Building new home in PA ZONE 5. Have 2x6 walls with r21 insulation. Do you think its worth it to add 1xps foam to avoid the thermal bridging? I would do it myself and would cost $750 to add a 1xps R5. Extension jambs are another few hundred. Electric in my area is around .06KWH. Home is 1570sqft ranch 9 foot flat ceilings with unfinished basement. Couple of HVAC guys and builder all say skip it. It like take a long long time to get that money back. I plan on living in the house for awhile (mabay like 5 years) but its not my dream home.

Do the 1"XPS foam or skip it?

Thanks

.06KW?????????????? That's as cheapest I've ever seen!!!! That's less then half of what I pay. Have you thought about ICF? It's amazingly how rates vary soooooo much!!!!!

Yes electric is pretty cheap in pa. Its was around .077KWH but I switched supplier and got it lower, think i exactly pay .062KWH

I did think about ICFs but the price is more and its not my forever house.

The proper way to answer your economics question would be to estimate your annual cooling/heating operational cost with and without this additional insulation. If the operational cost savings over the 5 years you plan to stay in this house is equal to or greater than the cost of installing the insulation, it makes economic sense to do it. You could use the free software on our website to accomplish this:

Borst Integrated Cooling System Performance Software

Borst Integrated Heating System Performance Software

Being able to show lower monthly utility bills might also help sell the house too. You should also consider using EPS in lieu of XPS as it is much greener and after a period of time both end up having nearly the same R-value.

Posted By nate848 on 22 Sep 2018 10:37 PM
Building new home in PA ZONE 5. Have 2x6 walls with r21 insulation. Do you think its worth it to add 1xps foam to avoid the thermal bridging? I would do it myself and would cost $750 to add a 1xps R5. Extension jambs are another few hundred. Electric in my area is around .06KWH. Home is 1570sqft ranch 9 foot flat ceilings with unfinished basement. Couple of HVAC guys and builder all say skip it. It like take a long long time to get that money back. I plan on living in the house for awhile (mabay like 5 years) but its not my dream home.

Do the 1"XPS foam or skip it?

Thanks

A few comments:

1. R5 is not sufficient for dew point control for 2x6/R21 walls in zone 5 locations. Per the IRC chapter 7y prescriptives, if it's less than R7.5 it will need an air tight interior and a Class-II vapor retarder such as "vapor barrier latex" on air-tight wallboard, or a "smart" vapor retarder such as Intello Plus or 2 mil nylon (eg Certainteed MemBrain.) All things considered it's probably better to go with fatter foam- either 2" EPS/XPS or 1.5" polyisocyanurate, which keeps the sheathing warm enough to skip the vapor retarders, which allows faster drying toward the interior.

2. "...1xps foam to avoid the thermal bridging..." is a complete misconception. The insulation doesn't avoid the thermal bridging, but it DOES mitigate it.



3. At 1" XPS is labeled R5 per FTC, but is only warranteed by the manufacturers to be 90% of that, or R4.5 over the lifecycle of the building, and it may not even hit that mark. XPS is blown with extremely high global warming potential HFCs (more than 1000x CO2), which give it it's initial perfomance boost, but at full depletion it will settle in at R4.2/inch, the same as EPS of similar density. EPS is blown with much more benign hydrocarbons (usually a variant of pentane), with a global warming potential ~7x CO2, but most of it escapes the foam and is recaptured at the factory, often burned for process heat. The blowing agent is not responsible for any part of it's performance, which is stable over time.

4. Polyisocyanurate is also blown with low impact hydrocarbons, and is labeled R6 -R6.5 @ 1". When on the cold side of the assembly most polyiso loses some performance in a zone 5 climate, but on the exterior side of a 2x4/R13 type wall will average at least R5 during the winter. Foil faced polyiso is also dead-easy to air seal using foil tape. For long term R5 or better performance with 1" foam this is your best bet. Due to the wintertime derating issue don't cheap out and use 3/4" polyiso, which is often labeled R5. If 2x6, go with 1.5", which is labeled R9-R10.

5. It's not about the "payback" as much as it is about resilience. With sufficient exterior R for dew point control the seasonal moisture cycling in/out of the sheathing become minimal.

6. The foundation is going to be at least the IRC 2015 code-mininmum R15 continuous insulation (such as a 2" +2" EPS insulated concrete form), right? If not, the rigid foam budget is probably better applied to becoming IRC code compliant on the foundation R. As a DIY 3" of reclaimed fiber faced roofing polyiso (labeled about R5.5/inch_ on the interior side strapped to the foundation with 1x4s through-screwed to the foundation with 5" masonry screws can be pretty cheap. Alternatively an ICF works.

7. If you're looking for a 5 year "payback" there isn't even a financial rational for going to code minimum, other than the fact that it's the crummiest house that's legal to build. If the best code-min house possible becomes the goal, concentrate on air sealing- a case or two of high quality polyurethane caulk and a powered caulking gun will usually "pay off" in that time frame. A bead of caulk under the bottom plate of the studwall and any doubled-up framing such as top plates window headers, jack studs etc, and caulking the perimeter of each stud bay to the sheathing inside every stud bay is a good start. An EPDM sill gasket between the sill plates is also usually "worth it". Use only air tight electrical boxes, and pay special attention to air sealing all penetrations of the ceiling plane or basement walls, including plumbing stack chases, etc.

thank you for the detailed response and also the calculator. thanks everyone.

Dana knows what the H he's talking about.

Posted By robinnc on 25 Sep 2018 06:20 AM
Dana knows what the H he's talking about.

Naw- I just make it up as I go along..;-)

Posted By Dana1 on 25 Sep 2018 03:15 PM

Posted By robinnc on 25 Sep 2018 06:20 AM
Dana knows what the H he's talking about.

Naw- I just make it up as I go along..;-)

Ah, so THAT'S the reason for all the pained groaning when you sit down...

Was wondering where you pulled this stuff from!

=)

Posted By Dilettante on 25 Sep 2018 10:41 PM

Posted By Dana1 on 25 Sep 2018 03:15 PM

Posted By robinnc on 25 Sep 2018 06:20 AM
Dana knows what the H he's talking about.

Naw- I just make it up as I go along..;-)

Ah, so THAT'S the reason for all the pained groaning when you sit down...

Was wondering where you pulled this stuff from!

=)

Naw- the pained groaning is when I stand UP! :-)

Posted By Dana1 on 24 Sep 2018 06:19 PM

Posted By nate848 on 22 Sep 2018 10:37 PM
Building new home in PA ZONE 5. Have 2x6 walls with r21 insulation. Do you think its worth it to add 1xps foam to avoid the thermal bridging? I would do it myself and would cost $750 to add a 1xps R5. Extension jambs are another few hundred. Electric in my area is around .06KWH. Home is 1570sqft ranch 9 foot flat ceilings with unfinished basement. Couple of HVAC guys and builder all say skip it. It like take a long long time to get that money back. I plan on living in the house for awhile (mabay like 5 years) but its not my dream home.

Do the 1"XPS foam or skip it?

Thanks

A few comments:

1. R5 is not sufficient for dew point control for 2x6/R21 walls in zone 5 locations. Per the IRC chapter 7y prescriptives, if it's less than R7.5 it will need an air tight interior and a Class-II vapor retarder such as "vapor barrier latex" on air-tight wallboard, or a "smart" vapor retarder such as Intello Plus or 2 mil nylon (eg Certainteed MemBrain.) All things considered it's probably better to go with fatter foam- either 2" EPS/XPS or 1.5" polyisocyanurate, which keeps the sheathing warm enough to skip the vapor retarders, which allows faster drying toward the interior.

2. "...1xps foam to avoid the thermal bridging..." is a complete misconception. The insulation doesn't avoid the thermal bridging, but it DOES mitigate it.



3. At 1" XPS is labeled R5 per FTC, but is only warranteed by the manufacturers to be 90% of that, or R4.5 over the lifecycle of the building, and it may not even hit that mark. XPS is blown with extremely high global warming potential HFCs (more than 1000x CO2), which give it it's initial perfomance boost, but at full depletion it will settle in at R4.2/inch, the same as EPS of similar density. EPS is blown with much more benign hydrocarbons (usually a variant of pentane), with a global warming potential ~7x CO2, but most of it escapes the foam and is recaptured at the factory, often burned for process heat. The blowing agent is not responsible for any part of it's performance, which is stable over time.

4. Polyisocyanurate is also blown with low impact hydrocarbons, and is labeled R6 -R6.5 @ 1". When on the cold side of the assembly most polyiso loses some performance in a zone 5 climate, but on the exterior side of a 2x4/R13 type wall will average at least R5 during the winter. Foil faced polyiso is also dead-easy to air seal using foil tape. For long term R5 or better performance with 1" foam this is your best bet. Due to the wintertime derating issue don't cheap out and use 3/4" polyiso, which is often labeled R5. If 2x6, go with 1.5", which is labeled R9-R10.

5. It's not about the "payback" as much as it is about resilience. With sufficient exterior R for dew point control the seasonal moisture cycling in/out of the sheathing become minimal.

6. The foundation is going to be at least the IRC 2015 code-mininmum R15 continuous insulation (such as a 2" +2" EPS insulated concrete form), right? If not, the rigid foam budget is probably better applied to becoming IRC code compliant on the foundation R. As a DIY 3" of reclaimed fiber faced roofing polyiso (labeled about R5.5/inch_ on the interior side strapped to the foundation with 1x4s through-screwed to the foundation with 5" masonry screws can be pretty cheap. Alternatively an ICF works.

7. If you're looking for a 5 year "payback" there isn't even a financial rational for going to code minimum, other than the fact that it's the crummiest house that's legal to build. If the best code-min house possible becomes the goal, concentrate on air sealing- a case or two of high quality polyurethane caulk and a powered caulking gun will usually "pay off" in that time frame. A bead of caulk under the bottom plate of the studwall and any doubled-up framing such as top plates window headers, jack studs etc, and caulking the perimeter of each stud bay to the sheathing inside every stud bay is a good start. An EPDM sill gasket between the sill plates is also usually "worth it". Use only air tight electrical boxes, and pay special attention to air sealing all penetrations of the ceiling plane or basement walls, including plumbing stack chases, etc.

On a related question. I don't know what code is in Colorado but my plan is R21 in 2x6 walls with 1" of spray foam behind that to completely seal it from air leaks.Then add 2" of rigid foam on the outside under the half log siding. Good idea? Bad idea? I prefer to spend more upfront on insulation and get that back in energy savings over the years. My home here in Texas that I built in '92 has 2x6 walls with R19, R5 on the outside, Anderson Low E windows with Argon, and R40 in the attic. I had a Lennox two speed a/c for 12 years until it failed. It was rated at 2 tons on Low speed and 3 tons on high speed with EER ratings of 18 on low and 13 on high (the best I remember). Even with our brutal summers it ran on low speed the majority of the time. I don't expect energy to get cheaper so the CO place will be way better than code- not not zero, just above average.

You are in US climate zone 6B. It takes R11.25 for dew point control on R20 cavity insulation in 6B, R15 in zone 7B. If you spend the spray foam money on bumping up the exterior foam it'll be higher performance than compressing R21s down to 4.5" (R17-ish) and would cost less than the spray foam. Sealing the framing to the sheathing with polyurethane caulk or a purpose-made sealant is cheaper than with 2lb polyurethane.

If the exterior foam is Dow Thermax polyiso you'll hit R15 at about 2.5", since it doesn't have to be derated for temperature. If you used reclaimed roofing polyiso bump it to 3". With R15 on the exterior you'll have plenty of margin in zone 6 for going with R23 rock wool instead of R21 fiberglass.

Reclaimed roofing foam is everywhere, and it's dirt-cheap compared to virgin stock goods. eg:

https://denver.craigslist.org/mad/d/iso-rigid-foam-insulation/6771778355.html

https://denver.craigslist.org/mad/d/iso-rigid-foam-insulation/6769305603.html

https://boulder.craigslist.org/mad/d/used-poly-iso-insulation-sold/6753112618.html

Posted By Dana1 on 14 Dec 2018 11:06 PM
You are in US climate zone 6B. It takes R11.25 for dew point control on R20 cavity insulation in 6B, R15 in zone 7B. If you spend the spray foam money on bumping up the exterior foam it'll be higher performance than compressing R21s down to 4.5" (R17-ish) and would cost less than the spray foam. Sealing the framing to the sheathing with polyurethane caulk or a purpose-made sealant is cheaper than with 2lb polyurethane.

If the exterior foam is Dow Thermax polyiso you'll hit R15 at about 2.5", since it doesn't have to be derated for temperature. If you used reclaimed roofing polyiso bump it to 3". With R15 on the exterior you'll have plenty of margin in zone 6 for going with R23 rock wool instead of R21 fiberglass.

Reclaimed roofing foam is everywhere, and it's dirt-cheap compared to virgin stock goods. eg:

https://denver.craigslist.org/mad/d/iso-rigid-foam-insulation/6771778355.html

https://denver.craigslist.org/mad/d/iso-rigid-foam-insulation/6769305603.html

https://boulder.craigslist.org/mad/d/used-poly-iso-insulation-sold/6753112618.html

Thank you sir!

De nada- es mi gusto!