Are my walls insulated and, if so, how well?
Houses built before 1960 often had little or no wall insulation. In almost every house built before 1920, the walls are completely empty. As house building increases, we begin to see some type of “insulation” inside.
Commonly found, besides to no insulation:
|1900||1/2″- 1″ straw/hemp “waffle” of pressed fiber.
Sawdust from construction: sometimes full; often partial, settled towards the floor.
Back plaster — an additional layer of wood lath and plaster about midway through the 3 1/2″ cavity.
|1920-1940||1″ thick newspaper batts, paper encased and sown.
Blown rock wool, usually 3 1/2″ with good density.
1″ to 1 1/2″ thick rock wool/glass fiber batts, kraft-faced.
|1940-1970||1″ to 1 1/2″ thick balsam wool batts, paper encased and sown.
1″ to 1 1/2″ thick rock wool/glass fiber batts, kraft-faced.
Formaldehyde foam, 3″.
|1960-1980||Same as above but also 2″ kraft-faced fiberglass batts become common.|
|From 1970 on||3 1/2″ fiberglass batts are widespread (R-11).|
Wall insulation – What the building codes require
Before 1979, there was no routinely-enforced or standardized energy code and no nation-wide requirements for energy efficiency in buildings or building materials. From 1970 or so, insulation “batting” for walls in new construction was usually a full 3 1/2″ fiberglass, faced or unfaced, so that the insulation would fill the standard 2″ x 4″ wall cavity (2″ x 4″ nominal; 1 1/2′ x 3 1/2″ actual). Previously, although wall dimensions were at least 3 1/2″, wall insulation “batts” were usually only one (1.0″) to one-and-a-half (1.5″) inches thick, with Resistance values ranging from about R-1.5 to R-2.5 pew inch.
Since 1979, the federal energy code mandated R-19 wall cavities and studs were increased to 2″ x 6″ to accommodate this thicker insulation. Under the current Minnesota building code, new wall construction insulation requires an R-21.
How do we know what’s in the walls?
An infrared camera, especially done in conjunction with a blower door test, can identify uninsulated and poorly insulated wall cavities. These are offered by MGT Insulation, and are commonly done by energy auditors for gas and/or electric utilities.
We recommend the investment in an independent Energy audit from your utility company. The cost of the audit is fairly low and its actual cost is heavily subsidized — meaning that its actual cost would be much higher without the contribution by the utility. Have the auditor include an infrared scan when possible, especially if there’s a question about an enclosed, inaccessible space.
However, the best way to know what’s in the walls is to look. The energy auditor will drill a small hole in an outside wall in an inconspicuous place to look, and then plug the hole with a tight-fitting plastic plug. MGT Insulation can do this, too. Just ask!
How are walls insulated?
Loose-fiber, blowing style insulation, either cellulose or fiberglass, is blown into the sidewall cavities with a small diameter wall tube using a high pressure, high capacity insulation blowing machine, installed in the work truck. The crew uses its own power for the machine with a gas-fired generator. A row of small 2″ or 2 1/2″ holes are drilled, at least one per cavity per floor, through the sheathing that lies beneath the house siding, after the siding has been properly removed and retained for re-installation. The cavity is then insulated to capacity by inserting and maneuvering the insulation blowing within the cavity to pack the insulation to a density of approximately 3.5 pounds per cubic foot for cellulose or 2.0 pounds per cubic foot for blown fiberglass. The density of the insulation is very important: denser material has less air space between the fibers so it is less prone to settling and creates a tighter barrier against air infiltration from the outside. A densely packed wall with cellulose insulation will equal the performance of spray foam insulation as an air barrier. Density is determined by the blowing capacity of the equipment and the training and experience of the installer.
Sidewalls are always insulated from outside, whenever possible. This is faster, cleaner, and easier. Our objective is to leave the house looking as good as it did before, so we NEVER DRILL THROUGH SIDING. SIDING IS REMOVED. Most siding is easily removed, just reversing the process of how it was installed. Except of stucco or brick, all siding is some type of lap siding — wood, wood shake, aluminum, steel, vinyl and cement board — and it is nailed in place at the top of each piece, lapping each other from bottom to top. The key is to remove or cut the nails holding the siding in place, even blind-nailed, without damaging or marring the siding. With good training and careful technique — gleaned from years of experience — successful siding removal and re-installation is done every day.
After the siding is removed, the exposed underlayment is drilled, filled, plugged with wood plugs, and the siding is reinstalled to its original position.
Stucco can be successfully patched by a trained stucco contractor. The skill is to replicate the texture and color of the surrounding wall area within a series of 2 1/2″ holes — and done in such a manner that the holes blend with the existing. This is always a challenge, because fresher material reflects and absorbs light differently, so patches can remain more obvious. However, newer exterior paints are now used over stucco that do not blister or peel the way older latex exterior paints did over stucco.
Brick siding and insulating wall from the interior
Drilling outside walls from the interior — whether drywall or plaster — requires good preparation of the site before starting. Items hanging on the outside walls are removed; furniture and other items from the moved away from the outside walls, about 2-3 feet or more; floors are covered next to the outside wall and furniture remaining in the area is covered.
Lead-safe Practices are always observed. When necessary, we test for lead based painted surfaces before proceeding. (There is an exterior lead based paint protocol as well).
When lead-based paint has been found, the crew will create a wall to ceiling enclosure to isolate the wall area from the interior, wherever we are drilling outside walls. After the insulating is completed, and the initial patching is done, the area is thoroughly vacuumed and cleaned, following mandated lead-safe practices, and the enclosure is properly disassembled and removed. The contaminated material does not mix with the house interior.
Holes drilled in drywall or plaster are plugged with foam plugs and then patched with coats of plaster patching or joint compound. The industry’s standard practice for residential insulators is to leave the holes “ready for light sanding and painting by others”. This means the homeowner should not need to complete additional patching unless otherwise agreed.