Most bang for buck approach to insulating home

Question

My home is a bit over 100 years old, wood frame aluminum siding house, that was not very well kept up by the previous (30+ year) owner. We've lived in it for two years, and are looking to improve the insulation in the home both to reduce heating costs and reduce in-home variation of temperature.

We have three bedrooms on the second floor and living space on the first floor. Modern windows (2-pane). We're in the upper midwest, so very cold for 4 months or so. 2 story, single family home. Brand new very high efficiency furnace with ductwork that goes up the middle of the house to the attic and back down into the bedrooms, and two-zone (each floor separately) controls.

Last winter we rolled one layer of fiberglass insulation in the attic (it prior had blown-in junk that was basically useless), and that seemed to improve things some, but it's still quite cold in much of the house even when the thermostat thinks it's 70. The walls are definitely cold, so we assume there is little to no insulation between the aluminum siding and the (mostly) plaster walls, and the couple of times we've had to dig into the plaster (for wiring) we haven't seen any evidence of any sort of insulation.

What is the next low-hanging fruit in terms of providing the most bang for the buck? We've considered foam in the walls, but that seems very expensive for the R-values we would get. We could just insulate the second floor walls, but we're unsure if the cold first floor would make it too ineffective. We're also not sure if we could realistically foam the whole floor without doing a huge amount of re-drywalling/re-plastering. Would it be easier/cheaper to go at it from the siding side instead (and would that work)?

Answer 1

I am from the Midwest and my crew and I have done green work in a number of historical home in the area. Some of my thoughts on your situation:

1. Don't ever put stuff in your walls through holes. I don't care what kind of sales pitch you are given, don't. My standard reaction would be, "How do you prove your installation, what r-value are you giving me, I will pay you in full once I hirer an independent auditor and they OK your job". You will never hear from that company again. There are too many issues for me to discuss but basically you could be putting something dangerous in your home, the chances of them filling the entire cavities are none, and whatever they use will surely get in the way if you ever remodel anything else.

2. If you have a basement you need to stop airflow coming into it. Caulk any gaps that are above ground. Rock wool all of the exterior joist cavities. Foam board is an option but this isn't generally high reward (you will lose cooling in summer and not much cold is let in below grade).

3. You have basically two options for your walls. #1 You remove siding and you just have some housewrap... So you are adding traditional insulation from the outside, rewrap, reside. Very low materials cost - would be a 2-3 day job for a crew. #2 You have a little extra under your siding, so getting in is harder. 3-4" XPS, tape, furring strips, reside. I have insulated the exterior of 5 homes so far. We stucco'ed after but you could put traditional siding on too. This is like putting a blanket on your home and is dramatic. To go with that - future buyers of your home will pay a premium vs. treating drilled insulation as nothing (or a problem).

4. New windows. These would be installed before exterior work if doing this in chronological order. Given that during window install that you take care of any air leaks by the windows.

5. Make sure there aren't major drafts in attic. Then you need to bury your attic in blown in cellulose at 2-3 feet deep.

I would start in your basement. From there it comes down to - how bad is this problem? If the cold is as noticeable as you say then you really need to get the walls insulated. I gave you two options that work. The first is much cheaper but not as effective (and maybe not doable on all houses). 2 & 5 can be done by you for $600-800. 3 is somewhere between 3-20K but is a complete game changer for your home (plus new look). 4 depends on how many windows but you can put decent windows in most homes for 3-4k.

Answer 2

You're on the right track with sprayed foam in the walls, but you're right that it's very expensive. It's also highly flammable and makes a small number of people terribly ill, rendering their homes uninhabitable. A better alternative: dense-packed cellulose blown into the empty cavities. It'll be a lot cheaper, less risky, and you should notice the impact immediately. Doing this won't disturb the interior plaster, and the crew doing the work can remove a layer of siding on the outside, drill holes, blow in the cellulose, and replace the siding, easy as pie.

More attic insulation is another very good idea. However, it's highly likely that your attic floor is very air leaky, which is a major source of heat loss. Unfortunately the best time to rectify that was when you removed all the old insulation, exposing the bare floor. If you can stand it, you could temporarily remove the batt insulation you added and apply caulk or spray foam to all the typical leak areas; here's a good overview: https://www.energystar.gov/index.cfm?c=diy.diy_sealing_attic. Then you would replace the batts, and then hopefully cover them with even more insulation of some sort. In the upper midwest, those brutal winters are trying to suck all the heat out of your house, which is trying to rise due to the stack effect. Heavy attic floor insulation, especially the cheap stuff (more blown cellulose or fiberglass) will do nicely and not bust your budget.

Finally, you probably have a full basement whose walls are in direct contact with the cold ground, making your basement really chilly in the winter. You can insulate the walls with rigid foam boards, taking care to completely air-seal the boards using tape, caulk, and spray foam (this is to prevent moisture-bearing air from being able to touch the cold walls and condense there). Then you would put up drywall over the foam, or even frame out the walls with 2x4s, additional insulation, and drywall.

Answer 3

Have you considered having a home energy audit?

Since all homes are slightly different, an energy audit would point out where your house is losing the most energy. Once you know where you're losing energy, you can address those areas first. Without knowing where you're losing energy, you're just stabbing in the dark.