How to Insulate Finished, Unfinished & Masonry Walls  

If you’re a do-it-yourselfer, you may find that finished walls present the most difficult of all insulating jobs that you had done in the past. Access is restricted, if not impossible, and in most cases, a professional is required. What makes things complicated, is that it is not easy to know how much insulation, if any, is already there.



To do a simple test if there’s insulation inside is to touch the wall on a cold day. If it’s too cold, there is perhaps no insulation at all. If you want to make sure, place one hand on the outside wall and another on an inside partition. If there’s an obvious difference, the insulation is either thin or none at all.
It’s more difficult to tell on a warm day, but you should not wait until subzero weather to decide whether or not you need insulation. One way of checking is to remove a cover plate from a wall switch and peek inside. If you can't tell by looking in, get a flashlight, and shire it through one of the holes in the electrical box. (Turn off the juice first, though, to play it safe.)

None of this may work, however, and it may be that you will have to remove some of the woodwork or drill a hole in the gypsum board. You might think you could check from the outside easier by removing a shingle or piece of clapboard, but there’ll be sheathing or plywood behind that which you’ll also have to go through, so check from the inside.

If you have to disturb the interior finish, do it at the top of the wall. If you do add more insulation yourself, you’ll be removing the top portion of the wall anyway.
The odds are great that the insulation is adequate and you will want to add to it in any case. It’s probably just as easy to call in an insulating contractor in the beginning and have him check for you. Assuming he’s capable and honest, he’ll be able to check with a minimum of disturbance to the walls. You’ll want to use a reliable contractor, or any case, to blow in some cellulose or foam, you may as well bite the bullet from the start. If you insist, however, there are ways to do it yourself.

Insulating Finished Walls

If your house was built in balloon-type construction, you’re in luck. Just go into the attic and pour your insulation materials down between the studs. Perlite or vermiculite works best here, since these materials are heavy and fluid enough to fill completely and find their way around obstructions.

You may have trouble finding enough of these materials, however, and the price may be way out of range. The next choice is cellulose. As always make sure the cellulose is treated with a borax to make it fire-resistance. The fire rating should be clearly marked on the bag. Mineral wool in bags may also be used, bit it is very lightweight and the may not fill as well as you want.

There isn’t much to tell you about using any of these materials when you have a clear space between the studs. Simply open the bags and pour until the material fills to the top.

Older homes, where you generally find this type of construction, may also have firestops, cross bracing, or ducts between studs somewhere down below. It will be difficult to determine this even a flashlight, especially if the obstruction is on the first floor and you’re above the second. When you can see that there is an obstruction, you should also attempt to make a hole in the wall below the obstruction and finish the job from there.

In most homes, you will have to remove the top one or two feet of the finish material in order to install the insulating materials. For two-story homes, you’ll have to do it on both floors. Most walls will be made of gypsum board. To remove this, make a clean cut all across the top of the wall with a utility knife. Several passes may be necessary. Once the cut is made, you can work the top back and forth until it breaks or pulls clear. This is a messy job, so put newspapers on any rugs underneath. Remove all nails and stray material now. It’ll have to do eventually anyway.

It’ a lot of work, but you can save some money removing the upper part of your walls and pouring in your own loose-fill insulation. Mineral-wool batts can be used to insulate the top section.

If the walls are paneled, it is best to pull off the panels completely. Take off baseboards and other trim first. Work at a panel corner with a screwdriver or chisel until you have it loose. The rest of the nails will either pop out or pull through. Your screwdriver, old chisel or dull wire cutters to pull out the nails.

You could also cut through the paneling at the 2-foot level, but you can’t every well patch up the paneling later. It is possible to put up a molding strip over the cut, but it won’t look at that great. Sometimes, with high ceilings, the paneling will have been too short anyway, and there’ll be molding or shelf where place to pull off the paneling and put it back the same way. Even if space is smaller than the recommended 2 feet, it’ll be better to work with the smaller hole than have to patch later.

Paneling may have been put up over the gypsum wallboard. If so, remove two feet of that. You don’t have to be as careful in removing the wallboard because it won’t show later.



Pouring the Insulation

Once the cover material is removed, the insulation itself is easy. Just pour it between each stud until it reaches the top. You will probably need a ladder to get the bags high enough.

But what about that last 2 feet which you removed? You can’t pout insulation there because you’ve removed the wallboard which holds it in. The solution is to staple small pieces of batt or blanket insulation in those spaces, getting as high as R or as you can. Install the mineral wool for new work.
Patching Up the Wall

This is the hard part. You now have to fix up the walls so that the patchwork doesn’t show. There are a couple of ways to do this, none of the entirely satisfactory.

The professional method is to install new framing at the juncture of the existing wallboard and the new. Using the same lumber as the studs, ordinarily 2x4s, saw a piece of fit between the two studs. The distance should be 14 ½ inches for relatively new lumber, 14 3/8 in order homes, but measure each one to make sure. Carpenters are perfect either.

Insert the new piece between each stud so that about half of the new cross-member shows above the existing drywall. The new piece is then toenailed to the studs, which isn’t easy since only the top is accessible. Nailing through the old drywall will help hold the crosspiece while you toenail at the top.
Actually, even though it isn’t the best construction practice, you can usually install the new wallboard just by nailing it to the studs. This may result in some buckling and unevenness, but it may be the best compromise. Just cement should cover up most of your sins.

After you get up the new pieces of gypsum board, the spaces are filled with joint cement. The perforated tape usually associated with this cement can be used but there won’t be any beveled edges to serve as an indentation for the tape. There is thin drywall patching tape on the market, which is better for this purpose. Either type will cause a slight bulge. But carefully tapered patch should hide the hump.

In any case, with or without the tape, fill the joints with taping compound or spackle, tapering it away from the edges with a wide drywall knife. Let it dry for a day or so, sand, then put down another layer of the same more carefully this time because it should be the last. Taper the cement carefully away from the center to minimize any bulges. If you do this skillfully enough, you may need further sanding. Chances are, though, that you’ll have to sand the joint after it dries to get a smooth surface and perhaps need a third coat.

If you work carefully, you should be able to produce a joint that isn’t noticeable, but it may be that it still looks unacceptable. There are several ways to mask the joint if this happens. One is to install a piece of molding all around.

A shelf going around the room at that level sometimes looks pretty nice. A “busy” wallpaper should also cover any imperfections. You may even want to run a ferent or plain awful, depending on your tastes. An imaginative decorator can probably come up with several other ideas.


If you’re just repainting the wall- and you will certainly have to do that if nothing else, forego the case of latex paint dealer for a paint that provides a nonpermeable film that also serves as a vapor barrier. He will probably recommend an oil-based paint. You don’t have to do the entire room that way, just the outside walls. You can leave other walls in a contrasting color, or perhaps find a latex paint that matches the oil-base.

Paneling is replaced the same way it was before. Use nails that match the paneling if possible. Otherwise, use 6d finishing nails, countersink with a nail set, and fill in both the old nail holes and the tops of the new nails with a matching putty stick. If a good match is not available, use wood putty mixed with an oil color or stain. When there is gypsum putting up the paneling. You don’t really have to patch up the joints, although a layer of spackle will provide a little more thermal protection.

Insulating Unfinished Walls

When the studs are exposed, as in an attic room or garage, mineral-wool batts or blankets are the treatment of choice. Compared to the pour method described above, installing mineral wool is a pleasure.

You’ll need a staple gun and utility knife, light gloves and a loose-filling long-sleeve shirt and other loose clothing. Eye protection shouldn’t be necessary for walls, although a face mask might be in order if you have respiratory problems.

Take one of the blanket rolls or batts and extend it all the way up to the ceiling, making sure to leave no gaps. The vapor barrier, as always, goes on the warm side. Measure the height and cut the insulation to size. Put a couple of staples on each side, either at the side of the stud or on the face. Smooth out the rest and continue stapling about every 6 inches. Continue until you get to the bottom, making sure again to get a snug fit and staple the end. Proceed to the next stud and repeat until the wall is finished. Use scraps to fill in around windows, switches, etc. Either staple through the edge of the vapor barrier, or remove the vapor barrier and cover the unfaced scraps with polyethylene.

Masonry Walls

All types of masonry-poured concrete, concrete block brick, brick, and stone – are poor insulators. The best insulation for brick or stone veneer is professionally blown-in cellulose or urea-formaldehyde. In some cases, the contractor will work from the inside, blowing his insulation into the interior stud wall. This type of job can also be done from outside by removing brick or drilling through mortar.

Some homes may use stone or interior-faced block as the wall surface, instead of having a stud wall. In that case, you can add rigid foam insulation to the surface for basement walls. Most brick walls are actually brick veneer so that insulating materials can be blown between the stud wall and the brick as well as between the studs.

If it’s all possible – and usually isn’t – to gain access to the top of a concrete-block wall, insulating materials can be poured into the cores, or hollow cells, from the top. Perlite or vermiculite is the insulation of choice here. Since it is ordinarily possible to do this once the wall is up, the usual application is with new work. If planning a new addition using a concrete block, it is best to insulate both cores and the inside face of the block.



How Is New Work Use for Insulation

New work is easily insulated, of course, the same way as the exposed studs in the previous section. The time to think about insulation is during the planning stages.

You will note for example, that the recommended R-value for walls in most parts of the country is 19. This requires 6 inches of mineral wool batts, an impossible task when the walls are nominally 4 inches thick. A 2X4 stud is actually 1 ½ by 3 ½ inches, which means that the thickest mineral wool blanket that can be installed is R-11 or R-13.

If you want your new or renovated room to be cozy and thermally efficient, seriously consider using 6-inch framing for the walls. Here, there’s some extra cost. And, for renovation, there’s some loss of living space. Adding 2 inches of framing to each outside wall can mean a lot less living area – although not necessarily. It depends on how much room you have.

If you are already planning an addition that will go to the limit of the setbacks provided by the building code, that means your living space will have to be cut back 2 inches on that wall. On an 18-foot wall, that’s 3 square feet less floor area.

But perhaps you can design the room so that the long wall is in the other direction. If there are no limitations with available space, it shouldn’t make too much difference. Instead of bringing the room in 2 extra inches, extend the outside walls out an extra 2 inches, leaving the living space the same.

Perhaps, even better, although more costly, is to use rigid foam, such as Styrofoam or High-R Sheathing, on the outside of the studs. Follow the manufacturer’s directions carefully.

You should also consider alternate hearing sources for any new work. An addition on the south side of the home, for example, is ideal for solar heating. Instead of adding on to the heating system, perhaps you may want to install a wood stove. If you are interested in such an alternate source, get a book on it.

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