Frost line depth

[powerwashman]

Hello All,
How can I determine the frost line depth for a project in Virginia? All I can find in the code is in R301.2 which leaves in up to the locality. The online version of the code is blank in this section. Any help would be appreciated.

 

[birneys]

Have you tried calling the local building department?

 

[JAE]

You can also do an online search for "frost depth map of united states" but you will get numerous "versions" of the map.
These typically show maximum frost depth in the ground and are not associated with buildings and building foundations.
The presence of a building affects the frost depth as there is some level of insulating/heating that occurs at the footing.

All that to say - do what birneys suggests...

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[oldestguy]

It is not all that simple. Sure there may be some local code, or cemetery guides, but it all depends on soil type and other factors such as snow cover, water table, soil moisture content, etc. What is the reason you need this? If you are afraid of frost heave for foundations, there may be the code, whether right or wrong. If you have relatively clean sand, likely no frost heave even if the freezing line goes deep. Here again, remember water,when freezing, gives off heat. The more water the less the depth of freezing, as for a lake. Silty sands are likely to have more soil moisture content than clean sands and thus less depth of freeing. However, even then this shallow stuff can heave significantly in the process. It all depends on the amount passing the No. 200 sieve and a rough guide. With P-200 over 10 percent heave is likely, except for clays which don't let moisture migrate to the freezing zone rapidly enough to be a problem.. Without any other info, see if the US weather bureau has any maps of "frost depth" averages, etc.

 

[aeoliantexan]

Foundation Engineering by Leonards has a map of "Maximum Frost Depth". The contours are pretty closely spaced across Virginia, from 5 inches in the extreme southeast corner to about 35 inches in the north. Leonards recommended placing footings at 3/4ths of those depths. That was before the use of perimeter insulation on the inside of foundation walls became common, so you might want to increase it.

Altitude will have an effect.

The county soil surveys by USDA may have information

Like OG, I would check with local building inspectors, house builders, etc for local practice.