This article was originally published in the September/October 1996 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.


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Home Energy Magazine Online September/October 1996


Insulation: The Inside Story

by Bill Van der Meer

Bill Van der Meer is director of the Weatherization Training Center at Pennsylvania College of Technology in Williamsport, Pennsylvania.


In Pittsburgh's South Hills district, it is not at all uncommon to see homes that are two stories tall on the street side and four stories on the back side. The view of the city skyline is nothing short of fantastic, but try to picture youself erecting and then working off of a ladder or scaffolding 40 feet above Mother Earth.

Have you ever turned down a dense-pack sidewall insulation job because you thought it was beyond your ability to retrofit safely or successfully? Whether the problem is unsafe heights or difficult siding, it may be time to try blowing from inside the house.

In hilly cities, there are often uninsulated balloon-framed houses on very steep hillsides. This forces insulators to go up 40 feet on ladders to insulate. Meanwhile, tight clearances between homes make the walls truly inaccessible. Under these conditions, there are some insulation contractors who insist that blowing from indoors is the only way to go. The advantages should be obvious to the veteran installer:

  • It's safer (there's very little ladder work).
  • Weather is not a factor.
  • All walls are easily accessible.
  • There's little risk of damaging siding.
  • It is easier to detect accidental spills or bulging interior walls.
There are also disadvantages. Since you will be working in your client's home, protecting them and their possessions from dust is of paramount importance. Also, some clients are understandably fussy about the finished appearance of their walls. Patching access holes becomes more demanding indoors.

Trainers from the Weatherization Training Center (WTC) recently held an In-Field Training in Pittsburgh, sponsored by ACTION Housing Incorporated. There were height and clearance problems on the house selected as the training site. The landlord agreed with our proposal to do an interior blow on those sections not accessible from outside. It was a valuable learning experience for trainers and trainees alike. We found that the interior approach was possible and desirable, and that the obstacles could be overcome.

The best tool for this part of the trade is a Relton Wood/Fiberglass cutting 2 1/2 inch hole saw. The carbide tip of this saw can produce a clean hole in plaster, and can penetrate the wood lath underneath.
Preparation Along with the usual preparation of defining the thermal envelope and developing an insulation strategy, it is critical to control workplace dust. Dust control may necessitate isolating sections of the home where work is being performed. To do so, tape plastic over all openings. As insulation work is completed in one section, clean it thoroughly before moving on to the next.

Protect the client's possessions by moving all heavy furniture into the center of the room. Cover the whole bundle in 6-mil plastic (lighter plastic may be easier to handle, but it's not as durable) and continue the coverage across the floor to the wall. Tape the wall-floor juncture and all seams with wide masking tape. Electronic equipment is especially vulnerable. Encourage residents to participate by removing all of their precious electronics, knickknacks, and family photos prior to your arrival.

Accessing the 
Wall Cavities As always, you must drill holes for the fill tube. For this we recommend a Relton wood-and-fiberglass-cutting, 2 1/2 inch carbide-tipped hole saw. This special combination bit is capable of producing a clean hole in plaster and penetrating the wood lath underneath. For drywall only, a standard hole saw is effective. Holes must be staggered vertically along the wall, or cracks along the plaster keyways may develop. Wherever possible, take advantage of wide base or chair molding, which may be carefully removed, drilled behind, and reinstalled. Drilling in closets, underneath cabinets, or behind furniture may save time on the finishing work.

Protect your workers from lead and general dust hazards by using OSHA-approved half-face respirators with appropriate filtration cartridges. Eye protection and full-body Tyvec suits are also highly recommended.

Actual insulation techniques are virtually identical to those used in exterior applications. Probe 100% of the wall cavities and dense-pack cellulose at 3 1/2 lb/ft3. The only difference is the goal of absolutely minimizing the dust. That takes an experienced hoser with an artist's touch on the remote switch. After inserting the fill tube into the wall cavity, it is a good idea to line the hole with a vinyl-covered insulation scrap to help keep product from blowing back. Some folks like to use a positive shutoff material gate in line with the hose, although this may slow down the production rate.

Holes need to be staggered vertically along the horizontal plane of the wall to avoid cracks in plaster keyways-here, working along a staircase allows the holes to be staggered without ladder work. However, this installer has neglected one important step, namely covering the stairs to keep the debris off the rug.
Patching and Finishing Once the wall cavity is full, install foam plugs the same size as the holes. These are available through insulation suppliers. A 2 1/2 inch plug will fit snugly into the 2 1/2 inch opening. Apply with gentle pressure until it is countersunk by about 1/4 inch. Never use wooden plugs! We found out the hard way that pounding them in caused hairline cracks in the plaster. Even if no cracks appear at first, wooden plugs are likely to affect the finish coat of plaster, because of differential expansion and contraction.

The next step is applying the plaster patch. Plastering, done correctly, is an art. With the right tools, materials, and techniques, you too can become enough of a master to get by.

There are three major categories of plaster patching compounds: dry mix and pre-mixed joint compounds, and spackling compounds. At the WTC, we have experimented with commercial patching plasters, including dry mix Durabond Plaster of Paris. As amateurs, we found them extremely messy and difficult to work with. I don't recommend either, although in the right hands they probably work well for large patching jobs.

We also tried the standard joint compounds used by drywall finishers. We found that Gold Bond's Pro Form Lite performed best, producing a paintable patch after the second coat.

Among the spackling compounds, by far the best one-coat finish was achieved with DAP's Fast 'N Final. This lightweight product proved to be very workable, dried quickly, and showed no visible signs of shrinkage-even when applied to a 1/2-inch thickness. Applied with a 9-inch flexible drywall knife, it required no sanding. The only disadvantage is its price, at $5.00 per pint. However this high cost may be offset by a reduction in finishing time. Dense-pack guru Jim Fitzgerald likes to use a 50-50 mix of Structolite and Durabond 45, followed by a thin finish coat of joint compound.

An array of patching products: dry mix and pre-mixed joint compounds or spackling compounds can be used to smooth patches after foam plugs (see foreground) are installed.

How will you ever match the original paint, short of refinishing the entire wall? You probably won't. The interior approach seems to work best with customers who are willing to accept having to paint the walls themselves in exchange for lower fuel bills and increased comfort.

Clean Up The process of cleaning up after any construction activity is such a no-brainer that it hardly seems worth mentioning in technical circles. Recently, however, there has been a lot of publicity regarding the hazards of exposure to workplace dust (especially lead dust) and the special danger it poses for young children. We don't have to turn into lead or asbestos abatement specialists, but we have to use common sense. With careful controls, these techniques will not produce nearly as much dust as a full-scale remodeling project. Here are some guidelines and suggestions for a thorough cleanup of the work area.
  • Gently sweep insulation and other bulky debris (including Tyvec suits) toward the center of the plastic you laid down during the prep work. Pull the corners and edges in, wrap it, seal it, and dispose of it properly.
  • Since there will probably be elevated levels of fine dust, a high efficiency particulate air (HEPA) vacuum is helpful for intermediate cleanup. For the final cleaning, use a diluted trisodium phosphate (TSP) wash, paying special attention to floors and other flat surfaces, such as window wells, where kids tend to congregate. Avoid the use of highly inefficient ShopVacs on home interiors; their filters allow significant amounts of dust to reenter the space.
With some adjustments in technical approach, interior insulation retrofits are not only possible but desirable when the options for exterior blows get thin. Don't be afraid to mix it up-just be careful!


Reprinted with permission from Weatherization Quarterly, newsletter of the Weatherization Training Center, 1995-96:2.



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