Estimating the ROI of Insulation
jefftk.com
jefftk.com
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.
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.
People believe it is focused on money rather than value of course.
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).
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.
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.
I used closed cell foam in one room that I tore back to the studs. It’s easily the most comfortable room in the house, so I like the product, but comparing the price of non-substitute goods seems not useful. Compare foam to other insulation products.
I take it you never worked in construction or home building and gave quotes. You would understand how people don't even give the mechanical any consideration (waste of money) but will spend 10's of thousands on cosmetics. You could build their foundation out of lego but you better use marble and gold leaf in their bathrooms.
I'm a mechanical engineer (non-practicing) and generally in a position to buy something well above the entry level "we do 50 of these jobs a month" so if someone could manage to make a cogent explanation, they stand to get the sale over the other two jokers who have probably explained how "the basic system is just fine; no one ever complains" or "hey, the whole job is less than 1 Bitcoin [or other irrelevant reference]". I have a plumber that I trust; he wasn't the cheapest. I have an electrician that I trust; he wasn't the cheapest. I have an insulation contractor; he was FAR from the cheapest but did an excellent job, so he'll get the return call as well. [He was the only one who didn't make obvious blunders in the bidding process; my favorite was the one who recommended I pay an extra $1000 for him to spray foam my rim joists; said it was the best money I could ever spend. I have a structural brick house with no rim joists, so I took him down to the basement to have him point out what he was proposing to do; hilarity ensued, of course]. I wish I could find a good HVAC contractor. I'm 0 for 2 so far there.
It's essentially a waste of money except for limited applications, which is why you won't find any builders at any price point using spray foam as a primary source of insulation.
Spray foam is also a pain if you need to get into wall/ceiling cavities for HVAC/plumbing/electrical repairs/additions.
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.
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.
We are literally replying to someone saying that the CCF will outlive the house!
I've done a bit of amateur archaeological digging and the viking houses are just stains in the ground, showing where the post holes once were. There's a beauty in that, I think.
Whereas in a thousand years will people be digging up CCF with the imprint of timber studs? Yuck!
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.
It's all about warm side/cold side and the dew point.
Demilic is based in Arlington TX.
* If air temp will never cross the dew point, you don't need a vapor retarder.
* Though the normal is "vapor retarder on the hot side", they can be on the outside of the wall assembly if condensed water can drain away. This is important for climates that have heavy heating and heavy cooling seasons, or for it's easier to put it on the outside.
[1]https://www.architectmagazine.com/technology/products/produc...
This comes to about R-10 for the floor, R-16 for the walls, and R-25 for the ceiling.
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.
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.
If you compared costs to heat, and said American homes were higher-cost, that would make more sense to me.
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.
For reference my place (in Chicago) costs lest than $60 a month to heat in the dead of winter.
Flip to a house, also in NYC, and the heating bill was 4x for 2x more space...I think mostly because it was a detached home with all sides open.
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.
https://ec.europa.eu/energy/eu-buildings-factsheets-topics-t...
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.
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.
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
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.
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!
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.
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...
You can also put it on the outside to give yourself 'triple glazing'. It makes a really big difference to the heating required to stay warm.
Looks a bit tacky though.
It's completely mind boggling that anyone was allowed to build housing with single pane windows in 2003.
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)
- 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.
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).
That being said, the consensus in building science circles is now converging to the idea of building airtight buildings (i.e Passive House) with layer air and vapour barriers, along with insulation to manage moisture and heat. That way you don't sacrifice heating to manage your moisture.
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.