What are the effective options to insulate existing walls?
mmarkose
| Posted in Energy Efficiency and Durability on
If this question has been answered please point the link – I am unable to find past material.
The home is over 50 years old. The wall cross section is: brick veneer, cavity, celotex type material, framing, and plaster on board inside. There is no other insulation material in the wall cavity between the celotex and the plaster.
The blown in insulation folks say they are the best option. The injection foam folks say they are the best in R value and performance – that the blown in settles over time and that it does not control air movement enough. Of course the foam is more expensive.
What is the right strategy?
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Replies
The effectiveness of the cavity behind the brick is going to be a big determiner of whether an insulation project will work, or just cause eventual moisture problems.
I have only seen a couple of injection foam installations, but have not been impressed. It appears easy to miss spots and leave gaps and voids in the wall. Then there are the possible chemical issues. You don't get much if any added R value over dense pack cellulose, so I wouldn't go with the foam.
The blown-in folks you're talking to... are they long-established companies that have done hundreds of homes like yours in your area? That's who I would go with.
I would select dense packed cellulose over the injection foam any day. As you already mentioned, foam is more expensive, and I think it is safe to say a less reliable product. I have inspected many homes that have had their walls insulated by cellulose or the injection foam. It does seam that the foam guys miss wall cavities more often, but mostly the product degrades over time. I have some Infrared images where it looks like the walls are on fire from the inconsistencies of the application. Even had a customer send me a photo where they cut into their wall and the foam shrunk about 25% and was floating in the middle of the wall cavity.
Now cellulose is the staple of the majority of Home Weatherization Programs throughout the country. And yes it can settle if it is not installed properly. But as David mentioned, if you select a contractor that has been doing it for awhile, settling will not be an issue. And it will help control air flow. My 1500sf ranch saw a 400cfm reduction from dense packing the walls alone.
Matthai,
You didn't describe the framing cavity, but I'm assuming that your house has studs that are 3.5 inches or 4 inches deep. If so, go with the cellulose.
The degree to which (or even whether) cellulose settles is entirely a function of it's installed density ad how much seasonal moisture cycling there is. Behind a moisture-reservoir cladding such as brick it will require somewhat higher density than behind back-vented clapboards, etc. In a cold climate zone it would also be wise to install variable-permeance vapor retarder (eg. Certainteed MemBrain) to limit wintertime moisture accumulation as well. For most installation 3.5lbs per cubic foot density is "good enough" and in warmer, less humid parts of the US even 3.0lbs density would be fine forever. But just depends.
The additional R/inch of low-expansion injection foam has only a miniscule effect on the whole-wall R when the thermal bridging of the framing is factored in, and isn't worth paying extra for. It's only modestly more air-retardent than 3lbs cellulose.
That type of foam is also not very vapor retardent, and does not protect the sheathing from wintertime moisture drives without a separate vapor retarder the way closed-cell polyurethane does. In an assembly with no vapor retarder the moisture buffering capacity of cellulose does a better job of protecting the structural wood from wintertime moisture drives than high-permeance foams.