Didn't want to derail another thread. I've been considering partial spray foam for my house, and sort of understand the envelope/sealing requirements, but could use some additional expertise/insight. I've got four small attics and three HVAC units in three of the four attics, plus a wood shake roof.

I really only think two of my attics would benefit from spray foam, and due to their small size, they'd be fairly quick and easy spray foam jobs. In particular, they get a lot hotter, and those HVACs run a lot more during the day (often 2-3x as long during a hot day as the other unit). Attic A is on the West side of the house, and has a natural gas furnace (80%). Attic B is above the 2nd story, has the largest faces on the South and West sides, and has a heat pump. Questions:

• Any issues with only spray foaming these two attics and leaving the other two with the existing blow-in insulation on the attic floor and batt insulation on the walls?
• I know I'd have to bring some kind of combustion air to the furnace in Attic A. What options do I have? Outside, or from elsewhere in the house, etc?
• Any issues with a wood shake roof? They're thick, class IV shakes, FWIW. Can't wait to eventually have it replaced

TIA

Bump - any experts? Even it it's just one of the questions?

Are your attics vented?

Yes - and I assume the 2 in question would need to be sealed.

Can you send me some photos?

markRmiller89@gmail.com

Attics in Texas should not be vented but should be conditioned space. You can put an open-cell spray foam on the underside of the roof decking and install a vapor diffusion port.

Are you sure that ventilation isn't required for blown insulation on the attic floor? Seems like it's been required by code for folks getting new roofs here, and a brief look over IBC seems to support (1203.2 Ventilation required). I would agree that ventilation is not required when you spray foam and move the attic space within the building thermal envelope (IBC 1203.3), but I don't think so for attics where the space is outside the building thermal envelope, generally speaking.

At any rate, here's some pictures. Diagram of the house:

Picture A (Attic A), hard to get a picture of the full length, this is about the halfway point. Long and narrow:


Picture B (Attic B), above the second story. Was able to get a panorama to show more the space, so it distorts it a little bit:

For what it's worth - moving forward this week. Just finished up a day of vacuuming the blown insulation out.

I'm definitely not flexible enough to crawl around in my attic and now I'm hurting in ways I've never hurt before.

How did you vacuum it out?

Got it all wrapped up. Very pleased. Feels great up in the attics and has added some nice space for us. I measured low 70's in the attics and it hit 90 outdoors today. First couple days of data on the thermostats look promising.

BenTheGoodAg said:

---

Got it all wrapped up. Very pleased. Feels great up in the attics and has added some nice space for us. I measured low 70's in the attics and it hit 90 outdoors today. First couple days of data on the thermostats look promising.

---

Got it done this summer. AC ran up to 30 hrs less per week, even when it was in the 100s outside. Can't wait to see how little it runs now that it's getting cooler outside.

who did your job OP?

It was a local business - Apex foam

Just want to add some data points here for those considering spray-foam. I'd like to track this for a couple years and if I remember, I'll come back with some results then. We've got a mix of gas (3 & 2 ton units) and electric (2 ton heat pump). Obvious reduction in gas in two months time, and it's been pretty cold here. Not enough data in the summer to see the electric impact, but it'll be fun to follow. Below are the consumption rates based on the average ambient temperatures on the bill.

Loving the ability to track this data and the energy savings bottom line to come.
That said, have to ask some details to put all that to good use for others considering this upgrade.
SF of house, Living and Total?
Cost of foaming?
Could this be also $/sf, which is dependant more of roof & its slope than ground floor SF.

Eventually - like all energy savings upgrades (e.g. windows) - a calculation would produce
How many years of savings will retire the additional "first cost" expenses.
Most good deals in past have been 7 years or less.

SF of the house is 3600 (livable), and 4600 (total).

They foamed about 3000 SF of the roof deck (8/12 Pitch). We didn't foam the small east attic (200 SF), the large garage attic (1300SF). These values are in roof SF, not floor SF. Obviously eaves and dormers and other ceilings that are built into the roof-line weren't foamed.

Total cost of the insulation was $4600. I rented a vacuum for the old blow-in insulation, but got a good deal. Normally, $300 for the day.

I was hoping that the payback would be 10 years, but already, the smart thermostat data tells a good story for our heaters. 2 months isn't enough time to really tell, though. The impact is definitely positive, but how much remains to be seen. There were other benefits that motivated us, as well. We've added some storage and are going to be able to re-pipe with PEX and abandon our old copper. We also were able to convert our two tanked water heaters to a single tankless unit in one of the attics and reclaim a couple of closets for storage.

Did you not also have soffit vents? Most vented attics would so I am curious how / if you addressed these.

Yep, we've got soffit vents. We don't have a baffle system, so there's a good line of site directly into the soffit cavity from the attic. I'm pretty sure the foam didn't completely fill the soffits, but probably a fair amount. There's a definite barrier between the attic space and the unfilled portion of the soffit, and it extends beyond the top plate into the soffit void, so we have a pretty good seal.

Interesting. We have 2005 slab on grade with vented attic and I assumed I would have to address all the soffits as well. Thanks for the quick reply.

You bet, just lucky I was on. Good luck!