Insulating a Masonry Building from the Interior
We are working on an existing home that is 2 wythe brick masonry construction, with existing 3/4″ furring and drywall on the interior. On the exterior, the existing brick is painted, which we know is not ideal. We would like to meet the prescriptive R value of R17 for a mass wall in climate zone 5A. We are considering furring out the interior walls to increase the cavity space to 2.75″. We can then spray closed cell foam in the cavity. If we hold the new furring off the brick wall, we can then have the foam get between the furring and masonry for a somewhat continuous insulation. We would like to minimize the additional encroachment to the interior floor plan. Are there any other considerations we should be mindful of with this approach?
Thanks in advance.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Know that the existing brick will be fully subjected to freeze/thaw in 5A once insulated on the interior. Some brick can handle this, some can't, and if it can't the outside brick faces can start popping off. Exposure matters. Overhangs and drainage can be a savior.
I'm parroting Joe:
https://www.buildingscience.com/documents/insights/bsi-047-thick-as-brick
Painted brick suggests that perhaps your clients are not attached to the look of exterior brick, and/or perhaps it's a little tired looking?
EIFS is not cheap, but doesn't take up floor space and you can get a fairly high performance wall in a retrofit with little to no freeze thaw damage.
https://www.nrel.gov/docs/fy14osti/61005.pdf
Hi Nathan,
According to Martin Holladay, there are some key things to be aware of. He offers a few words of caution for your situation in this article: Insulating Old Brick Buildings.
On the exterior, the existing brick is painted, which we know is not ideal.
Actually, if you are leaving the paint on the brick, this generally offers more protection from exterior rainwater wetting. In fact, this is a long-used technique to deal with poor quality brick:
BSI-095: How Buildings Age
https://www.buildingscience.com/documents/building-science-insights-newsletters/bsi-095-how-buildings-age
I love New York. Especially the parts that are "aging gracefully". Check out Photograph 1. Manhattan, Soho, right down town. What's so interesting about this streetscape? The house on the left is brick masonry. The house in the middle is painted brick masonry. The house on the right is stucco over brick masonry. Better and better water control from left to right. Owners figure things out. Now look at Photograph 2. Prague, Czech Republic. The house on the right is brick masonry. The house on the left is stucco over brick masonry. As brick and stone buildings get old they leak.3 So how do we handle it? We try repointing the brick first. Then we paint over the brick. And then at the end we stucco over the brick. We do this all over the world. As buildings age we repoint them, paint them and then stucco them. In many parts of the world we preserve and save old buildings by stuccoing them. The historic folks on this side of the ocean just had a heart attack reading this. The good news is most normal people ignore those folks. Not everything ever built is historic. Just cause you are old does not make you historic.
Overall, your approach sounds reasonable. But what is critical is to address places where water can concentrate on the exterior of the brick wall--window sills, disconnected downspouts, splashback, etc. Here's BSC's guidebook on this topic:
BA-1105: Internal Insulation of Masonry Walls: Final Measure Guideline
https://www.buildingscience.com/documents/bareports/ba-1105-internal-insulation-masonry-walls-final-measure-guideline/view
Thank you Kohta.
Years ago I lived in an old Sear’s Kit house built in the early 1900’s from concrete blocks made one at a time using the Sear’s “Block Wizard.”
Insulating the inside would have been a death sentence to the structure, but after insulating the exterior of the home with EPS - that home was marvelously comfortable in the winter. All that thermal mass insulated from the weather just radiated warmth.
A lot of houses in my neighborhood have Block Wizard foundations. Here's a video showing them being made, seems like a lot of work:
https://www.youtube.com/watch?v=akDqNgXqvKA
I cannot imagine the poor sap that had to make every block, but I commend his diligence in building a home that lasted 100+ years!
As far as other considerations to be mindful of, can we assume you are up to speed on the differences between HFO and HFC blow spray foam? Regardless, if it's aesthetically acceptable to put the insulation outside, that is better in most other ways.
If the home were mine, I’d be afraid to insulate the interior. I’m certainly not the authority... I just read a lot on the internet and so the best I can with the old houses I get my hands on. But I’m definitely following for additional opinions!
Hi Nathan, you should be commended for being humble enough to ask for help. I don't think many architects of your stature would be willing to do this. During our build, our impression was professionals with any number of credentials listed after their names tended to bluff their way through problems and potential solutions (with devastating consequences in some cases).
In addition, by doing it on a public forum like GBA you're no doubt helping countless others now and in the future who will be trying to work through the details on a similar retrofit.
Your clients should be impressed. They're clearly in safe hands.
In regards to your question, you may want to try consulting these resources (if you haven't already):
https://www.buildingscience.com/documents/building-science-insights/bsi-105-avoiding-mass-failures
475 can directly help you, or put you in contact with architects and builders who have direct experience: https://foursevenfive.com/masonry-retrofit-construction-photo-gallery/
http://www.bldgtyp.com (two of my CPHC instructors work here)
https://www.byggmeister.com/our-services
I don't have a copy in front of me, but I bet this book has a detail for something similar, if not exactly the same:
https://www.amazon.com/New-Net-Zero-Leading-Edge-Construction/dp/160358448X/ref=sr_1_1?dchild=1&keywords=new+net+zero&qid=1608751793&sr=8-1
I would even contact Maclay directly since the book is a couple of years old. They may have come up with details that they're even more confident in since the book was published:
https://www.maclayarchitects.com/
Closer to us in the Chicago area, you may want to reach out to this guy:
https://blog.delafleur.com/?page_id=2
I know he's been on the local Green Built Home Tour at least once, so you may have already been through his house and seen how he did everything, but, if not, he may be a good resource for finalizing product choices and working through specific details or problem areas as they arise.
Good luck with your project!