Insulating Your Old House, Part 3:
Adding Insulation to Your Old House

J. M. Edgar, CMC, CRC

Whatever material you choose, the key to success is careful and ceaselessly vigilant application. Sloppy or unskilled application can defeat even the best insulation material.

Insulating Closed Walls


To insulate a wall cavity, we need to gain access to the cavity. We can do this from outside your house through your siding, or from inside your house through the drywall or plaster. Generally, outside-in is the best choice since it leaves most of the mess outside. There will be some mess. It's unavoidable.

The process is roughly the same for all closed wall insulation materials. A hole between 3/4" and 2" is drilled into your wall at the top and middle of each wall cavity. A nozzle or tube is inserted and the wall cavity is filled with the insulating material.

If we are working from the exterior, we prefer to remove the row of siding where we drill. But, sometimes we cannot remove old and brittle wood, or steel or aluminum siding without damage. If we cannot remove your wood siding then we have to drill through it. We use a wood plug to match your siding (cedar for cedar, pine for pine), glued in the hole, and sanded flush. When painted it is virtually invisible. If you have vinyl or steel siding, and for some odd reason you did not insulate when the siding was installed, then we will have to remove at least one row of siding per floor. This entails the risk of damage to the siding. If we cannot safely remove the siding, then insulating from the inside may be the only available choice.

Certain kinds of exterior finish are difficult to penetrate: brick and stone veneers, for example. We can do it, but it is time-consuming because these materials are slow to drill through, and we generally work with a smaller 1/2" hole. It takes four times as long as working through wood siding, and is, therefore quite a bit more costly.

If we are working from inside your house, we plug with a Styrofoam plug and apply drywall compound over that. The foam plug holds the drywall compound securely. When dry, we sand it to blend it into the existing wall. Again, after painting, it is invisible.

Safety and Personal Protection
All insulation materials can be dangerous if not handled properly. If fiber glass, rock wools or foam gets in your eyes, it can cause serious damage. Cellulose is more benign, but still an irritant. Eye protection in the form of wrap-around tightly sealing goggles are a must. Fiber glass in the lungs can be very serious. Once in, it never gets out. Fiber glass and rock wool were cleared of any role in cancer formation in 2000, but glass in the lungs cannot be good for you. Cellulose is just paper, so less of a concern. But, never forget that Brown Lung disease is caused by breathing cotton fibers, so even relatively benign particles can cause damage. No matter the material used, always wear a good, UL-rated, particulate filter mask.

Protective clothing is not generally required for cellulose, foam or rock wool, but fiber glass is another story. Fiber glass in contact with the skin is an irritant, and itches like the very devil. Heavy clothing is optional. If you can stand the itching, then do without the clothing. The rest of us bundle up like mummies.

Be aware also that loose fiber glass fill in your attic remains a potential irritant for as long as it stays in your attic. If you need to go into your attic for any reason, wear the same protective gear you would wear for application.

Loose Packing and Dense Packing
Materials such as rock wools, fiber glass and cellulose are generally blown into attics and allowed to form a loosely compacted layer. This is "loose packing". Slightly more material than is needed to achieve the desired R-value is blown in because these materials in loose pack form will settle over time. In attics, that's not much of a problem because if they settle too much, more can be blown in later to bring the R-value back up. Expect about R-2.5 per inch from loose packed insulation.

In walls, settling is a bigger problem. If the material settles, it leaves a void at the top of the wall which cannot be fixed except by re-drilling and blowing in more material - a nuisance and expensive. So manufacturers and applicators have worked for years to develop the various techniques now known as "dense packing" to eliminate settling. The material is blown into the wall using a stream of air moving at a relatively high velocity — 100 feet per second or higher. These high-velocity blowers are a specialty tool. The insulation blowers you can rent generally do not have enough force to dense pack. They are for attic insulation — not for walls.

The mixture is deliberately kept very lean — much more air than material. In this environment the insulation behaves like a liquid, flowing around obstructions and filling all the nooks and bypasses in the wall. The aim is to reach the density recommended by the manufacturer for closed wall insulation. For cellulose, for example, this is usually an average density of 3.2 to 3.5 pounds of cellulose per cubic foot of wall cavity. This density not only provides excellent insulation, but blocks almost all air leaks and virtually eliminates settling. Not every square inch will contain just the right amount of material. The application is a blind process, we can't actually see what's going on in a closed wall. But, if, on average, we blow in 3.2 to 3.5 lbs. per cubic foot we know we have a well-insulated wall.

R-Value of Insulation and Other Common Building Materials
Insulation Materials
(PDF Table)
Material Application R-Value per Inch R-Value in a 2"x4" Wall
Fiber glass Batt (Standard)Open wall3.1411.78
Fiber glass Batt (Dense)Open wall3.8514.44
Fiber glass Batt (Dense - Foil Backed)Open wall4.3016.13
Fiber glass Blow-in (Loose Pack)Attic2.20-2.75-
Fiber glass Blow-in (Prime Fiber)Closed Wall2.75-3.1410.31-11.78
Rock Wool BattOpen wall3.1011.63
Rock Wool Blow-in (Loose Pack)Attic3.10-
Rock Wool Blow-in (Dense Pack)Open/Closed Wall3.7013.88
Cellulose Blow-in (Loose Pack)Attic3.13-3.50-
Cellulose Blow-in (Dense Pack)Open/Closed Wall3.71-4.00*13.92-15.00
Expanded Polystyrene (EPS, Beadboard)Attic, Open Wall4.0015.00
Extruded Polystyrene (XPS)Attic, Basement, Open Wall5.0018.75
Polyurethane Foam (Closed Cell)Attic, Basement, Open/Closed Wall6.2523.44
Construction Materials
MaterialR-Value per Inch (If Applicable)R-Value
Concrete Block 4"-0.80
Concrete Block 8"-1.11
Concrete Block 12"-1.28
Brick 4" Common-0.80
Poured Concrete0.08-
Spruce, Fir, Pine Lumber1.40-
Cedar Lumber1.33-
Plywood1.25-
Fiberboard2.84-
Hardboard-0.34
Wood Lap Siding-0.80
Aluminum, Steel, Vinyl Siding-0.61
Aluminum, Steel, Vinyl Siding with 1/2" Insulating Board Backer-1.80
Felt Building Paper-0.03
Gypsum Board Drywall (1/2")-0.45
Wood Paneling (3/8")-0.47
Particle Board1.31-
Hardwood Flooring0.81-
Vinyl Tile, Vinyl Sheet, Linoleum-0.05
Carpet (Fiber Pad)2.08
Carpet (Rubber Pad)1.23
Asphalt Shingles0.44
Wood Shingles, Shakes0.97
Single Panel Window Glass0.91
Single Panel Window Glass with Storm Window2.20
Double Pane Window Glass (Sealed)2.10
Triple Pane Window Glass (Sealed)3.20
Still Air and Dead Air Films
DescriptionR-Value per Inch
(If applicable)
R-Value
Dry, Still Air3.6-
Interior Ceiling Film-0.61
Interior Wall Film-0.68
Exterior Wall Film-0.17
Dense packing requires skill and a lot of practice. You have to use the sound and feel of the hose, and your sense of how long it should take to fill a cavity to determine when enough material has been inserted, but not too much so it does not blow-back and go all over the place. It's tricky, and, despite what the tool rental places and big lumber stores may say, it is not a job for the inexperienced. The usual result when untrained applicators try it is that not nearly enough material is applied, many large voids are left in the walls, and the insulation is not fully effective.

Photo: U.S. Department of Energy Energy Star Insulation Guide Click to Download the Brochure
(Requires Adobe Reader. Download Adobe Reader here.)

The Energy Star brochure for DIY insulators is full of useful facts, safety precautions, and helpful tips.
Cellulose can be dense packed, fiber glass cannot be. Dense packing fiber glass reduces its insulation effectiveness. Heavy rock and slag wools tend to settle even when dense packed due to its relatively great weight, so they are rarely used in closed wall applications in the U.S. these days. In Europe and Asia, however, they are still widely used. ("Dense" fiber glass is not dense packed fiber glass, although the terms are often confused. Dense fiber glass is composed of especially small particles and usually intended for blow-in wall application. Many companies call the material "prime fiber" fiber glass.)

In dense pack applications, cellulose has an R-value of about between R-3.5 and R-4.0 per inch — about R3.75 on average. Fiber glass formulated for blow-in application runs about R-2.75 to R3.50, depending on composition and manufacturer, and is about twice the price. Some companies make a special fiber glass product for wall and claim that it equals and even exceeds the R-value of cellulose. But, if any outside verification of these claims exist at all, they are usually from company-funded studies, and suspect. We know of no truly independent studies of these products that support these high R-value claims. If you do, please let us know.

When and Where to Insulate Your Closed Walls

You can insulate your walls from the outside, or from the inside. From the outside is easier and creates less mess and disruption to your regular routine. The best time to insulate walls from the outside is when you are already doing something major to the exterior of your walls — replacing the siding, or painting the exterior, for example. Insulating requires almost the same preparation as siding or painting, so it is a minor addition to the process compared to the work, mess and bother of either siding or painting.

If you are adding new siding, also consider adding an insulated sheathing. We don't mean the 1/4" foam board siders often use under new siding, but R-5 rigid insulation board. For Zone 5, which is where we are (just barely — Zone 4 starts at the Kansas border), the Energy Star program recommends R-13 in a 2"x4" stud wall and R-5 rigid foam sheathing under you new siding.

Insulating walls from inside your house can be a lot messier and require more preparation than insulating from outside. But, if you are painting the inside of your walls, it may be a good time to insulate from the inside. You will need to drill holes through the interior plaster or gypsum board walls, but Styrofoam plugs and a little spackling will hide the holes nicely, and once painted they will be invisible. The preparation you do for painting is usually the same as preparation for insulating — drop cloths cover the floor, the furniture is moved out or covered — so insulating is not much of an added step — and certainly well worth the added work and modest expense.

Insulating Your Attic
If your plan is to insulate your walls in a few years when you paint your siding, don't wait that long to increase the insulation in your attic. Even if your blew in some extra inches just a few years ago, it's time to add more. The recommended level of insulation has changed. The Nebraska Energy Code now requires a minimum of R-38 in your attic. The EPA Energy Star program recommends up to R-60.

Attics tend to be very hot in summer and very cold in winter, so spring and fall are the best times to insulate. If you are doing it yourself, wear the proper protective gear for the material you are using, and, especially in summer, drink plenty of liquids.

We recommend against trying to insulate a closed wall yourself. But, insulating an attic is well within the capabilities of a seasoned do-it-yourselfer. But, first read the very useful D-I-Y guide published by the federal Energy Star program (See sidebar above). The brochure is full of useful facts, safety precautions, and helpful tips. Also, do something a little different this time: read and follow the instructions and safety precautions that come with the material you are using.

The R-Value of Insulation and Other Common Building Materials


The reported R-value of materials seems to depend largely on how R-value is measured and the economic interest of the person or entity doing the reporting. Every manufacturer tends to extol its own product, and dismiss competing products. Fiber glass manufacturers exaggerate the R-value of fiber glass and under state the R-value of cellulose. Cellulose producers are no better. We see constant comparisons stating that blow-in fiber glass has an R-value of 2.25 while blown-in cellulose has an R-value of 3.9. Both statements are true, but what's being glossed over is that the fiber glass is loose pack attic insulation being compared to dense pack cellulose wall insulation. If wall insulation is compared to wall insulation, fiber glass and cellulose are much closer in R-value.

It's just the way things are marketed here in the Good Ole' U.S. of A. If you lie a little, it's advertising, and if you do it well, an jury of your peers may award you a Clio. If you lie a lot, it's fraud, and a jury of your peers may award you a stretch in Leavenworth.

All these half truths, while not exactly the big lies, do make it hard for the owner of an old house to figure out the R-value of various materials, and which materials to use to have the best insulating effect.

To eliminate some of this confusion, and to educate ourselves, we decided to try to ferret out the actual R-value of common insulation and construction materials. We discounted manufacturers' claims unless supported by independent studies. Where several different R-values are reported, we tried to determine how, and by whom, they were calculated. If the calculations were made roughly the same way, but different results are reported by disinterested parties (e.g. universities or government organizations, Consumer Reports), we took the average of the different results.

The R-values in this table may not be completely accurate, but they are probably pretty close. And, at very least, they are not self serving because we don't have any economic interest at all in promoting any particular product or material.

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