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Making an old house super efficient

I'm in the process of deciding whether to take a mortgage, and build a new home on a piece of land I have been offered...or fix up an older home, built in 1942. Completely strip it and gradually work on it.

The questions I have are mainly methods to effectively make the old house energy efficient and air tight. I've read a lot about 2x6 framing, double stud walls, and separate exterior walls. I'm wondering what would be an effective method, after stripping lath and plaster from an exterior wall...ripping 2x6 and nailing them on the old 2x4, or framing a new wall, and slapping it up next to the old wall, possibly insulating the exterior wall, covering it with a rigid foam, then adding the new 2x4 wall, and insulating it? Should I try to draw a picture to explain?

In addition to the walls, there is preexisting insulation in the attic. I was wondering about adding rigid foam to the ceiling, either a.) tearing out the plaster and leaving the lath (so old insulation doesn't come out) and nailing up rigid foam, then sheetrock. b.)leaving the lath and plaster, nailing foam and sheetrock over that. c.) tearing it all out, including old insulation, then foaming, then sheetrock.

Thanks for any comments / suggestions!

Edit :
Climate Zone 5 (Nebraska)
Yes, there is a basement, no insulation, and some settled walls that cracked many, many years ago.
Windows are the old style, single pane, weighted sash sliders.

Asked by Nicholas C
Posted Dec 2, 2012 10:16 PM ET
Edited Dec 3, 2012 8:56 AM ET


18 Answers

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What climate zone is this in? Is there a basement or crawl space? What's the existing heating system, and what are the windows?

Answered by David Meiland
Posted Dec 3, 2012 2:34 AM ET


Hey David, I updated some info from your request.

Answered by Nicholas C
Posted Dec 3, 2012 3:51 AM ET


In general, the best way to insulate the walls of an existing house is from the exterior. Assuming that you are willing and able to remove the existing siding, you can install several layers of rigid foam (or perhaps rigid mineral wool) on the exterior of the wall sheathing. Then you add vertical furring strips and new siding.

This will always result in a better job of insulation that working from the interior.

When it comes to the attic, you have too choices: add lots of cellulose to the attic floor, or create a conditioned sealed attic by adding a thick layer of rigid foam on top of the existing roof sheathing (followed by new roofing).

A third possibility is to work from the interior, as your propose -- gutting the walls. If you go that route, you'll probably end up using spray polyurethane foam. Otherwise, your results are likely to be disappointing.

A final thought: fixing up an older house often costs more than building a new house.

Answered by Martin Holladay
Posted Dec 3, 2012 6:30 AM ET


I was wondering why it would be better to insulate with rigid foam on the outside? Afterall, after one layer, that extends 2" out, then adding strips to put siding on, that seems like it would have a large over hang from the foundation, and not be secure to the studs of the framing.

I would add extra cellulose to the attic, but I was wondering if the old insulation needs to go (not sure what kind it is, but it's old) and if I add lots of new cellulose to the attic, would installing rigid foam on the interior ceiling before sheet rock offer more efficiency?

Answered by Nicholas C
Posted Dec 3, 2012 3:25 PM ET


Q. "Why it would be better to insulate with rigid foam on the outside?"

A. Because (unlike interior approaches to wall insulation) a continuous layer of exterior insulation slows down the heat that escapes through rim joist areas, partition intersections, and thermal bridges (studs and other framing members).

Q. "I was wondering if the old [attic] insulation needs to go?"

A. Usually not, unless it is filthy from rodent droppings or otherwise too smelly to save.

Q. "Would installing rigid foam on the interior ceiling before sheetrock offer more efficiency?"

A. As long as you have enough room in your attic for deep insulation, you'll get more R-value per dollar invested with cellulose on the attic floor than with rigid foam on your ceiling.

Answered by Martin Holladay
Posted Dec 3, 2012 3:42 PM ET
Edited Dec 3, 2012 3:43 PM ET.


Martin, what sort of rigid foam would you suggest using, and how many layers of this suggested foam? I assume the foam gets applied over the entire wall, and not just the height, stopping at the attic level? (I can see how that would benefit the area where internal insulation stops at the top plate).

Assuming I went with this method, would it be wise to find a form of spray foam and apply about two inches between the studs, then followed through with fiberglass batts/cellulose after installing new wire? I plan on extending the interior wall studs with ripped 2x4 or some similar method that would benefit. Possibly installing another whole interior wall.

Thanks for the suggestions so far! Hopefully I can be able to heat this place with a few heat lamps when I finish all of the remodeling. (okay, maybe not THAT efficient, but you folks get the idea. =) )

Answered by Nicholas C
Posted Dec 3, 2012 5:12 PM ET


Here's an article which will answer your question about what type of rigid foam to use -- as well as many other questions: How to Install Rigid Foam Sheathing.

Here's an article with information on your proposed method of wall insulation (flash and batt): Why Flash and Batt Makes Sense. In spite of the article's title, note that not everyone agrees that this method of insulation makes sense. If you install exterior rigid foam, it doesn't make any sense to choose the flash-and-batt method.

Answered by Martin Holladay
Posted Dec 3, 2012 5:26 PM ET
Edited Dec 3, 2012 5:33 PM ET.


Ah, thanks for the links. That brings up an important factor as far as vapor barriers inside. I like the idea of poly film before drywall to seal off any air leaks. I assume a properly foamed exterior is equivalent....and the walls need to breathe.

The other day when I fastened an attic vent that had came off, I noticed what looked like some sort of foam or cloth material...wish I knew what it was for certain. I believe the siding has been replaced since '42 and the homeowners but some insulation on the exterior. This would mean I probably should not install any poly on my interior walls after insulation and wiring, eh? And in that case...I would need to get the siding torn off and the old insulation method, and THEN install new foam and new siding. I had hoped to not do this until further down the road. Such as five years, assuming I was placing poly film inside my walls now. Thoughts? Suggestions? I didn't want to tamper with the exterior until finished inside and fully decided I want to live in the house. If it is truly suggested that rigid foam is better than spray foam and batts inside, then I probably should not install and vapor barriers before my drywall.

Answered by Nicholas C
Posted Dec 3, 2012 6:45 PM ET


I would caution you against thinking of poly sheeting as an air barrier. If you really want to air-seal right, you need a blower door (or a good imitation thereof) so that you can find and solve leaks with a pressure differential inside vs. outside. It will be very hard to make poly work, a lot easier to use caulk, aerosol foam, drywall, rigid insulation, plywood, etc.

Answered by David Meiland
Posted Dec 4, 2012 12:50 AM ET
Edited Dec 4, 2012 12:51 AM ET.


Right, I understand that part. But it is suggested that I do not use any poly if I use rigid foam on the exterior, correct?

Answered by Nicholas C
Posted Dec 4, 2012 1:04 AM ET


No matter what type of insulation you use, you shouldn't install interior poly. To understand why, read these two articles:

Vapor Retarders and Vapor Barriers

Forget Vapor Diffusion — Stop the Air Leaks!

If you are worried about the integrity of your interior air barrier, you shouldn't depend on polyethylene. You should be using the Airtight Drywall Approach: Airtight Drywall.

Answered by Martin Holladay
Posted Dec 4, 2012 7:56 AM ET


I don't understand why you believe you need to tear out the lath and plaster. It takes a lot of energy that could be used else where to remove and creates a lot of waste unless you downcycle it into your soil or some other use.

Answered by bruce john stracke
Posted Dec 4, 2012 11:59 PM ET


Hey Bruce, I believe I need to tear it out to remove the knob and tube wiring, replace it with 12-2 and 14-3 romex, I want to also address any termite damage that may have gone to the walls and not just the hardwood floors. I want to properly insulate the exterior walls, and not just poke it in holes or spray in fiberglass. I'm debating between insulation types and if I want to do a spray foam then I need the walls opened up.

Answered by Nicholas C
Posted Dec 5, 2012 11:22 AM ET


You don't usually need to do a full-gut to rip out k & t tubing and put up something else. Judicious rips in the right locations on the plaster & lath, &/or pulling some plank sheathing from the exterior will usually get you there. Termite damage would usually be inspectable from the exterior, if you're stripping it down to the sheathing.

Gutting would only be called for if the plaster & lath is a total wreck to the point that the nails are all rusting through and it wouldn't withstand the pressure of dense-packing cellulose in there. In genera plaster & lath (even funky horsehair plaster) is a FAR more robust interior wall than gypsum board. Ripping it out to replace it with half-inch gypsum would be a step down in structural integrity.

Spray foam can be somewhat tighter than dense-packed fiber, but it isn't an air-sealing & moisture control panacea by any means:


Note that the cellulose wall (wall #4) in that blog article was damp-sprayed ~2lb-2.5lbs density goods, and dense packing to 3+ lbs would cut the air leakage through the insulation by half or more. Detailing the sheathing, housewrap & exterior foam as air-barriers is still the right approach to infiltration, not foaming the wall cavities.

Closed cell spray foam is a greenhouse gas disaster at anything like full cavity fill depths, since the HFC blowing agents have >1000x the greenhouse potential of CO2. Open cell foam (and EPS and iso, but not XPS) are better, but none come close to being as benign as cellulose, and none have the termite mitigating aspects of the borate fire retardents used in cellulose.

The thermal bridging of the framing also makes the differences between R6/inch closed cell foam and R3.5/inch cellulose almost negligible, a difference of less than R2 on whole-wall performance. Put the cheap stuff in the wall cavities, and save the foam budget for the exterior where you reap pretty much the full-R on the foam layer.

Answered by Dana Dorsett
Posted Dec 5, 2012 3:55 PM ET


I understand that it is not necessary if the plaster is in good shape. I don't want to have to go through extra work to run wire and outlets. I do have to remove quite a bit to run wire to new outlets because most rooms only have one outlet on one wall, that's far from code. I understand that lath and plaster or plasterboard is better integrity, but most walls were paneled, and this means there is plenty of nails or glue that has destroyed the plaster. To properly use cellulose I need to clear the walls from their old insulation, and really removing the plaster will be the most effective way.

Answered by Nicholas C
Posted Dec 5, 2012 4:17 PM ET


I've seen it all done from the exterior, and it's not nearly as bad as you might think. I've even seen open-cell foam guys who were pretty adept at yanking batts out of a slot created by pulling a 1-2 clapboards and insulating the cavities with well-aimed and well-timed short-shots rather than ripping open a wall.

Gutting and fully re-finishing the interior also qualifies as " ...extra work..." too. But it's your project, your budget, your time, and every project has it's own quirks that make some methods more difficult than others.

Answered by Dana Dorsett
Posted Dec 6, 2012 4:02 PM ET


Ripping off the old exterior wood would be possible, I wonder if it's like the old sub floor, 1x12's or such instead of 4x8 sheets of plywood. If it were plywood I think it would be easier to rip off, and re-use and replace...if something else, likely more work. Unknown state at the moment, but blowing in cellulose would be interesting from the outside.

Answered by Nicholas C
Posted Dec 6, 2012 4:08 PM ET


Just figured I would post back here with an update. Basically not enough money or credit score to qualify for a home build mortgage, so it is going to be remodel the old 1940 home.

I've done more reading the past two months. I don't think I want to rip out the lath and plaster to insulate and install new wiring. Thinking about installing outlets along a 8" floorboard possibly, or moving them up into the wall if desired.

The siding is either aluminum or steel. Repainted 6 years ago and the sunny side is sure flaking bad. Possibly from bad priming method. I was wondering what you do about the attic sides? It doesn't make much sense to buy more XPS foam to go up the walls past living space (roughly 7-8'). Would it be best to fir out the gap for siding? The articles on here are for new builds, not retrofitting old construction.

Answered by Nicholas C
Posted Jan 30, 2013 8:05 PM ET

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