Home>Discussions>INTERIORS>Molding & Carpentry>blow in cellulose or take down plaster and use fiberglass insulation?
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Sarah S.
blow in cellulose or take down plaster and use fiberglass insulation?

I live in a small 1920's Craftsman-style home. Most of the plaster/lathe walls are in decent shape and we feel we can fix most of what's cracked. However, there is absolutely no insulation in the walls. We are in a temperate climate (mid-Atlantic states) and the recent sub-zero temperatures made living in the home, especially the upstairs, almost unbearable. We are beginning to save up to insulate and are wondering if blown-in cellulose (from outside) actually provides any insulation for our climate or if we should just take a pill, bash down the plaster and lathe, and insulate w/ the pink stuff from the inside and replace w/ dry wall. I know it's a nasty, dusty job to take down plaster. Our dining room might have to have that done anyway, as the exposed back wall plaster is the worst in the house. The cellulose stuff just looks... well, like ground up newspaper, which it is. Thanks for any advice!

Re: blow in cellulose or take down plaster and use fiberglass insulation?


No need whatsoever to do a nasty, dusty job & rip out the plaster---blown-in cellulose insulation from the outside of the house has been proven to be a very satisfactory alternative & can be installed with much less cost & needless labor; the experienced crew completely does the job in a day or less---they show up with a special truck that has a large blower motor connected to a long 3" diameter hose---they work entirely from the outside of the building, so no one in the house is disturbed; they remove a small piece of siding/shingle here & there, cut a circular hole in the wall cavities & force-blow the cellulose in until the cavities are completely filled; they then replace & seal the circular siding piece & the removed siding/shingle piece so it looks good as new.

It also does a much better job of keeping the house cool in the summer heat, especially the upper floors & attic.

Read the articles below, then consult the Yellow Pages under "Insulation", check for references, and call the cellulose insulation guy!

An experienced contractor/crew will do the job without leaving any fill-cavities; I had my 2000 sq.ft. house in New England done over 10 years ago when I was burning 1200 to 1500 gal. of oil per heating season---the following season oil usage dropped to 700 gal.---and it has remained at the 500-700 gal. level per season ever since---I couldn't believe it! At $4/gal.---well, you do the math! Not to mention the lower AC elec. bills in the summer. I've been in this house 30 years & I'm kicking myself for not doing it much sooner!


Re: blow in cellulose or take down plaster and use fiberglass insulation?

I don't know what the above poster is trying to sell but just insulating the wall will not result in a 50% reduction of your heating bills. Typically it results in about a 10% reduction. A 50% reduction is possible, but you have to do more than insulate the walls.

You have a brick house so insulating from the outside will be very difficult. Its different if you have some kind of siding, but with brick, that is not the best way to do the job. You can have small holes drilled in your plaster and fill through those, then patch the holes. You are planning on doing some patching and painting anyway.

But, taking down the plaster has two advantages. First, you can update your wiring in the walls. This can save you money on your homeowners insurance because new romex wiring is much less likely to start a fire than old knob and tube wiring. You can also make any other repairs that might be needed.

Second, sheet rock has about half the conduction of plaster. Plaster, with its high conductivity absorbs heat from the room and conducts it to the studs, which have a much lower R-value than the insulated cavities. The studs make up about 10% of your walls. sheet rock does the same thing, just not as bad because its conductivity is about half that of plaster.

You can put a 1/2" thick foam board over unfaced fiberglass, tape the seams, then sheet rock and you almost completely eliminate the lateral conduction of heat. The sheet rock will stay considerably warmer too so your room will feel warmer even at lower air temperatures in the room.

But really make the house more comfortable and less expensive to heat, you need to make sure everything else is up to speed as well. Good attic insulation, good storm windows or energy efficient windows and weather stripping. Insulation should be a complete system. As you improve the system, even small holes in the insulation suddenly become big heat losers and have a huge affect on heat loss. Then you need to find those holes and fix them. A thermal camera is the best way to find them.

One more thing, the biggest bang for the buck comes from weatherstripping. You can save up to 10% on heating by finding all the gaps and filling them and that doesn't cost very much. One really overlooked part is in the attic. Those vent holes for pipes going up through the roof let almost as much warm air out of your house as the exterior walls and windows and doors. seal around the pipes and insulate right up to the pipe walls.

Re: blow in cellulose or take down plaster and use fiberglass insulation?

Hey keith, I'm not trying to sell anything!

And I resent your small-minded insinuations, which are completely false; I could just as well contend that YOU'RE trying to sell things with your post, and contend that ALL YOU'RE STATEMENTS ARE COMPLETELY WRONG---but I'm not going to do that!

Lighten up! And in the future show some respect for your fellow contributors, you might learn something!

Re: blow in cellulose or take down plaster and use fiberglass insulation?

No bashing people here, OK? We get the forums we create and I like them nice and respectable- and friendly ;)

I don't think you'll see 50% savings with just wall insulation alone- that's not the usual result obtained by most folks so I wouldn't expect it, especially in your more moderate climate. I have to admit being torn between blowing in cellulose (which is a good retrofit insulation) or baring the walls (with the benefit of updating utilities like Keith mentioned). There's something to be said for both approaches.

Being the 'handyman' I'd do a tear-out because I can do almost all the work myself, thus saving a lot of money and ending up with a perfect job. You may or may not want to tackle something this big. It can be done in 'chunks' by doing one room at a time if your time or money is limited (and whose isn't?) and that approach causes less consternation for all the displaced people in the house during the work. And remember that interior walls also have plumbing and wiring, so unless you bare them too you're not fully updating the utilities.

You can rent cellulose insulation blowers but where I am it's not something worth considering unless you're extremely poor since the cost for a Pro is little more than this. The last time I priced this (several years ago) doing a small single-story would have saved me $180 but would have taken 2+ days time to finish repairing the needed holes. For $90 a day and not needing to lift anything heavier than my phone, I'll let someone else do it :D It's true that cellulose isn't the best insulation but it's good. Do make sure that there's no knob-and-tube wiring if you go with cellulose- even though it's fire-resistant it's not approved for those situations and it creates a big safety hazard. If you've got Romex you're safe with cellulose, but if you ever have to do a repair in the wall you get a big mess which having fiberglass insulation will avoid.

I think I'd have to consider how long I plan to be in the house. If it's going to be your permanent residence I'd do the tear-out. If you plan on moving within the next decade I'd go cellulose so long as the wiring and plumbing seem like they'll last that long.


Re: blow in cellulose or take down plaster and use fiberglass insulation?

von_steuben, I am retired and I have never been a salesman, as you have pointed out, I don't have the tact for that.

Here is the facts and any energy auditor that knows his stuff can confirm that between 20% (one story) and 30% (two story) of heat loss is through walls. The rest is lost through the attic, windows and doors, infiltration and the floor. The exact percentage varies on the house design and how it is built and insulated.

I do not doubt your drop in oil usage, nor do I doubt that insulating the walls was part of that. And I do not doubt that insulating your walls was a good idea as it was a good idea, but the total savings could not come from insulating your walls alone. What else did you do? Attic? Windows? New heater? The math just doesn't add up.

Re: blow in cellulose or take down plaster and use fiberglass insulation?

There isn't much to add to the technical answer to the question Sarah S posted, Phil summed it up.

But I can add that If someone disagrees on what has been written here, or any other posting, he/she can still do it respectfully. Beats doing it disgracefully and turn the forum into a third world market.

Re: blow in cellulose or take down plaster and use fiberglass insulation?

Ladies and gentlemen, be warned, if you wish to battle go else where for i will delete you. Challenging one another respectfully is allowed.

Blown in insulation or injected foam insulation does help in providing insulation and air infiltration blockage, however the biggest savings dose come from attic insulation and weather stripping including weather stripping of windows and doors.


Re: blow in cellulose or take down plaster and use fiberglass insulation?

I apologize for calling von_steuben a salesman, that was uncalled for, but I stand by everything else I said.

Re: blow in cellulose or take down plaster and use fiberglass insulation?

I am in almost the exact same spot (wood exterior) and I have chosen to go with blown cellulose insulation, even in the kitchen that we partly gutted. It's not possible to perfectly cut every piece of fiberglass so you will never fill all the voids that blown insulation will fill, leaving cold spots and places air can move through. So you will have much less air infiltration with blown insulation, and lately some researchers have been suggesting that the air infiltration is the most important aspect of insulation. We are going to do this once our electrical work is done (adding outlets and circuits).

I haven't figured out my attic yet, maybe spray foam or multiple layers of fiberglass, but much of the "attic" is too small for a human to get into so maybe just more blown insulation.

Also, if you are living in this house gutting it will be a nightmare. Unless you and all of your items move out during the work, expect to be cleaning up dust for months. Just the parts we gutted makes me never want to do it again.

Re: blow in cellulose or take down plaster and use fiberglass insulation?

Keith, as to the math of how to get a 50% reduction of fuel by insulating walls. Von-steuben only said the walls were uninsulated to begin with not the entire house. Walls are often the last place to be insulated. If the baseline is a house with a well insulated attic, decent windows, and the major air leaks sealed up a 50% fuel drop shouldn't be that much of a surprise for blowing cellulose in uninsulated walls.


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