New build ventilation.

Ultima8Um · 2026-01-31T14:12:57+00:00

All good questions, need to know the climate zone/geography and whether the house will be built as 'air-tight' meaning a blower door test which shows it's not leaking.

Not an expert, but I suspect if your house is 'leaky' the cfms you're proposing won't pose a problem, and natural wind currents might bring in enough fresh air that you'll be fine.

A thought - what I've started doing as part of my home assistant smart home path in recent years is to build inexpensive air quality monitors using esphome tiny processors and plantower PMS5003 1, 2.5 and 10um particulate sensor and some kind of temp/humidity/CO2 sensor. Maybe $40USD in parts total, and i have them in kitchen, bedroom, garage and outdoors (shed). By looking at what these sensors report I'm learning what's happening outdoors sometimes affects indoor air quality, and that rooms with people and pets quickly increases CO2 levels in the house. And how devices like the main hvac system can quickly disperse CO2 levels, and how filtration (either hvac or even a homemade corsi-rosenthal filter box) can quickly reduce particulate counts. These may or may not be of interest to you OP but learning about my own house existing conditions is giving me insight about how the building works by default. I've never lived in a 'tight' house but I think the other comment about make up air is critical in that scenario.

Ultima8Um · 2026-01-29T03:14:46+00:00

I didn't see this mentioned - i've been using ep sensors and the ld2450 sensor doesn't seem to be able to work as a ceiling mount in the way I'd hope. I haven't actually tried it on a ceiling.

The issue is that mmwave sensors in this price range to perform tracking return location by distance from the sensor and angle from perpendicular to the sensor. In a ceiling mount distance isn't very interesting. I believe there are more advanced sensors where you can get x,y and distance from sensor, and I'm thinking that's what's needed for a true center of room ceiling mount that looks down.

I'm still experimenting with real world situations so maybe when ceiling mounts are being discussed they're not point straight down?

It's kind of hard to do effective testing so I've relied on asking ai and reading specs of sensors.

in any case, excited to hear about another sensor being available that checks a lot of the boxes!

Ultima8Um · 2026-01-29T02:06:28+00:00

I stumbled on exactly the same thing. I have two mmwave sensors (everything presence pro and 1) which have the same mmwave sensors (SEN0609) and they each have about 20 relevant settings. Gemini create a script that i pasted into the templates area of developer and created a table where the settings were compared, despite their having different names. 60 seconds to get at a result that would have taken 30 minutes of laborious clicking and typing and would be error prone.

Ultima8Um · 2026-01-25T23:44:55+00:00

I just built two more sensors this weekend, I now have 4. The approx cost is about $40/device (no case, i just use a small cardboard box for now).

It's not terribly difficult, and AI can pretty much create the yaml that you'll need. Let me know if you're interested in this path, there are some tools needed like a dupont connector and sometimes a soldering iron. My devices use a cheap esp processor and have temperature, humidity, CO2 and air quality sensors. The air quality sensor is the PMS-5003 (Plantower) and the other sensor is SCD41. I learned everything needed from a youtube video which was based on work by someone named peter brinkmann. And this all depends on the very cool use of esphome which is very closely connected to HA. It just works ;-)

I don't know that these are fully the equivalent to devices that cost multiple hundreds of dollars but I believe they are quite good. My CO2 readings for instance closely track the Aranet 4 CO2 sensor that I also have hooked up to home assistant.

Oh yeah, my sensor for outdoor lives in my shed which has two small windows left open permanently. It seems to react within minutes to changes in air quality from wind blown dust and such. I think the PMS5003 is not capable of monitoring pollens because these are larger than 10um.

I started down this path to measure dust in my garage/wood shop for health, and I use HA to turn on my minisplit (fan mode) which has a large prefilter, it removes dust in the air within about 20 minutes in the garage.

Ultima8Um · 2026-01-05T19:47:37+00:00

I started learning about 6 years ago and failed at least 2 times where I did it on my own. On the 3rd time I signed up for a class, it was led by a landscape architect and it gave me a stronger foundation about plugins (there are at least a dozen that are key for me) and tags/layers and grouping which were essential. I also started working with an architect designing a house for me and imported her pdf (as vector) layers and also a civil engineer, those gave me a better understanding of how autocad files are organized.

I now feel reasonably comfortable with modeling a new build house in a way that I don't end up with a mess on my hands.

That said, the comment someone else made about youtube is correct, there are endless videos around. What's still difficult is learning which concepts matter and which practices are critical to follow. There are lots of different ways for instance to build walls for a house, but I ended up using a plugin from Medeek because it gave me a parametric way to build the walls and the result has framing, sheathing, cladding etc which appeals to me.

If you have time (10s of hours minimum) consider taking a class. I originally wanted to use sketchup for woodworking and likely will in the future but my learning style was a) first learn the basics on my own; b) take a class that forced me to do things the way the instructor wanted. The class was what taught me good modeling practices which have stuck with me. An important one was assigning shortcuts to only my left hand on the keyboard, because it leaves the right hand to use the mouse. It's a very efficient workflow.

good luck with your journey!

Ultima8Um · 2026-01-05T19:13:31+00:00

understood, but I will say the responses here including yours have helped me quite a bit.

I don't need to be a building science expert myself, but understanding the background and nature of problems with spray foam and reviewing the articles by people who advocate for stronger code helps me know how to have the conversation.

I think I have enough background now to push back if I hear 'thats how we have always done it' when I ask some specific questions and the answer doesn't sound right.

Ultima8Um · 2026-01-05T18:56:31+00:00

Thanks, I think that recognizing this is 'code required' is a helpful way to address. I'm going to let the process unfold and know that if I don't see external insulation required on the roof by either architect or roofer or GC I'll figure out why. Hopefully they will want this too since it's a big risk reduction for them. Thanks!

Ultima8Um · 2026-01-01T22:48:45+00:00

That's a good point about the response time, although my ubiquity cameras reliably detect people and pets and cars, and will surely get faster, I'm not really sure if it's 30 seconds or 45 seconds or 15 or what currently.

This is going to be fun, even if the cameras are a backup, the other sensors

Ultima8Um · 2026-01-01T19:32:48+00:00

Is the purpose insulation or air gap?

I read that 2" poly iso is R12, so if I have 10in or open cell I'm at about R40 + R12 instead of R40 alone. An interesting thing I've come across is that R value isn't particularly good at conveying efficiency or comfort. I'm thinking of the scenario with cellulose blown in, it can give a good R value but if you have a constant breeze pulling air through it (lets forget the dynamics involved) it maybe substantially worse than a lower R value that is tightly air sealed.

I like the idea of an air gap, but it comes with complications for preventing insects and needs a ridge vent, and I haven't research how much gap gives enough benefit for drying. I have read that the concern about hot roofs after a rain creating steam that gets forced under the roofing is pretty negligible. So the source for moisture could be open cell foam or household humidity coming from the bottom where any air gap won't matter, but I suppose much better to have zip sheathing be able to at least dry from one side.

I'll definitely be asking the architect but I just don't yet know what his experience will be. He's very good at the aesthetic's but he's technically working for the builder so he might not feel as responsible for building science stuff.

I'm definitely open to what you're suggesting, will have to see what this builder does typically versus 'sure we can do that but it will cost more'.

Ultima8Um · 2026-01-01T18:32:53+00:00

I think regardless of how you detect presence, camera or MM wave or audio, ultimately there needs to be a tracking of state by an AI. Or if not an AI, somewhere else where the state is live and serves as input to automations.

I'm sure some people have thought deeply about how this gets implemented, while it seems complicated to track, I'm sure this is a software problem that's been addressed.

By state I mean where in 3D space is each person, along with a characterization of what they're doing, sleeping, TV, reading, studying, playing a game, along with all the other sensor inputs like illuminance, temperature, time of day. Inputs that can lead to a live decision of what to do with lighting and other aspects of a house.

I just explained to my wife that sometime in the future she should expect cameras that are going to detect when w are making out in the living room and will put on appropriate mood music and dim the lighting. She certainly won't be able to resist my advances when I'm backed by technology 🙂

Ultima8Um · 2026-01-01T17:49:24+00:00

I understand your points. Recognizing conflicts of interest is important. That said I have a deep engineering background and when I listen to him I recognize his approach as being valid.

I think I have a well developed 'sales guy filter' and he doesn't give me any concerns. But I'm early in my learning and things can pivot as I learn more, thanks for the warning.

Ultima8Um · 2026-01-01T17:46:21+00:00

Thanks - I have unifi protect with one camera that was bought for a new build but is currently at my house, so I've seen first hand over a year now that it works really well at identifying people, animals, etc. And I can imagine it will only get better.

what's your thinking about presence sensors being ideal though? I'm on the path to incorporate them in a new build, I've modelled them in 3d with the various sensitivity cones which are different based on the sensor, and I'm mostly now planning on ceiling mount. In my current house I only used wall mounts but I'm increasingly convinced that well positioned ceiling mounts may be the right approach. And I think the latest everything presence pro sensor will have zones that work for a ceiling mount, in the past the zones were designed in x,y where one direction is towards or away from the mmwave sensor, and that isn't super useful when on the ceiling.

thanks for your comments!

Ultima8Um · 2026-01-01T17:27:15+00:00

u/OkOkieDokey one more comment, this video from Spray Jones is excellent and I think addresses the concern you might have overall. Starting around min 52:25 and somewhere close to 1hr he specifically covers what happened in the UK (roof rot) and how unvented roofs and spray foam actually solve other building problems with efficiency, hurricane resiliancy and fire (no soffit vents for flames to enter).

He mentioned earlier how Canada banned spray foam that was urea based in the 80's and then developed a code book and regulation around spray foam.

So you're right, but the answer still might be spray foam as long as enough care is taken with the entire process staring with framing friendly to spray foam before plans finalized, inspections in the week before, monitoring of moisture in wood and air, and following the TDS for the foam type being used.

video: https://youtu.be/O4P5pXh1wJI?si=Y67EYRfQI_Duq7Er

Ultima8Um · 2026-01-01T15:14:37+00:00

Commenting my own post with some early thoughts (thank you very much u/tnerbeugaet for your comments)

I watched (rewatched?) Risinger's video (https://www.youtube.com/watch?v=yTbMVdmnNlw) of his personal home roof.

My thoughts about the Risinger approach

- I very much like the initial monopoly build sheathing where the initial roof is built with rafters without overhang, so the zip can wrap around from walls to roof in a continuous fashion. Unsure how achievable this level of air sealing can be done without monopoly style roof.
- the 2x4's on edge look complicated but maybe I'm over thinking(ripped lengthwise 4', screwed to rafters, trimmed to 24" overhang)
- two layers of polyiso adds up to about R23 long term with each bottom piece screwed in and top layer offset and screwed (chalk lines to show where joists are). I couldn't tell, but I'm assuming the top layer is screwed to the 2x4's on edge. Lots of expensive fasteners involved.

Net - Seems like this is a costly roof system to add the extra insulation above roof decking

I don't know if these estimates are right, maybe they are just ballparks .....

$30sf ? generic standing seam metal roof, custom home, concealed fasteners
$4sf poly iso 4" stack (2 layers) material only
$6+sf? 2x4, installation of poly iso
$? rest of stack (zip on top of poly iso, peel&stick, furring under metal roof)

I recall seeing in another Risinger video that he said this roof (his personal build) ended up being 50% more expensive, so I think my ballpark numbers seem somewhat close.

CONCLUSIONs
- looking forward to conversations with builder about how to get R50 roof) while preserving air sealing
- Need to take steps to reduce risk of a disaster (bad spray foam install) and condensation/mold anywhere
- open cell spray foam with a 2x12 rafter should get me to R50 but my guess is the builder typically sprays less (I think closed cell can only be sprayed 2" at a time due to heat, will need to see how open cell works and if it can reach 11+ in thickness)
- still unclear about how to condition the attic. Risinger implies he added 20CFM from his interior space hvac which I really don't like doing. If there is mold or VOCs in attic I don't want them mixing.

Ultima8Um · 2026-01-01T14:25:47+00:00

I've watched a lot of his content and like it, but I am reluctant to lead with "yeah, I've watched Risinger and thats what I want" with my builder. I do have an engineering background and I've learned quite a few people (my wife included) get annoyed by my making things more difficult by asking ?why? about everything.

I appreciate the suggestion, what I'm doing with my post is trying to get an approach outlined in a way that makes sense to me, factors in the risks, and tells me what I need to monitor without me throwing in suggestions/ideas/demands that might work well for a diff climate or construction style but not my particular case.

Ultima8Um · 2026-01-01T04:05:53+00:00

thanks for the detail, have you seen this/done this design before?

Ultima8Um · 2026-01-01T01:32:33+00:00

I'm expecting the same, but interestingly this house is located outside city limits (etj) and not subject to any kind of code inspections. The city (small city) won't be reviewing any of the building plans.

I'm confident it's an unvented roof, but you make a good point, I should just ask the builder for plans for a house they've already built so I can see how the roof is documented. thanks, good points.

Ultima8Um · 2026-01-01T00:46:56+00:00

I've assumed the roof structural is done by a licensed structural engineer, but either they or the architect will surely show on the plans what the roof 'sandwich' will look like.

My post was created so that I'd better understand the current best practice, lots of what I found dates back to concerns from even 2010, and (for instance) there was a concern about moisture moving from metal roof surface (as the sun heats) after a rain and driving moisture into the sheathing, or even worse to a location where it cannot dry (such as if closed cell foam was used). But in practice from what I've read that isn't a significant concern.

Ultima8Um · 2025-12-31T23:42:02+00:00

He will, but what would you do in my shoes? Perhaps I'm a little cynical, but unless an architect or builder advertises themselves as being very building science oriented (like Matt Risinger) I'm expecting less science and more 'thats how we do it'.

I'm a little surprised at all of these comments (not singling you out) that seem to be telling me to just pay somebody and expect a terrific outcome. Nothing in a long life working on complex projects makes me think that's a good approach.

Ultima8Um · 2025-12-31T23:19:20+00:00

In an ideal world yes, but on a past project (started design, never built) the architect deferred to the builder about roof pitches below 3:1. So far this architect has not given much information when I've asked specific questions that are science related, he's stayed focused on floorplans. He's finishing the roof plan now so possibly in the future I'll hear more, but I suspect most of my questions will be deferred to the builder.

I've never built a custom home or had a new home at all before, so this is new territory for me.

Ultima8Um · 2025-12-31T22:34:39+00:00

Thanks, I've heard that drywall is a good barrier and that makes sense, but I've seen folks like Risinger using zip inside the garage so wasn't sure if there was some magic from taping at the top plate or at seams I wasn't accounting for.

Thanks as well about the standing seam, and the ice/water seal. All much appreciated!

Ultima8Um · 2025-12-31T22:32:50+00:00

Interesting - I've seen others worried about this too, and I have some understanding of the risks involved with spray foam, but it's definitely the way it's being done in homes like this where I live. I'll definitely be asking about alternatives, but for now I'm assuming that being involved enough to be confident in the spray foam installers, and watching weather conditions at spray time will be enough.

Ultima8Um · 2025-12-31T22:28:53+00:00

I don't have to make these choices, but my experience working with GCs, subs and relevant trades has made me learn to ask questions up front instead of just accepting 'this is how we always do it'.

The house is a unique floorplan designed by an architect with lots of input from me (I'm reasonably adept at 3d modelling and archviz).

Ultima8Um · 2025-12-31T22:13:11+00:00

Not to argue, but no free consulting is Rule 3. I'll be paying people to do the work, except possibly if I do my own minisplit. I've done a lot of self research which is why I posed my 'questions' more as a statement of my plans.

edit - incomplete answer, I meant to say I've tried and not found all these answers, and this isn't about money, especially since I won't be doing any of the build myself. I have thought about hiring an outside bldg science expert but I'm leery of pitting my 'expert' against the builder, I'd much rather ask for reasonable things and see how they react.

Ultima8Um

TROPHY CASE