Measuring house square footage
 

I was looking at a survey plat of a house, and it gives the exterior dimensions of the structure. When it comes to calculating square footage under heat/air, there must be some sort of adjustment for the volume of the walls. I am assuming there is probably some sort of rule of thumb, possibly a percentage factor. Would anybody know what that might be?

thanks
Fred

If it's for HVAC loads, you'd have to also factor in doors & windows, insulatioin, and other things like that.

I'd just use the dimensions given for a ball park number.

If you are getting serious about it, you need all the dimensions (plus height) and all the window, door sizes and the roof/wall constuction to do heat gain/loss calculation

You can go to the DOE website and down load their rescheck program which is very helpful if you are doing insulation.

Likely there's some ASHRE software to do the calc.

I think most people go with the outside dimensions of the structure. Seems odd, not entirely accurate but that's what I've encountered.

If you are doing calcs for heating/aircon, best use the outside dimensions, its better to be a little over-sized than under-sized. You can always turn a larger aircon down a little. Try turning an undersized one up when its already flat out !!

In a typical home about 2/3 of all heat loss is from leakage around doors and windows and loss from opening and closing doors, so any true calculation needs to calculate in all that.

In most cases though the hvac folks just say....hmmmm, 2800 sf about average windows etc....about 2.5 tons ac and 150K btu heat. (as an example)

And it works.