Roofing for ICF Home
I have an insulated concrete form home in Colorado Springs which is about to get a new roof due to our most recent hail storm. My question is regarding roof venting. I’ve read some of the info by Joseph Lstiburek regarding roof venting, but am a little confused about my particular situation. My roof is composed of several peaks and valleys which have asphalt shingles (photo below). Around the roof are parapet walls which have scuppers leading to downspouts. At each of these places the roof has an area of EPDM. Under the shingles is ice and water shield. The venting is a little confusing to me…there are ridge vents, but no other places on the roof for any ventilation. There are no soffits. My upstairs ceiling also has several recessed lights and some ceiling speakers which are encased in rubber boots. My last blower door test gave me an ACH50 of 2.24, although that was before the installation of the twelve 12″ speakers.
Before putting on a new roof, I’d like to make sure it is vented correctly. Are there any problems with my current roof design?
Thanks
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Replies
Louis,
My guess is that you have an unvented roof. It's hard to tell without a site visit, but with those parapet walls, the lack of soffits, and the fact that your roof is broken up by several valleys, I can only conclude that your roof is unvented -- or was designed to be "vented" by a builder who had no idea what he was doing.
For information on insulating an unvented roof, see "How to Build an Insulated Cathedral Ceiling."
Thanks Martin. So, do you think that my ridge vents are really not doing anything?
The roof vents don't even run the full distance of each ridge, and with valleys it's impossible to have an air intake in each rafter bay even if you DIDN'T have the parapet obstruction to deal with.
"...not doing anything..." would almost be true even if the rafter bays with the ridge vents had appropriately sized air intakes, given that less than half the total ridge length has venting. Without air intakes it's next to nothing even where ridge venting exists.
Louis,
As I said, it would take a site visit to figure out how your house is built. To be vented, your roof needs air intake locations -- either soffit vents, wall vents, or some type of slot where air can enter.
It also needs ventilation baffles to define the air space between the top of your insulation layer and the underside of your roof sheathing.
Finally, it needs a ridge vent (which your roof evidently has).
All of these components need to be connected. With roof valleys, this is close to impossible. So something is not quite right about your roof.
Martin,
I'm still giving some thought to my roof situation. I'm considering that it may be a good time before my re-roof to take a look under my roof sheathing in areas which are not accessible from my interior ceiling access. In particular, before my previous re-roof, which was in 2015, we had severe water leakage into the house at several scupper locations. While all of the interior damage was repaired, I don't think anybody examined the attic insulation at all of these sites. Additionally, I'm concerned that I may be missing something with regard to the roof venting (or lack thereof...). Even though I didn't notice any moisture issues from my observation through the attic access from inside, I'm thinking I should get a better look at the more remote areas of my attic . Still a bit baffled by the attempt at a ridge vent with no air intake locations... Would you be able to recommend anybody in my area that would be qualified to give me a site visit and evaluation?
Thanks
The complexity of the roof lines means it really can't be ventilated properly. It's expensive, but adding rigid polyiso above the roof sufficient for dew point control on any fluff insulation you have under the roof deck is probably "worth it" in the long term here, especially since you've now punched a number of big holes in the ceiling pressure boundary of the house.
The fully adhered membrane on the roof deck (which it may already have) will make it air tight if you cover over any holes they punched in it for ridge vents, etc. It's good idea since the whole design is a serious snow trap and you have known heat leak points (some of them new) creating melt-out/ice dam potential. Putting foam on top if the Ice & Water with a nailer deck through-screwed to the structural roof deck will self-seal/heal around the screws. A layer of #30 felt under the shingles on the nailer deck is all that would be necessary, not another full layer of Ice & Water Shield. You may have to get creative and relieve the foam layer around the scuppers for this to work.
In Denver at least 40% of the total R has to be above the roof deck for dew point control. Assuming there is something like R30 under the roof deck that means it needs at least R20 above. If you have R38 under the roof deck you need at least R25. So with R5.7/inch roofing polyiso that takes a minimum of 3.5" for dew point control on R30, 4.5" for R38. To take the sting out of the material cost (and with all those valleys you're looking at a substantial scrap rate on the foam) reclaimed roofing iso can be had at a fraction of the cost of virgin stock.
Repurposed Materials has a location in Henderson CO, and usually has polyiso in stock at a few different thicknesses, eg:
https://www.repurposedmaterialsinc.com/poly-iso-insulation/den-insulation-4-4-x-8-12pc/
What's in stock varies, and it may be possible to get a heads up from them when a new batch is coming in- worth giving them a call. https://www.repurposedmaterialsinc.com/contact#Denver
Insulation Depot has more stock, but I think their nearest facility to you is in Texas or Nevada. They often advertise truckload quantities in the Denver craigslist though:
https://denver.craigslist.org/mad/d/iso-rigid-foam-insulation/6659082213.html
https://denver.craigslist.org/search/sss?query=rigid+insulation
http://www.insulationdepot.com/
I say your house as a system seems to be working as is. Making changes to a, know working system is a risk. Assuming you do not have any big problems (ice dams, mold, rot) what would be the up side for any change? Maybe if you had lower vents the shingles would last longer? If you had lower vents water could leak in and damage walls, embers from a fire may enter the vent and burn down the house, or some other unlikely and unforeseen problem brought on by the new vents.
If your attic has R38 or more insulation and no major problems, build the new roof just like the old one.
Walta
"Making changes to a, know working system is a risk. "
The changes have already been made which may have increased the risks:
"My upstairs ceiling also has several recessed lights and some ceiling speakers which are encased in rubber boots. My last blower door test gave me an ACH50 of 2.24, although that was before the installation of the twelve 12″ speakers."
We also don't know for sure that the existing roof deck has not been compromized. Do we really KNOW that it has been working, or only that it hasn't sagged and caved in?
In an ICF house that tests at ACH/50 of 2.24 would usually have most of the leaks somewhere other than the walls. If the ridge vents account for any significant fraction of that leakage it might not really be working.
Thanks for all the information. I don't know what the R-value of my attic blown-in insulation is. Interestingly, I had my current roof put on only three years ago...also due to hail damage. I had Ice and Water Shield put on, but it did not have it before then. I'm not the original owner, but I'd presume that was probably the case since the house was built in 2004. So, I guess another change I've made is with the addition of Ice and Water. Perhaps I should get up into the attic and see what things look like...
Louis,
Q. "Perhaps I should get up into the attic and see what things look like."
A. In a situation like yours, that's always the first step!
To my untrained eye, I don't see any obvious issues in the attic. Insulation is cellulose blown in to R38. When I opened the ceiling hatch it was noticeably cooler in the attic. It's about 74 degrees inside and 76 degrees outside this morning. I did notice the two bath fans venting several inches below a shared roof vent...don't know if that's an issue. I don't see any signs of moisture though. Oddly, I noticed a couple baffles. My attic accessibility is not good and I only have the one access hatch, so I couldn't tell if there were more. That portion of the roof should be directly over an ICF wall, with no sign of an air intake anywhere that I can see. I'll attach photos below.
Something happened to the photos when I tried to upload. I'll try here...
Photo 2
Photo 3
Photo 4
Photo 5
Deleted
Baffle
Seems some of the photos got rotated during upload. Sorry about that.
Louis,
Those two exhaust ducts that terminate in your attic need to be connected to proper exterior terminations -- either roof vents or gable vents (if you have a gable).
Otherwise, everything looks pretty good. Attics don't necessarily need a lot of ventilation, as long as there is plenty of air above the insulation. Where you tend to get problems is in situations where there is insulation close to the roof sheathing (especially in cold climates). Cathedral ceilings are always riskier than open attics. Flat roofs are trickier than sloped roofs.
But I believe you if you tell me that everything is fine. For more information on why attic ventilation may not always be needed, see this article: "All About Attic Venting."
In the photos I can see no reason to change anything.
I do not like the way the bath vents discharge but even those do not show any evidence that anything was ever wet.
If you are reroofing you may want to add 2 vent hoods like this.
https://www.homedepot.com/p/Broan-Roof-Cap-636/202191718
Walta
Thanks for the responses. I really appreciate the input. I think I may not change things on the re-roof. Except I will connect the bath fans to the roof vent.