We have an old house and the energy auditor was selling us hard on attic air sealing and insulation. Claim was that windows weren’t gonna make as big of an impact given the stack effect. (They’re also historic “wavy glass” windows, and we’d like to keep them.)

Do you think attic air sealing, or more effective attic insulation would have a big impact? It does feel like the roof turns into a radiant heater in the summer.

(The only energy auditor available in the area is also in the business of providing the insulation, which is why I’m skeptical.)

It'll help. Ask for some customer references, maybe someone with a similar house. But it could also cause other problems. Older houses are naturally leaky and that helps keep them manage mold/mildew and radon. Your water heater and furnace could also backdraft. So that's something to consider. Modern houses are basically sealed inside a plastic bag so you need active mechanical ventilation to keep things in order.

If you have a really old house make sure you don't have vermiculite insulation which might make things way more expensive cause it likely has asbestos in it. Apart from that you can also DIY it but it's messy. Your state may offer incentives for doing it too.

https://www.energystar.gov/campaign/seal_insulate/attic_air_...

I'm not an expert but based on my personal research adding a ridge vent to the roof and getting a convection current drawing fresh air from the soffits through the attic and out the ridge supposedly makes a big difference. When you've got it all sealed up you've got a solar oven.

You'll still want insulation on the floor of the attic space, and seal off the living space from the attic.

From what I gather the main complication is keeping critters out while opening your attic to a substantial flow of fresh air. A pile of rockwool insulation sounds like a hell of a home for many small mammals, and bees can get past all but the finest of screen meshes. It seems feasible to diligently install screens on all the vents but it'll be a maintenance burden to keep them intact as the years go by.

I don't know much about this, but anecdotal info: my apartment (comparable to a 1-floor bungalow with lots of windows) has argon-filled windows, and it cost me around USD$1600 for the window themselves (I didn't change the frames, but my old windows were cheap/scrap).

I heat to 18oC in winter (Montreal) and AC to 24oC in summer. My electricity bill averages USD$40 per month. The windows made a nice difference, and still seem efficient after 10 years.