Estimating the ROI of Insulation

https://www.jefftk.com/p/estimating-the-roi-of-insulation

by luu • 6 years ago

92 69 6 years ago

jefftk.com

ComputerGuru• 6 years ago

Note: The comments go off on many tangents even more interesting and helpful than the article itself.

travisporter• 6 years ago

HN’s tag line

saeranv4• 6 years ago

Couple of thoughts:

- The other factor to consider here is the use of insulation to protect against moisture in the structure, which will deteriorate materials and decrease the thermal resistance of the structure. Looks like the comment section gets into this.

- I think it's mistake to not insulate the floor. Rule of thumb is soil underneath building is 2C less then average indoor space temperature[1] - for commercial buildings, probably more residential since there's less equipment. So there will be heat loss. More importantly, the ground consists of wet soil with moisture that wants to evaporate up into the structure. Insulation is one of the crucial components of preventing this (in addition to proper site drainage, and air/vapor barriers).

- I think this kind of steady-state calculation is great for a quick back-of-envelope calculation like this. But, for the sake of completeness, I want to mention that heating is a dynamic process with multiple modes of transfer, and not modeling it that way means we're neglecting the following impacts: air infiltration/ventilation that changes with pressure differences, solar radiation, heat generated from people and office equipment, latent energy impact of humid air, and the changing resistance associated with air films on surfaces. Thermal mass is also one, but is already mentioned in the original post.

[1] https://bigladdersoftware.com/epx/docs/8-3/auxiliary-program...

ETA: Now that I've thought about it some more, I think there is one possible source of error here that can really throw off even back-of-envelope calculations like this: accurately calculating the thermal resistance of the windows.

Specifically, one underlying assumption in this calculation is that the R-value for each material is uniform, even though in reality a wall (for example) consists of different materials with different heat transfer rates (i.e think of heat through a cross-section of the wall cut through a stud versus a non-stud area). The manufacturer=provided R-value for assemblies will incorporate the thermal bridging of studs, and fasteners, but won't account for the impact of thermal bridging at wall/roof/floor intersections and at windows. The thermal bridging impact is going to be negligible for wall intersections for a simple rectangular prism-type building, but the impact of window thermal bridging should really change the window thermal resistance.

Which in turn may really change the ROI impact of insulation calculated here, since windows are basically open holes in your thermal envelope, and even a slight reduction in its performance can reduce the efficiency impact of wall insulation. In my experience it's more common to go for higher-performance windows (double/triple-pane) before going for wall insulation increases in energy retrofits.

Assuming this isn't already incorporated, it can be approximated by looking it up in the window manufacturer specifications. They usually provide edge-of-window and center-of-window U-values (reciprocal of R-value, more appropriate for heat transfer in parallel constructions) that can be used to calculate a new area-weighted R-value for the window (i.e assume 2 inches offset from window frame for edge-of-window U-value).

I would also look up window air film coefficients, since there's a stagnant film of air on surfaces that can add about about 1/3 increased resistance to double-pane windows. R-values typically don't include film coefficients.

frankus2• 6 years ago

There definitely are some subtleties of building science involved. Insulation doesn’t so much keep your house warm (that’s what the furnace does) as keep the outside of your walls cold (at which point they radiate/convect less heat into the air). If the air reaches its dew point at an inopportune place in the wall assembly you can easily get moisture damage and/or mold.

jaclaz2• 6 years ago

Yes, if you want a good insulation you need a mechanical ventilation (with air heat exchanger) otherwise - besides mold - you will be living in a non-healty environment.

Even on non particuarly insulated houses our grandmothers and mothers did - at least once a day - change the air, opening windows for some fifteen minutes, there were reasons for that, and they remain valid.

Nowadays that tradition is largely lost (for whatever reason) and some way to change air needs to be provided (and it comes with a cost and complications attached).

I have seen too many houses built in the early days of energy saving (that began here roughly 10-12 years ago) with serious mold or however humidity issues, and even nowadays, when the issue is (partially) re-known, I see freshly built houses in class B or C (in EU they are classified with the best being A+ and the worst being G) without any mechanical ventilation provisions (houses in classes A/1/2/3/4 now largely have them).

maerF0x0• 6 years ago

Reminds me of this graph[1] years ago that, iirc, i saw in inconvenient truth.

There are a large number of existing, deployable technologies that have a positive ROI, but we just dont use them. (Everything on the left side of the graph)

The first curve from ten years ago wasn’t perfect. It vastly underestimated how quickly technology costs would fall for renewable-energy sources like batteries, LED lighting, wind turbines, and solar photovoltaic panels

[1] https://www.mckinsey.com/~/media/McKinsey/About%20Us/McKinse...

on https://www.mckinsey.com/about-us/new-at-mckinsey-blog/a-rev...

frankus2• 6 years ago

One of the pitfalls is split incentives. Builders and landlords pay for the insulation/appliances but buyers/renters pay for the utilities.

mapgrep• 6 years ago

Yup. I pay $3300/mo for an nyc apartment in a 2003 building. You’d like to imagine in a city with very cold winters and very hot summers they sprung for double paned glass. Nope. Single paned, poorly sealed glass means our thermostat is turned past 80 in the winter. If the living room (less window exposure) where the thermostat is isn’t 85 the rooms can be below 60.

bradlys• 6 years ago

This is true of insurance for homes as well. Be very careful of what home you buy in places like Florida where construction type can have a huge impact on your premium. (I’m talking 2-3x on an already high cost) Even just the years your home was built can have a 50%+ impact on your premium! (Some years regulations were strong, years later the regulations were taken down, and then came back... etc)

If the cost between a 2002 and 2003 home is nothing and they’re basically the same, you might find one is much cheaper to insure... (I don’t recall exact years but I can look it up if people care)

throwaway133372• 6 years ago

In Austria, when you look for housing for sale, you see an insulation rating. Not so in the United States.

It just so happens that all the Austrian homes I've been in are much warmer than those in northern US in the winter. American homes are surprisingly cold.

You make what you measure.

mod• 6 years ago

Wouldn't the homes just be as cold as their owners kept them? I don't understand that comparison.

If you compared costs to heat, and said American homes were higher-cost, that would make more sense to me.

throwaway133372• 6 years ago

It could be that Americans just prefer colder homes.

However last winter, my heating bill in my current American home was something like $400 USD/month for maintaining a colder house than I'm used to in Europe. As someone who lived in both places, you can bet cost does play a role.

Groxx2• 6 years ago

What would the "insulation rating" cover? E.g. the R-value of the stuff inside walls, which wouldn't cover windows or gaps or lots of other things, or do they somehow measure the R-value of the house as a whole?

Every house and rental I've encountered so far has given me the monthly heating/cooling cost up-front, which has so far been fairly accurate, assuming you hold at an area-normal temperature indoors. And they've all been able to tell me the R-value of the insulation in the walls and roof or attic. If ever it's more than like $100 for a single-family home, you pretty much know the insulation is bad or terrible.

bleepblorp2• 6 years ago

OP is likely referring to documentation required under the EU's energy performance certificates rules. See:

https://ec.europa.eu/energy/eu-buildings-factsheets-topics-t...

csours• 6 years ago

There's about 5 significant things that go into perceived temperature and comfort: Ambient air temperature, radiant heat, conductive heat, humidity, and air circulation.

So for instance, in an un-insulated shed, you could bring up the ambient air temperature with a space heater, but still feel cold because the walls are cold and not radiating heat back at you. (It would be convenient, but incorrect to say that they are radiating cold at you).

If you insulated the walls and ceiling, but not the floor, you could have a warm space, but cold feet due to conductive heating (of the floor, from your feet).

Humidity and air movement is more important in cooling, because the human body cools itself with sweat; but humidity in a structure has to be controlled, even if you want more humidity in the wintertime, it will condense and cause rot.

So basically I'm saying you want the insulation just for comfort even if it didn't make economic sense.

maxerickson2• 6 years ago

That's not what economic sense means. If you value comfort above the cost of insulation, it makes economic sense to purchase insulation.

You are talking about some lower bar, if it didn't pay for itself in short order.

This misunderstanding is a big piece of why economics is called the dismal science. Meanwhile economists model human actors as rational.

stkdump• 6 years ago

I think what GP is saying, you will save money with insulation because you can heat to a lower temp.

fred_is_fred2• 6 years ago

Noting how humidity affects perceived temperature is something that people don't think about in the cold. Everyone gets "dry heat" but dry cold is a thing too. 25 in Colorado and 25 in Boston are wildly different - if it's 25 here and the sun is out you can unzip your light jacket. The downside is that I have pretty bad eczema all winter, but I don't freeze to death.

justnotworthit2• 6 years ago

which one is "here"? You're saying Colorado 25 has low humidity and is more comfortable?

hourislate5• 6 years ago

Some things to consider.

This guy needs to learn more about insulation before attempting an ROI. The average new build has 2000 ft of linear cracks that allow airflow. It's like keeping your front and back door open all year around. Batt Insulation is rated to make batt insulation look good. It does not seal out airflow. If it were great wouldn't we use it in our freezers and refrigerators?

If you want to use Insulation than I would suggest Spray Foam (closed cell or open cell).

https://www.demilec.com/

It not only provides an air seal but can also act as a vapor barrier and is mold/mildew proof and has no nutritional value for pests or bugs. Closed Cell Foam (2 lb -it;s called 2 lb because a cubic ft weighs 2 lb)will strengthen the racking strength of a framed wall 200%. The foam is basically free because after a few years it will pay itself off and it will last longer than your house. I've seen walls in schools sprayed 30 years ago that still look like they were done yesterday.

Unfortunately the mechanical of a house is hidden behind drywall. So it is out of sight and and of mind. People will not hesitate to spend 50k on a kitchen that can be replaced at some point without knocking down the house but they will look at you like you raped their sister and killed their mother when you give them a quote for 20k to spray their whole house. You get one chance to do it right and not to many people care.

Here is a shot of spraying the outside of a foundation wall. The entire inside was sprayed foamed also. This spray foamed foundation stops the cold from even getting to the outside walls. Many schools and commercial buildings are done like this.

https://imgur.com/a/bZGyUJk

This house has geothermal HVAC and is entirely sprayed foamed. It has a fresh air recirc to keep it all healthy. HVAC bills are trivial, comfort is incredible in -40 or 100 +. I would be surprised if it cost more than $800 - $1000 a year to keep at a steady 78 in the winter and 72 in the summer. When the wood stove is going it heats the entire 2800 sq/ft house. You can't even hear thunder or heavy winds.

It was 24k to spray everything (2800 SQ/FT house). A little cheaper than the kitchen if you count the appliances.

btbuildem2• 6 years ago

Closed cell foam is amazing. Air and vapor barrier, high R-value, cures hard and semi-structural. Expensive, but worth it.

jointpdf• 6 years ago

How about rockwool? It seems like it has a lot of advantages: soundproofing, termite resistance, hydrophobic, fire resistance, recycled content, inexpensive. What am I missing?

turtlebits3• 6 years ago

Spray foam is way too expensive and should only be used in extraordinary cases. For a new house I'd just use a layer of polyiso on the outside to reduce thermal bridging and regular fiberglass batts between studs. If you really want high R-value, double stud construction with blown in is probably the most cost effective.

hourislate5• 6 years ago

$3 sq/ft at 3 inches thick and provides an R21 and a complete air seal and vapor barrier. That's less than most people spend on carpet.

oh_sigh• 6 years ago

Maybe I'm just getting sensitive in my old age, but IMHO there's no benefit to using brutal metaphors involving rape and murder when talking about insulation. I appreciate your comment otherwise though.

willvarfar2• 6 years ago

What's the environmental impact of CCF?

I'm starting out on a dream home project, but get uneasy thinking I'm building a house from lots of fossil fuel and concrete.

There's such a thing as 'green concrete' but the way its marketed smells like a pending dieselgate.

I'm currently leaning towards straw-bale and timber (I'm building in forests), but want lots of glazing and that seems really bad environmentally too.

alanfranz• 6 years ago

What's the environmental impact of CCF?

Did you consider the total impact of your new house throughout its whole life? Even though CCF may be fossil-fuel based (disclosure: I have no actual idea of how CCF is created), if it saves a lot of energy (which is probably extracted by fossil fuels as well) it may easily be a win for the environment.

pnut• 6 years ago

I can speak from experience, that insulation which forms a vapor barrier is not compliant with the residential building codes in Austin, TX and likely many other places due to the climate of the area.

Additionally, in the UK, many houses had this spray insulation inserted into their wall cavities, and the additional vapor barrier resulted in major damp and mold problems.

hourislate5• 6 years ago

In warmer climates like Austin/TX, you use 1/2 lb (Open Cell) to a depth of 6 inches. It does not create a vapor barrier.

It's all about warm side/cold side and the dew point.

Demilic is based in Arlington TX.

cycomanic• 6 years ago

It's worth noting that spray foam insulation has significant CO2 impact (measured as GWP). Some estimate is to have a payback time of 50-60 years (although the manufactures dispute the numbers)[1]. We have opted for cellulose insulation for our new house, which has most of the insulation advantages without the environmental impact.

[1]https://www.architectmagazine.com/technology/products/produc...

kls• 6 years ago

I did my house with a 2lb closed cell foam, and could not be more pleased with it. I had the (mis)fortune of getting hit by a major hurricane so the house had to be gutted to the studs. I ended up doing it myself with a fastkick binary gun as I already had an 80 gallon compressor. Ended up costing me 7k to do right at 2000 sq.ft, at an average depth of 3 inches, including under the floor (we are on a pier system) and the ceiling. We put foam board up in the attic and shot the foam between the rafters to the foam board, so there is a little extra insulation there.

qndreoi• 6 years ago

Author says "Most of the structure is exposed to air, which is generally much colder than the ground, so I'm going to ignore the floor."

The floor in Boston will be about 40 degrees F in winter. Cold feet are a miserable experience. Foam insulation would be money well spent.

londons_explore3• 6 years ago

The floor also has a very big thermal mass.

It will take days to warm up. After you have spent lots of money warming it up, it will keep the rest of the building warm (and leaking heat through the walls) when you aren't using it, wasting more money.

Thermal mass is very bad for any building only used some of the day/week

saeranv4• 6 years ago

If the floor slab is insulated on the bottom (so you're decoupling it from the earth), and it's around 100 - 200 mm thick, I think it could do some nice passive heating/cooling - cooling the space in the summer and warming the space in the evenings.

But, it's true any active heating would also be buffered by any thermal mass (especially radiative heat). But you can just cover up the slab with carpet to limit the buffering.

akvadrako• 6 years ago

In-floor heating is generally about as efficient as room radiators even though it keeps the house warm all the time.

gwbas1c• 6 years ago

There are products like Ekotrope and Resnet that do modeling like this. They can even predict cost based on heating system and location.

Also: In Boston, AC is a must for a home office. A building like this can use a mini split for both heating and cooling, which is much cheaper than resistive heating. (I heat and cool my home office near Boston with a mini split.) There's no point in a separate heating system anymore.

jefftk• 6 years ago

Update: I did decide to insulate, with 2" of XPS closed cell foam on the floor and walls, R-19 fiberglass on the ceiling, and then an extra 1" of polyiso on the walls and ceiling. I've put in the floor and hung the drywall, but I'm still not done with the drywall joints because my wrists have been hurting and mudding the joints has been aggravating them.

This comes to about R-10 for the floor, R-16 for the walls, and R-25 for the ceiling.

saeranv4• 6 years ago

It's cool that you're optimizing and constructing this yourself. I want to do that myself one day.

Since you're already using Python for some quick calculations, and are interested in continuing to model the interaction between your building and the environment, you might want to check out Ladybug, an open-source environmental and energy modeling library[1][2]. The honeybee-energy library has a wrapper for DOE's EnergyPlus simulation engine, and the ladybug, and ladybug-comfort libraries have a lot of useful methods for analyzing weather, and mapping it to thermal comfort.

[1] https://www.ladybug.tools/ and https://github.com/ladybug-tools [2] Disclosure: I'm on the LB development team, but also have worked in building science/architecture for many years and there really isn't any other library comparable in terms of developer-friendly modeling.

turtlebits3• 6 years ago

Air sealing is key, especially if you have an existing structure. Get a blower door test done, fix the places where air leaks in or out. That can make more of a difference than just adding insulation where you think you need it.

jaclaz2• 6 years ago

But you will need some good mechanical ventilation + heat exchanger, unless you like to live in a non-healthy environment.

utopcell• 6 years ago

[..] and ignore my installation time (since this is something I would enjoy doing) [..]

Therein lies the fallacy that has made many founders/CEOs rich, exploiting the sweat and tears of brilliant folks who were just having too much fun building products: My time is free because I enjoy what I do.

Bedon2922• 6 years ago

My house is a bit older, but not super old. Late 80s. And I have been thinking a lot about insulation and heat / ac bills lately. Because we are home all the time. No more timers that let it not run during the hottest parts of the day and such. Trying to figure out how much effort to put in. We got new windows recently and they are not as cold to the touch as the old ones, but probably are leaking more air too. So not sure it was a huge positive. Before that I blew more insulation into the attic, but don't think I did enough. Trying to figure out what next. Keep thinking about trying to find someone to blow in foam into the exterior walls, but know thats not going to be cheap. And take a very long time to pay itself off.

ed25519FUUU• 6 years ago

Buy a flir IR video dongle and take a look around your house on a hot (or cold) day. That will give you an idea of just where your inefficiencies might be.

DoingIsLearning• 6 years ago

I doubly recomend this. I actually borrowed a FLIR camera from work but I was amazed at how much insight it gave me.

Specially in older houses you can easily spot areas where insulation has degraded or even actual air gaps from previous bad jobs.

As bonus you will also discover that the IR emitted by you bounces off transparent glass as if it was a mirror! Scared the crap out of me when looking into the display, for a split second I genuinely thought there was someone behind the glass!

Bedon2922• 6 years ago

We have had on in our 'Saved for Later' in Amazon for probably over a year now, just never pulled the trigger. Best price I have seen is $200. But I suppose it might have paid for itself by now if we had done it initially.

hourislate5• 6 years ago

Your situation is not unique. There are many folks that have basically done what you did and still find it insufficient and experience cold rooms and drafts. This may not be a popular opinion but new Windows do very little to increase the comfort of your home unless the old ones were absolute trash. Sealing the attic and adding insulation can definitely help since it stops the chimney effect of warm air rising in from the bottom and fleeing through the top of the house.

Here are a couple of things you can do. Seal the area between the first floor and the basement along the perimeter of the structure, if you have a basement. This is the area above the perimeter wall top plate and the first floor joists. Typically the area between first floor joists lets in a lot of air and sometimes has no insulation. This area should be sealed and insulated.

The one other thing you can do that will make the biggest difference without tearing down all the inside drywall in your house to insulate (forget pour in foam, it's not worth it), is insulate from the outside of your home by applying Stucco. It's not cheap but is less intrusive for an existing house that is occupied. A contractor will basically apply a 1 - 2 inch thick foam board adhered to the outside walls (Brick?)and then apply stucco to that. It will prevent your outside walls from getting cold in the first place and seal your home to a pretty good level. It can be around $10 + SQ/FT. That is the advice I usually give folks who are in your situation and don't want to do a major interior RENO.

andrewmcwatters• 6 years ago

Guy does Manual J and figures out insulation is worth it.

Estimating the ROI of Insulation

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