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Need some help with wall envelope design for 110 year old masonry building

Sara Sweeney | Posted in GBA Pro Help on

I am working on a project which is rehabbing a circa 1890 masonry factory building into apartment units. The existing building is 3 to 4-wyth thick brick masonry walls and that’s how it’s been since 1894. We are looking at three options:

1 2×4 wood studs held 3/4 inches off the masonry wall, drywall and batt infill. Our least favorite option bc/of obvious issues with gaps in insulation and convective loop currents and more. It is a developer driven project however, and we have been asked to look at this.

2 2×4 studs held 3/4 inches off, 2 inches of spray foam (closed cell) and then batt infill, and drywall

3 2×4 studs held 3/4 inches off, infill cavity depth with spray foam (closed cell), and drywall

Has anyone had experience with a similar type of building project or knowledge and could you offer any insight and guidance on the above.

Thank you

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  1. Riversong | | #1

    What is your climate zone (location?) and do you expect to meet current IECC insulation standards?

    I would suggest option 3 but on the outside of the building to retain the thermal mass advantage and not put the brick at risk of moisture and freeze-thaw damage (but I don't suppose that would fly with either the developer or the historical commission).

    For an interior retrofit, I would suggest 1" of XPS or EPS with taped seams, framing and batt or blown fiber. This will keep the fibrous insulation away from the capillarity of the brick, help control infiltration and thermal bridging, and allow some drying to the interior to reduce the probability of exterior moisture damage.

  2. Sara Sweeney | | #2

    As soon as I posted realized I forgot to put location in. The building is in West York, PA, just south of Harrisburg, PA. Climate Zone 4 but it adjacent 5 on each side; Southeastern PA is right on the cusp of each. I would also expect we would need to meet current IECC standards as it is an affordable housing complex, so does receive funding and must meet State guidelines.

    Yes, insulation on the exterior would definitely not fly. Our historic consultant would likely have a small cow. The developer, likely a larger one.

    The other solution is an interesting one. It will definitely help the wall breathe better, one thing we are concerned about since we will be changing it's lungs so to speak after 110 years. It may also be more cost effective -which the developer will like.

    Thank you.

  3. terrell wong | | #3

    you could also add 1" roxul drainboard directly to the masonry and fill with roxul or cotton batts in between the studs. This would be less expensive than sprayfoam and more vapour diffuse. the controversy with insulating the interior of masonry has been well documented recently for both sides. Be sure to do some analysis of existing masonry conditions prior to making your final decisions.

  4. Sara Sweeney | | #4

    Thanks Terrell. Another inteersting option to add to the list. We are definitely going to do thorough analysis on the masonry too!

    Have either of you also read Lsitburek's transcript of the podcast on "Insulation Retrofits on Old Masonry Buildings?" if so, do you have any insight on how what he says there might translate to this building in this climate zone? I am reading that we could insulate on the interior, provided we take care of other factors, and use a few inches of high-density (but no more than three inches). Elsewhere he also seems to feel that if there is no real threat to freeze/thaw cycles and very wet weather, that you don't have to insulate on the interior of mass assemblies. I am concerned I am interpreting these two lines of thought incorrectly though.


  5. Riversong | | #5


    I have't heard Dr. Joe's podcost (I don't even own a pod), but I tend to be more skeptical than Joe about the ability of any kind of foam to breathe sufficiently.

    In addition to doing whatever exterior brick & mortar and flashing repair is necessary, I would encourage you to consider sealing the outside with a penetrating masonry siloxane-based sealer which doesn't change the appearance, is excellent at sealing out water but does not change the vapor permeance.

    I suspect that the reason most old masonry buildings were 3-wythe, in addition to the obvious structural integrity, is that 12" or so is the perfect thickness for a diurnal time lag and temperature decrement that brings the daytime solar gains and nightime loss (somewhat reduced) into the interior offset by half a day for perfect passive solar conditioning. That wonderful quality of a heavy mass structure is, of course, lost when the building is insulated on the interior.

    Typically, air tightening and attic and floor insulation are the most cost-effective places to begin improving the efficiency of a heavy masonry building. Insulating the walls comes with both gains and losses and the potential for accelerating deterioration if exterior weatherproofing isn't well done.

  6. Riversong | | #6

    I forgot to add window replacement to the list of necessary improvements.

  7. Roy Harmon | | #7

    Window restoration is another viable option for this type of project. The key to efficient windows would lie in the jamb extension detailing. Many times the original window jamb must stay, or be authentically reproduced to satisfy historic requirements. This can really dent a budget, or save it,depending on existing conditions. The additional space created by interior framing creates an opportunity to get creative within the jamb extension. Take advantage of the mass and put the money in the window design to create affordable housing.
    If the masonry is in decent shape~ no bulge or shear cracking, full mortar head and bed joints that are still solid, no brick face spalling and no signs of water infiltration then you have a gem. Most failure will show up in area's around problem gutters and down spouts, if the building has them.
    I have found that if the building has done well through the years, that adding sealant feels good, but can be limited to obvious problem area's and need not be done entirely. There are no weep holes in this type of structure and therefore it is critical that the walls breath freely. If the walls are made of a soft or high suction brick sometimes a sealer like siloxane will draw deep into the brick ,leaving less of the material on the actual brick face.I worked on a project that sounds similar to yours in Baltimore and for some reason, brick that had been doing fine for over a hundred years began to deteriorate several years after being sealed with siloxane based product. One would think that a soft brick would benifit greatly from this sealant, but I have learned that the test of time can't always be improved on. A complete existing condition survey placed next to the budget analysis will answer alot of questions early on.

  8. GBA Editor
    Martin Holladay | | #8

    The problem is not simply a question of whether the insulation can "breathe." (Can we stop using that word, please? I think people are talking about whether the insulation is vapor permeable.)

    The problem is that ANY interior insulation, assuming it is effective -- whether it is vapor-permeable or not -- will make the masonry walls colder, and therefore wetter, and therefore more subject to damage from freeze/thaw cycles.

    If you are using interior insulation, this is unavoidable. However, a decent roof with generous overhangs can go a long way towards keeping the walls dry and thereby lessening the risk.

    Another factor to consider: if any floor joists or wood beams sit in beam pockets in the masonry, the joist ends are likely to be cold and wet, and may rot, once you insulate the walls on the interior.

  9. Sara Sweeney | | #9

    Gentlemen -

    Thank you very much for all your responses. You are confirming all the various concerns I have had running through my brain but at the same time, was not sure how to begin weeding through them. I'd like to take your responses above and mull them over and also take them back to the team. I will likely post a part 2 to this question within the week. Just a few quick additional pieces of information on the roof and windows:

    Roof Overhang: The building has no roof overhang, unfortunately. The brick corbels out maybe about 8 inches total at the 4th floor, as the wall starts "to meet" the roof. The roof is a low pitch 2-12. But no overhang. We do have gutters -which will be replaced and I will make sure to take great care at the detailing of the gutters, as well as making sure a sufficient size is specified and installed to prevent backup during heavier rain events. I think this is about the extent of what we can do and will be able to do at the roof/wall juncture. Having said that, this will not be sufficient to keep the walls dry.

    Windows: We are also replacing the windows and the windows are in such bad shape that we will be removing everything down to the rough M.O. and replacing in entireity. We are currently evaluating various windows, ranging from wood/aluminum clad to aluminum.

    Many thanks again for responses thus far. This has been extremely helpful.

  10. Riversong | | #10

    Sorry, Martin, but I will continue to use the concept of breathing in discussing human shelter.

    As with most common and scientific concepts, we tend to have a very limited perspective which narrows our field of understanding. Even human beings breathe much more than air or oxygen but also breathe and transpire moisture through both our lungs and our skin. All living things must breathe in order to live.

    I prefer this term because it reinforces the generally overlooked notion that a structure for human habitation should be like an extension of our bodies if it is to maintain a healthy homeostasis. Like every living membrane, it should be semi-permeable and only a conditional separation between the inside and outside environments.

    "Green" building, as with most modern technologies, tends toward the absolute or the maximization rather than the optimization of qualities necessary to contain life.

    A house that can't breathe is a sarcophagus, not a shelter.

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