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Comment by jabart | Hacker News Reader

Things switched from insulating the wall cavity to insulating the outside of the house. Engineers started to factor in the insulation value of a 2x6 compared to the insulation it was next to and the heat loss in cold climates. Same applies for hot climates. Now these homes are being wrapped in insulation on the outside with all joints sealed, then insulated on the inside and essentially pressure tested for air leaks. The houses can be "tight" enough that you have to have a system to cycle in fresh air in a way that it heats/cools it with the air that is leaving. You also need a makeup air vent for things like a stove hood.

There is a new system that before drywall goes up, they pressurize the house and spray a caulk in the air that finds its way to all the pinhole leaks and seals them to further reduce air leaks during the building process.

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> You have to have a system to cycle in fresh air in a way that it heats/cools it with the air that is leaving.

This is quite nice regardless. Houses are unlikely to be so drafty that the air inside is always fresh, and a real ventilation system will deliver fresh, filtered air all the time.

> You also need a makeup air vent for things like a stove hood.

You need this anyway, at least in CA, if your hood exceeds 400cfm, and it’s probably a good idea regardless. Sadly, high end hoods seem to mostly have way too much airflow, and decent makeup air systems are rare and complex.

Heat exchangers are a big one, but they are not yet that common in the US. They are used to pre-heat the makeup air. I'm looking into one atm as part of a HVAC upgrade as currently running a bath fan with all the windows closed will draw air down the chimney.

Heat exchangers have been code for more than 20 years. Maybe not common, but only because there are a lot of old houses. Or maybe where you live didn't adopt the new code?

I have a house that's less than 20 and it doesn't have a heat exchanger. I haven't heard of the new construction around here having any. Perhaps it's only in certain states?

I'm most familiar with Minnesota of 20 years ago, which being a cold area does tend to adopt cold weather codes quicker than others.

How will I get to experience opening up a wall in the house I have lived in for a decade to find McDonalds trash stuck in the wall instead of insulation?

> Things switched from insulating the wall cavity to insulating the outside of the house.

Oh good they finally figured that out. Cause that's where you want the stuff. And insulating a bunch cavities is labor intensive.

I’m not at all convinced that exterior insulation would have lower labor cost. You have to competently install sheets of rigid insulation, and then you need to competently install siding over it.

Insulating cavities needs some skilled labor if you use mineral wool, but a skilled installer goes fast. Or you can use some kind of blown in product, which takes very little labor. (I have never seen competently installed fiberglass batts. I’m not sure they really exist.)

Insulting cavities well is immensely labor intensive and unfortunately is still required in homes with exterior insulation so you're kind of getting the worst of both worlds. Exterior insulation is an absolute breeze in comparison though, there are tons of product on the market that integrate the sheathing and insulation into a single unit so it installs just like any other exterior sheathing would.

I watched a crew install a blown fiberglass product: they stapled fabric over the walls, poked holes in it, and stuck a hose in each hole so a machine in their truck could flow fiberglass into the cavity. It went very quickly and fully filled the cavities.

John Mansville Spider Plus looks like another interesting product — blown fiberglass that is just sticky enough that it can supposedly be applied to walls and even ceilings without anything to contain it.

Exterior typically requires sheathing and insulation is attached to that sheathing. Extra work is required to tape up the seams though it eliminates the plastic house wrap required in most areas in the US which is attached with staples or a nail gun.

I understand you can just check the pressure during a blower test to see if there are leaks, but how do they actually identify where the leaks are? Go around all over the house with a smoke gun?

If there's a good thermal difference between interior temperature and exterior temperature, a thermal imager will help catch an awful lot of the leaks.

Largely yes. You don't need to survey every inch though since leaks aren't present in the middle of walls, but typically at complex areas (around windows, roof penetrations, can lights, outlets, rim joists, etc) so a little smoke quickly IDs those issue areas. Another way way to find leaks is to run the blower door tests on a day where there's a large temperature differential (ideally when it's very cold outside). You can use a thermal camera before the test and then after you depressurize the house for a 10 or 15 minutes - the leaky areas are perfectly obvious on the thermal since the cold outdoor air is washing over the walls near the leaks. Taking the before/during thermal videos on a walkthrough lets you compare the side-by-side later on and ID which spots need attention.

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