I'm looking to install some vinyl siding while also beefing up the insulation value coming at it from the exterior of my home. I live in Minnesota (Climate zone 6), have only about an inch of Batt insulation within my wall cavities currently and am looking for a lower cost way to add some R's. The drill and fill method seems that it will help out. The plan is to drill 3 in holes near the top and bottom of the wall cavities and blow in some cellulose. I would have to drill out the plugs, then cut through the inch of batt insulation just to be able to get the blower hose inside. I would then remove the rest of the old siding and tar paper and then put up the house wrap and new vinyl. Any thoughts on the drill and fill method? I'm aware that adding two inches of foam would be more ideal but it then opens up a whole new can of worms with having to adjust all the windows and doors the two inches as well.

I don't see drill and fill being as effective if there is already something in the cavities as that something can block the flow and distribution of the blown in insulation...

Dense packing cellulose over 1" batts is dead-easy compared to dense-packing over R11s. By inserting the hose to the end of the cavity and blowing under pressure it nearly air-seals the cavity by driving fiber into any air leak points. This is a pretty standard retrofit.

Simply inserting a ~2" hose barely into the cavity isn't likely to work very well, since you won't necessarily detect & correct obstructions, and you probably won't have sufficient density to eliminate settling over time. It's possible to do a DIY dense pack job with a 1-stage rental blower, but you'll have to fabricate your own dense packing tube and read up on how to do it. You'll want at least 3lbs per cubic foot average density- 3.5lbs would be even better in your climate, but not always possible for an amateur using a single stage blower (speaking as an amateur who managed only 3.2-3.3 lbs density in 2x4 walls with an old single stage blower.)

I did find a Force One insulation blower with a 2 1/2 in diameter hose at a local rental place. I'm assuming it's a one stage blower with more power than the freebie at Home Depot. Hopefully with the 3 in holes I would have enough room to maneuver the hose all the way up or down the cavities assuming it's a flexible hose. Otherwise will have to fabricate by trying to find an 8 ft flexible fill tube somewhere and duck taping it together. Any thoughts on leaving the existing tar paper on vs removing that and applying housewrap before I re-side?

I've seen Force-1 as a box store freebie, and you should have no problem hitting 3lbs density with it if you fab up a dense packing hose.

Don't even try to snake a 2-2.5" flex hose all the way to the end of the cavity- it's too floppy, and at 2.5" o.d. it's going to hang up on the batts and every picture hanging nail etc poking into the cavity. What you want is 8-10' of 1" i.d. plastic hose cut to a 45 degree angle at the end and a cone reducer for the transition between the hoses. If you can do it with metals it's better than with PVC plumbing fittings- the latter end up creating a large static electrical charge from the friction of the cellulose flowing by.

It's fine to just leave asphalted paper WRBs in place- they are "smart" vapor retarders, that become vapor open if the sheathing is damp enough to support mold growth.

Find yourself some online videos demonstrating dense packing techniques to figure out the details. I've explained it in written form multiple times in the past handful of years on this site in various threads, but a video is worth 1000 blog posts. A single 2.25-2.5" hole per stud bay will do.

A couple of typical online demos:

https://www.youtube.com/watch?v=3WvJbG-YXmU

https://www.youtube.com/watch?v=eqJtfTkwogo

Dana's right. I used this technique for years. I started with a couple of common plumbing parts. A 2" o.d. hose reducer then a screw in metal to plastic hose coupling.Standard hardware store parts. If you have to go up to 2.5 inch i.d. hose just use duct tape to increase the diameter of the fitting. Or you can skip all that crap and go to JR Products and order what you need. Make sure you start with the material feed almost shut if the machine has one. If not it won't work. You'll end up with a mess. The one thing that you should check since you have some insulation in the walls is the era that the house was built. Back in the 50's to 60's 3/8" sheet rock was common . This was installed with smooth shank blue nails. If this is your setup you are sure to pop the walls.

I'll start looking to fab a hose reducer to go from 3 in to 1 in. I did find a 10 ft hose with a 1 in diameter from Jr. Products that will work great. My home was built in '65 and I guess I just assumed it was plywood underneath so thanks for the heads up. So what exactly happens when you use a whole saw on sheet rock? I've seen a few vids on drill n fill done from the interior but I just noticed it was messy more than anything.

Hole saws work fine on sheet rock. Save the plugs (if you can) for the patch. But you can assess the depth just fine with a 1/4" hole that you can just mud over.

The issue with 3/8" interior sheet rock and smooth nails is that it can be easily blown out with a 2- stage blower. That's less likely with a Force-1, but never say never. You'll know after you've packed a few test cavities where it's less of a disaster if it comes apart.

The exterior sheathing of that vintage is most likely to be plywood or 1x ship-lap applied at an angle for better racking resistance. There's an outside chance that it's 3/4" asphalted fiberboard, which was popular in some areas, more common in the southern US than the upper midwest, but common enough everywhere under brick veneer siding. Any of those sheathings are just fine for dense-packing as long as they're still on pretty good shape, not rotting or chewed up by insects, etc.

The blower I can get from Home Depot is a Green Fiber one. I'm not sure the stage, is anyone familiar with the power on that for dense packing?

I am familiar with the Green fiber machine although they have a number of different types. You need one that allows you to close the material slide. If it's the type with no material slide it won't work. You can check your sheet rock thickness by taking off a switch plate or outlet cover on an exterior wall. Under no circumstances would I install insulation from the interior unless I wanted to spend an inordinate amount of time cleaning. Do it from the outside.
I cut 2 1.5" overlapping holes creating a figure 8. This allows you to slide the hose in the wall without eating cellulose. You want to maintain the integrity of the batt insulation as much as possible. If you destroy the batt putting the hose in the wall it will ball up in spots and you won't get a well packed cavity. Open up a bunch of cavities. If you see the insulation come out of the stud space next to one you're filling then the sheet rock is being pushed out. Once the celly is between the stud and the sheetrock you've got a bump or worst. I've had jobs that just the action of installing the hose in the wall pushed the sheet rock away from the stud. If this happens create a brace out of a piece of osb with 2 2x3 attached to keep it flat. 4 screws thru the osb into the interior studs should hold it. Install the insulation and move the brace as you go. Cut the brace down for smaller areas after you have done all the big walls.

Ive been trying to read up on how to fab up the connection between the blower house and vinyl house but haven't found out a whole lot. I think I'm going to rent the force one blower with the 2.5 in d house to keep the sizes between the two hoses as close as possible. I also found a 1 1/4 in outer diameter 1 in inner diameter vinyl hose at 10 ft length and a 2 1/2 in to 1 1/4 in plastic hose reducer. I guess I can just use duct tape or hose clamps to make the connections although it sounds like I may need to disconnect them at times to clear jams. I've got the 2 1/2 in hole saw so I can start drilling as soon as the weather warms up.

Usually you want a 15' transition hose that is 2". If you go from 2.5 to 1 in a short distance you will probably get a lot of clogs. You want to use hose clamps near the reducers for clog removal.

I have now found a Force 1 blower with a 2.5 in d hose and a 1.5 in d attachment for dense packing. The blower also has a slide gate so as long as I can shove the 1.5 in hose up the cavity this setup should work slick. I checked and my interior sheetrock is only 3/8 in so I'm a little worried. I'll test a cavity in a less noticeable area and look for signs of blowout I guess.

I started drilling some holes in the exterior and I realized a few things: The sheathing is fiberboard, there is a firewall in the cavities about 18 inches up from the bottom, and unfortunately the existing batt fiberglass insulation varies in depth between an inch and 3 inches. I'm thinking that I should just leave the areas that have 3 inches of batt alone. Would you guys agree with this? Always appreciated!

I'd replace the worst areas anyway. Will you be installing additional exterior insulation? If not, you probably want the wall to be as well insulated as possible -meaning full depth and no voids. The other issue is that the wall MUST be air sealed before covering it with siding - this may make a bigger difference than your fiberglass. The best way to do this is to buy a high quality tape such as SIGA Wigluv or 3M 8067 and tape every joint in the sheathing. Covering with a building wrap will work IF the fabric is are sealed and taped at all joints + top, bottom & sides.

I don't plan on installing any foam or other exterior insulation as then I'd have to also replace or bring out the windows and doors etc. to match depth. The tar paper still looks good so I was thinking of just leaving that on and putting the siding over it after I replace the drill holes.

Please check out MicroVent under vinyl siding insulation at http://barrett-inc.com/microvent.php

OK, checked it out, and not favorably impressed. The performance ratings of MicroVent are taking credit for the thermal performance of the sheathing and air films too, a common marketing sleight of hand in the radiant barrier world.

In MN with a dense packed wall, forget about it. You'd be better off adding perforated 3/8" fan-fold XPS siding underlayment (which might actually be "worth it".)

The drill-and-fill process is an innovative and effective installation where existing walls (interior or exterior) require insulation upgrading. Simply put, small holes are strategically drilled into the wall, between the wall studs. Loose fill insulation is then carefully blown into the empty wall cavities. On completion, the holes are patched and the wall finished.

For homeowners who are experiencing excessively high heating or cooling costs, the drill and fill upgrade is an ideal option. For those who have uneven heating and cooling throughout the home, this is also a good reason to upgrade insulation. One of the benefits of drill-and-fill is that it can be installed from the interior walls of the home or the exterior walls. Completing the installation via the exterior walls can be very advantageous, especially where interior access isn’t possible. And for some homeowners, this could be the ultimate insulation – description with upgraded R-Values that deliver substantial energy savings throughout the seasons.