As any experienced old house renovator knows, there are the 5/3-3/5 rules to keep in mind. It means if you do the work yourself it will take 5 times longer and cost 3 times as much as your estimate. If you hire help it will take 3 times longer and cost 5 times as much. I learned this in my past. However, I discovered a few ways to tilt that rule in our favor when working with walls. What I show you here is meant to be used on the outer walls but elements of this method are also useful when working with wall partitions inside a house.
The customary way to upgrade a wall in an old house is to tear off the old materials out to the wall studs (collect the treasures hidden in there) insulate, rewire and add new wallboard, plaster or another interior finish. In our saltbox farmhouse I wanted to keep the structural integrity intact. Removing the double wallboard and the inner layer of sawn boards would diminish that advantage. I also dreaded the thought of all that mucky work.
The idea of straightening the old walls back to some resemblance to plumb and bringing the floors and ceilings to level with jacks, pulleys, sledgehammers and bulldozers, as I have done in the past, was out of the question. It would weaken the structure. Plumb and level are elusive goals in an old house anyway.
What I wanted were flat, plumb, insulated walls with new wiring and smooth new wallboard. So I decided to build them – right in front of the old walls, all around the inside perimeter of the house.
This is how you do it. Remove the mopboards, moldings, door and window casing trim, light fixtures, and all other protrusions from the wall. Seal all the cracks with builders foam. Make the old walls as draftproof as possible. Building a wall in one room at a time is advisable if you are living in the house during renovation. Make it one big project if you are wisely living elsewhere during construction.
It is best to start with a less used room first for practice. To avoid conflict with the irregularities in the old wall and to make room for R19 insulation, build the new wall at least 5 1/2 inches thick. Snap a chalk line on the ceiling the whole length of the room 5 1/2 inches out from the old wall. Between the chalk line and the old wall, use a 20D common nail and a hammer to punch test holes in the ceiling. Find all the joists up there and mark their locations. Attach a 2x4 plate against the ceiling, aligned with the chalk line, with drywall screws through the plate and on into the ceiling joists. Using a plumb bob, mark spots on the floor at each end of the room exactly under the 2x4 on the ceiling. Snap a chalk line between them and attach a 2x4 plate to the floor.
Install 2x4 studs on 24” centerlines across the whole room. This will be a little annoying. Each stud will be a slightly different length. They need to be tight and plumb so careful cutting, and perhaps some shimming, will be necessary. The extreme end studs should attach to the intersecting walls firmly even if they end up not being as plumb as the other studs. Please, for many good reasons, use screws for all of this work.
Now you have a stud wall that is straight, flat and plumb, though probably not square, but that is okay. At this point you can lay in the wires for your new electric outlets and lights for the wall. Putting the wires in the hollow space behind the 2x4 studs is one way. I’ll show you another in a little while. If there are other items, perhaps speaker or telephone wires or central vacuum system piping you want to put in, now is the time. Or not. Read on to see why.
Attach the new wall studs to the old wall with blocks or other connectors for extra strength and stiffness. See the drawing. One connector on each stud about midway up the wall is plenty.
Fill the cavities between the wall studs with R19 fiberglass insulation. Paper backed or plain bats work fine. Stuff extra strips in the spaces behind the 2x4” wall studs for a little more insulation value.
Staple a 6-mil polyurethane vapor barrier over the studs and plates. From this point on, try to prevent any damage to this vapor barrier. Seal any rips or tears. It does not take much of a hole to allow water vapor to pass through the barrier and that would diminish efficiency.
Install 1x3 or 1x4 strapping, also known as furring strips, horizontally across the
wall on 16” centerlines with a 1x6 or wider strip where the drywall seams will be. See the drawing.