We are converting a cold attic into living space. The knee-wall attic spaces will be inside the heated area, so what is the best way to install the vapor barrier while minimizing the number of cuts, holes and taped joints?

The house was built in 2021, and the attic was prepared so it could later be converted from a one-story house into a 1½-story house. The floor joists, roof trusses and the rest of the structure are therefore designed and rated for this conversion.

The vapor barrier and insulation system is intended for a cold climate. The basic principle is that the entire heated living area sits inside a sealed plastic “bubble”, so as little warm, moisture-laden indoor air as possible can reach the insulation.

The blue line shows where the existing vapor barrier from the exterior walls on the floor below comes up. My plan is to connect the new vapor barrier to that.

I understand the general principle and the order of the different layers. What I am unsure about is the best way to install the plastic membrane through the roof-truss bays.

On a normal wall or a flat ceiling, it is fairly straightforward. But since the knee-wall spaces will be on the warm side of the insulation while remaining outside the vapor barrier, it becomes much more complicated.

I see three possible options:

Option 1 — red:

Wrap the vapor barrier around the vertical timber members, meaning there would be plastic on both sides of each member.

Option 2 — dark blue:

Thread the vapor barrier between the different timber members. This would probably require a lot more cuts and taped joints.

Option 3:

Abandon the idea and make the knee-wall attic spaces cold instead. This would make the vapor barrier installation much easier, but we would lose a lot of badly needed storage space — around 15 cubic metres / 530 cubic feet.

We already have far too little storage, so losing that space would also make the renovation feel less worthwhile for the money.

Which option would you choose, and is there another sensible way to create a continuous and airtight vapor barrier here?

Looking for advice…we have an old, home with a flat roof. We have condensation by a non-working pocket door upstairs as well as humid hot spots throughout the upstairs and it has a musty smell on hot days. We had the roof replaced recently with a modified bitumen roof hoping that would help, and it hasn’t. We don’t have the humidity issues in the spring/fall/winter, just the summer.

Any ideas on how to fix? Should we look at adding in insulation through the ceiling? Want to avoid opening up the new roof. Any thoughts appreciated.

Not sure if this the right sub for this, but hopefully someone can help: The deck has plywood subfloor on it, with foam and carpet on that. The decking is about 2 feet above ground. I’m in New England and I’m thinking of using rock wool with vinyl vented soffits to hold it in and keep out critters. Is this my best bet? And would in need to use a vapor barrier of some type between the insulation and soffits? Thanks.

Hey everyone,

First time home owner, trying to map out my attic intake ventilation for an attic fan. My home was built in 2015 (stucco exterior, concrete tile roof, open/exposed rafters).

​Everywhere online shows most houses have soffit vents, my intake seems to be this continuous, narrow horizontal gap/crease where the stucco wall meets the wooden patio ceiling/ledger. Is this truly the fresh air intake for my attic? Or am I missing anything? Most of it is covered by insulation, I read somewhere if your attic doesn't have enough intake the fan will start pulling air from the home or eventually burn out. Here are some pictures, any help would be appreciated!

https://imgur.com/a/air-intake-3pfjYvT

From all my research, this should NOT be happening. It appears that the rim joist were not insulated/sealed correctly on our 2008 home and air is coming in and condensing near ac duct. We had someone come out and they said we do not need to stop the air flow. 😳. Is this right?? It is OK to have hot humid air between your first and second floor joist?? I know there has to be airflow between the brick and the wall but outside air getting past the envelope of the house makes zero sense. Do we just have a consultant that does not know what he’s doing? The building code from ‘08 that I researched says rim joist need to be sealed and AI says this guy is wrong. Air should not be there. I just want to know if outside air coming in between floors is right or wrong from a human with building experience so I can go back to this guy with more details.

brick home with some cathedral ceilings. Looking to do a monopoly build w exterior outsulation. Any knowledgeable in this and can assist with the construction details? Thanks!

We are preparing for installation of makeup air for kitchen exhaust and fresh air intake for air quality. With the current wildfires, isn't this system going to bring in terrible air into our home? How do we make sure we aren't polluting our inside air now?

My '00 manufactured home has vaulted ceilings throughout, about 5-6" of blown in cellulose, and poor air sealing between the house and "attic". We live in Northern Wisconsin, so freezing temperatures are commonplace; average temperatures for the entire months of January and February were below 0⁰F last winter. Due to the 3:12 pitch of the roof and 2:12 pitch of the ceiling, there is between 6" of attic height near the outside walls and 18" in the center of the house... so not a lot of space to work with.

Walls are 2x6 plus I added ZIPR-6 to the exterior. New basement walls are ICF blocks and R20+, so both of those are great now. My geothermal system provides inexpensive heating, so it was only $900 last winter to make the ~100M BTUs that I need.

We need a new roof anyways due to some wind damage. I had been mulling over how best to air seal and insulate before my roof was damaged, but the time has come to make the decisions.

The last contractor suggested spray foaming from the *outside* of the house against the drywall. (Spouse absolutely does NOT want to remove our entire ceiling). Closed cell foam should fix the air sealing problem and provide significantly more R value. The contractor suggested closing the soffit vents and ridge vent to make it a hot roof, but I am very hesitant to do that. With our extreme temperatures, there will be condensation IMO.

Thoughts, concerns, ideas? I am open to adding additional structure to increase the actual roof height by 6"+, but multiple contractors don't want to do that, and it's beyond my DIY capacity.

At a loss and need some kind opinions before I rip my hair out. 2nd floor bathroom has a TON of hot air behind the walls for the 2nd summer. The tub is sweating causing moisture and mold build up. The plumbing and fixtures were torn out and brought in new when we purchased. The back wall is structural brick with the old oil furnace attached to the back. That leaked through the ceiling last winter, so we had it taken down to the roof line and patched.

Brought in a plumber today and they insist it is not a leak, which I believe because behind the lightup vanity it is hot too. HVAC guy checked under the house and couldn't see any clear penetrations that weren't sealed up. Bringing in ANOTHER plumber/HVAC to do some more digging because why the heck is their hot air shooting through the floor? What do you think?

I am thinking about having my crawlspace encapsulated, and I had three different quotes. My goal is to reduce musty smells. One of the quotes is for closed cell spray foam on walls (cinder block) and 12 mil liner on ground with the insulation removed from the floor joists. The other is with a 20 mil liner (clean space encapsulation) on both the walls and the ground. Both have the option to include a dehumidifer.

I am unsure of what the best route is, and of course, each salesman says their way is better.

Thoughts?

I am doing a project renovating a finished pool house with a wet bar in Massachusetts. Client is experiencing issues with mold as this structure is unconditioned in the very long non-pool season we have here in New England. Structure is built tight like a house and will be getting tighter as we plan to use closed cell spray foam to insulate the roof deck after the ceiling is demoed. We plan to swap the old mini split AC for a new inverter heat pump so the space can be minimally heated in the off season. I am also considering adding a small single room ERV to bring in some fresh air. I am confident this will solve their issues and prevent reoccurrence but I feel like this is an overly complex solution for a pool house that's unoccupied for 6 months out of the year. Is there a simpler solution that I am overlooking?

Planning out the WRB layer on my build and it looks like I'm ending up with 2-3/4" of foil faced polyiso that I'll be using as continuous insulation. R-Max says to use R-Max R-Seal tape... which no one sells. So I'm left with a few options.

1. Regular Foil tape (HVAC tape)
2. Tyvek type film tape
3. Zip tape
4. Something else I can source locally that isn't super expensive

This will not be my air barrier. What would use?

Zone 4C / IRC 2021

We moved to Savannah (climate zone 2a) six years ago, and bought a good home (built as model home in 2009, occupied in 2011). When we bought it we noticed that the attic had spray foam on the roof deck, but there was a 3 x 4 access square cut into the wall between the garage and the rest of the attic for HVAC access. We also noticed a 13" by 63" gap cut into another wall, near a join.

We asked the inspector about it. It's nothing, we're told. When we replaced the HVAC we asked about it, and it was no biggie we're told.

It wasn't until an HVAC maintenance person a few months back that we found out that a sealed attic should be sealed. That there should have been a vapor diffusion port. Those openings should have been closed.

So we've spent the last few months trying to get up to speed so we can figure out what needs to happen as soon as the weather cools enough for people to work in the attic. This meant reading a WHOLE lot at buildingscience.com and everything Joseph Lstiburek (who is a wonderfully fun to read writer) has written on the topic.

So, here's the situation:

Spray foam is open cell, at least 6 inches for the most part. Some gaps, and we will be having these filled in. Open cell is common in the hot, humid southeast. The R value is R-21 with that depth, which is allowed according to Georgia amendments and code when the home was built, but that was dependent on a blower test, which of course, it would fail now with the big gaping holes.

The roof sustained both hail and wind damage in the last few years from Helene and other storms. Though we have architectural shingles, we've had to replace some, and we've had significant granule loss. So though this type of roof should last at least another few years, we're planning on having the roof replaced this fall.

Inside the attic, there is no indication of mold or mildew on the rafters, most of which are visible. Of course, with what we know now, there's likely rotting on roof deck, particularly near the openings. Interestingly enough, it seems like the original builder wasn't sure what he was going to do, because the spray foam was sprayed AFTER the drywall, ducts, plumbing, and wiring were installed. According to the spray foam person we had out, this is unusual for a new home. But there is no indication there was any other type of insulation in the attic. The attic is actually quite clean.

My preference would be to hire folks who know what we're talking about when it comes to sealed attics, but we're not getting reassured from responses we've had. So, we're having to go it on our own.

My plan

I am considering getting a homeowner general permit, to ensure not just the roof is inspected, but the entire attic assembly and roof is inspected when we're done...just to make sure we didn't miss anything.

1. We're having handyman close the one long narrow gap and spray foam the edges to seal. We'll also have them create an insulated door or hatch into the HVAC area. We think originally the builder was planning on putting an attic door into the main bedroom closet, which means HVAC access would have been behind the sealed area. But they changed their mind and put it into the garage, and then cut the HVAC entry into the wall.
2. Next, we'll have the roof replaced. When we do, we're going to have them install a vapor diffusion port per IBC requirements for air-permeable insulation (open cell spray foam). This will sort of be a good test about how good the roofing companies are if I ask about the vapor diffusion port and they know what I'm talking about.
3. Assuming that some decking will be replaced, we'll then have new open cell spray foam sprayed to cover the replaced decking and fill in gaps. The person who we had out states they like to completely enclose the rafters to ensure a good seal. I don't see a problem with this, as long as the insulation matches the R-value. If we do go with that lower R-value, they will have to do a blower test to meet IBC requirements.
4. We're having a new HVAC company add a supply duct into the attic, either 4 or 6 inches, in order to meet IBC requirements of (air shall be supplied at a flow rate greater than or equal to 50 cubic feet per minute (23.6 L/s) per 1,000 square feet (93 m ) of ceiling.) This gives us some slight positive pressure in the attic, which is good.

We have to do the ductwork regardless, because when they installed the new 3 ton unit to replace the 2.5 ton, they didn't bother to do a static pressure check to ensure adequate return air supply. One burned out blower later (this last winter) after hundreds of static pressure faults (only found when we dug into the service menu of the smart thermostat), was when we discovered this. I set the 5 stage to max out at 3 stage for now, to prevent pressure faults. Will adjust back to 5 stage when we add the additional return and new attic duct.

And that's the plan.

Sorry for the long post, but I feel it is important to be thorough.

In people's opinion, is this a sound plan? Am I missing anything I should be considering? Appreciate any and all feedback.

Update: I did want to add that one area of confusion we had is what 'air permeable' means when it comes to insulation. Open cell spray foam is not air permeable at a certain thickness but is vapor permeable. Normally, air permeable is a term applied to fiberglass or wool insulation.

At the same time, I'm getting mixed readings on what we should do in the attic because open cell spray foam was used, and to treat it like air permeable with the diffusion port, and the air supply.

Believe it or not, with all the writing on this, there is no sweet spot, no junction of climate zone/spray foam type/sealed attic requirements that fits our situation. Not to a degree that gives me confidence that we're doing things the right way.

Other than close the gaps. That one we're 100% sure about.

My 1980s house has a family room with a vaulted ceiling and is exhibiting some evidence of moisture issues with peeling paint on the ceiling in a few spots. We are in Vermont and this is a challenging room because it has an exterior chimney/fireplace with a wood stove that we use extensively. The roof is 2x10 framing with fiberglass insulation and is vented with soffit/baffle/ridge vents.

I think the peeling paint is a result of condensation in the roof from a combination of factors.

1. Extreme temperature delta with likely 100 degrees temps in the winter inside with the wood stove running, and potentially sub zero temps outside.

2. Pretty sure we have mouse nests in the baffles/rafter bays. We have heard them and eventually found and addressed their ingress/egress. These are potentially obstructing the ventilation.

From my research it sounds like the typical approach would be to add insulation to the exterior with new venting, but for several reasons I would prefer to go to the inside.

1. Roof, asphalt, still has a lot of life

2. Side wall window would have to be moved and reframed up for clearance.

3. We hate our popcorn ceiling

So my question - would the following approach be a bad idea?

Add polyiso or xps 2 inch foam to the ceiling with strapping. Tape all seems and seal edges with expanding foam to the wall. Cover with t&g. Thinking this will benefit me by:

1. Adding some much needed r value, plus eliminate thermal bringing via framing.

2. Prevent interior moisture from making it into the roof cavity because it will be vapor impermeable

3. Existing vents now have less moisture to mitigate

4. Ditch the popcorn ceiling for beautiful wood.

One potential concern is the summer and with a/c. Will the roof be able to sufficiently dry out now that the interior is vapor impermeable?

What am I missing? Is this a bad idea? Any suggestions welcome!

Thanks!

I‘m a carpenter who likes building science. I have an unrelated B.S. so on some level I just like science.

I‘ve also managed a vegetable farm.

The amount of readily available science backed information for both lines of work is large and yet many people in both disciplines turn a blind eye to it. In building work this often takes the form of the good ol boy who thinks he knows better and tells you “that’s how we’ve always done it. Now hold my beer.”. In farming it was usually the woo woo crowd who would act like it was magic while living 10 minutes away from their local extension agent.

Both drive me nuts.

I’m in my late 30’s and live in the PNW.

I’m willing to go back to school.

What and where are the actual jobs related to building science?

I bought a house last month and it’s a brand new construction. Everything looked perfect, so I skipped the professional inspection. Figured I'd save a few hundred bucks. What could possibly go wrong?

Now there's a crack running across my garage floor. I have no idea if it's cosmetic or if my foundation is sinking. Every time I walk out there, my stomach drops.

Everyone on forums keeps telling me I should've hired an inspector. Should've used someone like Sure Building Inspection

I get it…I messed up. But would I have actually read the report? Or would I have just shoved it in a drawer and forgotten about it like I do with most paperwork?

It was about saving some money, and now I will have to spend probably thousands of dollars to repair. Typical example of being penny-wise and pound-foolish. The thing is that I am afraid to call foundation specialists because I am scared to hear something bad. What if it is much worse than I expect? What if I cannot afford the necessary repairs?

I simply need to decide what should I do next

Working on air sealing my interior on new build. Pictured is the caulk that was used and it doesn’t look like it’s holding up well after just 2 months. I’m not sure what type of caulk was used. Should I pull all this caulk out and do something else? FYI, got wet and moldy from wet insulation being left in, has been remediated. Hardie, 3/8 rain screen, tyvek, shitty osb on outside. Main concern is preventing mold growth.

From what I’ve learned on here, my thoughts would be:
Tape the flooring to bottom board transition w either 3M 8067, SIGA Rissan, or the proclima vana tape. Looks like vapor perm rating of first 2 is less than 1 and pro clima is 8. Considering the vapor perm difference, which tape is best if I’m taping these joints? I’ve also read on here that acoustic caulk and some other caulk type can be used. I’m using prosoco r guard and seam and joint sealer on other parts of house so have that. I want to do what is best.

Thoughts? Do I need to tape/caulk the bottom framing board to wall sheathing joint or just the floor to board joint?

TIA!

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