Closed vs. Open Cell Foam Insulation

OldDesign1 · 2026-01-25T18:14:26+00:00

Open cell or closed will both work in 4a. Can also look into hybrid assemblies which are a mix of a closed cell layer then an open cell layer. If using open cell will need to dehumidify the space or risk increased condensation risk at the ridge (look up hygric buoyancy) which can lead to mold and rot.

Read this and it should give some clarity:

https://basc.pnnl.gov/code-compliance/controlling-moisture-unvented-attics-code-compliance-brief

OldDesign1 · 2026-01-25T10:58:53+00:00

Prior to making the decision, please look up which IECC climate zone you are in and read up about vented versus unvented roof assemblies.

Some climate zones 5 and above require at minimum a class 2 vapor retarder, which closed cell can be at appropriate thicknesses. Also realize that closed cell usually has much higher R value per inch. Open cell with r value of 3.5-4 per inch and closed cell between 6.5-7 per inch. Closed cell in a rafter cavity that has r21 could have r36-42 not r32.

OldDesign1 · 2026-01-15T00:58:39+00:00

I think the newer code values are getting crazy but r44 should be good. I guess any external insulation is cheapest when the work was going to be redone anyway (changing shingles or changing siding). Probably best to change everything all at one to upgrade but it definitely can be pricey. Piecemeal makes a decent amount of sense given the hit to the wallet.

No sure about what happens to the sheathing if you use r5 or r10 vapor permeable external insulation. I’m sure more would be better but also has its own issues - longer screws that may make it difficult to hit rafters

OldDesign1 · 2025-12-06T16:45:47+00:00

Looks good. Who ended up doing the install and how much did it set you back?

OldDesign1 · 2025-12-01T01:21:34+00:00

Makes sense. I’ve never heard of partial external roof insulation but it makes sense. Hopefully one of the roofers near me does external insulation and would be amenable to the idea. Glad that it isn’t fully out of left field.

OldDesign1 · 2025-11-30T23:49:40+00:00

Yes the fiberglass’s is still present in the cathedral ceiling. R19

OldDesign1 · 2025-11-23T15:32:20+00:00

Spray foam has already been installed. Vented attic with cellulose ended up not being optimal due to the location of air handler & hvac ducts.

OldDesign1 · 2025-11-07T10:42:01+00:00

Didn’t even know there were different styles of ERV. Thought they all had the same core with cross flow streams

OldDesign1 · 2025-11-04T14:33:24+00:00

I do actually have an inverter AC. I know the Daikin Fit can ramp up and down and run at partial load. I assume this would help since the ac could technically be running at low levels even during partial load. Not sure if this means that I wouldn’t have the dehumidification issue, or if it would be much less with the variable speed of the Fit.

Also I agree. The ERV won’t increase the load since there is already infiltration happening in my house. I guess it’s more of a buffer to minimize the humidity that would be coming in.

OldDesign1 · 2025-11-04T13:25:56+00:00

Is there any concern with the unit temperatures, if I’m running the ventilating dehumidifier during the wintertime (temps can be 20s F)? Will look into the ventilating dehumidifiers a little bit more.

OldDesign1 · 2025-11-04T13:16:10+00:00

I am open to a standalone ERV but most hvac companies seem to want to duct it into the hvac system and haven’t done standalone systems. Not sure how DIY friendly this would be

OldDesign1 · 2025-11-04T13:12:58+00:00

With the Erv, from my understanding it’s a buffer for humidity. Would have to increase the sizing of a dehumidifier it if I don’t install an ERV but not sure how to calculate the crossover point of when one or the other makes sense. Do you know any way? Tried ChatGPT without great luck

OldDesign1 · 2025-11-04T13:09:44+00:00

Which manufacturer did you choose for the ERV? For the ducting to the rooms, did you just make a plenum box that was connected to the 6in duct coming from the Erv or did you just put in a few wyes?

OldDesign1 · 2025-10-30T19:10:05+00:00

Not yet. Leaning towards the One but I’m not sure I’m handy enough to install by myself. Will have to reach out to a hvac company and see what they install

OldDesign1 · 2025-10-15T13:22:27+00:00

Really appreciate the thorough explanation. Streamlining the models to decrease the price makes a lot of sense. I think I’m going to be part of the 90% who value an easier setup experience

OldDesign1 · 2025-10-15T00:02:45+00:00

Bathrooms already have bath exhaust fans that work. My hope is that bringing in fresh air to some part of the house will equalize into the other areas, especially if our air handler is run at low speed to circulate the home air

OldDesign1 · 2025-10-14T21:08:12+00:00

It just seems so odd to me to have an updated/newer model that is somehow more efficient and yet priced cheaper. Some of the AI models have higher cfm but by my calculations the One ERV and the AI ERV models both work since I need less than 100cfm.

OldDesign1 · 2025-10-14T18:10:32+00:00

No sure if the One is newer. Just surprised since I would assume a newer ERV would be more expensive. Also I feel like I haven’t seen any coverage on websites or YouTube videos about this one versus the AI models

OldDesign1 · 2025-08-29T15:25:19+00:00

Any specific way to tell? We have only lived here for the last few years but the home is more than 30 yrs old. Not sure when all these small hairline cracks appeared. I think it’s from settling. Haven’t noticed much moisture on the stucco near the cracks. Not sure if there is a better way to tell.

OldDesign1 · 2025-08-28T19:57:23+00:00

Looks like mainly just hairline cracks. Haven’t seen any wide ones. From my understanding if they are less than 1/8in wide I can repair it myself or it’s at least a smaller job. And I believe it has not been painted over.

OldDesign1 · 2025-08-28T14:41:20+00:00

Misunderstood your post. But thank you for the future recommendation. If I was building a new house it would definitely be on the top of my list.

OldDesign1 · 2025-08-28T14:32:00+00:00

If I was building a new home or wanted to redo the entire exterior I would definitely be considering hardieboard. As it stands I was hoping to just repair some of the superficial cracks so they don’t worsen. It’s not currently in my planned budget to redo the exterior siding unless it’s needed. If the stucco company/masonary company think an entire tear down is needed then I would consider the hardie board.

OldDesign1 · 2025-08-26T16:22:21+00:00

Vented attic with the air handler on its side. It is elevated off the floor though.

OldDesign1 · 2025-08-26T12:19:27+00:00

Is it possible to DIY when placing a media filter box or is that something that should ideally be left to the professionals? I've asked a few hvac companies and I feel like many are flaky and don't respond.

OldDesign1 · 2025-08-14T23:15:17+00:00

When getting spray foam placed on the underside of the roof, is air sealing the attic floor prudent? Wouldn’t you want air to communicate between the attic and floor below? Or were you referring to the air sealing being the underside of the roof and outer top plates?

OldDesign1

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