I'm no insulation expert, but I would suggest if you are going to have living space in that 3rd floor attic, that you add a separate unit to heat/cool that area. If you end up with a bedroom there and a shared hvac, when you try to get it cool enough to sleep comfortably, the people sleeping on the second floor will be freezing!

Our first house was a large cape cod style with the bedrooms in the "attic". We swore we would never own a cape cod style again and we haven't .

$800 in minimal in the whole scheme of things. Im’a firm believer in quality insulation, windows etc.

Pay for the extra insulation. And seriously consider a small dedicated HVAC system for the attic. If it's an open space, a minisplit heatpump would be ideal.

And if you aren't doing this already, you probably need independent HVAC systems for the first and second floors.

Its too bad they couldn't have installed the roof sheathing with the radiant barrier attached, its code here. We did put the foil between studs in our previous house and it definitely keeps the Attic cooler.

We pulled the blow out of our present house and spray foamed it so put us in the more insulation is better camp! Black roofs are attractive but don't seem like a great choice in a hot climate. It’s not going to be fun climbing through batts in the attic and reaching the bottom where trusses meet exterior walls could be difficult but I hope you can make it work!

Everyone - Thanks for your very helpful feedback. There actually is a separate HVAC system in that finished 3rd floor space. It's a small unit that is built directly into the top of one of the walls that provides both A/C and heating, as needed. The space is about 320 square feet, and it would be heated/cooled via this unit. I don't have the manufacturer of model, but it's to control the environment in that space without relying on the main HVAC system.

It sounds like the consensus is to add the R38 insulation (upgrade). Once we move into the house, we can always evaluate the extent of the temperature extremes and possibly add foil after closing, although it wouldn't be as good as a full-on radiant barrier installed during the construction process. Perhaps things will change over the coming months and these materials will be available again.

Thanks so much for your expertise and feedback! If anyone else has an option, please feel free to weigh in! :-)

You're in climate zone 3A which requires (2015 IRC and 2018 IRC) R-38 insulation in ceilings. There are some exceptions in the code for sloped ceilings which allow R-30 in sloped portions in lieu of R-38. I suspect the change order is to add depth to the rafters as needed for R-38 insulation in the sloped portions. You may want to get the scope clarified so you know what you're getting.

If the code requires r-38 attic insulation, then how is the builder offering it as an upgrade? He is just trying to make an extra $800 profit?

What does the "builder losing his radiant supplier" actually mean? Why can't he get the materials from another supplier? Has he tried Home Depot or Amazon?

@mike_home

I suspect the builder is referring to radiant barrier sheathing. There are supply logistics issues in the covid-19 world and roof sheathing is tough to get in any configuration. I don't think it's practical to look to Amazon as a supplier of roof sheathing, but then again, somebody's got to fund Jeff Bezo's space adventures.

We don't know exactly what the OP's getting for the $800 change order, but it's probably to change the insulation on the sloped portions--for which the code allows lower than R-38 insulation subject to a couple of conditions.

Charles,

The reference to Amazon was made more in jest than a real suggestion. The lead times on building supplies have gotten longer, and prices have risen. However I would think the builder could secure the radiant barrier from another supplier. For some reason he does not want to make the effort even if he has to charge a higher cost than normal.

I am also suspicious of this extra $800. It must be a very simple change order if the extra charge is only $800.

OSB sheathing is in short supply and priced in the stratosphere. In our market it's only available in 4' x 8' sheets--no 4' x 9' and no 4' x 10' sheets. I suspect the manufacturer of radiant barrier sheathing is running their regular OSB line at full capacity.

Thanks, everyone. The builder has been investigating other suppliers for the radiant barrier material, but the cost is too high and lead time too long to get it. As a result, he has removed the radiant barrier from the list of available upgrades, much to my disappointment in sunny/hot South Carolina. It's possible the situation might change, but I'm operating under the assumption that it won't. It's either take the R38 upgrade or not... possibly we could install a radiant barrier after closing, but I know it's preferred to install the barrier during construction of the home.

It seems like the consensus is to take the R38 upgrade for $800. Some additional thermal protection is better than less. I'm confirming with the builder exactly what this buys me, and I'll follow-up in this thread once I know more. Thanks again for your expertise and time in responding!

Contact your power company and ask what they suggest. Our electric company has energy anaylists available at no cost.