cellulose building insulation (C) Daniel Friedman Blown-In Building Insulation

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Blown-in cellulose, foam, or other retrofit building insulation products:

This blown in insulation retrofit article illustrates and describes the properties of blown-in or pumped-in building insulation materials.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Blown-in Building Insulation: settlement, vapor barriers, condensation, R-values, voids

Cellulose insulation in the handThis document assists building buyers, owners or inspectors who need to diagnose, identify, or improve building insulation for new construction or retrofit and energy savings projects.

The question-and-answer article below paraphrases, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.

Various materials have been used as poured-in or blown-in building insulation but the two most common are cellulose insulation illustrated in our photo and chopped fiberglass insulation illustrated in our next photo (below).

Blown In Building Insulation Characteristics, Advice, Moisture or Condensation Concerns


Does blown-in insulation settle and need to be added as time goes by?

Our house doesn't seem as warm as it did at first, though it could be because we are getting old. There is no vapor barrier - the builder said that I didn't need a vapor barrier in this climate. - Carl Whitis, Belen NM

Chopped fiberglass insulation in a modern attic

Above: chopped pink fiberglass insulation poured or blown into an attic in a somewhat sloppy uneven installation. This chopped fiberglass insulating material is discussed at FIBERGLASS INSULATION IDENTIFICATION.


Settlement in Blown in Building Wall Insulation

Insulation retrofit blow in hole (C) Daniel FriedmanIf the building insulation was blown in at the proper density, it shouldn't settle. This is true for both blown-in fiberglass and blown-in cellulose insulation. (Typically we're talking about insulation blown into building wall cavities)

If blown-in insulation has settled however, the gap at the top of the wall may sharply reduce the R-value of the wall.

Assume R-11 blown-in insulation in a wall cavity settles enough to create a void equal to 10 percent of the wall area.

This would drop the effective R-value of the wall from R-13 to R-9.75 - a 25-percent reduction in insulating value and a 25 percent increase in heat loss through the wall.

You can determine whether or not blown-in wall insulation has settled by a thermograph scan of the building.

Our photo (above left) shows an inspection test cut to expose blown-in cellulose in a building wall. - DF

See details about insulation settlement causes, effects, extent and other insulation voids at Retrofit Insulation Settlement, Voids.

Other Voids in Blown-in Building Wall or Ceiling Insulation

Watch out: in some blown-in building insulation retrofit projects we have occasionally found significant insulation voids where the installer was careless, or where the installer did not anticipate blockages in the wall cavity formed by diagonal bracing [Image file] or fire blocking.

An infra-red or thermal scan of a heated building during cold weather will make such insulation voids obvious - DF.

[We did indeed observe significant shrinkage, not settlement, in UFFI blown-in insulation in some homes insulated with that product in the 1970's, particularly if the product was not properly mixed in the first place.


Voids in UFFI Foam Insulation Pumped Into Building Cavities

Shrinkage and air bypass leaks at the sides of UFFI insulation in a Poughkeepsie Home (C) Daniel Frfiedman

Popular in the U.S. during the Arab Oil Embargo Urea Formaldehyde Foam Insulation was used as a pumped-in insulation retrofit in previously-un-insulated building walls and ceilings, particularly in the northeastern U.S. states and in some areas of Canada. Depending on how the product was mixed and installed, significant shrinkage occurred as the insulation dried and cured, leaving air bypass leaks around the sides and tops of these blocks of foam in building walls and around all sides of UFFI in building ceilings.

Details about UFFI insulation and air leaks at UFFI shrinkage taps are at UFFI SHRINKAGE, THERMAL BYPASS LEAKS

Happily newer open or closed-cell foam insulating products such as POLYISOCYANURATE FOAM and IAQ and ICYNENE FOAM SPRAY INSULATION do not seem to have this shrinkage gap problems.

Why Does our Blown-in Insulated House Now Feel Colder?

Your house may feel cold because the lack of a vapor barrier has let moist air from the house interior (or leaks in the house interior walls) has let moisture enter the walls.

As moisture enters building walls, it cools, causing condensation in the wall cavity. The effect is similar to an actual leak into the building wall but perhaps less severe, and possibly not a problem.

Effects of Moisture in Building Wall Cavities - Do We Need a Vapor Barrier?

If we have a limited amount of moisture in the wall cavity:

  1. moisture will be absorbed into the wall framing and insulation
  2. moisture will then diffuse or convect to the outside air or
  3. moisture will return to the house itself as the indoor relative humidity level drops

Even limited moisture leaking into some building walls can accumulate, leading to mold or other building problems depending on the wall structure and materials. For example leaks into EIFS synthetic stucco walls have led to serious rot and mold problems on some buildings.


Effects of Water Leaks into Wall Cavities

If insulation actually gets wet (from accumulated condensation or from a leak into the wall cavity or ceiling cavity) the insulation becomes less effective, and you may feel the result as a "colder house" or in some unfortunate cases, as a "moldy house" with indoor air quality problems depending on the amount of moldy air moving in and out of building cavities.

If moisture returns to the building interior or exterior (cases 2 and 3 above) then no harm may have been done.

Watch out: building insulation that has been wet from leaks or accumulated moisture may invite mold growth, insect attack, and rot, all of which can eventually lead to the need for costly repairs.


Effects of Missing Wall Vapor Barrier

Studies of several hundred houses without vapor barriers in Spokane WA and Portland OR, performed in the 1980's by George Tsongas of Portland State University found no structural damage to the buildings and only occasional higher than average moisture levels in the building framing or insulation.

Albuquerque NM (your location) is dryer than Spokane and has fewer degree days, so you should not have in-wall humidity problems unless they originated in building leaks.

Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

Moisture or Water in Sprayed Cellulose Insulation

According to Deborah Fallow, owner of MetroNY Insulation,

"Spray-applied cellulose insulation, which is most often used in new construction, is damp-sprayed, not wet - an important distinction. In the old days, [cellulose insulation] was a wet-applied product, and you could squeeze liquid moisture out of it.

For quite some time now, only a very small amount of moisture is added to damp-sprayed cellulose, definitely not enough to be able to squeeze water out of it. Under normal conditions, the cellulose insulation is ready to be covered by drywall in 24 hours, far less than the time that is routinely scheduled between the insulation and drywall jobs [in new construction]."

Fallow adds,

"In addition, cellulose manages moisture." According to Fallow [we are not sure we agree], "Cellulose insulation requires no vapor barrier in the overwhelming majority of installations. It does an excellent job of limiting air movement, and because it is hygroscopic [definition: hygroscopic means a substance tends to absorb moisture from air], it manages moisture as well.

Some insulations require vapor barriers because they do such a poor job of preventing air movement, air that can carry moisture with it.

The problem is that ... moisture and air don't always move in the same direction thorough a building, depending on the time of year. So what about those products that need a vapor barrier? Effectively half the year it's on the wrong side of the wall. Cellulose [that is blown in without a vapor barrier] doesn't have that problem."

Watch out: In our opinion the views above need some clarification:

It is accurate that building wall cavity insulation can safely "absorb" moisture driven into the wall cavity, store it, and later release it back to the living area as seasons and air and moisture movement direction change. We discuss the safe movement of moisture in and out of building cavities at MOISTURE in BUILDING WALLS, EFFECTS.

It can also the case that if moisture driven into a wall (usually most severely at wall penetrations such as openings at receptacles or light fixtures) is excessive in amount (such as in a poorly vented bathroom or in a home with water entry troubles) the amount can be enough to saturate the insulation (mold and loss of R-value). The ability of different building insulation materials to absorb moisture vapor and later return it safely to the building interior varies by insulation product.

Also, depending on the wall or ceiling's total R-value, moisture can pass through the insulation to the exterior sheathing where it condenses back to liquid form. That's a problem that invites mold growth, structural rot, and insect attack.

Fallow's explanation above may confuse some readers who mix up the need for a vapor barrier (keeping moisture out of a wall) and the need for an air barrier (keeping wind effects out of a wall from outside and/or minimizing air movement in and out of a wall from inside the building). Exterior house wrap is specifically intended to be an air barrier, not a moisture barrier, so that if moisture does pass through a wall's insulation it can continue to pass to the outdoors.

Or more generally, we place a vapor barrier on the "warm side" of a wall (or ceiling or floor) in order to prevent moisture from moving into and accumulating in the building cavity. In northern climates invariably that means the vapor barrier goes inside the building. In some southern climates where air conditioning is used, the "warm" side of the wall is actually the building exterior and a vapor barrier may be placed there rather than indoors.

An in-depth discussion of how moisture moves in and out of buildings is provided at MOISTURE PROBLEMS: CAUSE & CURE.

See our building moisture home page at MOISTURE CONTROL in BUILDINGS.

A Few Other Warnings about Blown-In Building Insulation

Blocked ridge vent (C) Daniel FriedmanWatch out: don't blow ceiling insulation into or around electrical fixtures or wiring that can create an overheating or fire hazard. Examples of problems to avoid when blowing insulation into a building include [-DF]

The link to the original Q&A article in PDF form immediately below is preceded by an expanded/updated online version of this article.


Continue reading at CELLULOSE LOOSE FILL INSULATION or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Suggested citation for this web page

BLOWN-IN INSULATION at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia


Ask a Question or Search InspectApedia

Questions & answers or comments about -.

Try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

HTML Comment Box is loading comments...

Technical Reviewers & References

Click to Show or Hide Citations & References

Publisher - Daniel Friedman