Insulation retrofit: Icynene, cellulose, fiberglass?

jerseyjudyNovember 17, 2005

Does anyone have experience with retrofitting an older house with Icynene in the walls or on the attic floor?

And, does anyone know whether corrosion or dust are still issues with cellulose?

My house is 75 years old, has no insulation in the walls, which are plaster-and-lathe. About a third of the attic floor has fiberglass batts, a third (the middle) is covered with wood flooring with no insulation below, and a third is uninsulated open rafters. I'm getting new energy-efficient windows, and Craneboard backed vinyl siding to cover my 3/4-inch-thick, 8-inch wood clapboard. (Clapboard has layers of peeling and previously peeled paint)

Obviously, I need attic insulation, and, if I'm going to get insulation pumped into walls, time would be now before new siding goes up. I'm leaning toward Icynene for the walls. Was quoted $3,200 for that. Was quoted $4,400 for dense-packed cellulose in walls and cellulose in attic.

I'm leery of cellulose because I've read that cellulose treated with sulfates could be corrosive. National Parks Service Restoration Brief 3, written in '79, warns against using sulfate-treated cellulose -- That may be out of date, but I haven't been able to find any reliable source that flat-out says this is no longer a problem. On the other hand, I hear cellulose treated only with borates is very dusty, and it doesn't seem to be available from installers here.

I don't know if Icynene can be used on an attic floor, or if it can, whether it would provide sufficient insulation. (My area calls for R49 in attic.) If 4 inches of Icynene were pumped in (I understand it would have to be covered), that would be about R16, although I'm told its superior air-blocking might make it seem like more.

Also, the foam's air-sealing quality seems desirable, or would that make my house too air-tight and unable to breathe? I guess there are plenty of air leaks from my old house to attic, but I doubt I'll find either the leaks or a contractor willing to search diligently to repair them, so Icynene would seem like an easy way to block them.

Oh, also, my central air conditioning unit and its ducts are in the attic. And, I've been warned by my roofer not to go the route of sealing off the attic and putting foam on the roof line.

Thanks for any experience or tips.


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You are obviously doing a good deal of research about your house before making plans, which is a very good idea. I am attaching a link to the entire Preservation Brief series, where you will find a wide range of topics covered, including the most up-to-date editions (available, now, for free on the net).

I have a couple of comments about your proposed plans. For your attic I would suggest adding additonal layers of fiberglass on the outside thirds of the attic floor. You can just lay it right over what you have there. (You may need to poke around a bit to discover where you can safely walk on the joists to get the material all the way out to the edge.) For the middle third, I would pull the floor, and insulate that cavity. It's OK to use a combination of materials. In my plastered house I have a thin layer of fiberglass, followed by as much high R-value foam sheets as will fit in order to get the highest R-value in the space available, without putting undue pressure on the plaster or squashing material under the flooring.

In your 75- year old house you probably have balloon framing which is easier to blow in insulation than some other type of framing. But blown in material may present problems due to lack of a vapor barier, and if you follow through on your plan to add vinyl siding, that may exacerbate the problem.

If your wood siding is still sound, you could have it scraped and sanded and repainted. Vinyl siding inevitably results in a change (and not for the better in most cases) of the details of your houses' exterior appearance. You could also have the siding removed, along with underlayers of sheathing, etc. and insulate (and add air and moisture barriers) before reinstalling the cleaned-up siding, though this is big job. I would opt for just scraping and repainting.

As for your proposed new windows, well, I wouldn't do that either, if your existing windows aren't completely rotten. In most instances wooden windows can be vastly improved energy-wise by rehabilitation, instead of simply replacing them. Unless you are extremely lucky or prepared to devote enormous sums to having exact replicas made, the new windows will be, at best, a compromise stylistically. The loss of both the siding, trim and window details will change your houses' appearance significantly.

In this year of energy-cost worry, it is hard not to spring for any and all improvements, but you can make a big dent in your energy-use by adding additional insulation to your attic, good weatherstripping around doors, diligent caulking all over the house, perhaps even temporary interior storm windows, etc. These relatively small-scale jobs will give considerable payback in both energy costs saved and increased comfort. And they will buy you time to assess the big picture and find solutions that do not result in so much loss of your house's historic character.

With old houses, I find it's really important to go as far as you can in adding energy efficiency, but not worry much if you can't achieve R-49 in your attic. That's the standard for new constructin and in most old buildings not a realistic goal.

Good luck with your house!


Here is a link that might be useful: Home page for Preservation Brief series

    Bookmark   November 17, 2005 at 11:34AM
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I know what you're going thru..I went thru it last year.My 102 year old stucco house, with plaster and lathe walls was basically uninsulated. When we opened up the kitchen walls to renovate it there was a little pile of compost,only inches high ,where the original insulation had ultimately migrated to! After talking to some people, getting a professional energy audit, and doing some research I went with a combination of foam and cellulose (due to the complexity of the house).I found a good cntractor who knows what he is doing, but I'll be honest,it wasn't cheap. I am also in a cold area(zone5) and finally, I can say my house is comfortable..even on the 1st floor, with 30 windows! If you're interested here's a link to the guy I used.

Here is a link that might be useful: insullation contractor

    Bookmark   November 19, 2005 at 3:35PM
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We put a small addition between two balloon framed houses, joining them. They each had different types of drop siding, special ordering enough to repair and match one side to the other was not an option.

We insulated with cellulose, purchased from Home Depot and installed with their rental blower. One half of the house we blew in from the outside, before Tyveking over the old siding and covering all with cedar shingles. The other half, we blew in from inside the house, before drywalling and beadboard restoration. The Tyvek is the exterior vapor barrier, inside, the kitchen and bath wall surfaces are enamel painted drywall or beadboard, stained and Varathaned. Attic insulation is fiberglass batts. It has been two years since the cellulose installation and we are very happy.

    Bookmark   November 20, 2005 at 7:22AM
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Re KellyinWA post:

Just for clarity TYVEK is *not* a vapor barrier, and fortunately so, as a vapor barrier in that postion could result in serious structural damage by trapping outwardly migrating vapor from indoors inside the wall cavity. (And vapor retardant paint is just that, not a complete barrier to vapor transmission.)

TYVEK is a moisture barrier that is vapor permeable, meaning that it blocks free moisture (wind-driven rain, for instance) but is intended to permit air-borne vapor to pass through.

I point this out because if someone installed a true vapor barrier product in that postion in the walls it would not be a good idea.

But TYVEK in the wall assembly is fine.

Moisture barriers and vapor barriers are NOT interchangeable products.


    Bookmark   November 20, 2005 at 11:24AM
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Are the borates or sulfates in cellulose used to prevent mold growth? Because cellulose provides food for mold, if there is moisture.

I will never use cellulose again. I had it in my last house and in my present house and it just doesn't seem to insulate as well as the specs say it does. I added insulation to my attic and put fiberglass batts over the cellulose. I don't know if my last house (built 1996) was lacking a vapor barrier or what but in the winter we always had a slight draft coming STRAIGHT THROUGH the wall. Walls were 6" thick wood framed with cellulose for insulation.

    Bookmark   November 23, 2005 at 9:21AM
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chuckr30: Insulation is made up of air plus something to keep it from moving. With the exception of foam type insulation, which has an integral vapour and wind barrier, wind can always blow through insulation. It is like wearing a sweater on a windy day. You need a windbreaker to keep the wind from penetrating the sweater. Only then can it do its job of keeping you warm. What your last house was lacking was a wind and vapour barrier and caulking. I would call that really shoddy work for 1996 construction.

    Bookmark   November 24, 2005 at 6:54AM
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