Attic Leak: Is it a roof leak or poor insulation?
In our attic, sometimes when it rains really hard, we get a leak in our attic that then appears in our bedroom underneath it. My big question is: Is the leak coming from a roof leak or is it the result of a failed attempt at insulating for a conditioned attic?
As you can see in the pictures, we have attempted to condition our attic. We did this work several years ago. In the middle section, we have drywall on the ceiling with R-19 batt insulation underneath it. In the section behind the knee wall, we have batt insulation between the rafters and then 1/2″ foam board nailed onto the batt insulation; this is sealed with tape at the seems. We also have foam board on the walls. Where the roof pitch meets the floor, as you can see, we have two layers of R-19 batt insulation.
In the picture that shows where the foam board on the ceiling and the batt insulation on the floor meet, that is where we have seen some water leaking. The water rolls off the underside of the foam board. I have pulled one section of the foam board back, and I can see a trail of where water droplets have rolled down the underside of the foamboard, and then the water drops onto the floor. I can’t see exactly where the water is originating because the entire ceiling is covered with the batt insulation/foam board.
Because the idea is for this to be conditioned space, we don’t have any soffit vents or baffles installed. We do still have a ridge vent at the top of the roof from before we conditioned/insulated it. There is only this one area where the water has appeared; all the other areas seem to be dry.
Have we done anything wrong? Is there any way this is something other than a roof leak?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
If you see the water only when it rains, that is indicative of a roof leak. I think that's what you're seeing.
That said, you do have some problems here. You can't safely do an unvented roof with batts. You said you still have a ridge vent, but did you leave vent channels of at least code minimum 1" depth between the underside of the roof sheathing and the top of the insulation? If you didn't, then you're likely to have moisture problems due to condensation within the roof assembly during the heating season. Those "moisture problems" can lead to mold growth, and, in really bad cases, rot of the structure. The foil faced polyiso will help limit how much moisture can get up into the roof assembly, especially if you taped the seams between panels and sealed the perimeter, but it's not a 100% safe way to do things.
The best way to do it would be to leave vent channels from soffit to ridge in every rafter bay, add soffit vents, then you could use batts and the interior side polyiso. If you want to go with an unvented roof, then closed cell spray foam directly against the underside of the roof sheathing is really your only completely safe option from a moisture control standpoint.
Bill
It sure sounds like a roof leak. Have you went up on the roof to try and find it? You may have to remove some of the insulation to track it down. Regardless, you'll need to track down where the water is coming from so if you don't see an obvious location on the roof where it is leaking then you might as well go ahead and start pulling back the insulation in the affected area to determine where the water is coming from.
Thanks, Bill. In every rafter bay, the batt insulation is up against the underneath of the roof, so no, I don't think there's any vent channels. I'm confused, why would we add soffit vents if we're trying to have it be conditioned/unvented? I'm worried we need to just tear everything out and install soffit vents and baffles and just do traditional venting?
I think Bill's just saying that you can either do an unvented attic, which you don't currently have, or a vented attic, which you do currently have but which isn't vented enough since there's no vent channels. Putting in vent channels would help address your issue w/ the vented assembly, or you could spray foam against the deck and block off the venting to have an unvented assembly.
The vent channels need to allow for convection air flow, which means they need an intake down low (soffit vents) and an exhaust up high (usually a ridge vent) to be able to work. The ventiallation airflow will carry away moisture so that you don't have problems on the underside of the roof sheathing with condensation, mold growth, and rot.
You are conditioning the interior living space, not the roof assembly. The roof assembly is just a barrier to air movement between indoors and outdoors, and an insulating layer to keep heat in or out. Moisture can get up into unvented roof assemblies that are build with permeable insulating materials (like batts), and that can lead to mold growth and rot. Sometimes you get lucky and things are OK, but it's not reliable, so it's not considered to be a safe assembly. Venting the assembly is much safer and more reliable, or use closed cell spray foam where the fully adhered spray foam material prevents any moisture from reaching the roof sheathing.
Bill
I was hoping to just replace this section of the roof shingles and call it good. But it sounds like we have other problems according to Bill?
My guess is if you remove a few of the fiberglass batts you will find mold has been growing on the wood behind them.
The is because the warm moist air can easily pass thru the fiberglass. The air comes in contact with the plywood that is colder than the dew point of the air in your attic. The water condenses out of the air and onto the woods surface. If the surface is above freezing the wood will absorb most of the water. If the wood is bellow freezing the water freezes if it stays bellow freezing for a long-time large amount of ice can accumulate. When it does warm up all the ice melts at once and this could be mistaken for a roof leakage.
Simply blocking your attic vents and stuffing fiberglass between the rafters is a recipe for failure.
One of the few times I think closed cell spray foam is a good idea is homes like yours. Older half story homes are notorious for leaking air 15 or more air complete air changes per hours are common. Making the homes drafty and energy inefficient. What spray foam can do that almost nothing else can is quickly seal the air leaks and provide a high R value per inch in the very limited space you have in your attic. Yes, CCSF is ungreen, expensive and risky but it is almost the only answer for older half story buildings.
Note one of the risks from spray foam is that it can hide roof leaks so you would want a new roof before it gets applied.
https://www.greenbuildingadvisor.com/article/five-cathedral-ceilings-that-work
https://www.greenbuildingadvisor.com/article/insulating-a-cape-cod-house
Walta