I get asked a lot about insulating old houses, especially in the wintertime. It makes sense. People fall in love with the character rich architecture of these homes, but they don’t want the crazy heating and cooling bills that come along with that character.
Chances are good that if your house was built before the 1960’s there is little to no insulation. Before the energy crisis of the 1970’s energy was abundant and cheap in America and it was cheaper to heat your old house than it was to insulate it. Today, things have changed and to save yourself lots of money it’s a good idea to learn how to insulate an old house without destroying it.
Before you start, check out the EnergyStar website to see what the recommended levels of insulation are for your climate zone.
You have lots of options as far as materials you can use and I won’t go into too much detail about those here. You can read all about the differences, performance, and pricing in my earlier post All About Insulation. For the purpose of this post I’m going to be speaking about blown in cellulose and batts since they are the easiest to retrofit into an old house, but just know that you do have other options.
Insulating the Attic
Before you do anything else this is where you should begin insulating, especially if you live in the hot southern states. The majority of heat loss and gain occurs in your attic.
The attic is often the easiest place to add insulation. If you have an unfinished and unconditioned attic like many old houses my first recommendation would be to add batt insulation on the underside of the roof.
Measure the size of the roof rafters. Are they 2×6, 2×8 or bigger? The bigger they are the thicker the insulation you can fit. You’ll also need to determine the spacing of the rafters. Are they 16″ O.C. (on-center) or 24″? Sometimes they aren’t evenly spaced which means more work trimming your batts to size.
Here’s a quick tutorial on How to install batt insulation.
Once you’ve insulated the the underside of your roof it makes sense to beef up the insulation even more by blowing in cellulose insulation on the floor of the attic. This will help to keep the living spaces below more comfortable year round. You can rent an insulation hopper from most big box stores to blow in your own insulation with little difficulty.
The trick for blown-in insulation (and any insulation for that matter) is to fill as much as you can without compacting it. Insulation looses its insulating abilities the more it is compacted. It should be installed light and fluffy to work best.
Tip: Be careful not to block any soffit vents with insulation if they are present in your attic.
Insulating the Walls
“How can I insulate the walls of my old house without tearing down the plaster walls?” This is by far the biggest insulating dilemma faced by historic home owners. Can it be done? YES! You don’t have to tear down your plaster walls to insulate them. I’ll show you how.
The best way is to remove a course of siding or a few shingles from your home’s exterior. If you have a masonry exterior then sadly this won’t work for you.
Step #1 Remove & Mark
Remove two courses of siding from the wall. The first about a quarter of the way up the wall and the second just below where your ceiling is. If your house is more than 1-story you’ll have to do this for each story. Many old houses have diagonal sheathing underneath the siding. Some don’t but either will be fine. You want to find a wall stud. The siding should have been nailed through the sheathing and into the studs so use the location of the original nails as a guide. Mark the center between two studs. You want to be right in the middle of the stud bay.
Step #2 Drill an Access Hole
Using a spade bit drill a hole in the sheathing big enough to fit the hose nozzle on the insulation hopper (usually 1 1/2″). Stick a coat hanger in the hole and poke around to see if you are in the right place and adjust accordingly. Once you are certain you’re in the middle of the empty stud bay you can measure 16″ to each side of the hole all the way across the wall which should give you the center of each consecutive bay. You’ll need to drill two holes in each of these stud bays, one on the top and one on the bottom course of siding.
Step #3 Fill with Insulation
Fill the hopper with insulation, turn it on and start filling the lower hole with insulation. Once the hole is filled enough the machine will start to whine indicating that that portion of the wall is full. Pull the nozzle out of the hole and repeat the process on the top hole.
Step #4 Patch Up
Once you have filled all the bays with insulation we want to cover up the holes. I prefer to cover the hole with a small patch of adhesive backed flashing tape (aff. link). When the holes are covered nail your siding back into place and you’re done!
Occasionally you’ll run into blocking between the stud bays which will block off the flow of the insulation. It can be difficult to tell where and when this blocking is installed. If you have access to an inspection camera with a light to see into holes that’s the easiest way to determine where they are. It may require removing a few additional courses of siding to access these areas, but you’ll have to determine that as you go.
Insulating the Floors
If you have a basement or crawl space the best way to insulate the floors of the living space above is much the same as the attic, by installing batts into the stud bays of floor joists. It will be a slow process in tight crawl spaces, but once it’s finished you won’t have to do it again and your floors will be much more comfortable year round.
The one tip I’ll give you is that if you are insulating in a crawlspace make sure you have rodent proofing wire screens installed around any opening to the crawlspace. If you have critters able to access your crawl space they can make a mess of your newly installed insulation over the years. Rodent proof the crawlspace first then go about installing the insulation.
I really hope those tips help you to get the job done quickly and easily. You don’t need to go throughout expense and mess of tearing down all your walls just to insulate. That is one of the 5 worst mistakes of historic home owners, but with the information in this post I know you’ll be smart enough to avoid it.