Does snow on a roof simulate insulation? (2023)

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Mike T., Swampeast MO Member Posts: 6,928

December 2006 in THE MAIN WALL

While I don't claim to truly understand I've been taught and have read that the roof will always "see" 32F when covered with snow regardless of the air temp outside.

  • D107 Member Posts: 1,814

    December 2006

    Since I'm planning a ventless attic

    with polyicinine foam in the 8" joist bays under the eaves, I thought a good 8" snow (dense pack I'd hope) would give me some idea of the insulation I'd get. Of course the gable walls could not be part of this test, so I guess the value would be limited.

    Thanks,

    David

  • jp_2 Member Posts: 1,935

    (Video) Insulating on TOP of the Cabin Roof...but why? / Ep73 / Outsider Log Cabin

    December 2006

    south facing?

    I've seen south facing shingled roofs with no venting curl in a couple of years.

    snow will insulate, I've looked and looked but have not found the insulating factor i wanted to see. i've wonder the same about ice.

  • Mark Hunt Member Posts: 4,909

    December 2006

    No

    If the heat gets that far David, it is of no use to you anyway.

    Once the heat leaves the thermal envelope, it is lost.

    About the only thing that snow on the roof does is: 1) Indicate that you have little heat loss in that direction
    2) Reflect any solar gain away from that direction.

    I could argue that snow accumulation on a roof is bad and good at the same time.

    Confused yet?

    Mark H

    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

  • jp_2 Member Posts: 1,935

    December 2006

    snow is water......

    remember, snow is water, and how many btu's to change that water 1F? so it has buffer like qualities.

    fluffy snow, say 20F, will act like fiberglass insulation, little air pockets.

    ice and snow will get as cold as the surrounds, but again with a time delay dependant on either mass or 'fluffiness'.
    so sleeping in a snowbank during the night will help keep the night lows away from you.

    'they' say a snow cave will keep you 'warmer than'.

    but i have not found any numbers to the above.....sorry

    in canada we kept dead cows covered in snow so they wouldn't freeze before we butchered them. I was totally amazed that this worked, left covered for several days and they did not freeze, easy to skin.

    added:

    according to wikipedia, snow has a R1 rating per inch

    http://en.wikipedia.org/wiki/R-value_(insulation)

    so your 8 inches would increase total seen by house, an increase of R8.

    (Video) Metal Roofs - 2 Ways to INSULATE UNDERNEATH!
  • 'once heat leaves thermal envelope'

    well I was hoping that snow would be the edge of that envelope. In unvented attic, envelope becomes the foam under the eaves; with snow it would be pushed outward 8-10"....I guess I was thinking of the igloo--but of course those are probably constructed with a special technique by the Eskimos.

    As for it being good and bad, you gave the two reasons. If you had others in mind, I'd say that being snow it has by definition a sub-freezing temperature which will be conducted downward into the house, while at the same time it may insulate against transmission losses upward from house.

    (To answeer JP's question, house eaves face NE and SW.)

    Thanks,

    David

  • realolman Member Posts: 513

    (Video) Snow Load Calculation - How to Determine Snow Loads Including Snow Drift

    December 2006

    I wonder if you would mind explaining a little more about what you're doing. I'm not getting it.

    I have an old house and I installed insulation everywhere, One of the best things I did was to tear off all the existing soffit and facia and drill big holes in the old wooden soffit underneath and then re-install the aluminum with vents.... and a ridge vent... along with over a foot of insulation in the attic

    Up in the attic the rafters were at non standard spacing so I made things from sheathing to hold the insulation down from the roof deck.

    I used to have icicles 15' long. Now I got a nice covering of snow and no icicles. It's one of the few things about the wintertime that makes me feel good every time I see it.

    Anyway.. I'm not understanding what you're doing . I wonder if you would explain it in some more detail. Thanks

  • D107 Member Posts: 1,814

    December 2006

    Check buildingscience.com

    It's called an unvented attic. that website has a lot of free pdf files (and books for sale) that show how to construct both a vented and unvented attic. Frequent wall visitor Constantin has constructed same kind of attic with no apparent problems.

    In my situation I have a nice attic space (10ft peak) that I don't want to lose by dumping cellulose a foot high on the attic floor--above the 6" or so existing old fiberglass batts which is the only way I would get a decent level of insulation.

    So spraying foam between the eave joists and the gable walls will give both a good seal and insulation to the attic, making it a conditioned space. When I install a new roof, it is recommended to put some rigid insulation above eaves as well to lessen any possible heat damage to shingles. Building Science claims damage to shingles from reflected heat is minimal if it's done right. Probably good to have an HRV installed at same time to ventilate newly tightened house.

  • jp_2 Member Posts: 1,935

    December 2006

    sorry but,

    (Video) Roof Collapse due to Snow Loads: Common Causes and Prevention Strategies

    this statement does not make much sense:

    """When I install a new roof, it is recommended to put some rigid insulation above eaves as well to lessen any possible heat damage to shingles. Building Science claims damage to shingles from reflected heat is minimal if it's done right."""

    adding insulation 'under' a shingle will damage more than protect. it will help keep heat within the shingle. reduce ability for the shingle to shed heat.

    also: from where is this 'reflected heat' coming from?

    sounds like you better do some more research?

  • D107 Member Posts: 1,814

    December 2006

    I am sending you privately the pdf off the building science

    website since it's probably copyrighted material. Though my wording may be inexact, I believe the article will sustain the general idea. In an unvented roof, as I understand it, the additional heat comes from the insulation under the sheathing that does not permit the heat to dissipate as it would ordinarily with a vented roof. There you generally have a soffit vent leading air under sheathing up to a ridge vent and out. Again, Building Science claims that if done right, this additional heat should not be a significant factor in shingle life.

  • D107 Member Posts: 1,814

    December 2006

    I am sending you privately the pdf off the building science

    website since it's probably copyrighted material. Though my wording may be inexact, I believe the article will sustain the general idea. In an unvented roof, as I understand it, the additional heat comes from the insulation under the sheathing that does not permit the heat to dissipate as it would ordinarily with a vented roof. There you generally have a soffit vent leading air under sheathing up to a ridge vent and out. Again, Building Science claims that if done right, this additional heat should not be a significant factor in shingle life.

    Thanks,

    David

FAQs

Does snow on a roof simulate insulation? ›

4. MYTH: Snow on the roof is just a fact of life in winter. FACT: While a certain amount of snow on your roof will act as insulation, too much can cause collapse, leaks, or damage when the snow slides off the roof onto whatever is below.

Is snow a good insulator? ›

Snow is a great insulator because it is comprised of 90-95% air. That air is constricted, which then slows the process of heat transfer from the cold air outside through the snow layer. This is why some animals in colder climates build snow caves to borrow into for hibernation during winter.

What does snow on the roof mean? ›

(idiomatic, euphemistic, often humorous) Gray or white hair on one's head, especially as an indication of aging.

Can you put insulation directly on the roof? ›

A layer of rigid insulation board can be added either on top of the roof's weatherproof layer or directly on top of the timber roof surface, with a new weatherproof layer on top of the insulation. This is best done when the roof covering needs replacing anyway.

What is the insulation value of snow? ›

How much is enough? insulation R-value of R-18. 2. One inch of snow has an R-value of 1.

Why is my house warmer when it snows? ›

The snow acts as an insulator and helps keep your house warmer.

Should you leave snow on your roof? ›

Although most roofs in northern climates are designed to withstand the heaviest of snowfalls, it's essential that you routinely remove snow from your roof to prevent ice dams, water infiltration, and even roof collapse.

Is it bad for snow to sit on your roof? ›

Calculate the weight of the snow on your roof.

Ten inches of fresh snow equates to about five pounds per square foot, which means your roof likely can support four feet of fresh snow. Packed snow, however, weighs more: two feet or more of old snow is enough to exceed weight limits.

Is it good to have snow on the roof? ›

A snow-covered roof means your attic is doing its job. Also keep an eye out for icicles — another sign of heat loss. If your roof is warm enough to melt the snow but it's cold enough outside for snow to refreeze, your roof is losing heat. That's not healthy for your energy bills or the environment.

Should you insulate the underside of your roof? ›

roof insulation is no-contest. The floor wins every time. Insulating the floor is standard practice for an unfinished attic space. The exception to this rule takes place when families opt to convert an unfinished attic space into something usable or livable.

Is it better to insulate ceiling or roof? ›

If you are deciding between insulating the roof deck or the ceiling, Insulating your ceiling should be the priority. Not only is it easier but ceiling insulation is beneficial in a number of ways: Keeps the temperature in the building regulated. Saves on energy costs.

How do I know if my roof is insulated? ›

If you notice that your energy costs are higher than usual, it is wise to get the insulation inspected by a professional roofing company. If you find that a few of the rooms in your house are colder than the others, or if the ceiling and interior walls are cool when you touch them, it is a sign of improper insulation.

Is snow an electrical insulator? ›

Snow is an insulator. It is a poor conductor of heat due to its low density and the great amount of trapped air in between the snow crystals. If you are asking about conduction of electricity, it would be about the same. Only salt water conducts electricity.

Does snow help insulate the ground? ›

Early winter snowfalls insulate the ground by preventing heat from escaping into the atmosphere and by blocking cold air from moving into the soil. By trapping heat energy, snow restricts the depth of the frost layer, or area of soil containing ice.

Why is ice a good insulator? ›

Because ice's thermal conductivity is low, like the thermal conductivity of air, an igloo works by stopping heat being transferred into the surroundings, even when the temperature is really low. The ice and the still, unmoving air both act as highly effective insulators.

Why is it warm the day before it snows? ›

First because rain and snow are caused when warmer air meets colder air so at least 50% of the time it is actually getting warmer. And secondly there is sudden drop in humidity caused by precipitation, and cold dry air feels warmer than cold humid air because it transfers heat slower.

Is it colder when it snows or after? ›

The simple answer is: The snow keeps it cool, like putting ice in a cooler. The real answer is the snow keep us cool through evaporational cooling.

Does snow on the ground make it colder? ›

When snow covers the ground, the incoming radiation is reflected into space. The amount of solar radiation that an object reflects is known as its albedo. For a fresh snowpack, the albedo can be as high as 80-90%. Therefore, much of the incoming radiation is reflected into space, keeping the surface colder.

What does it mean when snow doesn't melt off your roof? ›

Snow on Your Roof Is a Sign that Your Roof Is Doing Its Job

If the snow isn't melting quickly, it means that heat from your home isn't escaping through your attic floors and then transferring from your roof to the exteriors.

How many inches of snow can a roof handle? ›

Most roofs can support about 40-45 inches of fresh snow. Packed snow is more dense than fresh, fluffy snow. Therefore, a roof can support about 20 inches of packed snow. One inch of ice is the equivalent of one foot of snow.

Should you remove snow around house? ›

Indeed, keeping snow away from the perimeter of your house is one of the best things you can do to prevent foundation damage. When snow melts, the water has to go somewhere. If snow is built up around your house, the water may seep into any existing cracks in your foundation, leading to basement flooding.

Can you have too much insulation in your attic? ›

It's possible to over-insulate an attic as too much will cause moisture buildup and eventually result in mold. Eventually, adding more insulation leads to diminishing returns in trapping heat as well.

How often should attic insulation be replaced? ›

However, due to its construction with natural materials, eventually the product will lose effectiveness. Fiberglass insulation typically needs to be replaced 15-20 years into it's life, as it can easily become dirty, wet, moldy, and ineffective if there's a roof leak or water damage of any kind.

How do you super insulate a roof? ›

One of the best ways to insulate a roof (whether sloped or flat) is to install rigid foam on top of the roof sheathing. Exterior foam can reduce air leaks, limit condensation at the sheathing layer, interrupt thermal bridging through the rafters, and make ice dams unlikely.

Can you spray foam the underside of your roof? ›

Open-cell spray polyurethane foam or closed-cell spray polyurethane foam (ccSPF) insulation can be sprayed along the underside of the roof sheathing to provide a conditioned and insulated attic space that can be durable and efficient in all climate zones (see Figure 1).

How do I test my home for insulation? ›

Inspecting and Evaluating Your Insulation

Inspect the exterior walls by using an electrical outlet: Turn off the power to the outlet. Remove the outlet cover and shine a flashlight into the crack around the outlet box. You should be able to see if there is insulation in the wall and possibly how thick it is.

What happens if your attic isn't insulated? ›

Without proper insulation in the attic floor, you will find that rooms in the upper levels of a home will become colder quicker, making for a long, uncomfortable winter. With an insulated attic floor, the temperatures in the house's upper levels are heated evenly, and much less warmth is lost through the attic.

How do you tell if your attic is properly insulated? ›

How to Inspect your attic insulation - YouTube

Is snow insulator or conductor? ›

Snow is an insulator. It is a poor conductor of heat due to its low density and the great amount of trapped air in between the snow crystals. If you are asking about conduction of electricity, it would be about the same. Only salt water conducts electricity.

Is snow a better heat insulator than ice? ›

Snow is better insulator than ice because snow contains air packets inside it and air is a good insulator of heat . Due to this , snow takes longer time to melt than ice of same mass .

Why is freshly fallen snow a better heat insulator than old hard packed snow? ›

This snow contains large number of air pockets which prevent the heat flow through it by convection process.

Is wood a good insulator? ›

Wood exhibits a low thermal conductivity (high heat-insulating capacity) compared with materials such as metals, marble, glass, and concrete. Thermal conductivity is highest in the axial direction and increases with density and moisture content; thus, light, dry woods are better insulators.

Does electricity flow through snow? ›

When impurities such as salt are added this means that there are also positive and negative ions than can become mobile in order to create an electric charge. In snow however, those ions are not mobile, which means it is not a good conductor of electricity.

What happens when electricity flows through ice? ›

As electrical fields pass through the ice crystals, they become polarized and align, generating energy that is discharged when lightning flashes—at times creating so much energy that a bolt can heat the air it passes through to 50,000°F.

Does ice conduct electricity? ›

is ice conducting electricity ? A: Yes, but it's a poor conductor. The H+ ions don't tunnel around very quickly.

Why it is much hotter above a fire than by its side? ›

It is hotter for the same distance over the top of the fire than it is by the side is mainly because. air conducts heat upward.

What is the purpose of snow? ›

Without snow, milder temperatures and the sun could warm the soil surface, leading to damage from soil heaving, which can break roots and dry out plant parts. Snow also helps conserve soil moisture over the winter.

Where does the particles of snow fell? ›

Snowflakes nucleate around particles in the atmosphere by attracting supercooled water droplets, which freeze in hexagonal-shaped crystals. Snowflakes take on a variety of shapes, basic among these are platelets, needles, columns and rime. As snow accumulates into a snowpack, it may blow into drifts.

What is latent heat fusion of snow? ›

The latent heat of fusion is large, approximately 333 kJ kg-' of snow. The energy required to melt 1 kg of snow (already at O°C) therefore is equivalent to that required to raise the temperature of 1 kg of water 79°C. Latent heat is released to the environment during freezing, when liquid water crystallises.

Is wood or Styrofoam a better insulator? ›

The wood blocked at least 10 degrees more heat than styrofoam or silica aerogel, which had been awarded the Guinness World Record for 'best insulator'. The nanowood, which is white, also effectively reflects sunlight.

Is Cardboard a better insulator than wood? ›

The added layers of paper provide more wood fibers and more pockets of air, resulting in better insulation. The heavier the cardboard, the better its insulation qualities.

Is Styrofoam a good insulator? ›

Sometimes polystyrene foam is called Styrofoam but this is a trademarked name, not the technical name. In its expanded form, polystyrene has low thermal conductivity which makes it a great insulator.

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