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How can a homeowner find a contractor to install rigid foam on top of roof sheathing?

ThriftyMom | Posted in General Questions on

To everyone, but especially anyone in the Chicago area:

We live in Wheaton Illinois, a suburb west of Chicago. Our home, built in 1959, needs a new roof, new gutters, and more insulation. We may consider metal shingles if there is a good option that does not cost too much. We would like to convert one or both of the attics of our split level from conventional, vented attics to un-vented attics to be used for storage. As described in Martin Holladay’s article, “How to Install Rigid Foam On Top of Roof Sheathing” (option 1 of the article), we would like to install R49 of rigid foam (about 12.5 or 14 inches of EPS, 10 inches of XPS, or about 9 inches of polyiso) above our roof sheathing. We’ve been told that this would take a lot of work and cause a large expense in fascia, etc. but we have not found any contractor willing to give us a quote. We would also consider option 2 of the article, which is to install part of the insulation as rigid foam above the roof sheathing, and the rest of the insulation underneath the roof sheathing. The height of each attic is very minimal (~45″ max in one attic and ~35″ max in the other), so we would like to aim for an option that preserves the meager attic height that we have. Access to each attic is by ladder at the present. If there is an affordable way to build a fixed stair to make the attic(s) more accessible, we would like to find it. We have been hoping to put off this project for a few years, but we keep having leaking in the roof area shown in the attached picture, where the roof of an addition we put on 5 years ago (the closest part of the picture) joins the old part of the house (the siding on the right in the picture.) If we, by hard work or time spent, can decrease the cost to accomplish all these goals, we would like to try, but we are only somewhat handy. If you know of anyone who would be interested in this project, please help me contact them. Thanks!

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  1. brendanalbano | | #1

    Passive House Institute US is based out of Chicago. Maybe reach out to them for contractor recommendations. They have a list of PHIUS certified builders, and there are a number in Illinois:

    A contractor comfortable building a passive house ought to be comfortable putting a big pile of foam on your roof and dealing with all of the issues it presents.

  2. Expert Member
    Dana Dorsett | | #2

    BTW: Over the lifecycle of an asphalt roofing shingle XPS will drop to about 90% of it's rated R value, and over the life of a building it'll drop to about that of EPS of similar density.

    In your location and all-foam stackup, for performance purposes derate polyiso to R5.5/inch.

    Type-II EPS (15lbs per cubic foot density- tough enough to be "walkable") only takes 12" to hit R50+ . Even low density Type-I (don't use Type-I here!) would beat R50 at 13". I'm not sure where you came up with the 14".

    If the goal is to hit the R49 code-minimum, note that is for insulation thermally bridged by rafters or joists. When the insulation is continuous it doesn't need to be that thick, and you can meet code on a U-factor basis. According to TABLE N1102.1.4 in the IRC it only needs to be U0.026, which would be a "whole assembly R" of about R38.5, and you can include the R-value of the roof decking, ceiling gypsum, the R-value of the shingles & felt, as well as the interior & exterior air films. All that other stuff adds up to about R2, so the foam R only needs to be about R36.5. That means you can get there with 9" of EPS (instead of 12") or 7" of polyiso.

    But there's more...

    With as little as R20 above the roof deck you can install up to R30 of fiber insulation under the roof deck with very little moisture risk which would probably be cheaper if the rafters are that deep. Assuming they're 2x6s, go ahead and use damp-sprayed cellulose (~R20) or carefully sculpted R23 rock wool or R21 fiberglass filling the cavities, but still not taking up any headroom below the rafter edges. With a hipped roof and 24" o.c. rafter spacing you're looking at about a 10% framing fraction, in which case the foam, rafters, roof deck & shingles, air films etc all add up to about R18.5, in which case you would only need (R38.5- R18.5=) R20 on the exterior to make code on a U-factor basis.

    That means with 5.5" of fluff between the rafters you can fully get there with only 5" of continuous EPS, or 4" of continuous polyiso. That's relatively easy to install and build new facia for WAY easier than the 9-12" you were looking at. With 4" of polyiso held down by a half inch OSB nailer deck through screwed to the structural roof you are at the depth of a standard milled 1 x 6. But you can also get 6" commercial drip edge to cover the edge rather than a prettified facia board. It comes in galvanized, powder coat white, deep brown, dark gray and a few other colors. You can probably find something that won't look too outlandish. It won't be at the home center, but a roofing supply place catering to commercial rather than residential would have it (or order it.)

    Also note: The greenest foam of ANY type is reclamed/reused foam, which costs way less than half what virgin stock goods run. Roofing EPS and polyiso are regularly scavenged during commercial building demolition & re-roofing, and in Chicagoland you probably have multiple outlets for buying that stuff, if the local craigslist is any indication:

  3. ThriftyMom | | #3

    Thank you, Brendan! I plan to contact a PHIUS certified builder tonight.

    Thank you, Dana! This is the third question of mine that you have answered, and I plan to give the builder all the info you have given me, to guide them in how to get this project done right.

  4. ThriftyMom | | #4

    For Dana Dorsett & anyone who has installed 6" commercial drip edge to cover edges of rigid foam:

    I have a question about 6" commercial drip edge. The man I talked with at a roofing supply company near me was very helpful. He was concerned that, since the commercial drip edge has an angle of 90 degrees and ours is not a flat roof, we would need to bend it on site to match our roof pitch (approx. a 3" per 12" or 4" per 12" pitch.) He thought the bending process would be pretty difficult. It does seem that we would have to bend it to an angle much larger than 90 degrees. He thought maybe we should ask someone at a sheet metal shop to bend some of their metal to the desired angle for us. Any thoughts?

  5. GBA Editor
    Martin Holladay | | #5

    The man at the roofing supply company was right. Any sheet metal shop should be able to help you.

  6. ThriftyMom | | #6

    Thanks, Martin! I will try calling sheet metal shops.

  7. dankolbert | | #7

    Before you bother, many roofers also do siding and would own a sheet metal break. They could bend it on site.

  8. ThriftyMom | | #8

    Thanks, Dan! I didn't have much success yet with finding the right sheet metal shop. Another man at the roofing supply suggested I use coil fascia 1"x 6" pre-bent (no lip, just an L) 019 aluminum. He has 14 colors to choose from for $13.80/12 ft which might be within our budget. If our roof pitch is only 3" per 12", then the face of the trim would only be 14 degrees off vertical even if we don't bend it at all.

  9. DIYJester | | #9

    Depending on the length of the flashing you could add the extra angle yourself. The orange big box store rents aluminum brakes around here for $60 a day. They are pretty easy to use.

    My wife and I cut, slit, and bent about 200' of coil stock for our house in about a day.

  10. ThriftyMom | | #10

    Thanks, Mike! My husband and I may try to do the same.

  11. Expert Member
    MALCOLM TAYLOR | | #11

    Before you make, or commission someone else to make the flashing, you should draw a scale section of the roof with the new insulation to see how the flashing integrates with your roofing, fascia and gutters.

    The purpose of the flashing is not only to protect the exposed ends of the insulation, but to make sure the roof drains into either your gutters or off onto the surrounding landscaping. The shape, dimensions, position of hems and fastenings all need to be thought out before you can meaningfully ask anyone to provide it.

    Good luck with your project.

  12. ThriftyMom | | #12

    Thanks, Malcolm! I think drawing a scale diagram is an extremely good idea that I hadn't thought of. We have been looking at diagrams on GBA website, but I think most of the ones we've been looking at have been for new construction. I talked today with the man who may do the project for us, and he is helping me to understand that it may be a lot more difficult to succeed than I had at first thought. Thank you, everyone, very much for your advice. We sure do need it.

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