Why Spray Foam Under Asphalt Shingles is a Bad Idea
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- Опубліковано 10 лип 2024
- In this episode of Smith House, Jordan Smith, a design builder with Smith House Company, dives deep into the controversial topic of using spray foam on the backside of asphalt shingle roofs. With a focus on building houses that are beautiful, functional, resilient, and healthy, Jordan explains why he believes this common practice may not be the best approach.
⚠️ Key Points Covered:
Warranty Concerns: Some shingle manufacturers don't allow spray foam directly against the decking, potentially voiding warranties.
Replacement Challenges: If decking needs replacement, the spray foam must also be replaced, leading to added costs and complexity.
Exploring Alternatives: Jordan explores the drawbacks of traditional ventilated attics, the benefits and limitations of spray foam, and proposes a third approach for optimal performance and longevity.
🔍 Video Breakdown:
Introduction: Jordan introduces the topic and outlines his concerns.
Ventilated Attic: Discusses the benefits and challenges of traditional ventilated attic systems.
Spray Foam Solution: Explores how spray foam addresses some attic ventilation issues but introduces new challenges.
Optimal Roof Assembly: Introduces a continuous insulation house as a potential solution, highlighting its benefits over traditional methods.
🔧 Building for the Future: Jordan emphasizes the importance of thoughtful building practices that prioritize durability, energy efficiency, and ease of maintenance.
💬 Engage with Us: Share your thoughts in the comments below. Agree or disagree? Let us know! Have suggestions for future topics? We're all ears!
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Thanks for watching, and see you in the next episode of Smith House!
Definitely interested! Thank you for taking the time and sharing this.
I’ve been wondering specifically about this and I’m very glad to see a builder who I respect going straight at it with an explanation.
The hvac is inside the insulation. You need to rewatch this video.
@@sparksmcgee6641I’m not sure what my comment has to do with HVAC ?
I've been a journey carpenter for 35 years, and I love your building envelope system. I live in Canada, and built R2000 homes for years. Your method is very well founded. 👌
Spray foam does not void a shingle warranty. The Magnusson-Moss Warranty Act prevents this. What it does do is give the manufacturer the easiest out to be able to deny a warranty claim because the deck is unventilated and the manufacturer will inevitably claim the inadequate ventilate caused the failure and it’s not a manufacturer defect. All manufacturers have issued TB’s on this.
I have seen a 50% drop in my electric bills: I had an energy audit done on a 33 year old home that had R38 on the ceiling joist(attic) and no insulation in the roof rafters. New Energy Start standard in Baltimore is R60 in the attic -- local power company is pushing R47 -- local code is R38. My basement and crawl spaces were vented to the outside and there was no insulation in the basement ceiling. Energy auditor wanted to spay foam the rafter and crawl space walls. My neighbor has his own roofing business and he said I should not/not put spay foam in the rafters -- I agreed. I had no problem with space foam on the crawl space walls. I decided to install Rafter Baffles, R38 fiberglass insulation in the rafters, and Perforated RadiantGUARD under the rafters-the house already had ridge vents. The attic temperature now stays about half way between the interior house temperature and outside temperature. The attic can dry out like a vented attic via the Perforated RadiantGUARD though the fiberglass insulation (Rockwool would have been better, but $$$$). Rafters sheathing can dry out via the air space between the sheathing and Rafter Baffles. My effective attic insulation is now a little less than R72 (R38 in rafters plus R38 in ceiling joist) because of the R13 insulation in the attic side walls. The attic HVAC system temperature now stays near the half way point between inside and outside temperatures -- better than setting in 17F in the winter and 140F in the summer. I also added foam boards to crawl spaces and basement walls. I also installed an ERV In lieu of Energy auditor 's suggestion to use a bathroom vent set to vent the house at 50cfm - 50cfm would have cost me $$$ in the winter and summer. by the way, I only turn on the ERV when the outside temperature is +/- 3 degrees of my inside temperature. (might have been more cost effective in using the bathroom fan but no one sells a controller connected to the house inside and outside temperatures to control a bathroom fan.) I still have some insulation work to do behind some knee walls and when the HVAC system is upgraded, I'll add R8 to the attic duct work.
Hi hi. If I wanted to install a standing metal seam roof, would the OSB sheathing layer be required at all?
(Assumption being that I include horizontal boards in addition to the vertical boards included in the mockup.)
Hi Jordan, this might be a silly question, but is there a risk of condensation on the inside face of the 2" of polyiso? Or is it considered permeable enough that any moisture would condense on the roof deck and be dried out by the venting? In the case of the former, should the attic be conditioned appropriately to remove moisture to in the interior?
Why not secure the old deck the best you can then add a second layer on top of it?
Yep that's the standard. Only issue is not being able to inspect trusses to make sure your nails are hitting.
Foam adhesive takes care of most of the risks of anchoring being an issue.
Modern sheathing issint going to end up like 1970s plywood.
I thought the same thing, but could possibly have an issue with moisture getting between the two layers of decking, then being driven towards the inside and into the spray foam. Could resolve that issue with furring strips between the two layers for an air gap, like in his 3rd option. Would then just need to deal with the increased deck thickness when it comes to the facia and any penetrations that have to be a certain distance above the decking.
I’m redoing the attic insulation and ducting in a 1960’s home in Dallas. What methodology would you recommend for this?
I really like the idea but what if it’s a more complex roof with valleys, no one really builds simple gable houses anymore.
This can be done on almost all roof types...the more complex the roof the more attention needs to be paid to the details related to roof transitions.
I sprayed a hip roof because you just can't get enough ridge ventilation.
@@semosancus5506 not really a builder here - just a guy who spends too much time thinking about how to solve problems on my own homes/projects 😆
Pretty sure you would need some engineering/design help but you could probably size roof vents that can be set close to the peek of the hip roof on the faces to aid in venting the roof assembly..
This is not insurmountable problem in my mind...a good engineer or architecture (or builder) should have a solution since such roofs are fairly common even on new builds and as long as they have experience with such a roof system, they have probably dealt with the problem before...
In my area the hip roofs are mostly on ranch style homes so they still have a substantial amount of ridge go use for venting but I live in an older neighborhood so yeah...
IMO, just spraying it at the deck is a recipe for disaster in the long run...
You'd be happy to know that I built a simple rectangle with 1 single 4/12 roof pitch. Very easy very simple. It's also vented
Well, they should. :) The trick will be getting enough ventilation at the peak of the witch hat roof. Ridge vents up the hip? I would be concerned about getting enough ventilation with or without the insulated deck.
Interesting, are there any issues with bugs & mice?
This is a great primer for anyone learning about attic insulation and a decent idea, though, i think attaching the decking to the rafters and then using attic baffles/vents between decking and foam/fiberglass might be easier. Seen guys make baffles fast and easy out of foilfaced/rigid foam and handle joints/valleys with irregular rafter layout. Thoughtful stuff about the envelope though, enjoyed this video!
How do you get your shear values on this assembly? I assume a structural screw through the flat 2x?
I would run that by your engineer for exact specifications, but Zip has a good starting point for their zip R system
@@JordanSmithBuilds There's really no getting around the fact with this type of foam insulation. You are putting all the screws in bending, which drops their strength by a ton. Plus, you lose the added strength that closed-cell spray foam gives you. I would rather have CCSF with a plywood deck; you can cover it with an ice and water shield type product and build an airgap with 2 by material and another layer of decking over it.
Could you put polyiso on the roof of a traditional vented attic to help reduce ice dams?
Yes, but it would require a whole face be covered or its just going to move up the face.
Hi. Great video. The preferred roof assembly shown is rafter, 2" foam, 2x4 on side for air gap, sheathing, then roof assembly. Makes a ton of sense.
Is the advice to framers & roofers to just be careful with stepping on the foam until the sheathing is laid?
Most rigid sheet foam is 150 to 250 PSI so you would have to be pretty rough to gouge it with steps. Also, most builders are used to walking rafters, the purlins laid flat over the foam would give even better footing than a rafter on edge. Only real risk I see would be a dropped tool, that's moving fast and is going to hit on a small point.
@@22kmclarenthanks for this!
So your saying the r value of the 2" foam board is the same as the spray foam?
Question. In Texas what about Ridge Road in Texas ventilation
Could this be used in a retrofit application by mounting to the bottoms of the joists? How would you handle humidity in the attic at that point?
You would have to get the details right, but I think it would be possible. I run whole home dehumidifiers in my builds and will allow for some dehumidification in the attic
Would the 2x tails need to be beefed up to create the soffit?
Would you be willing to share what software you are using for that 3D rendering? Thanks in advance!
Chief Architect!
How much more expensive is the 3rd option though?
Looks great functionally. I'm not quite sure how you could build it though without putting down a deck before the rigid foam. I don't believe the rigid foam would support anyone's weight.
That being said, I've seen you do some really impressive work, so I imagine you'd pull it off somehow.
This is my concern as well especially if rafters are 24" oc that's not a lot of strength
I was looking at that and wondering the same thing. One misstep and you've got a huge hole through your foam board.
Sure. I thought of that as well. However, we have people traipsing through attics with drywall ceilings below, and we manage not to go through…. often…. I think this would be a single step install, foam and then osb, foam and then osb, sheet by sheet up the roof.
@@JordanSmithBuildsMaybe reversed? 3/4 structural sheathing (plywood/OSB), air barrier, insulation (polyiso/rockwool), laths, 1/2 or 5/8 sheathing, shingles. The inside layer could be one of the combination sheathing-insulation products from Rockwool or Huber if you wanted to save install time. Or old school a layer at a time. Good video. Thanks for the thoughts!
Same thoughts, however, people traipse through attics knowing drywall will not support their weight. Unless this becomes a common building method, when this decking gets replaced, I strongly doubt the roofers are going to question whether or not this additional layer over the rafters is solid enough to walk on.
I also just see the install being too tedious, time consuming, and the details difficult to accomplish. How are they going to air seal the foam if other layers are being put on before you get adjacent sections put up?
Would the code be satisfied with 2x10 rafters (r30) 1/2 in poly iso and 1x4 furring strips on roof For a Most affordable version?
You have 2in foam and 2x4 furring… requiring some specialty fasteners?
I would assume a jumbo nailer but I’d like to know as well.
I'd assume 5" or 6" powerlags to hold down the 2x4 furring. Those run about 30¢ each when bought in bulk.
Will the foam layer that the roof sits on squish down over time? Seems like a lot of weight.
No, it will be able to maintain the weight for the long term. This has been a commercial roof detail for decades.
I've got a small cabin in a heating microclimate, so zero worries about hot days. I'm tired of the insane price of delivered propane, and I need to replace the wood-fiber siding and asphalt shingles anyway, so I thought I'd super insulate, cancel the propane, and go all electric.
I've puzzled over insulating the roof. I considered closed-cell spray foam on the underside of the deck, but the building department requires peel-n-stick roof membrane on the lower half of the roof deck to avoid damage from ice dams. I pictured my roof sheathing turning to rotting mush from trapped water. Also, I've got the impression that getting a decent R-value with only spray foam could get pricey.
I came up with exactly the same idea you show. I'll remove the shingles and roof sheathing, place multiple layers of rigid foam board insulation directly on the rafters, tape all joints, line up wood furring strips with the rafters, put plywood or OSB decking on the furring strips, finally install the peel-n-stick and shingles.
Polyiso is brilliant for Texas, but not so great in Colorado. They've changed the blowing agent over the years to address pollution issues, and have currently settled on an agent that loses R-value as the temperature drops. However, the R-value for XPS goes up with dropping temperature. Maybe I would like a bit of closed cell spray foam between rafters, so any type of polystyrene mounted directly on the rafters is out (EPS or XPS). So foil-faced polyiso directly on the rafters, then a layer or two of XPS above that.
I recently picked up a 250-count box of 10-inch TimberLOK screws from my local big-box store at a really good price. Assuming 1.5 inches to penetrate the furring strips, and at least 1.5 inches to anchor into the rafters. This leaves 7 inches for rigid foam board insulation. 1-inch polyiso and three layers of 2-inch XPS sounds about right. This should give about R40 at 25° F. Of course it'll be water-tight, air-tight, and moisture-tight, so by comparison it'll destroy the performance of any type of fluffy insulation. Even so, I might need to add a bit of insulation between rafters as my building department requires at least R49 on top (they seem to be counting on people using fluffy insulation).
I think it could work.
You should reevaluate the XPS product you are able to get today. It is not what you think it is. All foam plastic insulation manufacturers were required to change their blowing agents. The XPS industry just ignored and lobbied their way out of the change for 2 decades. Now they have a new blowing agent, new resin mixture and different additives. The XPS (NGX) made today is a completely different product than what existed 5 years ago. It should not be compared to the older XPS products as they have very little in common. It was more than a color change.
I agree with one aspect of this, your last model may, because of the continuous outside shell be the most energy efficient, but also maybe not.
That having been said, what are your costs associated with this?
You mention the main benefit being if you need to reroof, but realistically, a properly installed roofing would only need to be replaced once in one's lifetime, if upkept properly.
Closed cell foam performs very well even with only 3" applied in a wall cavity, and as far as sealing your framing seams, that is pretty much something required in any build today.
Applied correctly I believe Closed Cell (and possibly just some suppliers) outperforms any system on the market, in bang for the buck.
I think that is indisputable.
Could you spend a lot of time and money and come up with something that could outperform a few inches of closed cell? Probably, but at what cost?
I have watch a lot of videos because I am a contractor too, but I do see people in the business spend a lot of other peoples money doing things that won't return them their money.
Personally I think we need to (at least for the most part) come up with a design that will build a good tight home without breaking the bank for the everyday build. We are driving the cost of homes up too high too fast in my opinion.
I agree with your exterior insulation and air gap. Would a radiant barrier be effective within that gap or do you not need to worry about it with the foam board? I disagree with using shingles. They are a terrible product: They don't last, they damage easily, greater chance of leaking, and they absorb heat and run way hotter. I just had my standing seam metal roof installed on our 1,500 sq/ft new build a few weeks ago for only $7,200, so the price isn't that bad either. We are also spraying foam under the roof deck, which is zipped and taped.
Short answer is yes. Medium answer and long answer below and in the link.
“Interestingly, the air-space could be able to resist the incoming or outgoing heat flux from indoors even more than the external cladding when reflective insulation is used on one of the sides of the cavity.” From Rahaminijad
Full paper here- www.tandfonline.com/doi/full/10.1080/23744731.2021.1898819
I dont get why builders still lap rafters and ceiling joist. Run a rim board on the ceiling joist, plywood the top of the ceiling joist and zip tape the whole deal. Cellulose the cavity and put rigid foam over the plywood. You get proper air sealing and you avoid that weak R value by the eaves.
If you are doing a metal roof, could it go framing-sheathing-underlayment-rigid foam-strapping-metal roof?
Absolutely! This is my preferred method. I pretty much exclusively build metal roofs, but I’m playing with designs that might* help people who are trying to build at lower costs.
@@JordanSmithBuilds I'd love to see it. I'm picking up ideas for a very simple yet high performing house I might build to rent.
Taping the joints isn't a vapor barrier.
Defiantly lose some shear strength when you put 2" foam board between the rafters and furring strip/ventilation gap… the labor costs and additional materials for this complex.. I don’t see the advantage when you look at studies of spray foam on the roof deck only increasing temperatures 2-3 degrees
I'm curious if this could be done with the same results and significantly less cost by using house wrap in place of the 2" foam.
No there isn't a shear strength loss. From the foam.
@@sparksmcgee6641 you lose strength when you add two inches of foam between the boards and sheeting. You may wish to educate yourself on installation of Huber Zipp insulated sheeting in R12.6 as an example of the detail discussed in this video. -Additional requirement of code - engineer and fastener requirements
@9:24 you can see that the foam is being placed between the rafter AND the furring strip before the OSB.
Typical construction - no specific training- no special fasteners - no engineering +and the strength of spray foam is a far superior method. Don’t argue it Sparks - build the roof he’s saying - I’ll be happy for you. :)
@TriDaddy I know that vs the same OSB without foam.
The point is you adjust for that so it meets thr specs you need or just code.
You're saying that's a "problem" or unaddressed issue with this system. These videos are targeting trades so commenting as if the work addressing shear limitations of the products or that you can't get the same shear strength installing the product as without the product just isn't true.
Every construction video doesn't need to start with "First the earth cooled and then came the dinosaurs...........".
@@sparksmcgee6641 Its possible to get the same shear strength in your approach - but it will cost you more in skilled labor and likely need engineering approval.
Likewise it would be nice for you to validate the fact that spray foam attached to the roof deck increased stregnth of the building assembly over your proposed approach.
Here is a nice video on sprafoaming the roof deck. We began doing this in 2022 that I've tracked/validated no cause for concern with shingle life. ua-cam.com/video/hJTDvDPtF0A/v-deo.htmlsi=cBpoF8Yh3FtBoZYt
I'd encourage you trying this aswell.
If switching roofs wasn't another mortgage I'd really think about making my house more energy efficient.
You can put that foam board on the inside of your roof, get the foil backed foam board-tape the seams. I’m an HVAC contractor and weve done that to a few homes that didn’t wanna tear there whole house apart
Is there addional insulation under the 2" of ridged foam?
Yes, you would insulate between the rafters as well
what if you don't have soffits?
I prefer to vent everything where possible. The biggest problem i see with spray foam is the weather barrier that is applied on top of the sheathing. Spend big money on spray foam and put cheap synthetic felt down over it..
Why are you putting your mechanicals in an unconditioned space? Given modern building science and logic this is a poor design. The delta for air con or heat in a ventilated attic is huge, energy inefficient and asking for problems.
Can always spray foam the duct work.
I would worry about bugs in the air space, in the siding at least,
We use a screen detail at the vents to keep the bugs out
Replacing the roof wood is more of a pain in the ass than calling a guy out to spray the repaired areas. There’s houses from the 20’s with original wood on the roof, your first two concerns about spray foam are not even worth stressing over.
IT IS A REAL EASY SOLUTION BY USING ZIP PANELS FOR ROOF PANELS.
SIP PANELS ROOF GOOD ALSO!
AND NEVER USED SHINGLES - METAL ROOFS LAST FOREVER!!!
I'd second the ZIP roof panels.
This set up is overthrowing and it's labor intensive. The number one thing in construction now is labor, it's the reason housing costs are going up.
It may pencil out cheaper right now but if he keeps using it, im betting it'll cost more in the long run as the cost increase will be very noticeable before reassessing and realizing something else would have been better for the last couple years.
My two cents.
Just discovered this " fix" when water began running into my living room under hard rain.. ive been here 4 years and its thr first time its ever leaked. Some dumb bandaide repair that i get to repair
Cover, insulating the slab,
No offense Jordan, but the code already specified how many inches of impermeable insulation or impermeable + permeable combo will one need. In case of low pitch roofs not enough roof slope to create "greenhouse effect" due to pitch thus there is not enough pull for hot air to properly vent it. I do understand your concerns about rood decking not able to dry to inside. BUT Leave engineering to engineers.
I don't recommend Matt Risinger diagonal sleepers over roof decking either.
he's not as concerned about the ventilation with it being nominal. He's talking about not having to replace all the foam under the roof deck. In his assembly the roof decking won't be in as much jeopardy because there is a slope for any water penetration possibilities, roof decking can be replaced easily.
It would be more helpful for the rest of us if you actually explained the details. Saying it is in the code is only marginally helpful. Explaining where it is, what is says and what it means would be much more helpful since the rest of us are trying to understand this. Leave the communication to the communicators.
@@spenceralridge4958 "Leave the communication to " .. that is stupendous, sorry. I posted the engineering. Are you asking where is that in Your local building code considering 1 millions jurisdictions? Joseph Lstiburek, Ph.D., P.Eng, ASHRAE See: www.energy.gov/eere/buildings/articles/building-america-webinar-high-performance-enclosure-strategies-part-i . But using your own words -- Leave engineering to the engineers 😁, and not the communicators. Ha ha ha ha
@@jsongraham There are eng details how to do roofs correctly based on USA zone hose is in. The decking will be fine if it can dry in some way. It should NOT rot, I own 70 y.o. farm house with good decking, still original. Jordan vs Joseph Lstiburek, Ph.D Building Science -- who should we all listen to?
As well as Spray Jones channel
So the trick is to sprayfoam over polyiso foam or use matts
if you have a poly iso under the roof decking with out the air/rain screen (on the roof) then he is saying that the roof decking will still need replacing. It's actually worse if you put a closed cell poly-iso under the roof decking without the rain screen. Because you'll actually never see if you have a roof leak until it is too late. With an open spray foam it'll sponge and discolor so you can actually see.
I agree with your continuous air barrier and the "perfect" wall assembly, but it's not the spray foams fault for a leaky roof. I'm still putting spray foam insulation below my roofline, but am definitely going to create space for things to dry out using furring strips.
Spray foam below a roofline is a good idea, when the roof assembly is proper! Just dont agree with the title of your video. It's yet again, anti spray foam propaganda.
spray foam is bad period i work as a volunteer firefighter in 2020 Christmas we sat down for dinner we had a house fire to go to wanted to have a table empty fast to start a fire my fire all work as on in some way
the house had a renovation done to it before the young family moved into it before Christmas the 4 deaths of the young children went to a murder charge on the contractor I helped with this investigation the young father before he passed away did ask me to look into this contractor work he did wow we did fine the fold that they had everything that was to done to the renovation to this house and all the permits were fake for this job to
the house did not pass any of its inspections what we did catch quickly was the wiring that did start this heavily black toxic smoke in this fire cell we had that night
the same date was on the re-inspection of this house and all of the same person passed all of the variations
from the others who did this inspection was a cousin to this company who done this work electrician who did this was not one too was and another cousin
as to the fire, spray foam was covering up all of the bare wire that needed to be fixed ot the bad plumping to the farm was melding and making the toxic heavy black smoke in the house there was in the contract that did say NO spray foam in the reno they did ask for the Rockwell insulation to be used they did not use it at all
murder charges have been laid in all of the companies who worked in that reno he was in the Middle East when he was tipped off he would be arrested when it came back here
we did hear he was killed over there by the terrorist group he was with he was a while known one to hide inand another county to stay out of reach of being killed
his family came over as refugees Americans forced canadian to take their refugees too how all of them did make it to Canada be American not taken there refugees themself
🤔.....WTH are you saying🤨
what is happening here ??
This is the type of comment that keeps my coming back to UA-cam! Hope you’re good buddy…
Spray foam is rated to 1100° and it doesn't spread like fiberglass insulation or blown in. The only thing better would be mineral wool.
Dumb people that think the only foam is the Styrofoam used in packaging electronics.
I think spray foam is bad and never should be used for many reasons. But if you did want to go the spray foam route, you could put tyvek over the roof before sheathing. That will at least solve the problem of it sticking to the sheathing. I'm not sure if having a breather material on top of the sheathing would be approved by the shingle manufacturer.
That’s a good detail.
Why is that? There are many extremely good applications of spray foam.
Tape isn't insulation.
lovely climate! lot of energy