Conditioned Crawlspace Vs Attic: Which Is Better Encapsulated for HVAC? (with Matt Risinger)
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- Опубліковано 23 лис 2024
- If a home layout is smart, it includes space for ductwork and HVAC equipment, and two huge spaces that make it very simple are an encapsulated attic or crawlspace. You'll see lots of conditioned attics on the biggest builder channel on UA-cam, but I don't think it's because they're better than crawlspaces- in fact, I'm pitching this to Matt Risinger @buildshow directly, and we'll see if he and the rest of my audience agrees.
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This video was interesting, but it kind of felt like choosing between the better of 2nd and 3rd place, rather than the best option of a full conditioned basement with a mechanical room. I understand some places have soil conditions where a basement doesn't make financial sense, but anywhere that a basement is possible, it is the best choice by far. In addition to having all of the same benefits of the conditioned crawlspace, it also adds additional living/storage space, and the added ceiling height makes maintaining equipment much more comfortable and convenient, which means you are more likely to do it.
Basements also have benefits during inclement weather and natural disasters. If you live in a place prone to tornadoes, it is pretty easy to add a tornado shelter into a basement. Or if you only see tornados once a decade or so, the space under the basement stairs makes a decent substitute for a shelter.
In Canada, we usually put the air vents below windows to remove moisture from the inside pane. Even double paned windows can get to near freezing on the coldest days. Since ventilation is primarily used for heating, most people want the vents in the floor to mix up the colder air. Houses in Canada almost always have a basement since we need to go down 4 to 6 feet to avoid frost line issues, and it's not much additional expense to make a full basement. Older homes don't have conditioned basements while newer homes usually do to make the space more usable (since the space is being paid for anyway).
Conditioned attics are very rare, unless they're being used as a living space. "Attic rain" is a growing problem with increased ceiling insulation, as there isn't enough heat escaping to heat the attic. A roof at -30 will collect moisture on the inside when a warm and humid front blows in through the vented attic, and when the roof warms up, the ice melts, causing water and mould problems.
I live in Louisiana and All the reasons you listed for basements and attics in canada are completely flipped here. You don’t build a basement bc it will become a moldy nightmare unless you completely insulate and condition it. And attics are being conditioned and insulated bc why not if you’ve already built and have the space
@@methos424 Basements will still get mouldy in Canada if not conditioned. It's a colder space, so moisture will condense. Or some aren't sealed properly. I nearly died from anaphylaxis from basement mould. It's just not as bad here as the humid southeast US.
I think the lesson is unconditioned spaces are generally bad.
Would love to see a series on high performance home retrofits
Doing both here in a late 1800's Victorian in Texas. Attic is done (also standing seam roof), crawlspace is next. Dehumidifiers in both of them.
Conditioning both the crawl space and attic are what we're planning for our next house as well. My 1st home was on a slab with a vented attic. Our current home had a vented crawl space before we sealed and conditioned it. Both sucked. Conditioning the attic reduces pests and allows more options for HVAC vent placement. A tall conditioned crawl space means never having to bust up up another slab to fix a plumbing issue.
most houses in TX and FL (where i live) are slab on grade so there are no crawl spaces hence why condition attics are prevalent in his videos
I think the one advantage with a conditioned attic is that creating an airtight home is easier if the attic is included. Essentially, where do put the air barrier? If you are building a traditional attic, the ceiling becomes the barrier and you must then seal all penetrations of the ceiling... and that can be a lot, and that air barrier will likely get broken at some point in the home's life by someone running wire through the attic or adding lighting.
With a conditioned attic... you move that air barrier out to the exterior skin of the building (the roof), where it belongs. And ensure that the only time you need to worry about the air seal, is when your already worried about the water seal.
It may've been Matt's channel but I'm not sure, the builder that was interviewed used large complete spanning trusses. After the trusses were up and before the interior walls built, a drywall crew came in and rocked and finished the whole ceiling THEN the interior walls put in place. The continuous drywalled ceiling eliminated a break where normally every interior wall is placed. This was of course for a vented attic. And they had other unique things for keeping the duct out of the attic and electrical stuff. Slab on grade iirc
@@95thousandroses I have seen that (he had a floating osb floor too, pretty cool). But he still has the same problem. People do not treat drywall and paint as a critical "system" even if the architect intends for it to be.
Give me a combined air/water barrier. Even the worst homeowner understands we need to seal holes to keep water and bugs out... So they may maintain the air barrier without even knowing they are doing it.
I’m a homeowner who will be building a house in a location that has little or no cooling load (central Oregon coast) so it makes sense for me to use the gyp board walls and ceilings (with two coats of acrylic paint) as my air barrier and use the exterior plane (Zip wall and roof sheathing) as my weather (i.e., water) barrier. I will require my contractor to seal the perimeter of all gyp board planes as well as all openings and penetrations and then bring in AeroBarrier to seal all the micro leaks. So we homeowners are not all clueless idiots 😂.
Still unsure about the cost and benefit of sealing, insulating, and conditioning my crawl space as it will be pretty deep in places (steeply sloped site) and I plan to use a hydronic radiant floor heating system and no AC. So the only ducts I need to accommodate are for the whole house ventilation system with ERV and dehumidifier. I’m thinking a combination of running ducts from below in partial basement and from above in lowered ceilings over hallways, bathrooms, closets to keep all system components in conditioned spaces. Just need to minimize the number of elbows to minimize loss of static pressure. I will not have an attic.
Here in New England we use mostly full basements. Most new builds will have a conditioned basement with a mechanical room (which is what I'm doing for my build this summer). Most of the new Passive House builds (or near-Passive) are using slab on grade. So the crawlspace design doesn't seem to be very popular up here.
And regarding Matt's suggestion about Unico... I've read a LOT of reviews on that system and noise seems to be a consistent issue.
Unico is not noisy if installed correct. They have very specific instructions and you have to follow them which means they get installed wrong. I have been doing HVAC for 25 years and have seen complete hack jobs with these system. They’re not forgiving like a standard system.
Excellent points. I think there's more that makes a house with a framed floor a better house too such as the floor is softer and conditioned beneath and it's possible to make it really flat. A (good) unconditioned attic is such an amazing assembly that it seems a shame to use something else if it can be avoided. Matt's explanation of his reasons for doing conditioned attics goes to show just how much a site drives design.
Good points Thomas
Some great info, advice and opinions here Corbett. Unfortunately much like Matt, here in SE Florida we building slab on grade so we are stuck battling attics and shotty foam applications!
Here in Michigan 90% of the new homes built are on a full basement. Our building code now requires the basement walls to be sealed and insulated. Because of this almost all HVAC systems are in the basement with floor vents on the main floor
@HomePerformance I learn so much from you. Thanks for the content. New construction (could not afford a custom build), no attic only a conditioned crawl space. Yes to radon mitigation. The build is very subpar on everything you talk about. I am going to try and fix this. Step one, I am getting a blower door test since they aren’t required to do this in Utah. It does have closed cell spray foam for insulation. Step 2, if leaky I am thinking aerobarrier BUT the home is finished. @aerobarrier itself has been unhelpful with telling me how to prep for them. Have you found aerobarrier to be beneficial if the home is already completed? Step three, I want my crawl space looking like yours. Mine is just dirt with some cheap fiberglass batt that is falling down. I am wondering if it’s possible to add a thin layer of concrete since it’s done? I was thinking insulate over the dirt, then some plastic and tape it good, then thin concrete (but I don’t know if thats possible for a retrofit?). We do not have an ERV, I am thrilled to see your ERV ducting down in the crawlspace. @HomePerformance how to you exhaust the EVR out of your crawl space? @buildshow and @HomePerformance please more videos for retrofit! Those of us with crappy builds need some guidance!
If you’re in a cooling dominated climate and you use an air-based radiant heat system like Legalett, suddenly a conditioned attic starts to make a lot more sense. Your ERV is in the attic so fresh air is circulated better, so with fewer opportunities for dead zones. Dehumidification is more efficient and more effective. The duct work expense for sheet metal is drastically decreased. If you put a heat pump water heater and condensing washer / dryer unit up there you have extremely short water runs and you’re recapturing a lot of that warmth. And everything is easily accessible, so inspection, maintenance, and repair are a breeze. There is a downside though, an that’s leaks. You have to put a drip pan under everything, and tie it into the air conditioner condensate drain.
Nice collaboration!
Gracias buddy
Great episode! Love the cross over with Matt too!
lol @ the Risinger appearance. Awesome video. Here’s something I can’t find: the best way to “retrofit” a slab on grade home in south Florida (hot/humid almost year round) climate with spray foam under a shingle roof.
It’s an older home, no head room for ducts between the attic and ceiling in their own chase. So much conflicting information about roof deck rot and overheated shingles, closed cell vs open cell, etc. How would you personally re-insulate, spray foam or not, a slab on grade, shingle roof, concrete block home in this climate these days?
Thanks for any input!
What would be good to hear you talk about is moving away from central AC totally... North America loves central AC!!!
At my house in Thailand we have a Daikin VRV; so a centralized compressor and then room base wall or ceiling AC units.
Oh and our ERVs are plumbed INTO the indoor AC, so it is working with the AC.
My issue with the overwhelming majority of ductless AC systems is that the wall units and even the ceiling cassettes are so darn ugly. A lot of people don’t seem to mind having these visual blemishes in their space and a lot of the building science wonks that frequent this channel probably enjoy seeing an efficient piece of mechanical equipment hanging on the walls of their house 😂. I could get on board with putting the indoor units in an attic or crawl space and running short duct runs to the conditioned spaces (including the attic and/or crawl space of course), but this quickly becomes more expensive than a central heating/AC system and requires a separate ventilation system (which is a good idea anyway, but a ducted heating/AC system at least gives you the option to piggyback off the ductwork for your ventilation system as most people have budget constraints).
@@MichaelJ674 some fair points, but I would say that vendors are getting more inventive about the systems. One unit in my living area is hidden above the plasterboard so all you see is the vent into the room
Ductless units have several disadvantages:
They don't dehumidify well, or at least not efficiently, so they don't do a good job handling the "shoulder seasons" when homes need to remove humidity without cooling the air. (Probably not an issue in Thailand.)
Their filtration is generally terrible.
They're usually blowing at people.
They're ugly.
@@DeuceDeuceBravo interesting I have the opposite problem, they are too efficient at reducing the humidity in our house!
But also I think missing the pro's, no need to worry about all the loss of performance from ducts running through the house, potential for mold and other build up in the ducts, more fine grained control of the temperature in each room
I like Matt's comment about high-velocity systems with outlets mounted high up on the walls. The lower airflow rate of the Unico system gives you much lower dew points compared to a conventional system; Unico has some of the best sensible heat ratios of any manufacturer I have seen. Plus, the higher velocity will generate better in-room mixing and temperature uniformity.
They’re a scam, right? Higher velocities in smaller pipe equals much higher friction. A Unico system will never be as efficient as a properly sized air handler and ductwork. What is their SEER rating, like 15 max? The only people who use them are those that have minimal cooling needs and don’t want big ducts running through their houses. SHR is not a good measure of performance you would be better off upsizing a VRF system to match your latent load even if that means over sizing the sensible load. The higher efficiency would mean you are still better off that Unico.
@@matthewwilliamson6325 This is my favorite answer as an engineer, it depends. If you live in a super dry climate like Las Vegas for example, sure a high SEER vrf can be great. But, if you live in a place that has high humidity levels (most of the US), all a high SEER system will do is get you cold and wet. Not a good combination in my opinion. That strategy will require you to buy a separate dehumidifier (as Dr. Joe says, "there is no thermodynamic free lunch"). That strategy can work well, as shown on this channel and Matt's. But, it's a second peace of equipment that needs to be specified, purchased, installed, operated, and maintained properly. Personally, I would much rather have one piece of equipment that sacrifices a few SEER points for the ability to properly control both the temperature and humidity.
As far as the Unico system, that's just one example, the static pressure and duct design has nothing to do with SHR values. Any air handler with a smaller evaporator and lower flow will have a better SHR.
My ideal air handler would have a modulating chilled water coil followed by a modulating hot water coil. That's how a lot of commercial and industrial air handlers are set up; and, in my opinion the only real way you can precisely control both temperature and humidity.
I’m building a 2-story or ranch on a full basement. How about 2’ trusses between the basement and upper floor to run all the ductwork and place the mechanical room in the basement. Then just vent and insulate the attic traditionally. Thoughts…
Sounds perfect to me as an HVAC guy. Just make sure it's an insulated and sealed basement. Also you should have at least 2 large return air ducts and grills. Make sure your ductwork is sized right and accounted for in the plans for your home.
You don't have to have 2 returns but you do have to have a larg return duct and grill that's sized right.
@@KPHVAC thanks! definitely insulated. Sealed to the best of my ability. I felt like this would be the most economical option, efficient and nothing in the attic to sweat, leak, etc.
@@davidmarbut One day I plan to get a custom home built. It will be a single story home with at least a 4 foot tall crawl space. Then everything is easy to get to. Ductwork, plumbing, electrical, etc. I plan on putting the air handler in the attached garage or a utility room in the home.
@@KPHVACAre you going to condition the crawl space? I’m preparing to build on a pretty steeply sloped site and I will have a crawl space that may be as much as 8’ deep under the uphill side of the house (with walk-out basement under the downhill side). I’m concerned about the cost to enclose, insulate, and condition that much volume and I have no need for the additional basement space.
Thank you. As we do not need AC in our Northern California home an attack remains intriguing for space saving.
Did you get a response to this. Looking to put duct work in Bungalow, 1 story
Why not have dropped ceilings with ductwork between ceiling and attic. I have lived in a couple of slab homes with underground return air ducts and the combo avoids both attic and crawl space.
do you stil setup your dehumidifier and erv in the crawlspace with rest of HVAC?
Yes
Your calculations about the insulation are way off. If you don't insulate your roof to condition your attic, you're going to have to insulate the ceiling instead. The extra insulation for running the envelope under the roof is only the difference between the roof area and the ceiling area, not the full area of the roof.
Roof deck insulation will be much more than insulation at the ceiling. Blown in insulation is a quarter of the cost of roof deck insulation.
@@nolanbillings8426 We don't use blown in insulation anyway, so that's not a consideration around here. Batts stay where you put them and don't settle.
@@tealkerberus748 are you suggesting fiberglass batts stay put and don't settle?
What about neither and a mech room in conditioned space
Sure, but where do the ducts go? It’s the whole package.
@@HomePerformance soffit down 10ft walls to 8ft in the hallway and bathrooms is the plan haha (just finished the video btw, good stuff)
That makes a lot of sense. So if the property and space requirements dictate a walkout basement, the points still apply correct? Maybe a mechanical room in the basement then ability to run ducts, etc? Also at that point, would you do a vented attic or, as is making a lot of sense to me, the monopoly style? Cost/budget probably plays into this at some point.
@Austin-fc5gs that’s an excellent plan- if homes were laid out properly I’d do that all day long.
@@HomePerformance I just watched Matt's video on this design yesterday. ua-cam.com/video/Rb17LQzgRLg/v-deo.htmlsi=rOXDcJz8oFyk7zfs It seems to solve a lot of issues if you can plan ahead.
What about an old house with 18" crawl space ?
All i can say is there's nothing better than having ductwork in crawl space. Heat rises as we all know. It's gonna take much more power to have heat or cooling to fully cover room area. Any conditioning will require an erv. That's automatic.
Warm air rises. Heat radiates, convects, or is conducted.
What do I tell my contactor, to get a basement like this. I want it encapsulated, with concrete floors?
You want a sealed and conditioned basement. You also need to make sure the house is built with proper drainage around the foundation, with downspout water taken away from the side of the house, to avoid moisture problems.
This slab is commonly known as a rat slab. It's about half the concrete and reinforcement as a typical concrete floor in a living space.
I'm very familiar with Matts reasons for not building crawlspace houses. They were very rare in the 70s and earlier and nothing is built with them now. I do like the overall idea of the crawlspace design that has been laid out however... I live in one of those older rarity crawlspace houses and it's the only one I have ever lived in and I would never build one myself. I hate wood structured floor systems. I much prefer a solid slab of concrete under my feet.
Now one way to make the best of both would be to have a minisplit in every room which would eliminate all duct losses and would keep room temps exactly where you want them easily. However it's very costly to do and room invasive unless ceiling mount units are used. And then there aren't small enough units for many room sizes available. You also end up with lots of condensers outside to run power to etc. I am not a fan of multi head minisplit units as they cost as much as two separate units and I'd rather have the reliability of separate systems which are also cheaper to replace down the line.
It's a shame no one makes "microsplits" for small rooms
I’m very surprised about not liking floor vents. Half my house has a basement the other half is a conditioned crawl space. When I finished the basement I worked really hard to get the vents to the floor so the ground would not be so cold.
Did I do that wrong or are things different because my house was built in 1994. I can say the one vent that blows on me while watching tv is great in the winter but terrible in the summer because it is so cold down there anyway. I have a 5 degree difference in the summer between the second story and the basement.
My two cents: hot air rises, cold air sinks. I want to bring cold air in through the ceiling, and I want to heat the floor directly and let the warmed floor warm the air in the room.
Also, there needs to be separation between floors. A traditional two-story cold climate house would have the living rooms downstairs and the bedrooms upstairs. You warm the downstairs through the day and evening, and then at bedtime you open the door to the stairs and all that warm air goes up to warm the bedrooms. It only works if the stairs are fully enclosed and there's insulation and a good air barrier at the ceiling of the lower level.
Ive lived in both types of homes (ceiling vent vs floor vent). Both homes in Utah. I loath the ceiling vent. It blows on your head. Cannot stand it. I don’t mid the floor vent at all.
High performance houses need the sunside roof to be a simple rectangular plane for maximum photovoltaic mounting area. The ridiculously over-decorated roofs of current "upmarket" houses are a trend that needs to go the way of all trends. They're a waste of resources to build, they're hard to insulate effectively, and they're prone to leaking much sooner than a simple roof.
Here in TX the Sun side roof is the entire roof. Remember in the summer the sun is directly overhead. And all roof planes will produce power most of the year here. As well as you want large overhangs and NO direct sunlight in any window unlike up north where you want sun in the winter. And yes I hate the jumbled box design that they have been doing here since the 60s that wastes materials ending up in a smaller house for the $ and one that is more expensive to heat and cool because it has more wall area and dumb shaped roofs.
@@theinfernalcraftsman If you've got more roof than you need for your own household electricity supply, you can sell the excess into the grid or start up a home business that needs a lot of electricity.
I'm in southern Australia and the only time of year the sun's warmth would be welcome coming in through my windows, the sky is too overcast to tell where the sun is anyway. Fortunately, wide verandahs are traditional for Australian farmhouses. They're also a good cheap source of extra catchment area for household water supplies.
@@tealkerberus748 Buyback rate is 3 cents per KWH. (we pay 9.5 cents per KWH) Some places you get nothing back if you are in a Coop elec company.
I have a plan to power my workshop off of solar and export excess to the house but too many other things soak up that budget. If I covered the shop roof I could max it out at 15,000 watts. I'd like enough to start off with being able to run the minisplits in the shop and go from there. Hybrid inverter and batteries as it's not worth selling extra back.
Looks as if your crawlspace flooring has a few "stress cracks" in it. Will you need to seal/fix those or are they just the facts of life ? Also if you could, would you have raised the crawlspace higher at all?
He has a plastic barrier under the concrete but yeah I noticed that too.
@@theinfernalcraftsman Yep, I remember that when I watched his foundation/slab video. But I also recall Corbett saying that he had wanted to seal the basement slab, & I'm not sure if he did or if would have helped diminish the amount of cracks in the slab
It was assumed to crack, no biggie. One of my mentors predicted it would, and when asked how soon, he said ‘let’s see, how long does it take a 2” slab to dry… 2 weeks? So yeah, about 2 weeks.’
@@HomePerformance Yeah I couldn't remember if it was 2 or 3. Serves the purpose though.
Concrete cracks. That’s just what it does no matter how well it’s detailed. Just plan for it and don’t be upset when it happens.
Rheia is a better system than the Unico Matt reference. The distribution system is plug and play and can be contained within conditioned space. Walls, interior soffits, and or specialized trusses.
Here he goes again.... Corbett fighting the good fight. 😃
;)
isn't a basement just a tall crawlspace ??
Not if I have to feel compelled to buy furniture and dress it up and think about a future bathroom setup
The Boss!
Ice dams
Floor grills result in furniture over them
If you're going to condition your crawlspace, go the extra bit and make it a full depth basement. Your future teenage children will thank you!
"extra bit" Thats a pretty costly "bit" lol
@@95thousandroses Depends where you live. In my neck of the woods foundations need to go down 6 feet anyway for frost, so it's not much extra to take it to 8 feet.
It’s not just the cost to build. It’s costly to condition all that additional volume, too. I’m struggling with that on the new build I’m planning as I have a sloped site that makes it fairly easy to build out a full basement, but I don’t need the extra square footage either now or in the future (my kids are grown up and gone 😊). So I can have a generous crawl space, but I can’t use it for ducts or mechanical equipment unless I condition it (both in terms of best practice and code requirements). That’s a ton of area/volume to seal, insulate, and condition, so I’m not really sure what to do.
@@MichaelJ674 It'll help the resale value. You don't need to finish/drywall the inside. Conditioning a full basement is not that much more expensive. The earth outside is the same temperature as your average yearly temperature below the top few feet, so the temperature delta between the ground beneath floor and the inside will never be that big, plus heat moves slowly through dirt unlike a wall exposed to wind, so even the basement walls exposed to the top layers of ground lose less heat than your walls. A couple inches of outside foam insulation on the basement will do a lot. You'd want to do that with a crawlspace, too.
@MarkRose1337 good point. Living in warm weather I didn't consider that
Crawlspace and or under slab because radon. And if talking air quality one air change an hour makes for poor air quality. I like a warm roof with exposed rafters and roof board. Radiant heat no ducts. And hanging ervhrv up high with skillion design.
what do you do about air conditioning ? window units !?!