More Q&A Spotlight
Our latest Question of the Week comes from a homeowner in New Jersey. Monica is uncertain of the best way to insulate the roof of a new second-story addition on her Cape Cod home. She wonders whether it’s wise to insulate directly under the roof sheathing — especially since the mounting system for her photovoltaic array requires 54 holes to be drilled in her asphalt shingle roof.
Monica wrote, “Is spraying the roof deck with foam going to increase the possibility of a major problem down the road if a leak should develop? There will be 54 holes drilled for the solar mounting system, and even though the installer assures me they won’t leak….well….of course they will say that!”
Robert Riversong pointed out that it makes sense to bring her attic inside the home’s thermal envelope — especially since she has a furnace in the attic.
Martin Holladay pointed out that there are mounting systems available for standing-seam metal roofs that don’t require roof penetrations.
John Brooks reminded Monica that it will be expensive to dismantle the solar array when her shingles wear out.
What do you think?
To read Monica’s question and all of the responses it generated, see “Insulation options are of concern with solar panels.”
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12 Comments
Twice as Many Members Agree
as of today ....67% agree that Compact Insulated Roof assemblies are more problematic and should probably be vented to avoid problems!
Do you realize that we are taliking about 2 out of every 3 members! ;-)
*voting members
Surge in Voting
A recent surge in voting is swinging towards non-vented
OK, Sorry about the joking around
Consider a hypothetical .....there is only a 2% chance that a penetration might leak.
If there are 54 fasteners.....what are the odds that at least one fastener/penetration leaks?
of course I am just making up the 2% number
that would be 98%^54 = 34% chance that the roof does *not* leak.
Your 2% figure is must be very high, or these installation methods would never be used ... BUT it certainly shouldn't be zero. I'm likely going to go standing seam on my new roof for this exact reason; but nothing is prefect.
Note for the OP - using a "belt an suspenders" approach is always a good idea - for example there might be ways to add or adjust flashing to divert the majority of water runnof at the locations of fasteners. But, FWIW, any holes would make me very nervous, too.
apples and oranges
I don't see what one has to do with the other. How does spraying the roof deck increase the likelihood of a leak? As mentioned by John, I would be more concerned about the difficulty (and higher cost) of future roof repairs.
The decision as to whether to encapsulate the attic comes down to cost vs. potential energy savings. Closing an existing vented roof can be expensive. The ceiling insulation must be removed and the roof vent system closed. And if the roof extends over a porch or garage, that portion should be blocked off, otherwise you'll have to seal off and insulate a larger area than necessary. It's important to align the air barrier with the thermal boundary.
In order to calculate potential savings, it's necessary to estimate how much energy that particular HVAC system (presumably there is more than one) contributes to the overall energy bill. It would be reasonable to expect encapsulation would save 10% to 15% of that system's operating costs. The percentage would be higher in mid winter and mid summer, and less in milder weather.
Finally, don't confuse conducted heat loss with duct leakage. The latter typically represents a bigger loss and is much less expensive to fix.
The likelihood of a leak
Whetstone,
You're right — spraying foam against the roof sheathing does not increase the likelihood of a leak.
However, it complicates leak detection and leak location, leading many to worry that a small leak might cause sheathing rot before it is detected.
Insulated Roof deck with a few inches plenum to vent
I thought an insulated roof deck can be vented by creating a suspended plenum on top of the roof deck - perhaps a little additional material for an extra layer sheathing and some 2X purlin. But you get both insulated attic and roof venting. Isn't that what the 1st PH in IL did?
Venting roof sheathing
Harry,
You're right, or course. It's possible to build a ventilated insulated roof with the vent channel on top of the roof sheathing. Such a design usually requires a second layer of sheathing, unless you use metal roofing.
Replaceing shingles under solar panels
While it is true that it will be difficult to re-shingle under the solar panels, the need to do is also likely to be much less.
After 30 years, I had to re-shingle my house (built during the Carter administration) and was faced with this very question. Getting up close to my Revere Solar panels, I was able to see that the asphalt shingles (Timberline) under the panels were as good as new. So, we just re-shingled around them - for another thirty years of life (I hope). After 60 years, it may be time to replace the solar panels anyway.
The panels do a good job of protecting the underlying shingles from ultra violet insult and most other weathering influences, so the life of the shingles is likely to approach that of the panels above.
Will Solar Panel Mounts Cause Roof Leaks?
Yes it is right to Solar Panel Mounts Cause Roof Leaks.But it can be prevented this not a bigg issue.here i give you some suggestion to you First is to pack the whole is very carefully.another most important things is Typically, there are four options: aluminum, stainless steel, angle iron and wood. Which of these materials you choose will depend on your budget and your location. For example, aluminum is lightweight, making it easy to shape and weld. In addition, it is hardwearing and will resist corrosion. However, it can be an expensive option.
Thanks
Will solar panel mounting cause roof leaks.
No leaks will be caused by a properly done solar installation. A holed drilled for a mounting will be filled by the bolt or screw. Plus a sealing compound is used as well. A flashing can be installed also. Three mechanisms to cover the hole. So how is water to get in? Hire a reputable installer. Don't be afraid to spend a little extra.
My mounts leak, but they dry out because the attic is open
I used pretty good practice when mounting my PV array on aluminum racking. Drilled pilot holes, filled them with polyurethane caulk, added a wad of folded butyl tape under the feet, and a litte piece of coil stock tucked under the tab above, to push the water out of the way.
There are other ways to go, but this is what professional solar companies around here do--I see their installs on houses we work on. I think they omit the poly and the flashing actually, but I see the butyl under the feet.
That was seven years ago. This summer I noticed some black staining around two of the holes, they are definitely leaking. But the wood is dry and sound (at least for now), and I was able to stumble upon the issue, because the roof deck is exposed.
The "spray foam your rafters" idea is decent but risky. Adding vent/drain channels is a minimum requirement IMHO. At least that way you have a chance with these intermittent, minor leaks.
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