Crawl space for permafrost preservation 1

[anousone]

Hello,

I am looking for the design requirements for crawl space under building in arctic areas. More precisely I am looking for the minimum height of the crawl space.

I have found engineering rules by searching on the internet, in ufc_3_130 for artic design, and different other sources. They provide required height for typical building (Example: 4-5 feet for large building, although "large" is not explicitly defined) but I haven't found any explicit formulas for the calculation of the required height.
The installations I want to design is quite different and may not fit any of the typical building described. So I need something that is more specific. I know Russian standards provide such formulas and I was wondering if there was any american or canadian equivalent.
Alternatively, the goal of the crawl space is to allow cold air to flow beneath the building and thus preventing excessive warming of the soil (and the permafrost below). So the minimum height requirement is probably calculated to reach a specific ventilation rate. I am not sure and I have not been able to find any value for this. If anyone has references or advices.

Thanks for your help.

Regards

 

[Phidelt218]

where are you designing. I live in Alaska. I have not heard of this minimum. A lot of buildings are on stilts in areas with huge variance in the active layer (seasoning freeze thaw). We also use siphon tubes in areas to keep the permafrost frozen too. I think most of it has to do with insulation and getting the correct insulation to protect the permafrost if you have shallow permafrost.

this might help

http://www.uaf.edu/files/ces/publications-db/catalog/eeh/HCM-00952.pdf

 

[CarlB]

The standard i've seen quoted most often is 3 feet minimum of clearance. This is not referred to as a crawl space, just a clearance under the building to allow unhindered air flow. An open skirting such as chain link is often provided to discourage users from placing objects under the building. It's generally allowed to have less than 3' clear for relative small projections such as piping utilidors.

I believe you can find reference to this in the cold climate utilities manual and others, I'll check when I get a chance.

 

[anousone]

The installation is located in Russia.
In the russian standards, there is a formula to calculate the minimum clearance height beneath the building (You're right it is not always referred to as a crawl space, I have been using this term way too much lately). This height depends on the temperature inside the building, the size of the building, etc..So I actually have a formula to calculate the requested minimal height. The thing is I am not sure that it also covers the type of installations that I have.

What I want to found out is the actual philosophy behind it and the actual performance that is to be reached with this formula. As you said the clearance under the building allow unhindered air flow, so surely all the prescriptive heights found in standards must have a minimum implicit ventilation rate behind them. My idea is that if I can check that the ventilation rate under my building is higher than the minimum ventilation rate implicitly assumed by the standards, then the design should be OK. As I don't read or speak russian, I was trying to look at any hints in the US or Canadian Standards. And so far all I have been able to identify are prescriptive measures (ex: 3/4/5 feet minimum) rather than performance criteria.

Thermal siphon are our last resort because their use will make it really really hard to build the installations.

Thanks for your help and having taken some times to read my problem!

 

[CarlB]

The rationale for ventilated foundations is addressed somewhat in this government publication, found on the web:

TM 5-852-4/AFM 88-19, Chap. 4
TM 5-582-4 is now incorporated in UFC 3-130-04