Sources for Frost Depth Values

[CodyScottThomas]

Hello all, this is my first post here so please bear with me.

Where do you go to find accurate frost depth/line values?

At my job, we often have to design footers/foundations rapidly so as to get them to a costumer for the purposes of an estimate. Because everything needs done ASAP, contacting local municipalities all over the US (as well as internationally) every time we have a new location that needs a design is far from feasible. I do my best with online maps, local documents, and the like when trying to get reasonable numbers for frost depth, but I've never found any one source for this information. Occasionally, I reference Unified Facilities Criteria (UFC) which does help sometimes, but the locations that are in that document are often very scattered (or worse, all in the same place and not near where you would like them to be).

In a perfect world, the ATC website I use regularly (see below) for wind and seismic would have frost depth as well, but that's not the case. I would love it if something similar exists for frost depth.

https://hazards.atcouncil.org/

Thank you all in advance for the input.

 

[EcoGen]

I found a couple websites claiming to provide frost depth by "zipcode" but it looks like there isn't a centralized location. See below for two tables from ASCE 32-01. There's a lot more to this ASCE standard than these two graphs but I don't know how reliable this is since I think the local jurisdiction often has the final word on frost depth. Almost all jurisdictions should have the frost depth information available online. You first need to determine who has jurisdiction (city council, county, or state) and then usually a google search for that jurisdictions name + frost depth would get you what you need.

EcoGen Consultants
Structural Engineers
ecogenconsultants.com

 

[CodyScottThomas]

Thank you, I'll have to check that out in more detail, but that might be a helpful route to go.

And yes, everything I've ever seen says things like here's a map, but don't trust it, you need to check local codes. Unfortunately, said jurisdictions are notorious for taking their time to respond.

 

[HTURKAK]

You may look IBC 1809.5 Frost protection.

 

[phamENG]

HTURKAK - what edition did you find that in? I believe it's been removed from more recent versions because it's been identified as a very local issue - especially in the western US where elevation plays a significant role. Now the IBC says to do it based on the locality or ASCE 32.

That said, that map is a decent starting point for estimates. You'd be wise to put a caveat in the estimate stating that foundation pricing is based on XYZ and is subject to verification with the local AHJ. Additional pricing may apply. Something to that effect.

 

[LuK13]

Word of warning on that ATC website you linked OP.

I have done a lot of work in Connecticut. While the CT State Building Code (SBC) adopts the IBC and IRC, both are amended to replace a lot of the maps with tables that provide wind speeds and snow loads for each city/town. I checked one town on the link and it seems like you are just getting wind speeds straight from ASCE 7, which may or may not be conservative when compared to the CT SBC.

I have faced similar schedule pressures to crank out what others consider as "standardized" products, but with civil/structural once you change the street address you need to jump through all of the site specific hoops again as the sites are never standardized...

I hope you have some way to CYA for the occasion where ATC doesn't meet the local AHJ's requirements.

 

[EcoGen]

You'd be wise to put a caveat in the estimate stating that foundation pricing is based on XYZ and is subject to verification with the local AHJ. Additional pricing may apply. Something to that effect.

This would be the way to go f you can't find information online from local jurisdiction right away and you need to get something out quick.

both are amended to replace a lot of the maps with tables that provide wind speeds and snow loads for each city/town.

I've seen some jurisdictions in our area specify higher ground snow loads than ASCE 7 but I never thought that wind speeds would also be altered relative to ASCE 7. This kinda makes it impossible to do work in a new jurisdiction without going though all of their structural amendments one by one.

EcoGen Consultants
Structural Engineers
ecogenconsultants.com

 

[ChorasDen]

I never thought that wind speeds would also be altered relative to ASCE 7

This is fairly common on the west coast, we have special wind regions (Pacific Coast and Columbia River Gorge come to mind) that ASCE 7 does not provide information on and generally require more in-depth, localized wind studies. Maybe some of the areas that Luk13 work are similar?

 

[HTURKAK]

I found in 2018 International Building Code Illustrated Handbook by International Code Council ..But similar map is available at AWWA D100 ..

I think if local data for the frost line is not available, this map could be a reference..

 

[BigH]

Why not check with your local city engineering department . . . I'd think they would be more attuned to depth of frost than some map . .

One other thing to remember, not all soils are frost susceptible. Take advantage when you can. I did a job in Northern Ontario for a plant. Plant already existed and they were adding an addition. We did the investigation and discovered (actually confirmed) that the plant was on clean sand stratum of some depth. Groundwater was 5 m or so down. The "Map" showed a frost depth of 3.5 m. Why take a footing down 4 m when the soil was not frost susceptible and the groundwater level was so low. Didn't make sense - so the foundations were put at about 1.2 m depth. No issues that I have heard about and this was some 40 years ago.

 

[LuK13]

I don't think there is anything special about the wind in CT, I think its more from a simplification standpoint. No more letting people interpolate between contour lines on small maps, its as simple as if your building is located in Hartford, CT thou shalt use this wind speed.

On my end I made some excel lookup tables where I pick the town from a dropdown list and I get the values populated in my spreadsheet. I just need to check the lookup tables every time the CT SBC is revised. So in my experience it has made the process simple and automated, but to an outsider its a potential stumbling block.

I use to work internationally as well, and when you have to switch from US codes, to EN, to a jurisdiction that doesn't have codes so you got a mish mosh of US, EN, BS, and DIN codes hand picked by your customer.... I wish things were more streamlined, but I know they never will be as someone always has a better mouse trap.

 

[CodyScottThomas]

HTURKAK - Thanks, I'm always happy to have another point of reference.

Thank you all for the input and concerns. Good to know about CA and CT.

 

[EcoGen]

Why take a footing down 4 m when the soil was not frost susceptible and the groundwater level was so low. Didn't make sense - so the foundations were put at about 1.2 m depth. No issues that I have heard about and this was some 40 years ago.

I understand your logic but would this be technically compliant with the current IBC? Like does IBC provide an option to override frost depths specified by local by doing some sort of specified field investigation/testing?

The only other time I didn't bother with complying with minimum frost depth is when I'm enlarging an existing footing which has already been placed too high. Otherwise, if we are horizontally expanding an existing building, I'm not sure if I would specify anything less than the required minimum for the new addition.

EcoGen Consultants LLC
Structural Engineers
ecogenconsultants.com

 

[dauwerda]

I understand your logic but would this be technically compliant with the current IBC? Like does IBC provide an option to override frost depths specified by local by doing some sort of specified field investigation/testing?

It sure does, take a look at section 1809.5 Frost Protection:

ASCE 32 - "Frost-Protected Shallow Foundations" states:
4.1 GENERAL
In regions of seasonal ground freezing, shallow
foundations not extending below the design frost depth
shall be protected against frost heave by one or more
of the following methods:
1. use of non–frost-susceptible layers of undisturbed
ground or fill materials (Section 4.2);
2. insulation of foundations to mitigate frost penetration
and effects of frost heave (Section 4.3); or
3. approved design and details supported by engineering
analysis.

...

4.2 FOUNDATIONS ON NON–FROSTSUSCEPTIBLE
GROUND OR FILL MATERIAL
Foundations placed on a layer of well-drained,
undisturbed ground or fill material that is not susceptible
to frost shall have the thickness of such a layer
included in meeting the design frost depth defined in
Section 3.2. Undisturbed granular soils or fill material
with less than 6% of mass passing a #200 (0.074
mm) mesh sieve in accordance with ASTM D422 and
other approved non–frost-susceptible materials shall
be considered non–frost-susceptible. Classification
of frost susceptibility of soil shall be determined by
a soils or geotechnical engineer, unless otherwise
approved.