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

Adding insulation to your old house is always going to be messy. We have found no absolutely clean way of dealing with the stuff. It is also a lot of hard work and can be time-consuming. Most reasonably handy homeowner can add insulation to an attic but it takes a fair amount of skill and experience to blow loose-fill insulation into a wall without gaps around electrical wire, pipes, and shear plates. This sort of installation is best left to the professionals with the right equipment, experience, and skill.

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 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 fiberglass, rock wool 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 is a must.

Fiberglass in the lungs can be very serious. Once in, it never gets out. Fiberglass 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 fiberglass is another story. Fiberglass 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 fiberglass 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, fiberglass, 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 at Big Lumber Store 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 also 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.

Dense packing requires skill and a lot of practice. You have to use the sound and the 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.

Cellulose can be dense-packed, as can fiberglass but only to a point. Over-packing fiberglass 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" fiberglass is not dense-packed fiberglass, although the terms are often confused. Dense fiberglass is composed of especially small particles and usually intended for blow-in wall application. Many companies call the material "prime fiber" fiberglass. Dense fiberglass can be used for dense-packing but it's not packed until it is installed.)

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. Fiberglass formulated for blow-in application runs about R-2.75 to R-3.50, depending on composition and manufacturer, and is about twice the price.

Some companies make a special fiberglass product for wall and claim that it equals and even exceeds the R-value of cellulose. But, if any outside verification of these claims exists at all, they are usually from company-funded studies and somewhat 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 a minimum R-13 in a 2"x4" stud wall and R-5 rigid foam sheathing under your new siding.

R-Value of Insulation and Other Common Building Materials
Insulation Materials
Material R-­Value per Inch R-­Value in 2"x4" Wall
Fiberglass Batt (Standard) 3.14 11.78
Fiberglass Batt (Dense) 3.85 14.44
Fiberglass Batt (Dense - Foil Backed) 4.30 16.13
Fiberglass Blow-in (Attic Loose Pack) 2.20 - 2.75 N/A
Fiberglass Blow-in (Prime Fiber) 2.75 - 3.14 10.31 - 11.78
Rock Wool Batt 3.10 11.63
Rock Wool Blow-in (Attic Loose Pack) 3.10 N/A
Rock Wool Blow-in (Walls Dense Pack) 3.70 13.88
Cellulose Blow-in (Attic Loose Pack) 3.13 - 3.50 N/A
Cellulose Blow-in (Walls Dense Pack) 3.71 - 4.00* 13.92 - 15.00
Expanded Polystyrene (EPS) 4.00 15.00
Extruded Polystyrene (XPS) 5.00 18.75
Poly­ure­thane Foam (Closed Cell) 6.25 23.44
Construction Materials
Material R-Value per Inch R-Value per Unit
Air, Dry & Still* 3.6
Block, Concrete 4" 0.80
Block, Concrete 8" 1.11
Block, Concrete 12" 1.28
Brick, Common 4" 0.80
Concrete, Poured 0.08
Drywall (1/2") 0.45
Felt Building Paper 0.03
Flooring, Carpet (Fiber Pad) 2.08
Flooring, Carpet (Rubber Pad) 1.23
Flooring, Hardwood 0.81
Flooring, Linoleum 0.05
Flooring, Vinyl (Tile or Sheet) 0.05
Lumber, Cedar 1.33
Lumber, Softwood (Spruce, Fir, Pine) 1.40
Panel, Fiberboard 2.84
Panel, Hardboard 0.34
Panel, Particle Board 1.31
Panel, Plywood 1.25
Paneling, Wood Decoative (3/8") 0.47
Roofing, Asphalt Shingles 0.44
Roofing, Wood (Shingles or Shakes) 0.97
Siding, Aluminum, Steel or Vinyl 0.61
Siding, Aluminum, Steel or Vinyl w/ 1/2" Insulating Board Backer 1.80
Siding, Wood Lap 0.80
Window, Double Pane (IGU) 2.10
Window, Single Pane 0.91
Window, Single Pane with Storm Window 2.20
Window, Triple Pane (IGU) 3.20
Dead Air Films
Film Location R-Value per Inch R-Value
Interior Ceiling Film 0.61
Interior Wall Film 0.68
Exterior Wall Film 0.17
* Still Air exists in theory but, in an actual house, air is almost never still. It circulates constantly, carrying heat with it.

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

We will need to drill holes through the interior plaster or gypsum board walls but Styrofoam plugs and a little joint compound 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 you 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 DIY guide published by the federal Energy Star program. 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. Fiberglass manufacturers exaggerate the R-value of fiberglass and under state the R-value of cellulose.

Cellulose producers are no better. We see constant comparisons stating that blow-in fiberglass 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 fiberglass is loose pack attic insulation being compared to dense-packed cellulose wall insulation. If wall insulation is compared to wall insulation, fiberglass and cellulose are much closer in R-value.

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.

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, a jury of your peers may award you a Clio. If you lie a lot, it's fraud, and if you get caught, a jury of your peers may award you a stretch in the graybar hotel.

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.

Rev. 10/14/18