We are talking with an insulation guy about having Icynene reformulated in a slow-grow mix blown into the walls of the house. Someone raised the concern that Icynene blown into the walls can cause problems with buckling of the lathe-and-plaster or oozing out of holes like electrical receptacles.

Does anyone have experience blowing Icynene into an old house without taking the walls down, and would they care to share their experiences?

It was my first choice but we couldn't afford it. Went with blown-in cellulose instead.

We are currently renovating, and I've gotten varying advice on insulating my 1896 four square/colonial revival with horse hair plaster and zero insulation is:

- Blown in cellulose or icynene in the walls
- Icynene in the rafters (attic is "finished" and we will add unico in a few years)

My concern that this along with air sealing will make my house too tight, primarily the attic. Worried about moisture, rot, sick house syndrome, radon, etc. I've been told by HVAC and other folks that I can't make this old house too tight.

Anyone have experience with either or both products in their old house? Any other thoughts or suggestions would be greatly appreciated! Thanks in advance!

Down-sides:
- icynene is expensive, probably the most expensive means of insulation per square foot
- as diygene points out, the frequent diagonal bracing in older houses leaves them sturdier against gale force winds, but does mean that you need to blow in the insulation in multiple holes, so you don't have big uninsulated gaps in the wall.
- We did have some patches of lath-and-plaster buckle under the pressure of the expanding icynene, making damaged wall sections as big as 2'x3', some patches were 18" square, and it did mean some extra work for our plasterer. As luck would have it, we were having all the walls re-plastered anyway, but if you're not prepared to deal with that kind of possibility, I wouldn't go with icynene.

Now the plus sides:
- Old houses tend to be pretty porous by nature. I don't think that putting icynene is going to lock in too much. It certainly has made our house hold on to heat or coolness for an extra day or three compared with before the icynene was installed.
- Because the house retains heat more efficiently, the winter after we put in the icynene, our heating bills dropped by a good 50%, so you will get some of it back in saved utility costs.
- Cellulose and fiberglass insulation are not waterproof, and lose insulation power if they get wet. Icynene serves as a natural vapor barrier, and keeps damp and dank from getting into the house (and hence mold and such).
- Bugs and pests hate the stuff, and won't eat it. I've noticed that our house has been remarkably free of infestations or invasions (apart from fruit flies), and I don't know if it's the icynene that is keeping them out, but I suspect that's part of it.

As a whole, we don't regret at all getting icynene insulation, and would do it again in a heartbeat. But those caveats do need to be kept in mind, and you shouldn't go with it if the cost or the wall issues are a problem.

Now the major problem is going to be heat traveling on air flow. Blocking this is a weather-sealing, not an insulation problem. Foams are good at weather-sealing.

So is cellulose. Foams are about 4-5 times more costly than cellulose, but not 4-5 times more effective. So if cost is not a factor, absolutely go with foams. If cost is a factor, dense-pack cellulose delivers more value for the buck.

Low expanding closed cell foams are a little dangerous to loose plaster, but seldom to properly adhering plaster. This risk is often exaggerated -- but if you want to find out where your plaster is loose, this is a good way to do it.

I would generally recommend cellulose, then spend some of the savings on weather-sealing around the windows, doors and house sills and pile up some more insulation in the attic. The overall improvement will be greater than if you just insulated with even the best foam without weather-sealing.

Keep in mind that either product is absolutely dependent on proper insulation -- so know your contractor and absolutely take infrared photos to verify full coverage with no gaps.

Best of luck with the project.