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Soil on foundation wall (C) Carson Dunlop AssociatesInsulating R-Value of Soil or Dirt

Insulating or R Value of soil: this article describes the insulating value of soil or dirt such as the insulating value of soil against a building wall or foundation wall.

We include soil R-values and we discuss the effect of moisture and soil density on R-values or heat loss rates.

Our page top sketch, courtesy of Carson Dunlop Associates, a Toronto home inspection firm, illustrates the effects of soil density and moisture as a source of pressure on a foundation wall.

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What is the R-value for earth, dirt, soil, backfill, or earth berms? How about the R-value of gravel & sand?

Photograph of our contractor's radiant heat folly, a really bad radiant heat slab installation that had to be abandonedReader question: Sir: Does InspectApedia have an R-value for earth when used as a berm on an exterior concrete house wall? Thank you R.J.

Reply: Earth or soil has an R-value of about R 0.25 to R-1.0 per inch at 20% moisture content and other assumptions discussed here

Sand or gravel aggregate has an R-valueof about 0.08 to 0.11 per inch at 20% moisture content or less.

Some sources quote a much higher R-value for sand and gravel aggregate but you need to look at the thickness or amount of sand or gravel when you see such quots.

For example some cite sand and gravel aggregate as providing R 1.11 FOR 8 INCHES of thickness.

That's equivalent to an R-value of R 0.1388 per inch, but without considering moisture level.

But really, the insulating value of earth depends .... as we elaborate below. A complete table of the R-values of soil and other mateirals is found

at INSULATION R-VALUES & PROPERTIES.

At left we illustrate the preparation of a radiant floor slab in contact with soil. A contractor SNAFU left exposed soil (visible in our photograph) that conducted heat away from the floor - discussed separately

at RADIANT HEAT MISTAKES .

As we note below, the R-value of the wet soil (sketch center) will be much lower than dry soil outside of the same volume of dry soil (sketch left). Freezing at the upper level of such wet soil also will affect its heat transfer rate as well as risking foundation damage as we show here.

A short answer to the R-Value of Dirt - about R 0.125 to R 0.25 per inch.

Some sources we researched assert that "one inch of 'insulation' is equal to about two feet or more of soil.

If we take 'insulation' to be a bit more specific, say the most commonly-used material, fiberglass, that's about R3 /inch for fiberglass, or if we believed the soil R-value rule of thumb about dirt, that's about 24/ 3 = about R 0.8 for arbitrary "dirt" insulation value.

If 24" of soil = R3 the R-value of 1" of soil = (3 / 24 ) or R 0.125

- Thanks to reader Timothy Carlson, 8 June 2015 for correcting this calculation.

R 0.125 per inch for soil sounds pretty reasonable if we assume about 20% moisture content, and if we consider for comparison or a "sanity check" that the R-value of uninsulated concrete is about R 0.8/inch.[1]

Other engineering sources cite the R-value of earth as about R 0.25 per inch or double our calculation. Without normalizing for soil properties and moisture content, these numbers are very arm-waving rules of thumb.

But these soil R-values may be rather unreliable given the discussion below about the effects on heat transfer of soil properties and soil moisture. Heck even snow does better, at about R1 per inch.

In addition to avoiding the confusion that comes from an unreliable R-value for earth (take R 0.25 if you like), discussions of earth berm housing and underground housing usually consider the effects of thermal mass on building comfort, not just R-values.

R-values measure resistance to heat flow or transfer between materials. But thermal mass considers the storage effects of the mass of soil (or concrete block or ?) or other materials that comprise and surround a building.

Thermal mass stores heat and returns it during cooler periods, evening out swings in building temperature. So let's keep in mind that while the R-value of two feet of soil outside of a building wall, say, may be between R 0.135 and R 0.5, that 24" of dirt has much greater thermal mass than the same quantity (in equivalent R-value) of an insulating material such as fiberglass or solid foam insulation.

What all of this means is that it is a mistake to try to equate thermal mass and insulating values, and it makes no sense to forget about heat flow rates in or out of a structure if you are paying to heat or cool a building.

Details about the Insulating Properties of Dirt, Soil, Backfill, or Earth Berms

The R-value of earth depends on the type of soil and its water content. Even more significant can be the movement of groundwater through the surrounding soil, as moving water will significantly increase the rate of heat transfer from warm to cool areas.

At least important to anyone asking this question will be the assumptions about

The soil temperature Ts at some depth where it is stable (such as below the frost line in a freezing climate, perhaps as deep as 20 feet. A Journal of Light Construction online forum discussion of soil insulating properties includes the observation that

" [earth provides a ] huge amount of thermal mass, and that's what you'll be working with or fighting against. The soil temperature at about 20' is equal to the year round ambient temperature, so that will tell you what you'll be working with/against.

If you want the room warmer or cooler than that, it's easier to install insulation and create a thermal mass inside that insulated envelope, if the ambient temperature is close to what you want, well, you don't need heat."[2]

For a more scholarly discussion of the insulating properties of soil you should consult a heat transfer engineer or a soils engineer. But here are my views of some important parameters to consider when assigning an insulating value to soil:

Material I've reviewed about earth sheltered homes and schemes that use electric radiant heated floors over un insulated soil (where electricity is dirt cheap), but I'd prefer to evaluate that "design" with comments by heat transfer experts since it seems to me that any system that pumps heat into un insulated ground in a cold climate is spending a significant portion of their heating dollar to return heat to Mother Earth rather than to Mommy upstairs.

The claim that "heat you pump into the ground under or around a home doesn't really go anywhere" is in violation of the basic laws of thermodynamics and is simply not so. Heat flows from warmer to cooler materials.

Sure we can expect there to be a temperature gradient in cool soil beneath or against a heated building, but heat flows from warmer to cooler materials, it doesn't magically stop dead at some arbitrary distance. Just where energy costs are very low and are expected to stay low might it sound plausible to use un insulated earth for heat storage under or around a building.

Research on insulating properties or R-Values of soil or dirt or earth

...


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Reader Comments, Questions & Answers About The Article Above

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Reader Question: more on how to figure out the R-value of soil or dirt

Hello, just noticed that your insulation value for dirt is inaccurate. if you are saying that 24inches of earth insulates the same as 1 inch of fiberglass, or R3, than that means 8 inches of dirt has R1, or that an inch of dirt is R 0.125. Am i wrong? Cheers, - G.R. 2/29/2013

Reply:

In this article, just above, we include a longer discussion of this question about the insulating properties of soil or dirt.

In fact there is no single right soil R-value answer without considering soil moisture levels and soil density, particle composition, but our research did find some interesting scholarly articles that gave a range of values. Above we give quite a few source citations on this topic.

In sum, if you like a dirt R-value of R=0.25 per inch of soil (which is within the range for soil R-values we discuss), then 24-inches of dirt at that R-value and moisture assumptions would be about (0.25 x 24 = 6) or R-6.

Reader Question: 2006 IECC: effectiveness of foundation perimeter insulation and insulation recommendations for radiant-heated floor slab designs

I would like to know what the persons that wrote and researched this article thinks about what Montana has on research. On their web

page MONTANA SLAB EDGE INSULATION ANALYSIS FOR 2006 IECC ADOPTION [PDF]. There seem to be so many theories on this.

One thing we have found that if the soil conditions are quite damp, there definitely needs to have some type of insulation under the slab.

Another theory I have read is that the heat as it goes down, which it will, some is that it radiates horizontally, which makes insulating the edge quite well. - Wendell Schubloom

Reply: thorough under-slab and perimeter insulation and proper tubing depth are critical for radiant heat floor slab designs

Wendell, there is not actually any contradiction between the Montana (DOE) research you cite above and radiant heat floor slab insulation requirements. The study you cite does not focus on radiant slab heating designs but or a more narrow question about the benefits of foundation/floor slab perimeter insulation.

The DOE photo (below left) shows a typical Montana construction practice that gives a thermal break between a concrete floor slab (not yet poured) and the exterior foundation wall.

I've read quite a lot of supporting research on slab and slab perimeter insulation for radiant heat flooring, and I have some direct experience with installing radiant heat and more with inspecting radiant heat flooring problems.

Typical Montana interior slab insulation design - U.S. DOEQuoting from the conclusions of the Montana DOE-sponsored study you cite, [2] [photo at left showing interior foundation insulation before the slab is poured, U.S. DOE, op cit.]

This study shows that insulating slab edges with R-10 insulation to 4-ft depth along the slab edge saves about 3% annual energy and reduces annual fuel cost by between 1 and 2%.

The energy savings vary slightly depending on the insulation configuration and building type.

Although the current installation practice in Montana does not extend the interior footing insulation to the top of the slab, based on empirical data, this study concludes that irrespective of the insulation installation configuration, Montana buildings will save energy by insulating the slab edge with R-10 insulation to a depth of 4 ft.

The payback period could vary from 4 years for small retail commercial buildings to 12 years in small office buildings.

This study, using eQUEST, Version 3.0 simulation modeling, compared full versus partial slab perimeter insulation schemes and found that there was useful energy cost savings even with partial insulation.

The study data includes comparison with fully-insulated slabs too, but most important for our discussion, it does not address radiant-in-floor-slab heating designs that, without full insulation, can find an easier heat flow into the ground than into the building - not what we want to see nor pay for in heating bills. Quoting:

The local practice of insulating the slab footing on the interior allows heat loss along the slab perimeter and thus does not achieve the full savings that could be achieved with full edge insulation configurations, but the savings are still significant.

The risk in misinterpreting the Montana study conclusions above would be to apply them generally to radiant heat floor designs and that to improperly infer that complete under-radiant-heat-floor-slab insulation is not needed in cold climates.

That study makes a general conclusion for all Montana buildings and by no means does the conclusion adequately address radiant in-slab heating system designs. The fallacious concept held by the contractor in our horror story was that "once you heat up the earth below your building it will start "giving back" heat to the building and you'll be just fine. His theory was nonsense, as both expert advice and actual field experience proved.

The earth in a cold climate like Montana or Minnesota, is for practical and design purposes, an infinite heat sink. A radiant floor slab heating system will, if improperly designed, keep pumping heat into the ground as long as the heat is turned on.

Forever.

We saw this in astronomical heating bills and a cold building interior in the Minnesota home discussed above. Heat always flows, and continues to flow from a warmer material into a cooler material.

Heated the soil beneath a building where insulation was incomplete, inadequate, or omitted, will never reach some magic perimeter after which it stops sending heat into the surrounding soil any more than an ice cube placed into the sea will stop melting because it's "cooled down" the water around itself.

As the principal author of the original material

at RADIANT HEAT MISTAKES

 I relied largely on the concrete industry and the radiant flooring industry's radiant floor slab design specifications and advice [1] as they, above all, have a huge vested interest in their installations being successful.

There is no doubt that in virtually every radiant-heat-floor-slab design we need continuous insulation under the slab and at slab perimeter, though the appropriate insulation amount might vary depending on the local climate.

The folks who seem to disagree have been people like the bully contractor who himself admitted he had never read instructions, attended a class, nor asked for expert advice. As is often the case with small contractors in remote areas and without expertise, he was "winging it". Don't try mentioning "thermodynamics" or "heat flow theory" to a bully.

Just how bad an un insulated, under-insulated, or incompletely insulated floor slab will perform with radiant in-slab floor heating depends on some additional variables: climate, soil moisture (read thermal conductivity as you suggest), and critically, the depth of tubing in the slab. In ALL cases we want the insulation in place.

But in the horrible installation we describe in these articles, the contractor not only provided incomplete and no perimeter slab insulation, he also buried the tubing so deep in the concrete that heat moved much more down into the cold earth than upwards into the occupied space.

There was so much heat loss that we could not get the room temperature up even in cold but not bitter cold weather, and even though the same contractor had done a great job insulating the upper portions of the structure's roof and walls.

(He was a framer/carpenter, and should not have attempted radiant slab installation nor tile work.) That's why we had to abandon the whole radiant floor installation.

If the floor slab had been very well insulated, the installation still would not have performed well because of the excessive tubing depth in the slab ( over 12" down in some sections ).

I appreciate the Montana reference and have added it to this article below at references [2].

 


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Reader Comments, Questions & Answers About The Article Above

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I hit bedrock before I could get my pipes below the frost line - now what?

Hi i installed a sewer pipe just below grade around 28" deep because unfortunately i hit bedrock before I could reach the min 4 foot requirement. So i installed 2" rigid insulation around the entire pipe and then put the soil back on top.

My question is, is this enough to satisfy an inspector? If not what is the reasoning behind it and is the calculation i can use to determine the r-value that is needed.
Thanks - On 2020-11-11 by Anthony -

Reply by (mod) -

Anthony,

With apology, I can't say what your local septic inspector will accept or not.

If the only question is one of freezing the addition of rigid foam around the piping may give some partial freeze protection that, combined with active use and proper slope of the sewer line, might work.

The R-value you'd want depends on the climate zone where your sewer system is installed.

Watch out: no amount of insulation will protect from freezing if the drain line is not properly pitched or is very long in run as during a period of disuse the surrounding soil temperature will reach the drain line as well.

Insulation slows the loss of heat into the cold surrounding soil but it does not stop it.


What R-value of soil can keep my water lines from freezing?

I'm laying a water pipe line and was wondering what the R value of soil is at two and half feet deep. I'm in NM so we are pretty dry most of the time. Don't want my water freezing. - On 2020-06-13 by Freddy -

Reply by (mod) -

Freddy,

Earth or soil has an R-value of about R 0.25 to R-1.0 per inch at 20% moisture content and other assumptions discussed here

I wish I had read this article before my project

Interesting article I wish I had read it before starting building a small underground refuge .

It’s covered by earth 2 feet deep and I added 32 mm of extruded polystyrene overhead , it’s cut into a hill so the walls have considerably more than 2 feet cover I’m actually surprised by the lack of insulation that the earth plus insulation provides .

Yes it has lots of thermal inertia but 3 days of hot or cold weather and you feel it ok it does have one 6” concrete wall exposed to the elements .
But I can’t help feeling the 2 ft is equal to or probably worse than 1” of insulation .

I now have a very good book on the subject that states 3 ft of earth equals 1” of insulation and I feel this is probably even more correct .

This book suggests 10 ft cover approaches stable conditions , that’s really thick cover !

I pity people that spend so much money on earth covered roofs 6 inch thick in the belief that earth is a good insulator it’s an urban myth . - On 2020-05-14 by John -

Reply by (mod) -

Thank you for the helpful comments, John. I agree with you.

Bottom line, imo, earth is a great thermal conductor and a poor insulator.

Perhaps the msin gain is stopping air leaks.

On 2016-11-19 by Malek - definition of "R" when discussing R-values

What is the unit that you are using for R , is it btu/h/s.feet/F ?

Reply by (mod) -

Malek, R refers to R-value, defined in detail at DEFINITION of HEATING, COOLING & INSULATION TERMS - https://inspectapedia.com/heat/HVAC_Definitions.php


On 2016-10-25 by Anonymous - R-value of pea gravel fill

What R value is pee fill

Reply by (mod) -

Anon:

if you are asking the R-value of pea-sized gravel fill, sand and gravel have an R-value of about 0.08 per inch.

But

Watch out: as we discuss above about the R-value of soil, the presence of water or moisture drops that R-value down to essentially nothing or worse-than nothing since wet materials become very good conductors of heat away from the warm are and into the cold.


On 2016-08-01 by Marvin K. - This is the most awesome site I have ever visited

I plan to install PEX in an experimental tiny (partly underground and bermed) house. Project is way behind schedule.

Have long searched for sound advice to help figure out a reasonable insulation design for my proposed swanky hydronic heating system. Holy Hand Grenades! Thermodynamics and soils engineering for the layman! This is the most awesome site I have ever visited. : )

Reply by (mod) -

Thanks, Marvin.
We're extra happy when a reader finds all of this scribbling useful.

Be sure to search InspectApedia for RRADIANT HEAT MISTAKES so that you can make some new ones instead of copying my old snafus.

Question: OK to skip insulation below the floor slab?

(Feb 7, 2015) Jaden said:
So if I was building a shop where I wanted the inside temperature to be 50 degrees all I would need to do is super insulate the walls and footings? No insulation under the slab and
theoretically no heating system at all, just use the earth since it is 50 degrees in my area?

Reply:

I'm not sure I get this right Jaden. But in general if you minimize the un-wanted heat gain or loss through the building walls, windows, doors, roof, and don't have any air leaks, and use a heat-exchanging ventilation system, then you're on track.

Question: insulating a well pit

Jaden's interests are the similar to mine. I want to passively warm a small pump house to keep the interior temperature above freezing by using heat from the ground.

Thoughts are to sink the concrete floor about a foot below grade where it can still drain any unwanted water accumulation to nearby lower terrain. The concrete foundation would extend below and above the slab to support a well insulated and sealed building enclosure above ground.

Thoughts are to insulate the exterior of the foundation vertically some few feet below the ground level.

Under the concrete floor, the plan is to have one or more large (6"? diameter) plastic pipes filled with water (and sealed) and extending from the slab to several feet below into the earth The theory is that water, with an R value of virtually zero, will conduct the heat from the earth up into the slab floor by natural convection within the plastic pipe(s).

My guess is that 6" pipes located on 18" centers would be sufficient.

The ground temperature here is about 55 degrees and typical low winter temperatures range in the 20's and 30's, averaging about 30 degrees. A typical once in 10 year low is about 5 degrees for a few days.

Any thoughts appreciated. - (Apr 2, 2015) Don M

Reply:

Don Well pits have been used for more than 100 years to avoid freezing at the well head; the pit bottom and all equipment in it need to be deep enough to be below the frost line unless an active heat source is added. Those pits were never even insulated, though attention to cover, possibly cover insulation, and keeping out drafts and water leaks from above were and remain important.

What I don't know with certainty is what happens when you bring the well pit up to a higher elevation and then try to protect it and its contents by insulation. My opinion is that that approach works - some of the time but not reliably in prolonged cold periods.

The idea of a passive ground source heat pump is an interesting one. Hepbasli has done some related research.

See

  • Hepbasli, Arif, Ozay Akdemir, and Ebru Hancioglu. "Experimental study of a closed loop vertical ground source heat pump system." Energy Conversion and Management 44, no. 4 (2003): 527-548.
  • Hepbasli, A., and O. Akdemir. "Energy and exergy analysis of a ground source (geothermal) heat pump system." Energy Conversion and Management 45, no. 5 (2004): 737-753.
  • Hepbasli, A. "Performance evaluation of a vertical ground‐source heat pump system in Izmir, Turkey." International Journal of Energy Research 26, no. 13 (2002): 1121-1139.

Question: Correcting the math of the R-Value of Soil

I think the discussion of the R-value of soil and its relationship to heat loss and mass is an excellent one. However, I am still somewhat confused by the math on the actual R-value calculations for soil. If "one inch of 'insulation' (at R=3) is equal to two feet or more of soil," then R3 divided by 24" = R.125 per inch of soil, not 0.8 per inch.

At R = 0.8, 24" inches of soil would have a total R value of 19.2. At R.25, 24" of soil would have a total R value of 6, or twice the value of "an inch of 'insulation'" at R=3.

As you mention, the true value of earth/soil covered spaces is not the r-value of the soil, but the moderating massing effect that several feet of soil has compared to the rapid fluctuations of hot and cold outside air.

Both conditions require insulation to reduce heat loss and/or gain, but earth substantially less so. - 06/08/2015 Timothy Carlson

Reply:

Thanks Timothy. We reviewed and corrected the article above. We appreciate your careful eye.


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Citations & References

In addition to any citations in the article above, a full list is available on request.

  • [1] Building Envelope, Basement, Kansas State University engineering extension, Energy Extension Service, KSU Engineering Extension 133 Ward Hall Manhattan, KS 66506 Phone: 785.532.6026 Fax: 785.532.6952, web search 08/16/11, original source: www.engext.ksu.edu/ees/henergy/envelope/basement.html
  • [2] "R-value of Dirt", Journal of Light Construction Forum, archive, web search 08/16/11, original source: forums.jlconline.com/forums/archive/index.php/t-42036.html
  • [3] National Research Council, Canada, NRC Institute for Research in Construction, web search 08/16/11, original source: http://irc.nrc-cnrc.gc.ca/fulltext/nrcc43093/
  • [4] Hait, John, Passive Annual Heat Storage (PAHS), Rocky Mountain Research Center; 1st ed(1983), ISBN-10: 0915207001 ISBN-13: 978-0915207008 "Passive annual heat storage: Improving the design of earth shelters, or, How to store summer's sunshine to keep your wigwam warm all winter "
  • [5] Hait, John,Passive Annual Heat Storage: Improving the Design of Earth Shelters, quoting Amazon review: a unique approach to using the earth as a low cost heat storage media which surrounds one's house. Technically accurate and from this physicists point of view a correct assessment of the laws of nature involved and how to use them to our advantage.
  • [6] Hait, John, RMRC earth sheltered vaulted-roof modular building system, Rocky Mountain Research Center (1989), ASIN: B000736VRG
  • [7] "Earth Thermal Storage Systems, [radiant floor heating], ", Therma-Ray Inc. 670 Wilsey Road, Unit 6 Fredericton, New Brunswick Canada E3B 7K4 Tel: 866-457-4600 (toll free) or 506-457-4600 Email: info@thermaray.com Web: web search 08/16/11, original source: http://www.thermaray.com/solutions/earth.html
  • [8] CanGEA Canadian Geothermal Energy Association, PO Box 1462 Station M Calgary, Alberta, Canada T2P 2L6 Tel:(403) 801 6805 Email: info@cangea.ca web search 08/16/11, original source: http://www.cangea.ca/
  • [9] RADIANT HEAT MISTAKES illustrates a horrible radiant floor installation that couldn't overcome heat losses through soils & possibly also through the foundation perimeter - a Northern Minnesota fiasco at which the builder insisted that "once you heat up the soil under that floor it'll just keep you warm all winter" - boy was he wrong.
  • Oregon state energy conservation department gives typical radiant heat floor operating temperature at 85-140 °F (30-60C). Web search 10/11/2010, original source: http://www.oregon.gov/ENERGY/CONS/RES/tax/Radiant.shtml - but it appears that the actual author of this info is: Radiant Panel Association - Radiant Professionals Alliance 8512 Oswego Road Suite 180 Baldwinsville, New York 13027 Phone (315) 303-4735 Fax (315) 303-5559 http://www.radiantpanelassociation.org/ Here's their page on hydronic floors: http://www.radiantpanelassociation.org/i4a/pages/index.cfm?pageid=99 where you'll see some vague "source temperature required" graphs that give relative but not absolute temperatures.
  • Radiant Floor Company, Barton, Vermont USA 1-866-Warm-Toes (1-866 927-6863) info@radiantcompany.com web search 10/11/2010 original source: http://www.radiantcompany.com/faq/
  • Portland Cement Association: www.concretethinker.com/Papers.aspx?DocId=8 indicates that
    - tubing for radiant heat in a concrete slab is installed UP TO two inches below the surface of the slab
    - the slab is insulated from the ground at all sides to direct heat upwards to the living space [this is our preferred design for a cold northern climate]
    - "Radiant Heating with Concrete", Ingrid Mattson & Gary Fries, Concrete Technology Today, Portland Cement Association, Vol. 18, No. 1, April 1997
  • The Radiant Panel Association: Radiant Panel Association - Radiant Professionals Alliance 8512 Oswego Road Suite 180 Baldwinsville, New York 13027 Phone (315) 303-4735 Fax (315) 303-5559 http://www.radiantpanelassociation.org/
    www.radiantpanelassociation.org/i4a/pages/index.cfm?pageid=1 offers design guidelines at http://www.radiantpanelassociation.org/i4a/pages/index.cfm?pageid=115 including these insulation R-value and coverage details:
    Application#, Minimum R-Value, and Insulation Coverage
    The following insulation alternatives are given for Slab on Grade construction:
    Alternate #1 [(Ti-To)x0.125)=R-value, with coverage from perimeter to below frost line ["Ti-To" means we calculate the necessary R-value as (Ratio of indoor to outdoor temperature) x 0.125]
    Alternate #2 R-value=5, with coverage 4' horizontal or vertical at perimeter
    Alternate #3 R-value=5, with coverage under entire slab and slab edge [this is our preferred design for a cold northern climate]
    The Radiant Panel Association offers education and publications in radiant heat design. See radiantpanelassociation.org
    Here's their page on hydronic floors: http://www.radiantpanelassociation.org/i4a/pages/index.cfm?pageid=99 where you'll see some vague "source temperature required" graphs that give relative but not absolute temperatures.
  • "Basic Hydronic underfloor - thermal storage 8 to 14 hours of control", this sketch, provided by OPTCO, is not a conventional radiant heating system design - and you'll see that the designer places the tubing too deep for efficient radiant heat delivery to the occupied space. However this design is intended for heat storage, such as in a solar heat storage system. See PASSIVE SOLAR DESIGN METHOD for more information.
  • In addition to citations & references found in this article, see the research citations given at the end of the related articles found at our suggested

    CONTINUE READING or RECOMMENDED ARTICLES.

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