GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Roof insulation – 1/2″ EPS worth it?

wzrdmatt | Posted in General Questions on

Hi Everyone,

I posted earlier about this roof assembly, but a different question this time around. 
California Zone 3 climate zone.

We’re doing a metal roof, with R-38 spray foam on the underside of the roof deck.   Our roofer is recommending 1/2 EPS foam on TOP of the roof.  Why is unclear.  He says it might help smooth out the sheeting…or help with insulation…or perform some magic 🙂

From an energy perspective, is there any material value in laying down 1/2″ of EPS, at an R-Value of ~2?   I guess I could say I get an R-40 roof now?!!  

I asked my manual-j rater to update and see what happens, and he just changed the roof insulation from R-38 to R-40, and it lowered our BTU requirements by ~500BTU.   

$6,800 dollars for the upgrade. Feels like I should spend my money elsewhere. 

Am I missing any other energy savings value? Would the 1/2″ help create any materially beneficial thermal break between the metal roof and the spray foam? 

Thanks for your ideas and advice!

Matt

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.

Replies

  1. walta100 | | #1

    Is it to late to change your plans?

    Spray foam is a mistake in new construction! It is the most expensive and least green way to buy r value.

    Consider taking the time to plan an HVAC system that can be located below the ceiling inside the conditioned space and covering the attic floor with cheap fluffy insulation.

    Walta

  2. Expert Member
    Deleted | | #2

    Deleted

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |