Renovation to address heat gain (summer), heat loss (winter) and ice dams
We have a home at about 6000 feet elevation in Utah. It’s dry, and the temperatures can vary from below zero F in winter to over 100 F in summer. Our house was built in 1994 with some attic space and lots of cathedral ceilings. From what I have observed, the roof/attic was not insulated well when built. This has been partly remedied by blowing in extra insulation into the attic, but most of the cathedral ceilings where framed with 2”x12” with probably 8” or 9” thick batts of fiberglass. In short, the roof has lots of heat gain during the summer and lots of heat loss in winter. It appears that the builders tried to overcome this by installing a huge AC unit (for the summer) and several hundred feet of heat cable (for the winter). Not surprisingly, our electric bill is quite high and we have massive ice dams.
This website is by far the best resource I have found for the issues I am describing, and I have spent several weeks reading articles. I was originally thinking of adding a cold roof, but I now realize that won’t help with a ceiling that is poorly insulated to begin with. Based on what I have learned I am leaning toward the following solutions:
-Add rigid foam insulation (nailboard or SIP) on top of the existing roof sheathing to bring the R value up to R-49 for the cathedral ceilings (we will do this at the same time we replace the roof).
-Add additional blown insulation to the attic to bring it to R-49.
-Improve attic ventilation with soffit vents+baffles and roof vents.
-Get rid of the skylights.
-Build a utility room in the attic so that the attic furnace/AC operates in conditioned air space.
-To the degree possible, move flexible attic ducts into conditioned air space.
Does this plan sound reasonable or am I missing something fundamental?
Why do I never see heating cable in cold regions in Europe? In fact, I have several German friends and colleagues and they don’t even know what I’m talking about. Is my perception correct and if so what is different about the way their houses are built? Obviously the roofing materials are different – many of those homes have tile or steel roofs.
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I can't respond to your heating cable question but think your overall plan is a good one. The one thing I would suggest is undertaking a thorough air sealing exercise (in combination with blower door testing). Your insulation will be far more effective if you make the structure as tight as possible.
Make sure you heating cables are plugged into a smart controller. Being on only when really necessary will reduce power use (over dumber controllers).
Can you please tell us your name?
Q. "Does this plan sound reasonable or am I missing something fundamental?"
A. In addition to following Steve's advice -- performing air sealing measures -- you'll also need to find a way to block the air intake into the ventilation chutes in your existing cathedral ceilings, and to also block the tops of these ventilation chutes near the ridge.
Adding rigid foam above the roof sheathing to supplement the performance of the fluffy insulation between the rafters is a great idea, but that approach will only work if you can exclude exterior air from the ventilation channel between the top of the fiberglass batts and the underside of the roof sheathing.
Once you have meticulously sealed the areas I describe, you can build new ventilation channels above the top of the rigid foam layer if you want, making sure that the soffit vents and ridge vent connect with the new ventilation channels.
To pick up the thread mentioned by Steve -- the need for air sealing work -- I'll provide a link to a relevant article on air sealing work for attics: Air Sealing an Attic.
Q. "Why do I never see heating cable in cold regions in Europe?"
A. Installing heating cables at the eaves of a roof is a terrible idea, so the simplest explanation is that Europeans are smarter than Americans. Seriously, though: most areas of continental Europe don't get as much snow as New England or the upper Midwest, so ice dams are rare in the Netherlands, Belgium, or the lower elevations of France or Germany. In areas of Europe where deep snow is more common -- I'm thinking of Sweden, Norway, and Finland -- building practices are better than they are in the U.S., and it's probable that these Scandinavian homes have better air barriers and thicker insulation than most ice-dam-plagued homes in the U.S.
I'm not sure why you recommend that User-6890841 install heating cables. Heating cables are a bad idea. They are used on poorly designed houses with air leaks and insufficient insulation.
I didn't - User-6890841 already has heating cables.
That's true -- but the heating cables should be unplugged and removed.
I'd be interesting in seeing your data showing that heating cables are never part of a "most cost effective" remediation solution.
I'm happy to admit that heating cables for roofs are cheap to install (although they require energy to operate), and are therefore the go-to ice dam solution for cash-strapped homeowners.
The fact remains that any house with heating cables at the eaves suffers from fundamental design errors that can be avoided during the design & construction phases of any new home.
Thanks for the thoughtful replies. My name is Chris Butson (I just updated my profile so my name should appear from now on). It sounds like the points I should add to the plan are:
-Blower testing and air sealing: good point! However, this might have to wait until after the windows are replaced during the renovation, since the existing ones let quite a bit of wind and water through the seals. On this subject I also read the article about air sealing an attic.
-I will need to remove conditioned air ducts from the cathedral ceilings and block airflow between the rafters (I think this is what you meant by ventilation chutes), especially at the eaves and roof ridges.
More broadly, I am slowly coming to terms with the fact that I will have to do most of the engineering work for this renovation. That's fine - even though I don't have a background in residential construction, I do have 3 degrees in engineering and if I can find time and good advice (indeed, I am learning a lot from GBA) then I can plan the details. I have hired an architect who can create plans and construction details for what I want to execute. What I have not been able to find is a builder who seems to understand these issues or possible solutions. There are several I have spoken to who have repeated some variation of "If you get snow then you must have heating cables," as though this is a law of physics. I fundamentally disagree with this, but I doubt I will be able to convince them otherwise, and even if I do then I don't have confidence in their ability to execute the necessary modifications and details. I am open to suggestions about how to find a capable local builder.
Q. "I will need to remove conditioned air ducts from the cathedral ceilings and block airflow between the rafters (I think this is what you meant by ventilation chutes), especially at the eaves and roof ridges."
A. Ventilation chutes (or baffles) are usually made of thin rigid foam or cardboard. They are used to separate the fluffy insulation batts below from the air gap above. In some homes, builders omit the ventilation baffles, and just leave an air space between the top of the insulation and the underside of the roof sheathing.
Regardless, there will be a gap near the soffits that allows exterior air to enter the ventilation channel, and there will be a gap near the ridge that allows air to exit the ventilation channel. These gaps -- at the bottom of the rafter bays and at the top of the rafter bays -- need to be carefully sealed to prevent air flow in the ventilation channel.
Q. "What I have not been able to find is a builder who seems to understand these issues or possible solutions. ... I am open to suggestions about how to find a capable local builder."
A. One option is to contact a local energy rater certified by RESNET or BPI. (Visit the RESNET or BPI web site to search for certified experts in your geographical area.) Call up the energy rater and ask for the name of local contractors who understand energy issues, building performance issues, and building science issues. Good luck.
Thanks Martin for explaining about the ventilation chutes. We will need to look at these carefully and make sure that they are sealed at the soffits as you suggested.
I looked at RESNET and BPI and have contacted two local contractors.
If I remember I'll post an update on this thread once we get the renovation underway.
I want to make sure I understand one sentence written above:
"Once you have meticulously sealed the areas I describe, you can build new ventilation channels above the top of the rigid foam layer if you want, making sure that the soffit vents and ridge vent connect with the new ventilation channels."
Do you mean install an air gap/channel between the top surface of the rigid foam and the new layer of roof sheathing? If so, is this achieved with furring strips between them? Thanks.
If you want to create ventilation channels between the top of a layer of rigid foam and your roofing, the usual method is to install 2x4s on the flat, 24 inches on center, perpendicular to the ridge. These flatways 2x4s create ventilation channels that are 1.5 inch deep.
If your roofing requires solid sheathing, you would then install a layer of OSB or plywood above the 2x4s, followed by roofing underlayment and roofing.
If you are installing a screw-down metal roof, you could install 1x4 or 2x4 purlins, 24 inches on center, perpendicular to the first layer of 2x4s. The metal roofing could then be fastened to these purlins (which will be parallel to the ridge).
All of these details are explained in my article, How to Build an Insulated Cathedral Ceiling.