Attic insulation

CNCAppsJames · August 29, 2023, 05:14 PM

@mkd our home had regular insulation in the attic (about 18" thick) AND the looked like mylar coated styrofoam on the underside of roof sheathing. I'd say it probably kept the attic below 100 on all but the hottest days. If I still had that house, I was seriously considering getting a fan to pull hot air out just to get the extra few degrees down.

If I could have got my wife to buy in on opening the windows when/if it cooled off in the evenings, I would have went after a whole house fan. She refused so we kept the house at a balmy 71-ish deg.

RobertELee · August 29, 2023, 05:34 PM

Quote from: CNCAppsJames on August 29, 2023, 05:14 PM@mkd our home had regular insulation in the attic (about 18" thick) AND the looked like mylar coated styrofoam on the underside of roof sheathing. I'd say it probably kept the attic below 100 on all but the hottest days. If I still had that house, I was seriously considering getting a fan to pull hot air out just to get the extra few degrees down.

That's probably what my recommendation would be. The foam on the underside of the sheathing is likely polyisocyanurate, it's ridgid foam with aluminum foil coated on one side. It helps reflect the infrared heat away. Could also use what's called Reflectix, it's basically bubble wrap with mylar facing. Works really well if installed correctly, it's not always installed properly.

Here's Johnny! · August 30, 2023, 07:25 AM

You can't really insulate without a vapour barrier unless you spray foam. Also your roof sheathing needs to breath, if you insulate against the sheathing you should have vent channels that allow air to travel from the soffit to the peak.

Adding roof vents should help the air flow, not sure if you have shingles or tiles.

Of course my experience is from Canada, we have 4 distinct seasons.

mkd · August 30, 2023, 07:40 AM

Quote from: RobertELee on August 29, 2023, 05:06 PMSo zero insulation? I'm not sure what standard practice for SoCal is but here in MN we don't care how warm the attic is, the goal is to stop the heat from transferring through the ceiling, so we typically insulate the attic floor with 20+inches of blown in insulation. Works great and definitely the cheaper option.

sorry to have left off an obvious detail. Yeah, got original 1986 blown insulation. Replacing it and with better product and installed better would be good.

pmartin · August 30, 2023, 07:47 AM

Quote from: mkd on August 30, 2023, 07:40 AMsorry to have left off an obvious detail. Yeah, got original 1986 blown insulation. Replacing it and with better product and installed better would be good.

1986 blown insulation? Better make sure that it isn't vermiculite. Vermiculite was banned in 1991 because it can contain asbestos.

mkd · August 30, 2023, 07:56 AM

Quote from: pmartin on August 30, 2023, 07:47 AM1986 blown insulation? Better make sure that it isn't vermiculite. Vermiculite was banned in 1991 because it can contain asbestos.

holy @#$% didn't know that.
from memory being up there, it does seem like it's the color and consistency of vermiculite. Wife already got stage 3 lung cancer, but she never went up there. Duct leaks are certainly possible.

Here's Johnny! · August 30, 2023, 07:57 AM

If going for batt type I would only use Rockwool (mineral fiber), it is made from the slag from making steel. Excellent product, when I worked in a jobbing shop we made some machines for their local plant.

Here's Johnny! · August 30, 2023, 07:59 AM

@mkd Have you have had your house checked for Radon gas? This can cause cancers.

pmartin · August 30, 2023, 08:00 AM

Quote from: JFord on August 30, 2023, 07:57 AMIf going for batt type I would only use Rockwool (mineral fiber), it is made from the slag from making steel. Excellent product, when I worked in a jobbing shop we made some machines for their local plant.

I like Rockwool. One nice feature about it is that it doesn't become compacted if wet.

mkd · August 30, 2023, 08:01 AM

Quote from: JFord on August 30, 2023, 07:59 AM@mkd Have you have had your house checked for Radon gas? This can cause cancers.

that's more of a thing for houses with basements, not slab /western construction, as far as I know. Granite produces radon, right?

Here's Johnny! · August 30, 2023, 08:01 AM

Quote from: pmartin on August 30, 2023, 08:00 AMlike Rockwool. One nice feature about it is that it doesn't become compacted if wet.

Also fire proof, we use to cut with a cutting torch in the plant. It would melt a little but it would not burn.

Here's Johnny! · August 30, 2023, 08:03 AM

Quote from: mkd on August 30, 2023, 08:01 AMthat's more of a thing for houses with basements, not slab /western construction, as far as I know. Granite produces radon, right?

Yes more of an issue with basements, not sure about the granite item though. A lot of people that work in excavation get lung cancers without ever smoking. Same with the logging industry.

mkd · August 30, 2023, 08:32 AM

Quote from: JFord on August 30, 2023, 08:03 AMSame with the logging industry.

that's unexpected

RobertELee · August 30, 2023, 08:36 AM

Quote from: mkd on August 30, 2023, 08:01 AMGranite produces radon, right?

No, Uranium produces radon. It can come from all dirts types, however it can travel easier through loose and porous dirt. It typically gets released and dispersed naturally into the air, however a crack or opening in your foundation can cause it to accumulate in a home. And with these newer homes that are fully sealed its causing a bigger issue.

RobertELee · August 30, 2023, 08:40 AM

Quote from: pmartin on August 30, 2023, 07:47 AM1986 blown insulation? Better make sure that it isn't vermiculite. Vermiculite was banned in 1991 because it can contain asbestos.

Vermiculite was a poured in insulation. Came in bags and was dumped into cavities and such. Kind of looks like potting soil. If it's fluffy, it's not vermiculite. Likely fiberglass or cellulose.