Terrain Elevations

[builtright3]

I'm trying to understand terrain elevations because I'm getting more and more jobs where I have to show the correct slope on the elevations.

I noticed that "0" seems to be the finish floor height as far as what the terrain see's. In this it says subfloor but that's not what I get in my section when I measure it. I get top of finish floor.
Looking for clarification and some advice of where I should be having my "0" at? Im assuming subfloor, but I know usually plans I have seen in the past call it FF (Finish Floor) but the subfloor makes more sense because different rooms have different finishes such as wood, carpet, tile...

Any advise would be helpful
Thank You

Oop's, I does read from subfloor.
Still would like some advice on elevation starting point though. Should I start with the terrain to "0" and In the terrain specs box when I'm setting terrain elevations.

Edited September 5, 2020 by builtright3
Clarification

[Chopsaw]

20 minutes ago, builtright3 said:

Still would like some advice on elevation starting point though. Should I start with the terrain to "0" and In the terrain specs box when I'm setting terrain elevations.

 

Yes set your terrain to "0" if you are using the sub floor as your reference.

[Alaskan_Son]

When you're defining the terrain, don't worry about too much about the building elevations at all.  Define your terrain using any reference datum you wish.  Maybe it's sea level, maybe it's the street, maybe its a stump where you're placing your transit, or maybe its a walkway.  Doesn't really matter.  Just use whatever works best for you and your specific scenario.  The terrain elevation data has nothing whatsoever to do with the floor heights.  The relationship between the terrain elevation and floor elevation is easily adjusted as necessary using that Subfloor Height Above Terrain setting.  That setting just adjusts the 0" terrain elevation plane relative to the 0" subfloor height.  This means if you're using sea level as your elevation datum and your flat terrain is 55' above sea level, you would set the subfloor height above sea level to 55' + the thickness of your floor system + the thickness of your sill plate + the desired distance to grade (typically about 6").

[builtright3]

8 minutes ago, Chopsaw said:

 

Yes set your terrain to "0" if you are using the sub floor as your reference.

Perfect! Thank you Chop!

[builtright3]

3 minutes ago, Alaskan_Son said:

When you're defining the terrain, don't worry about too much about the building elevations at all.  Define your terrain using any reference datum you wish.  Maybe it's sea level, maybe it's the street, maybe its a stump where you're placing your transit, or maybe its a walkway.  Doesn't really matter.  The terrain elevation data has nothing whatsoever to do with the floor heights.  The relationship between the terrain elevation and floor elevation is just adjusted as necessary using that Subfloor Height Above Terrain setting.  That setting just adjust the 0" subufloor height relative to the 0" terrain elevation plane.  This means if you're using sea level as your elevation datum and your flat terrain is 55' above sea level, you would set the subfloor height above sea level to 55' + the thickness of your floor system + the thickness of your sill plate + the desired distance to grade (typically about 6").

That makes a lot of sense. Typically I use the subfloor of the main living space as Zero when I measure elevations of a property and make that consistent to all my subcontractors so we are all on the same page. So I can use negative and positive numbers from there depending if I'm above or below. I'm assuming the plan checker will except anything as long as it makes sense to them.

[Chopsaw]

12 minutes ago, builtright3 said:

That makes a lot of sense. Typically I use the subfloor of the main living space as Zero when I measure elevations of a property and make that consistent to all my subcontractors so we are all on the same page. So I can use negative and positive numbers from there depending if I'm above or below. I'm assuming the plan checker will except anything as long as it makes sense to them.

 

A lot of plan checkers don't like to see negative numbers as they don't show well on black and white drawings.  It is old school but they sometimes insist on the subfloor being 100'.

 

Might be worth checking what the local requirements are.  Not sure what happens when there is more than 100' of fall on a lot though.  Then it gets even more confusing.

[builtright3]

23 minutes ago, Chopsaw said:

 

A lot of plan checkers don't like to see negative numbers as they don't show well on black and white drawings.  It is old school but they sometimes insist on the subfloor being 100'.

 

Might be worth checking what the local requirements are.  Not sure what happens when there is more than 100' of fall on a lot though.  Then it gets even more confusing.

 

Yes, I do see 100' FF on topo. drawings

[builtright3]

3 minutes ago, builtright3 said:

 

Yes, I do see 100' FF on topo. drawings

 

Although, as a builder if the sections are saying 0" than I may want to match that.

[Alaskan_Son]

3 minutes ago, builtright3 said:

 

Although, as a builder if the sections are saying 0" than I may want to match that.

 

This relationship can be adjusted as well...

 

That being said.  Sometimes it makes sense to go this route and sometimes it doesn't.  If you have a complex terrain that's been surveyed using sea level and your house is 734.52' above sea level, it would be silly to label all you sections and elevations as 734.52'+ (unless specifically required by your building department) and it would be very inefficient to adjust all your terrain information to subtract 734.52'.  Elevations are typically meant to communicate information about the house relative to itself and the house relative to the lot.  There's rarely any logical reason to communicate information about the referenced elevation datum in an elevation like that (unless you're in a flood plane).  

 

If the building department or the situation requires it, then that's one thing, but forcing terrain data to mesh with section view data for a lot of situations just isn't worth the time or effort.

[robdyck]

3 hours ago, Alaskan_Son said:

If the building department or the situation requires it, then that's one thing, but forcing terrain data to mesh with section view data for a lot of situations just isn't worth the time or effort.

If you remember, you created a great macro for me that accomplishes that task while still enabling the terrain elevation inputs to be normal. I need to show several of the building's elevations with a metric geodetic match. And the macro you created for me works in every section view.  

[builtright3]

5 hours ago, Alaskan_Son said:

 

This relationship can be adjusted as well...

 

That being said.  Sometimes it makes sense to go this route and sometimes it doesn't.  If you have a complex terrain that's been surveyed using sea level and your house is 734.52' above sea level, it would be silly to label all you sections and elevations as 734.52'+ (unless specifically required by your building department) and it would be very inefficient to adjust all your terrain information to subtract 734.52'.  Elevations are typically meant to communicate information about the house relative to itself and the house relative to the lot.  There's rarely any logical reason to communicate information about the referenced elevation datum in an elevation like that (unless you're in a flood plane).  

 

If the building department or the situation requires it, then that's one thing, but forcing terrain data to mesh with section view data for a lot of situations just isn't worth the time or effort.

 

Thank you, that really helps me.