I have had good results with foam injected into the stud spaces from the exterior. Holes are drilled in the outside surfaces, the foam in injected into the wall, and the holes are plugged. Depending on the kind of siding, the holes can be well concealed. Sometimes, concealing the holes can be a pretty involved process. Still, this method involves no interior work (or repair) and can usually be completed in a shorter time than any other method. This method works with partially insulated walls and non-insulated walls. The R-Value of the foam is far better than any other alternative.
There are basically two ways to do it, from the interior or the exterior. Either way you will have to drill about 1"-2" holes for the new insulation material to be pumped in. We recommend cellulose or fiberglass depending on how much R-Value you require. The best time to do the work is if you ever do any interior/exterior remodeling that involves the tear off of drywall or exterior stucco/siding to the studs. Once you have the wall opened up your options expand to spray in foam or a tried and true fiberglass batt.
We did a remodel several years back in which the exterior walls were not insulated. The homeowner decided to have insulation blown into all of the stud spaces. They did this from the inside of the house and knocked two holes in each stud space, one high and one low.
About a year later we opened up one of the walls that was insulated ( by the insulation contractor) to find that the coverage was less that 40%. I would not trust this method to provide proper insulation.
Foam blown in from holes drilled between studs at top of wall from either inside or out. I prefer to do it from the inside as I find it much easier to patch and blend the holes after insulation is applied. Can be done from exterior easily too, but the holes tend to remain visible even after plugging and painting. That will dramatically increase your ‘R-value’ and help lower your utility bills.
Cavity blown cellulose when installed at 3.5lbs / sf density is a very cost effective means of insualting and air sealing. The wall needs to be packed, not filled with fluff that will settle. The foams are great too, but at a higher price point.
Anything blown into the walls must be done with thought. Obstructions can impede proper installation. The only way I know of checking is with an infared camera. Not to excuse a less than perfect job, but a 98% job is far superior than not.
Take any residing as an opportunity to increase r values. Rigid foamsapplied to the exterior of the buildings are great. They help seal the building and provide a thermal brake between warm wood and the cold air. I’ll skip the long lesson, but if interested, research how it transfers the dew point as well. This assists with moisture problems in the walls.
Check with State, Federal and utility credits. Dsireusa.org
The best way to insulate your existing exterior wall is spray foam. spray foam spreads consistent and you will get the R value that you are looking for. Another reason is that when you spray foam there is no demolition required your repairs are very minimal
