So many homes have poorly installed fiberglass insulation. Have you been successful with a retrofit dense pack cellulose?

Doing testing of existing homes it is typical to see mottled patterns of surface temperatures with the FLIR Infrared Thermal Imager during Blower Door Testing.  

Part of the problem is air sealing and the other part of the problem is poorly installed fiberglass insulation.

This is not a rant against fiberglass insulation (I am a fan of both Rock Wool/Roxul and dense packed cellulose) for retrofit projects.  Fiberglass batt or blown insulation can perform fine, if it is installed properly and the air sealing details are paid proper attention.

How successful have some of you folks been with going into a sloppy fiberglass insulated house and doing dense pack cellulose into the wall cavity?

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Hi TJ,

I've never recommended it due to the cost benefit of adding the dense pack.  Even a poorly installed assembly will benefit from whatever insulation is there limiting the improvement that can be credited to drilling, dense packing, and repairing all of those holes. 


Hey TJ, using the tube fill method with cellulose, contractors in the Puget Sound area (that would be around Seattle WA) have been dense packing right over the R-11 fiberglass batts with good success.  Keep in mind, this probably does not have an SIR over 1 unless you are able to do very large amounts of walls and accurately record and account for the air sealing improvement on the building.  King County Housing Authority, one of our LIHEAP agencies, does a fair amount of this work in multi family buildings.

It does take the right size tube and a decent amount of experience.  I made a mess of it when I tried it, but then again, I am a consultant these days and have hung up the tool belt :-)



Do your self and your wallet a favor and get injection foam. The traditional insulation's are not worth the dust, allergy's, rodents, bugs and loss of "R" value with time. Do your research and you will not buy anything else.  

I am doing lots of dense pack cellulose over batted walls. Huge reduction in air leakage, no off gassing. Tracked billing history for two years, very cost effective. SIR greater than 1. O yea.

We are dense packing walls with insulation present and receiving good results in the Denver CO area.  Overall home air leakage reduction of 300 cfm per job.   Bestway Insualtion has been dense packing existing fiberglass walls for somewhere between 25-37 years.  Even medium batts have been able to be dense packed.  If it is done in knee wall areas where no attic side air barrier or sheathing is present then it can be more difficult and prices may be different.  

Short term cost benefit is higher than foam.  30 year payback is higher with some foams with higher R value such as closed cell, polyiso, etc. Avg length of time one stays in a home, a few years ago was 7 years.  Payback also depends on location.  CO is ideal since the temperature is cold here, but the climate is dry so we do not have as many moisture issues and additional steps are necessary to make sure moisture does not condense on roofing, etc.  Insulation is tested at 65 degrees not accounting for a large temperature change for cold temperatures.   See the Colorado Study for difference between 2 warehouses insulated with fiberglass and cellulose.  Does fiberglass freeze at lower temperatures?

Other Concerns:  A second concern with dense packing is that it does not account for thermal bridging.  Other things to keep in mind is that brick homes may struggle with this method unless insulated from inside or if individual bricks are removed.  Method can be used even when no gap is present.  Dense packing insulation will increase per inch value of fiberglass, possibly lower per inch of cellulose slightly, but reduce air flow tremendously and is a good option for homes that do not want sheetrock removed.  Effective R value may be tested with an R-value tester.  

Also, the mean radiant temperature is greatly increased in most homes causing significant comfort results from customers we have insulated.  Some of these results have been used to create new standards as well.  In the old days, this method was also used to dense pack some mobile home walls in our area.  

This area is in definate need of several more studies for a higher sample size especially in different locations!  "Walls are the most under prescribed efficiency measure" Residential Energy.  

Bestway insulated CO governor's mansion and helped lobby for workforce specifications.

Our Condolences to Richard Knaub


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