisture sources are controlled with dedicated exhaust fans. Then perform a heat loss analysis and downsize the mechanical systems with high-efficiency units.

  4. Riversong | | #4


    Of course, you can improve the thermal boundaries at the bottom and top (first floor and upstairs ceiling), and do whatever is necessary to maintain a dry basement.

  5. Author - Scott Bellner | | #5

    To clarify, when I say, "exterior walls" I mean to say that we will be insulating on the interior. We would never want to touch the beautiful facade of this historical building, but want to make it super insulated from the inside. That is the dilemma. If we did not care about the exterior we could easily build the structure out. The great thing for us is the house is expansive on the interior and so losing even 8" of interior space is something we are very willing to sacrifice. Thanks all for your posts!

  6. CHRIS | | #6


    Isn't the diurnal effect of uninsulated brick walls ineffective in cities w/ sub-zero winter conditions and low solar radiation? Also, I'm 90% positive Katrin mentioned that closed cell insulation wouldn't be allowed for passive house certification, due to issues mentioned above.

    Insulating them on the outside destroys their aesthetic integrity
    This is a really subjective statement. you can insulate the exterior, and do a rather elegant rear-ventilated rain screen application. This isn't that uncommon for EU retrofits. Not all brick is aesthetically pleasing.

    Regardless of method, upgrading windows/doors and increasing airtightness absolutely make sense.

    Also, in an apples-apples comparison of a simple brick house calc'd in PHPP, an exterior-insulated 3-wythe wall w/ rear ventilated rainscreen had 27% the annual heating demand of the uninsulated wall.

  7. Riversong | | #7

    Chris: You're correct that uninsulated mass walls are not effective in consistently cold climates, particularly with low winter solar radiation.

    Scott: Insulating a structural brick wall on the interior creates thermal issues, not moisture issues. If there is no heat flux from inside to out, then any moisture in the brick or mortar will freeze and create cracking or spalling. And you'll lose all the potential thermal mass benefit (which is available in cold climates only with exterior-insulated mass).

    If you choose to insulate on the interior, make sure the exterior facade is well-protected from rain by roof overhangs, gutters, and other architectural features, and the exterior surface well-sealed with a siloxane masonry sealer, reapplied every 5-10 years as needed.

  8. Jesse Thompson | | #8

    Chris Schumacher at Building Science is doing very interesting research on insulating load bearing masonry structures, his recent presentation is available here:

    They are currently testing actual bricks from structures to be insulated, subjecting them to freeze / thaw cycles and then testing their strength with strain gauges to determine their durability.

    They said the risk varies widely depending on how many hours a water saturated brick wall will sit below freezing temperatures. In Portland ME, even right on the water with full soaking noreasters there are so few hours below freezing the risk seems to be fairly low. In Toronto the risk is much higher because of the total hours a year the building skin would sit at temperatures that could freeze water saturated brick.

    They are designing new testing standards, they feel there are flaws with the old ASTM testing methods.

    It's an interesting and important area of research here in the Northeast.

    Jesse Thompson
    Kaplan Thompson Architects

  9. Riversong | | #9

    Of course, there's an almost infinite variety of bricks in older buildings, so no testing standards can be universalized.

  10. Jesse Thompson | | #10

    I don't think they are trying to universalize recommendations, but instead remove actual bricks from several locations in the specific building to be insulated and test those bricks to determine just how much risk there might be in those specific brick batches.

    This process as currently described wouldn't make economic sense on individual single family homes, but seems perfectly reasonable for large institutional projects or historic renovations (mill buildings, multi-family, etc.).

  11. user-705006 | | #11

    Scott, I am in the exact same dilemma as you are with my deep retrofit of a 100 year old Chicago three flat ( It feels like I have researched the insulation options forever, but still have not come across a conclusive answer. Most of what I have come across points to open cell foam.

    Have you made any progress in determining how to insulate or made any decisions? If so please let me know!

  12. GBA Editor
    Martin Holladay | | #12

    Scott and Marcus,
    The basic answer is, you insulate such buildings on the exterior.

    In two recent presentations, I've heard architect William Rose challenge the historic-preservation community to rethink their automatic rejection of exterior insulation on historic brick buildings. At the risk of oversimplifying:

    - Many historic masonry buildings throughout the world have had exterior plaster at one point.

    - Exterior insulation serves to preserve the building. The building is still there.

    - If we aren't willing to insulate our historic buildings, we may not be able to muddle through the coming climate-change crisis, and we'll lose everything -- both buildings and population.

  13. user-659915 | | #13

    "The simple answer is "you don't"."

    As so often is the case Robert hits the nail on the head. Insulate on the inside of the wall and you'll destroy the quality of the spaces and probably threaten the structural integrity of the brick. Insulate on the outside of the wall and you'll bury a perfectly good exterior finish. Old framed buildings, which form the vast majority of our outdated housing stock, are often perfect candidates for super-insulation, done right. Old masonry buildings are mostly not. As the Irish are reputed to say when asked for directions to an unlikely destination: "If that's where you want to go I wouldn't be starting from here."

  14. user-659915 | | #14

    Just a couple of further thoughts: mass insulation is a heavy blunt instrument. Working with a quality building like this you need a scalpel. Here are a few straightforward interventions which are likely to dramatically improve the thermal performance of the building without wrecking its character.

    1. Tops and bottoms. How's the attic insulation? Is the basement/crawl space properly insulated and air-sealed?

    2. Windows and doors. Weatherstripping, exterior insulated glass storms, replacement are options.

    3. Increase the radiant component of the heating system. These buildings were not designed for forced air heating. A natural gas 'woodstove' in the main living area might be just the job to supplement whole house systems.

    4. Improve the heat-reflective character of the walls. Plaster on solid masonry does an excellent job of sucking heat out of a nearby human body. Wood wainscot about 5' high is a classic traditional treatment that makes sitting near near an exterior wall on a chilly evening far more comfortable. Use a low-density wood such as pine, you can back it up with 1/2" of foamboard, not for the gross R-value but for purely localized effect. In most cases you can do this without major impact on existing trim. Think heavy drapes over the windows, too, for cosy winter evenings.

    [The last two will improve comfort levels at a lower set temperature, reducing the delta-T and improving overall heating-season performance. If you air-condition you already have a good airtight wall system - airtightness is far more important than total R for a/c effectiveness. Delta-T in the winter in Chicago can often be 50° or more; in the summer it's seldom more than about 15°. Dehumidification is your main a/c issue.]

    6. Make sure your mechanicals are in tip-top shape. Supplement with active solar if you have the budget.

    Having implemented all these steps will your house be super-insulated? No. Will you have made huge improvements in the energy performance of your home while respecting its authenticity and character? Absolutely. And you will have the peace of mind of knowing that a future owner will never review your interventions and think "What the hell were they thinking? I've gotta tear all this s**t off!"

  15. Scott Bellner | | #15

    Thank you all for your insight and experiences - they are all well taken.
    To James and Martin, your answers make complete sense to the engineer in me and will be considered in our final decision.
    To Marcus, we too have researched insulation and windows to the end of the world, and the majority of our needs are met by open cell foam. However two things scare us away - 1. The countless issues with foam installs in homes where off gassing, lingering smells, chemical / body issues resulting from chemicals, etc., and 2. It is still a relatively "new" product that has not been proven on a home owner life time cycle.
    This is to be the home we move into with our two babies. So that means that it needs to be safe for them (and us) and it needs to last because we hope to be in this home until they head off into the world.
    Wet sprayed cellulose is the next best option it would appear, but 8" deep walls of newspaper and moisture, and the freeze thaw cycles do not appear to be the best idea either.
    There is spiderglass from JM seems like a solid product and cold get us over R-30 in an 8" cavity per their spec sheets (if you believe them). But it's very new and how will it hold up?
    There is also airkrete, although the local installer would not take on our project, and did not elaborate why, but I think it was because of the extreme depth and he did not want to take a chance on it.
    So after months of trying to decide I am leaning towards spray foam and absolutely hounding the installers to maintain the maximum pass depth of 2" to reduce what seems to cause the majority of issues and hope for the best. But then I see my kids and our bank account and don't think we can take that chance.
    Our house is very large and so interior space is not as much a concerned as a typical chicago lot, so passive house insulating values are achievable, but I still don't know how...
    I wish I could give you the final solution, but alas I am more confused now than when we begin our quest to make the most energy efficient house in our wonderful chicago suburb.

  16. Riversong | | #16


    If you're concerned about the health of your family, then cellulose would be the most wholesome option and there's no need for damp spray. Do a dry densepack installation, either with insulweb or closed wall blow.

    The borate fire retardant is the same one used in baby clothes, it is an effective mildewcide and insecticide and highly fire resistant, sound resistant, and able to store and release considerable quantities of moisture (up to 30% of its weight).It is also inhospitable to rodents.

  17. scott Bellner | | #17

    Thanks again for your detailed response that is sensitive to our situation.
    Do you think 8 to 10 inches of dense packed cellulose would 'work'?
    If it will hold am transfer that much water that alleviates my largest cellulose concern.
    Insulating on the exterior is an interesting idea.
    What would be recommended?
    Alternating direction foam board?
    Spray foam directly against exterior?
    Could you still use cellulose as long as you can thermally break the exterior cladding.
    Could you then finish with hardie board or similar?
    If you did this exposed brick would be ideal to ensure the thermal mass was in direct contact with the living spaces?
    Please advise.

  18. Riversong | | #18


    There are too many variables for a simple answer. You'd probably be best served by consulting with a local green renovator with experience in historic preservation. By the way, Vermont Public Radio is broadcasting a discussion on green historic preservation today at noon:

    But some principles to consider:

    If you insulate on the inside and reduce heat flux through the brick, drying will slow down and the brick will become more vulnerable to moisture and freezing, so exterior waterproofing and rain shielding and shedding become critical. A siloxane masonry sealer will do wonders to prevent water absorption.

    If you insulate on the outside, you retain the thermal mass advantage of the brick, perhaps too much so. You will then have a high inertia shell that will be very slow to change temperature. Warm air heat will work best with this option since it has faster recovery time than any form of radiant heat.

    And, if you insulate on the outside, you're changing the appearance of the building. Often foam and stucco systems are the most appropriate since they maintain the masonry aesthetic more than other options.

    If you choose another cladding and can extend the roof overhangs, a parallel-chord truss can be installed for a thermally-broken insulation cavity that could be dense-packed and far more breatheable than any foam system. This may be important if the brick is wicking moisture up from the foundation or the ground.

    And, depending on whether you build inward or outward, you'll have to decide whether to leave windows in place or upgrade to better units that can be aligned with the new wall plane, either "innies" or "outies".

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |