Aaron Stein, Senior Energy Analyst in the Office of Sustainability's Energy Management Division (OS-EMD) in San Antonio, TX posed this month's stumper.

Aaron asks, "Does anyone have experience weatherizing or retrofitting historic homes without sheathing or any kind of weather-resistance barrier? The walls in question also have interior shiplap that was covered in drywall but nothing in the cavities (in some cases you can see through the exterior siding). The home is in a historic neighborhood so wrapping it and adding new siding isn't an option."

How would you go about insulating balloon-framed walls in a historic-aged home in South Central Texas?

Reply to this thread with the best response to be featured in BPI's November newsletter!

Tags: historic home retrofit, weatherize

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Hello Aaron,

Well, this certainly presents more problems than most homes in terms of weatherizing!  If you insulate, and don't add some kind of vapor barrier, then you could accidentally trap moisture in pockets, which would be terrible.  And I know this part of Texas can get very humid, too.

The only thing I can think of that would do the trick, for the walls, at least, would be to spray in a minimal-expanding spray foam, that would both seal and insulate, without warping the boards. (Everyone, feel free to explain why this wouldn't work in the walls.) I would remove the drywall, and then a top board on the inside, and spray slowly & carefully to fill the bays.

You don't mention if there is a crawl space, or basement, or how the building is attached to the ground. If there is a crawl space, at the very least, install a vapor barrier underneath, staked to the ground.  Don't let the vapor barrier touch any wood.

I am assuming that there is some kind of attic space?  Foam would work there, but then you would lose being able to see the historic details in the attic.  I am also assuming that the wiring in the attic is already upgraded here.

You will need to add, at the very least, some ventilation in the kitchen and bath -- you don't say how it's heated or cooled. Keeping the air moving will remove moisture.  This is probably the biggest danger, in sealing the house up too well, and then not providing adequate ventilation.

We have a similar situation with a very, very old ranch home in Concord, CA.  The walls are really just three flat boards, one upright, with two horizontal on either side, built up.  No stud bay to insulate, only little 1" thick rectangles that you can't get to without removing every single interior board.  We've decided to let it be, and when we use the place for special events in the winter, use a couple of space heaters, and keep moving to stay warm!  The house is not occupied year round, so there is really no need to add heating and ventilation to the place.  It has some amazing construction details, though, and is about 150 years old.

Good luck with your project, and let us know how things go.

Hi Aaron,

Mt. Pleasant Missionary Baptist Church, Denison, TX.


This was a 150-year-old building we coated with our Radiant Control Coating, Cerama-Tech.  No R%-rated insulation was added.  Only the interior walls and ceiling of this large main building were painted / coated.  We dropped the cooling and heating requirements from $1,800 and $2,300 per month down to $400 per month


Contact Pastor Rusty there and meet with him.


I am available for any questions.


Hal Skinner

Senior Engineering Representative



I live in a 135 years old balloon framed house. Family members live in a 180 years old timber framed house. I've consulted on 18th and 19th century building preservations, renovations and conversions. There's no pat answer or magic one size fits all solution. One project required seven different insulating systems to avoid moisture related issues downstream. Our son's home required three different insulating systems.

I have no experience with old buildings in Texas. My advice is to find an experienced consultant who demonstrates an understanding of old building systems and the impact that new insulating materials can have on them.

The big concern should be avoiding moisture related problems. The energy saving benefit doesn't matter if "improvements" end up destroying the building.

Be cautious and good luck.

You are going to want to include pest control (ant's, termites) consultant in your planning meetings.  Some of the easy solutions (spray in foam),  may offer a great home and food source for the pests.

Hi Dennis,

Which foam would that be?  One of the soy-based ones?  I've had foam installed in both residential and commercial buildings, and hadn't ever heard of this as an issue, even in foam roofs.  I'd love to know if there is a problematic brand of foam out there.


Bob provided a good answer below.  Since this is a building of historic value I'd also check with universities in the state to see if they have preservation specialists.  Step back and work the problems together and while the cost might be slightly higher up front - the work (and building) will last much longer, with fewer problems in the future.

Caution re: pest infestation is prudent. My experience indicates that pest control mechanisms are available with respect to most types of commericially available insulation. I've been around the insulation industry for over 50 years. Find someone local who has broad experience with various insulating materials and systems to help figure out what to do and how to do it. Shy away from folk whose agenda is selling a particular insulating method. There are no perfect "one size fits all" insulating materials. Don't create moisture problems by incorrectly placing the post-retrofit dewpoint.

Soy-based SPF is hardly different from non-soy-based SPF. Whether the "orgainic" or "bio" constituents are derived from soy beans, sugar beets or whatever, petroleum is the source of most of their chemistry.

Which foam? Maybe none. In retirement I do tech work for an aminoplast masonry foam producer. We also offer a more refined aminoplast foam that's suitable for retrofitting framed structures. More refined means practically no emissions or shrinkage.

A paper published years ago by the National Park Service advises against injecting foam when preserving historic buildings; thus, I personally defer to their experience. As stated previously, there aren't any magic one-size-fits-all insulating materials.

It's important to understand how old building systems work before introducing modern materials. For example, different parts of my 135 years old farm house were insulated differently at different time by different past residents. Materials included kraft bags filled with cedar sawdust, "Kimsulation" ... a layered crepe paper insulation offered years ago by Kimberley Clark and hand-packed loose limestone rock wool. There was no sheathing. Much of the studding was round poles. Much of the house was built using post-civil war scrap lumber e.g. facia boards from Confederate ammo crates etc.

Pest protection consisted of rock salt plowed into the soil within the house' footprint. Termites burrowing through the soil ingested salt, swelled up and died. There was zero evidence of termite damage.

Hi Bob,

That's great info -- do you know the name of the paper published by the NPS?  Or when it was published?

The pest protection using rock salt is interesting too -- I'm guessing there was a lot of rock salt used; otherwise, it would have dissolved in seasonal rains.

Here in CA, we've been using a combination of a vapor barrier on the ground, which we did with the historic building in Concord, CA, and  three inches of sand about 18" wide on either side of the foundation for termite protection; the termites don't seem to be able to negotiate the loose sand. 

Quinn, good luck -- lots of great information here for you!


In answer to the OP - the answer is simple, I wouldn't without being able to see it & look over everything thoroughly. If you can't verify there is no water intrusion you are just asking for trouble as the reason many of these older houses have survived so long is there ability to dry out. One of the other big issues is trapping moisture in the siding & having it peel when it never did before.

With that, one trick used is foam board insulation inside the house with maybe just a bit in the wall which still allows for the cavities to dry out.

I work with a group that does quite a bit of work on historic homes in Charleston, SC. Our office is in an 1880's Charleston Single that was retrofitted with several different insulation strategies behind plexiglas. We have shiplap exterior siding, no sheathing, and are in an area where wrapping the building was not an option due to the Building Architecture Review board (BAR).

We have dense-packed cellulose, wet sprayed cellulose, foam board, fiberglass batts, and closed cell sprayfoam in the walls. While no mildew or rot has occurred in any wall... when it rains sideways (we are on the SC coast) moisture does get past the shiplap and bulk moisture is visible in the cellulose and fiberglass. I imagine that water vapor is getting in and condensing about 10 months/year as well.

The best solution I have seen from what we have tried is the following:

1/2" Cedar Breather or Enkadrain or similar cut to fit in the wall cavities and then wrap the entire wall around the studs with felt paper or building wrap from the inside. The closed cell is then sprayed to the wrap inside the wall cavity so that it does not make contact with the historic framing members and is therefore reversible (a requirement of the BAR).  With attention to detail you can have an R19 wall assembly with a half inch of breathing space between the shiplap and the pressure/thermal boundary that allows the wall to dry through weeps at the bottom of the building or to the outside through the breaks in the shiplap.   

It is time consuming and detail driven but it has the approval of the local Historic Society and makes a pretty awesome wall on a 130 year old house that can "breathe" without compromising the energy use, comfort, or indoor air quality of the folks that have to breathe in the building. 


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