Cold Access Room – Gaps in Air Barrier
Re-posting to the proper Q&A category
Hi –
I recently bought a house outside of Chicago (climate zone 5) which has been added on to several times (including “popping the top”). On the second story, there is a crawlspace / dryer vent access “room” which is on the front side of the house. The front wall to this room (approximately 12 feet long) is an exterior wall of our wood frame / metal sided house. The roof slopes down through this room and continuously extends onward to our front porch. The room is unfinished (studs all around the interior) and is only accessible via a scuttle door from a bedroom, but is part of the thermal envelope, with conditioned space on the three other sides of this room.
With the cold temperatures in Chicago, I noticed that the room was far colder than it should be (even for having no direct heating source). After feeling around the slightly torn kraft faced fiberglass batts (approx. R-19) which fill the cavities between the roof studs and the exterior wall studs, I realized that cold air was blowing into the room around where the roof line intersected the exterior wall. Pulling back one of the batts revealed a 10” high gap between the roof line and the exterior wall (through which I can look down into the interior of the porch ceiling area). These 10” gaps are present between each of the 16in o.c. exterior facing studs in this room and presumably also on most of the rest of the front of the house since the porch spans nearly the entire front of the house. The kraft faced batts have (sort of) plugged the gap and hidden the issue until now. The floor of the bedroom near this room (also on the front side of the house) is also cold – I suspect because the joists below are not insulated well.
Questions / comments:
– Is there any legitimate reason for having these gaps in the air barrier? I assume no, but wanted to check before I plug all of them
– I have started to plug the gaps with 1in polyiso and caulk, which seems to help. My thoughts are to plug the rest of the gaps with the polyiso, add a bit more unfaced insulation in the cavity (as properly as I can) and then tack another inch of polyiso onto the interior side of the studs and further air seal accordingly (I would add furring strips and drywall if needed). Thoughts on this approach? Any concern with having two layers of polyiso separated by a couple inches of fiberglass (e.g. moisture in the cavity around the wall studs and roofline studs)? I don’t have any observable moisture problems currently in the house.
– The access room just has plywood in some areas. If I can open up the floor and then see what I suspect (i.e. not much insulation around the rim joists), should I try to get polyiso down there too?
– Any other ideas why the nearby bedroom floor would be colder than other parts of the floor on the same story?
Given that we don’t actively use the access room, I am fine for it to be a bit colder, but want to reduce the energy loss and hopefully bring some improvement to the nearby bedroom (as I’m pretty sure the air barrier gap / cold air is impacting the wood under that room). I guess longer term I need to get into the porch roof area and assess all of the air barrier gaps across the front of the house, but that’s a summer project.
I appreciate any feedback provided. Thanks in advance. This is a great site.
Joe
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Replies
Joe,
Q. "Is there any legitimate reason for having these gaps in the air barrier?"
A. No.
Q. "I have started to plug the gaps with 1 inch polyiso and caulk, which seems to help. My thoughts are to plug the rest of the gaps with the polyiso, add a bit more unfaced insulation in the cavity (as properly as I can) and then tack another inch of polyiso onto the interior side of the studs and further air seal accordingly (I would add furring strips and drywall if needed). Thoughts on this approach?"
A. Your approach is fine.
Q. "Any concern with having two layers of polyiso separated by a couple inches of fiberglass (e.g. moisture in the cavity around the wall studs and roofline studs)?"
A. No.
Q. "The access room just has plywood in some areas. If I can open up the floor and then see what I suspect (i.e. not much insulation around the rim joists), should I try to get polyiso down there too?"
A. All of your home's thermal envelope (floors, walls, and ceilings or roofs) need a good air barrier -- that means no holes, gaps, or leaks -- and an adjacent layer of insulation that is in direct contact with the air barrier.
Q. "Any other ideas why the nearby bedroom floor would be colder than other parts of the floor on the same story?"
A. This sounds like a classic example of air leakage. The solution is simple: Plug the air leaks. Once the air sealing work is done, improve the R-value of your thermal envelope.
Thanks Martin. I appreciate the feedback.
Martin, All,
I am nearing completion of my access room insulation project (described above), but self-doubt and continuous reading of GBA Q&A (including the many vaulted ceiling questions) have caused me to fear that I may have unwittingly made a rookie mistake by creating an unvented vaulted ceiling which may experience future problems. Specifically, I tacked 1 inch foil-faced polyiso on the interior vertical wall of the room and then also tacked 1 inch of continuous polyiso directly onto the sloped ceiling studs (which are 2x10 roof rafters with unfaced fiberglass within the cavities). I air-sealed the continuous polyiso on the underside of the roof rafters with a combination of spray foam, caulk and Nashua foil-faced tape at each seam and everywhere the polyiso meets wood. I now realize that polyiso and fiberglass batts are not listed under the unvented ceiling options...
See attached photo better illustration.
Facts:
- Climate Zone 5A (near Chicago)
- Sloped Ceiling stack-up from inside to out: 1in continuous polyiso, 9.5in of low density fiberglass batts between 2x10s, plywood and standard shingles on the roof. I doubt we have any "fancy" stuff / Ice & Water shield on the exterior side of the roof given other construction techniques used when the second story was added on, but I cannot (yet) be sure. I can find out.
- This room (and the sloped ceiling) faces the west and represents the "mid-section" of our roof (between porch roof and uppermost attic roof) and does not span the entire length of the roof.
- Adding baffles / venting channel would be possible in certain places, but may be somewhat ineffective because I don't have a completely clear path to the main attic / ridge vent in all cases.
- No direct HVAC in the room
- Room held temperature reasonably well once polyiso was up. (We still had cold temps in March)
- We don't heat above 66 degrees in the winter and therefore this room (even with the polyiso) will likely never be above 60 degrees in the coldest days of winter. (We also don't blast AC in the couple weeks that it is needed)
- A dryer exhaust ducting goes through this room, adding some heat occasionally. The ducting is air sealed where it means the polyiso. There are also PVC and black iron penetrations which are air sealed
- No apparent moisture issues before during or after the project
- I don't want to use spray foam
Questions
- How risky do you judge this setup (i.e. how bad did I screw up)?
- If risky, does wintertime condensation present the biggest risk?
- Can I mitigate / monitor the risk (without removing the continuous polyiso)?
I appreciate your thoughts.
Regards,
Joe
Joe,
You screwed up.
How bad is this situation? That's hard to assess. Normally, unvented cathedral ceilings insulated with fiberglass batts (like yours) fail because of air leakage. Interior air (humid in winter) enters the rafter bays through ceiling cracks, leading to condensation at the roof sheathing.
By creating a tight ceiling, you have lowered the risk. That's good. However, we can't assess whether you missed some cracks. For example, interior air can enter rafter bays by devious paths -- for example, through partition walls that rise up to the sloped ceiling. If your roof assembly has some of these hidden air leaks, and if you have cracks near the ridge of your roof -- most roofs do -- your roof assembly is at risk.
-- Martin Holladay
Thanks Martin. I appreciate the feedback.
Would your assessment change if there was a 1.5in venting channel (made of 1/2in EPS or XPS) moving cold air (in winter) from my porch roof cavity to the main attic (which is vented)?
Absent the venting channel option (and nixing the foam option), I guess my only other choice is to remove the polyiso and put up drywall (creating an air barrier that can dry to the interior)? Any other solutions come to mind?
Regards,
Joe
Joe,
Q. "Would your assessment change if there was a 1.5 inch venting channel (made of 1/2 inch EPS or XPS) moving cold air (in winter) from my porch roof cavity to the main attic (which is vented)?"
A. Adding the vent channel would definitely lower your risk to the level of "don't need to worry about it" -- as long as the vent channel is located between the top of the fiberglass insulation and the underside of the roof sheathing.
-- Martin Holladay