r/buildingscience

This is a shot in the dark as I know we’re not always ready to provide technical advice in this sub. I have been searching for eons and trying to find a floor assembly for a steel truss (not c-shaped joist) that meets 2 hours. Perhaps they need serious blocking because of the open nature of the trusses? Not wanting to create a smoke baffle?

Any insight would be GREATLY appreciated!

My fiancé and I bought a house in January. It’s beautiful but every time we upgrade/fix something another issue pops up. We got a new HVAC system recently and the new thermostat has a humidity readout, so now we’re aware of how humid it is inside. HVAC guys have done everything they can, even upgrading us for free to a unit with additional dehumidifying power, so it’s not on them anymore. Went in the crawl space and it’s very humid in there. No standing water, but a lot of moisture. The vapor barrier is in horrid condition, so we’ve had a couple contractors out, but they both have refused to quote for a new vapor barrier and insist on upselling us to a full encapsulation system. We find it hard to believe that the house has stood for a hundred years and suddenly needs a very modern invasive intervention. Does anyone have any insight on humidity issues in old homes?

For context:
- coastal Virginia
- humidity fluctuates between 66 and 74%
- pier and beam foundation with block brick wall and brick facing

I have a room with a cathedral ceiling that has open cell spray cell foam insulation in the roof deck between 8x2 rafters. I consulted with a building scientist who performed a bunch of tests on my house as a whole, as well as the room in question, which has significant spray foam odors that are particularly bad during hot and humid days (Atlanta, GA). Specifically, the building science engineer concluded that aside from having a somewhat leaky house, the spray foam is the source of the odors in that room.

This raises the question of having the roof converted from a hot deck to a traditional soffit / ridge vented system. I consulted with a roofing expert and his assessment was that indeed the conversation can be done. He informed me that taking out the open cell spray foam and placing rock wool with baffles would be an appropriate conversion. His question, however, was that he may be able to get 6” at most of insulation inbetween the rafters, and that as far a R value goes, it might be worse than what I have now. That said, my main objective is to get the spray foam out of the roof because the VOC odors it emits during hot humid days is rancid and objectionable, and makes using that room impossible for the many months of the year that it’s hot here in Atlanta, GA. The contractor said that while this project is entirely possible, he cannot guarantee that the odor issue will be resolved to my subjective satisfaction, which I thought was an honest consideration.

I’d love to get some feedback on this project— perhaps the overall feasibility, the likelihood that removing the spray foam will reduce the interior odors, and perhaps any other risks or considerations to keep in mind. There seems to be little experience out there doing this conversation to specifically address odors from spray foam that is roughly 18yrs old.

Thanks to all.

Climate Zone 8b - My 1981 house is being reconstructed and the old insulation in the attic has been removed. I asked my general contractor to air seal any penetration before he blows new insulation in. My contractor said that the HVAC vents would be air sealed, but said that air sealing every penetration would make the house too tight, which could be a problem.

I read on here that air sealing is recommended, but are we talking about sealing the HVAC vents or any penetration in the attic?

I screwed up. I had the opportunity to add insulation when the space was open but just didn't feel it was that important. I have a cantilevered space, bedrooms above and porch below. It's been hot lately and I can feel a difference of around 10d when measuring the floor over the porch vs the floor over a room. The cavity between floors is 8" when above a room but 18" in the cantilevered space. The top 8" of the cantilevered space has joists while the bottom 10 is pretty much unobstructed.

Accessing from the inside is a no-go as I believe there is a beam that runs the length of the interior wall. Access from teh upstairs floor will lead to some great pain as they are new floors.

Two options (maybe you guys have more):

Option A: Access from the porch might work if there is an insulation I can use given the walls don't have any moisture barrier. I could make 4" holes, maybe 10' apart, in the porch ceiling then blow something in (several feet on either side of the hole, to fill the space? I would then add lights where the holes were.

Option B: I might be able to remove the exterior siding (one or two boards) then add the insulation from the outside. I would need to have some new pieces milled but access would be greater.

Thoughts appreciated.

Pic 1 Bedroom Floor A - Bedroom floor, showing the 18" of space

Pic 2 Bedroom Floor B - Bedroom floor, showing the same cantilevered space. Hard to tell but it is an "L" shape and about 2/3 of the that room.

Pic 3 Outside view to illustrate the space

https://preview.redd.it/0xm3s7sogwth1.jpg?width=3024&format=pjpg&auto=webp&s=cf59abe42d5666c872ec2cf886585dd4c6418da4

https://preview.redd.it/7jea07sogwth1.jpg?width=3024&format=pjpg&auto=webp&s=d2aafd944d2ab67eb8fe3863d6c9d017e3a6b805

https://preview.redd.it/tidea8sogwth1.jpg?width=4032&format=pjpg&auto=webp&s=7bfbf300afb77157d51f160075aed91f0673a3a4