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Unvented Enclosed Rafter Disaster, R806.5

H

HouseHacking

SAWHORSE
Joined
Feb 6, 2025
Messages
7
Location
Seal Beach
Greetings,

I have a 3.5-year-old home that is generally great, but we have ongoing issues with roof condensation and mold forming under the eaves and down the siding. I suspect this is partly because our GC’s insulation subcontractor—his “expert”—believes our town does not need to follow R806.5. I find that hard to believe. I still checked our city’s residential code amendments, but I couldn’t find anything on the topic.

From what I can tell, the easiest way to get to a code-compliant solution would involve removing the solar panels, tearing off the existing roof (including OSB), taking out some of the old insulation, and then rebuilding with a rigid insulation layer on top. We would also need to spray PU foam below the roof deck and then patch that back up. I plan to have an independent inspector review everything this time around.

I’m looking for feedback on code compliance to better understand whether our GC or his subcontractors might have some responsibility for the repair costs.

Seal Beach, CA. New construction, Finished in 2021, California Energy Code Zone 6 or IRC Climate Zone 3B
2016 CBC, 2016 CRC, 2016 CEC, 2016 CPC, 2016 CMC, 2016 CA ENERGY CODE, 2016 CALGREEN, SEAL BEACH MUNICIPAL CODE, RLD-9
 

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Radiant barrier adhered to OSB sheathing requires a minimum one inch air gap.
 
Air movement is critical. If the temperature differential can allow condensation, the only remedy is drying, which is usually a function of air movement. Any enclosed rafter assembly or non-vented attic makes me nervous. It is very hard to maintain balance between outside temperature and inside, and by extension the condensation that can occur. Roofing manufacturers are discovering that a lot of air movement in attics used to come from air leakage from the house, and the tightness of buildings has cut that way down. There have been a lot the types of problems you are calling out cropping up. There have also been a lot of condensation issues with spray foam. IMHO spray foam must be installed PERFECTLY in order to work properly. How often is the word PERFECTLY used in construction?

Speaking with a roofing expert and association rep, he advised that ventilation (lack of) is a huge issue they seeing right now.
 
Do you know if the mold is only on the siding and eaves, visible from outside, or is there evidence of it within the building?

The fix of removing roof and building up solid foam is interesting. I've not seen it often in residential but, in fact, exactly what I planning (though not sure I'll build it.) But I will have no insulation under roof sheathing, and 10" - R50 - in foam - with just purlins and metal roof on top.

I don't know if you can be assured of no condensation in the fibreglass or underside of roof deck. It would depend on "perfection" in most parts. And I prefer very tolerant and easily maintained and renewed building systems.
 
Were the construction plans prepared by the general contractor, or by someone else?

Anecdote: Last year I had a project that tore off the flat roof sheathing on a motel in Huntington Beach about 3 miles inland from the Bolsa Chica tidal inlet (somewhat close to Seal Beach), first built in the1980s. The roof had R-30 batt insulation between 2x joists. It is not a perfect installation. The roof assembly was unventilated.

We found some water damage to the sheathing due to the built-up asphalt roof membrane leaks, but there was no evidence of condensation, or related mold or mildew damage where one might potentially anticipate a "dew point" within the assembly. Perhaps the whole building is so "leaky" that the assembly did not trap condensation, or perhaps the climate is so mild that condensation had not been an issue.
 
Thanks for all the feedback! Going in order:

TheCommish - regarding hiring a lawyer: Hopefully we’ll be able to work this out with our GC, but that’s the backup plan. Finding a construction defect expert sounds good regardless.

ICE – regarding the radiant barrier on the OSB: thanks, we plan to replace that layer in the unvented areas and that’s consistent with what our plans asked for.

Sifu – regarding the spray foam. I’m hoping to avoid this option for everywhere except roof-top-deck. Otherwise, I think we would need to tear into it from the top.

Bill1952 – we have some mold on the inside of the house along the exterior walls, both downstairs and upstairs. However, since we’ve already done roof-leak repair in specific spots, and the bottom of the siding has been trapping water around the home’s perimeter, so it’s hard to tell if the interior mold is due to roof insulation / ventilation issues or combinations of other things. For example, we had this growing into the room below the roof-top-deck:
1738906316259.png

Yikes – The plans weren’t made by or GC, and they didn’t clearly specify the roof insulation layout. The plans state on page 1 that the home must meet Title 24 requirements regardless of what is shown elsewhere.
Unless there’s an easier way, we plan to pull off the roof and osb over the unvented areas, so we can replace water damaged insulation if we need to.

Mark – thanks for clearing up the climate zones because it has been driving me crazy! I think my confusion is coming from some CRC R806.5 tables use IRC zone definition (8 total zones, where I’m 3B) and others the CEC definition (16 total zones, and I’m 6). Either way, I think I’m in the R-5 category for rigid-above-the-fluffy for section 5.1.2.

A question for anyone: I'm interpreting that I need to meet the requirements of 806.5.5.1.2, and not 5.1.4, for a mixture of batt below the roof deck and rigid above?
If 5.1.4 could be used, then the rigid could be R-0 (nothing) in my warm climate? Assuming there's enough room in the rafters below to meet the R requirement.
 
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This is a good reminder that CA (like some other states) makes statewide amendments to the model code. Also in this state, the latest edition of code is a mandatory minimum across the state. Local jurisdictions can make more restrictive amendments but cannot go less restrictive. As compared to some other places where a jurisdiction can choose to stay on the 2008 electric code indefinitely for example.

Thinking about the climate zone issue, and reminding myself that CA has its own system, I wanted to verify my own climate zone. The CA Energy Commission has this "zone by zip code" spreadsheet, and I thought I would share it here:

Building Climate Zones by Zip Codes

www.energy.ca.gov www.energy.ca.gov

File format is not supported by the forum, so I posted a link to the page where I downloaded it.
 
Joe.B said:
I recommend checking with your local building official and see what they're going to expect. I would require a permit for the work you're proposing. Because a permit is going to be required, I would default to the current 2022 CA Residential Code. If the applicant wanted to request (in writing) to design the repairs to the 2016 Code based on the problem being construction defects, I would probably allow that. In this case I don't think there's much difference. For the safe of discussion, here is the code section you're asking about:

2022 CA Residential Code
R806.5 Unvented attic and unvented enclosed rafter
assemblies. Unvented attics and unvented enclosed roof
framing assemblies created by ceilings that are applied
directly to the underside of the roof framing members and
structural roof sheathing applied directly to the top of the roof
framing members/rafters, shall be permitted where all the
following conditions are met:
1. The unvented attic space is completely within the
building thermal envelope.
2. Interior Class I vapor retarders are not installed on the
ceiling side (attic floor) of the unvented attic assembly
or on the ceiling side of the unvented enclosed roof
framing assembly.
3. Where wood shingles or shakes are used, a minimum
1/ 4-inch (6.4 mm) vented airspace separates the shingles
or shakes and the roofing underlayment above the
structural sheathing.
4. In Climate Zones 5. 6. 7 and 8. anv air-imneimeah1e <-
insulation shall be a Class II vapor retarde~, or shall
have a Class II vapor retarder coating or covering in
direct contact with the underside of the insulation. <
5. lnsulation shall comply with Item 5.3 and either Item
5.1 or 5.2:
5.1. Item 5.1.1, 5.1.2, 5.1.3 or 5.1.4 shall be met,
depending on the air penneability of the insulation
directly under the structural roof sheathing. <
5.1.1. Where only air-impermeable insulation
is provided, it shall be applied
in direct contact with the underside
of the structural roof sheathing.
5.1.2. Where air-permeable insulation is
installed directly below the structural
sheathing, rigid board or sheet insulation
shall be installed directly above
the structural roof sheathing in accordance
with the R-values in Table
R806.5 for condensation control.
5.1.3 . Where both air-impermeable and
air-permeable insulation are
provided, the air-impermeable insulation
shall be applied in direct
contact with the underside of the
structural roof sheathing in accordance
with Item 5 .1.1 and shall be in
accordance with the R-values in
Table R806.5 for condensation
control. The air-permeable insulation
shall be installed directly under
the air-impermeable insulation.
5.1.4. Alternatively, sufficient rigid board
or sheet insulation shall be installed
directly above the structural roof
sheathing to maintain the monthly
average temperature of the underside
of the structural roof sheathing
above 45°F (7°C). For calculation
purposes, an interior air temperature
of 68°F (20°C) is assumed and the
exterior air temperature is assumed
to be the monthly average outside
air temperature of the three coldest
months.
5.2. In Climate Zones 1, 2 and 3, air-permeable
insulation installed in unvented attics shall meet
the following requirements:
5.2.1. An approved vapor diffusion port
shall be installed not more than 12
inches (305 mm) from the highest
point of the roof, measured vertically
from the highest point of the
roof to the lower edge of the port.
5.2.2. The port area shall be greater than or
equal to l :600 of the ceiling area.
Where there are multiple ports in the
attic, the sum of the port areas shall
be greater than or equal to the area
requirement.
5.2.3. The vapor-permeable membrane in
the vapor diffusion port shall have a
vapor permeance rating of greater
than or equal to 20 perms when
tested in accordance with Procedure
A of ASTM E96.
5.2.4. The vapor diffusion port shall serve
as an air barrier between the attic
and the exterior of the building.
5.2.5. The vapor diffusion port shall
protect the attic against the entrance
ofrain and snow.
5.2.6. Framing members and blocking
shall not block the free flow of water
vapor to the port. Not less than a 2-
inch (51 mm) space shall be
provided between any blocking and
the roof sheathing. Air-permeable
insulation shall be permitted within
that space.
5.2.7. The roof slope shall be greater than
or equal to 3: 12 (vertical/horizontal).
5.2.8. Where only air-permeable insulation
is used, it shall be installed directly
below the structural roof sheathing,
on top of the attic floor, or on top of
the ceiling.
5.2.9. Air-impermeable insulation, where
used in conjunction with air-permeable
insulation, shall be directly
above or below the structural roof
sheathing and is not required to meet
the R-value in Table R806.5. Where
directly below the structural roof
sheathing, there shall be no space
between the air-impermeable insulation
and air-permeable insulation.
5.2.10. Where air-permeable insulation is
used and is installed directly below
the roof structural sheathing, air
shall be supplied at a flow rate
greater than or equal to 50 CFM
(23.6 Lis) per 1,000 square feet (93
m2) of ceiling. The air shall be
supplied from ductwork providing
supply air to the occupiable space
when the conditioning system is
operating. Alternatively, the air shall
be supplied by a supply fan when
the conditioning system is operating.
Exceptions:
1. Where both air-impermeable
and air-permeable insulation
are used, and the R-value in
Table 806.5 is met, air supply
to the attic is not required.
2. Where only air-permeable
insulation is used and is
installed on top of the attic
floor, or on top of the ceiling,
air supply to the attic is not
required.
5.3. Where preformed insulation board is used as the
air-impermeable insulation layer, it shall be
sealed at the perimeter of each individual sheet
interior surface to form a continuous layer.
Click to expand...
Is it any wonder that humans screw this up?
 
ICE said:
Formatting is not the issue. The folks that wrote this bit of code are under the impression that they solved an age old riddle.
Click to expand...
No, I know. But I was hoping to make it easier to read, when I tried editing the post something went very wrong. When I logged back in, the post was gone, so whatev's.
 
HouseHacking said:
I think my confusion is coming from some CRC R806.5 tables use IRC zone definition (8 total zones, where I’m 3B) and others the CEC definition (16 total zones, and I’m 6). Either way, I think I’m in the R-5 category for rigid-above-the-fluffy for section 5.1.2.
Click to expand...
Yeah, I see what you're saying now, I never really looked deeper into this because I'm in climate zone 1. It is definitely a conflict and I'm not sure I have the answer yet, but here's a little more on the topic:
 
It looks to me like you have to use this table to determine your climate zone for the purposes of 806. For example, I've always "known" that I am in climate zone 1. But if I'm analyzing 806, I need to consider myself zone 4. That appears not to be an issue as everything still works and I have not been giving people the wrong information. It appears though in your case it does make a difference, and I would say that you should be using zone 3 for this section.
 
Thanks, this zone stuff had me going in circles.
ICE said:
The folks that wrote this bit of code are under the impression that they solved an age old riddle.
Click to expand...
Yes! I still don't get it, but I'm guessing R806.5.5.1.2 is what I need to use as the guide for batt in the rafters and rigid on top, and that 5.1.4 can't make the rigid layer magically go away.

Meanwhile, I made a list of 24 potential code violations from our new construction that we hope to address with our repair project. I'm hoping the city will be harder on us this time... that said, I didn't include all of the code violations that the uh... homeowner created. I guess I might be covering things like this up a little better now that I'm drawing inspectors into the house.
1739325028057.png1739325068240.png1739325109837.png1739325134496.png
 
That's where the slide transitions from a round to rectangular cross section. The part on the right is a workbench now.
The last drop is pretty steep, around 55-deg down. I had it at 65-deg originally, but that was really dangerous.
Here's what it looks like from inside the slide and from the hallway.
1739335229583.png1739335270186.png1739335448621.png
 
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