Replies

1. 
   Riversong | Jan 01, 2011 02:24pm | #1

   You're not going to be able to bring the house up to current insulation standards without a major rebuild, but if you just want to improve its energy efficiency without disrupting the stucco and with minimal disruption to the interior plaster, blowing dense-pack cellulose into the walls will make a dramatic difference and should not result in moisture problems if the basement is dry and the interior humidity is controlled with ventilation, as the wall can breathe in both directions.

2. 
   davidmeiland | Jan 01, 2011 05:07pm | #2

   My opinion is that blowing cellulose into old-house walls without first verifying that there aren't exterior water leaks is dangerous. A house like the OP's can easily go many decades with some yearly leakage into the walls, and it will never show on the interior or cause much damage, assuming the walls are uninsulated and the framing is old growth lumber. Board sheathing and lath/plaster on the interior help to "catch and release" any moisture, and the fact that it's balloon-framed may mean very significant ventilation thru many of the stud bays. Hard to tell without inspecting the whole thing in person.

   I would concentrate on air sealing and insulating the attic, weatherstripping the doors and windows where appropriate, install efficient heating, etc. Cost/benefit on wall insulation may not pencil out when the risk of long-term problems is factored in, especially since those problems may take a while to surface. If you are in the position to carefully monitor the walls over the long term (IR and moisture meters) then you may be able to catch and rectify any isolated problems that occur if you insulate and water leaks occur, but that's not the average homeowner.

   Without offering any particular endorsement, here are opinions from someone who seems fairly well respected in the historic preservation community. http://www.bobyapp.com/blog/2009/06/myths-about-insulating-old-house-walls

3. 
   Riversong | Jan 01, 2011 05:42pm | #3

   David,

   It's certainly worthwhile to repair any obvious exterior stucco cracks or flashing problems, and it's true that dense-packing the walls will decrease the drying potential of the structure by decreasing the two things that are the enemies of energy-efficiency: heat flux and air movement. But cellulose also offers the "catch and release" quality that all hygroscopic materials share (though far more than most) and will not create problems that don't already exist.

   But before linking to someone you believe to be "fairly well respected in the historic preservation community", you might check his knowledge of building science, which seems to be at least 30 years behind the times.

   For instance, Bob Yapp states: "Heat loss primarily happens in an upward movement." Warm air rises, but heat loss is isothermal - equal in all directions. He recommends insulating rim joists with kraft (mispelled craft) faced fiberglass batts, arguably the worst option for that (or almost any) location. He says "Most building codes today require that when a new house or addition is built in a northern climate, it must have a vapor barrier." Current codes no longer require - and building science contraindicates - a vapor barrier such as poly sheeting.

   Bob further states that "warm, moist vapor is attracted to the exterior walls." Moisture, too, is isotropic and disperses equally throughout the interior space. He continues, "In new construction, the plastic vapor barrier under the drywall stops the wet air from getting to the insulation and condensating (sic)." Of course, the vapor barrier (or vapor retarder required by code) slows vapor diffusion and is not meant to stop air movement - that's the function of the air barrier which may be, and often is, a different part of the assembly.

   Bob explains, "In old houses with plaster walls, there is no vapor barrier under the plaster so the wet air hits the insulation and condensates (sic)." Again, he confuses vapor diffusion with air movement, and does not understand that condensation rarely occurs within the insulation but rather at the next solid cold surface such as sheathing. He continues, "This wets down the blown-in insulation making it a wet mass at the bottom of the wall cavity creating an inviting place for termites and dry rot." Rarely does insulation dampened by vapor diffusion or internal convection result in a "wet mass at the bottom of the wall cavity". That happens only rarely from a massive leak.

   Bob further explains that "the moisture enters the exterior sheathing and wood siding causing permanent exterior paint failure." While moisture movement from inside to out can cause paint blistering and peeling, no paint failure is "permanent", such as structural failure might be, and it's probability depends on the breatheability of the paint film - with oil paints far more likely to fail.

   So, by all means, take precautions - as I suggested - to eliminate moisture sources, such as damp basements and crawlspaces (80% of all moisture problems according to HUD), and use both point source and whole house ventilation to control indoor humidity - but don't avoid improving the building envelope because of the kind of ignorant warnings that one such as Bob Yapp espouses.

   Bob emphasizes, "One of the top reasons for exterior paint failure, termites and structural damage to old houses is loose cellulose or fiberglass insulation blown into the sidewalls". Clearly he's not aware that loose fill cellulose in sidewalls is a thing of the past. Modern blowers and techniques allow dense-packing of sidewalls which does not leave the voids that are prone to air movement and condensation.

4. 
   2tePuaao2B | Jan 01, 2011 06:01pm | #4

   Did this question get posted 2 times? I'm sure that I posted an answer earlier today.

5. 
   David Meiland | Jan 01, 2011 07:27pm | #5

   Roy, it did get posted two times.

   will not create problems that don't already exist

   Robert, I completely agree, and to the extent that the OP can verify that no problems already exist, she is safe to insulate the walls.

   I agree that there are holes in what Bob wrote in that link, but I do think he has inspected a lot of old houses with new insulation and new problems. I have read similar things from other historic preservation folks quite a few times. Anyone considering insulating old walls ought to make sure they understand all of the variables.

6. GBA Editor
   Martin Holladay | Jan 02, 2011 07:03am | #6

   Diane,
   Unfortunately, the answer to your question is No -- there is no "simple not so messy solution." If you really want airtight superinsulated walls, there is no easy or cheap way to do it.

   If I were you, I would have the cellulose installed. Here in the Northeast, cellulose contractors have been dense-packing the walls of existing homes for 25 years, and the vast majority of these installations are performing very well.

   All of the usual caveats apply, of course: inspect and maintain the exterior water-management details for your home's walls.

7. 
   user-1044545 | Mar 20, 2022 07:24pm | #7

   sorry for piggybacking a very old thread but I have a very similar home to the Op. Is there a rough way to quantify how much gain in terms will I get by insulating rim joists, all basement walls & attic vs exterior walls? Is it roughly 70/30 and do most agree heat loss occurs upwards?

   Thanks