At your request, I have inspected the subject property the building at ???. , and my My
inspection report summary follows. The This summary makes no attempt to describe
all the materials and conditions in the building. The summaryIt only addresses
concerns about insulation and ventilation in the roof structure.
The report is not an engineering document; I did not perform measurements or calculations to determine how the planned assembly will perform. My analysis is based on my and other contractors experienced my experience. in working on
buildings with moisture problems.
Moisture problems in roof assemblies are caused by warm moist interior air migrating
up into attics and rafter spaces by stack effect occur when the stack effect drives
warm moist air from the interior of the home into the attic and rafter spaces. Building
science shows that small openings around fixtures, electrical device openings, door jambs, or other bypasses allow this moisture laden air to enter the overhead space and condense into water. Water in enclosed unventilated attic or rafter spaces causes mold growth, resulting in poor indoor air quality, marginally performing
insulationinsulation performance, and ultimately, major structural damage.
Modern building materials, like those used in your building, are extremely susceptible to damage from moisture. The wood is tree farm material and nearly devoid of the
decay resistant properties of old growth lumber. During manufacture, what little
decay resistive materials that exist are extracted to allow the plastics and polymers
to adhere to the wood. Additionally, the plastics and polymers hold moisture into the
wood. In short, manufactured and engineered lumber materials are mold candy. They?re fantastic when kept dry, but when moisture is present, they degrade and fail with
The current plan for your building is to install an R38 kraft faced fiberglass batts
between rafter spaces. A 2x4 sleepers is are to be placed on top of the rafters,
ostensibly to provide 1 1/2? of air space. In some cases, you indicated you might install styrofoam baffles to prevent insulation from expanding and completely filling the spacethese spaces.
My summary isIn my opinion the insulation and ventilation scheme currently proposed for your property will not work. I believe you would, either in the short or longer term, have moisture problems related to stack effect and condensation in the roof
You mentioned the project architect based their his (or is it her?) plan on the current
building code, which roughly stated, requires a 1:150 ratio of ventilation to surface
area. (I?ll also note, to illustrate how vague the numbers are, that some State state
building codes require a 1:300 ratio.)
As a start, thisThis calculation is not based on any mathematical or engineering work; the ratio is, quite literally, a guess by individuals approximately 35+ years ago, and the numbers have remained with us.
Second, theseThese ratios were initially intended to describe a relationship between ventilation area relative to attic floor area in simple/conventional pitched roof assemblies with attics having substantial cubic volume, . i.e., no individual rafter
spaces that require individual ventilation arrangements.
Additionally, the ratio was intended to have the vent area split between soffit and roof vents so there was both an intake and and an exhaust. Lacking one or the other
(intake or exhaust), there can be no convective air movement, meaning ventilation will, at best, be marginal, and essentially not calculable.
Some argue that vapor drive (the pressure differential created when water molecules convert to water vapor) will suffice to drive moisture out of the structure. I suppose this is feasible, but given the complex nature of your roof, you would need ventilation much greater than the proposed 1:150. Since no engineering exists to determine what that new ratio might be, I cannot offer an can offer no opinion other than skepticism.
So all questions are answered, there there is engineering to describe vapor
transmission in wall, floor,
and roof assemblies, but these engineering reports are intended for appropriate design in new buildings, not retrofitting ventilation into existing structures. There are
newNew studies are coming out, but again, they are not appropriate to determine what you might do with this existing structure. So, there?s not much to go on in the way of engineering for your retrofit options.
I will digress brieflyHere’s a story to illustrate how important it is to have an intake and exhaust at each rafter space.
We work on buildings. When we have opened up ceilings in effected affected
buildings, we see reasonably clear rafter space where a single mushroom vent and accompanying intake/soffit vent are located. If there isn?t an accompanying soffit intake, there is spotting of mold. In the immediately adjacent rafter spaces, to either
side of the vented space, we see more mold. The further we getAs we get farther
from the vented space, there is a corresponding (near exponential) increase in the amount of mold. As we get closer to the next vent, mold accumulation lessens, and at
the next vent, we get small spots of mold. Essentially, if each rafter space is not vented effectively, meaning intakes and exhaust, we find mold.
When Where there are small openings provided by the builder to provide lateral air movement between rafter spaces, there is still a lot of mold. IOW, airAir in the rafter
space does not move ?sideways?, it?s only convective, meaning from bottom to top. So, if each rafter space is not vented, you greatly increase the incidence of mold. Ventilation planning for your roof structure is exceedingly complex. There are a
dozens of what I and my colleagues refer to as ?traps?, areas of individual rafter spaces that dead end into beams, supports, walls, or other obstructions. Traps prevent any conventional arrangement for including both intake and exhaust. As previously described, ?trapped? spaces grown grow mold.
Your plan calls for R38 (approximately 10?) kraft faced fiberglass installed between rafters. Fiberglass always expands well beyond it?s stated depth, so it?s likely that the fiberglass will fill the rafter space completely. The roof assembly provides 2x4 sleepers on top of the rafters to provide a 1 1/2? air space above the insulation. 1
1/2? is not enough air space in my opinion. This will probably not be enough space.
I know there are specifications that indicate 1 1/2? is sufficient, but, again, this is
usually for conventionally framed vaulted/cathedral ceilings that have easily aligned soffit and ridge vent arrangementsvents. We You have a roof structure full of traps.
Whether or not 1 1/2? is sufficient is outside my ability to make a competent
determination. Again, the best I can do is be skeptical.
Your plan also called for the possible installation of foam baffles to increase air space and prevent insulation from expanding and filling the space. This may give you enough air space, but without an intake and exhaust in each rafter space, it doesn?t matter. As I previously described, air doesn?t move sideways between rafter spaces, so you are still left with the problem of providing intake and exhaust for each and every rafter space. Given the roof plan, this is nearly impossible without undertaking major alterations with accompanying major cost.
Which brings us to closed cell foam. There are different manufacturers and chemistries for closed cell foam, but I am not going to describe all options in this report.
Closed cell foam is a modern insulation material that is both an air and moisture barrier. It is used increasingly in new construction because it has very high R value per inch and it eliminates the need for ventilation.
Closed cell foam prevents moisture laden air from penetrating into the rafter or attic spaces. If all moisture laden air is contained, and the insulation thickness is sufficient to establish dew point inside of the insulation, there cannot be any
condensationcondensation can’t occur.
Thickness of insulation is critical. There has to be adequate thickness so dew point doesn?t occur in any wood framing members, and there cannot be any air pockets or other hidden areas that could hold trapped moisture. Competent installation eliminates these concerns. In my experience, the only problems with closed cell foam have been with incompetent installation.
There are open cell foams that might be used, but open cell foam is not a moisture barrier, and it has to be applied in sufficient thickness to provide an air barrier and to keep dew point inside the foam. Since this roof is complex, there would be a number of locations where different thickness might be necessary. IOW, open cell foam brings
The open cell manufacturers and installers argue that it?s dangerous to use closed cell
insulation because unforeseen or hidden roof leaks can remain undetected, ultimately resulting in major damage. My response to these complaints is to, install a roof that
The roofing industry figured out every last problem in roof material design and installation a few decades ago, and if a roof material is installed in the manner the manufactures specify, the roof will not leak. Roof leaks are the result of roofing contractors, not roofing materials. So, I can?t take the ?roof leak? argument seriously;
it?s the argument of peddling inferior materials looking for any way to disparage a
You indicated you had read things on the internet regarding people?s dissatisfaction or
problems with closed cell foam. Lacking a clear understanding or knowledge of what the specific issues are, I can?t commentoffer a rebuttal. I do know that closed cell
foam is installedhas been installed in thousands of homes with no problems. I have
personally been involved in complex building projects where closed cell foam was used effectively and successfully. I am not making a sales pitch for closed cell foam, but I am statingknow that the material works when installed correctly and with all
variables accounted for and taken into consideration.
After talking to my colleagues, sharing the pictures, and talking about all possible options, not one of us thinks the fiberglass option will work. There are too many
variables that can?t be addressed effectively, or without major alterations to the existing roof plan. Every individual indicated foam was the only option.The roof plan has boxed soffits and assemblies ?outside? the pressure envelope, specifically the large cantilevered boxed soffits at the eaves, the rear patio roof, and the curved roof extending out over the central entry area toward the rear patio. These boxed soffits, roofs, and extensions need to be sealed so they do not communicate any air path to the interior. This could be accomplished by the
insulation contractorYour insulation contractor can do this. These boxed assemblies
could be ventilated with conventional soffit vent material. If no moisture laden air from the interior migrates into these boxes, there won?t be condensation. There might be some incidental moisture from rapid weather changes, but it would be minimal and I have a hard time imagining it could result in damaging amounts of condensation. This works will work only if there is a complete seal between the
interior and the boxed assemblies. Since portions of these assemblies are already built, you will have to disassemble some amount of them to make sure there is no
communication of house air into the boxed assemblies.
You indicated one idea of boxing the recessed lights and fixtures with styrofoam. Hand built improvisations are unpredictable. It would be better to install "air lock" recessed lights and air seal them at the penetration. Until we finalize the light plan, this remains a variable.