# Several buildings, 1 lot, "Imaginary Line"



## SCbuild (Aug 13, 2021)

I have attached my site plan here. We intend to build several houses on 1 lot, separated by 4' between houses, this 4' would be an easement.   Building Inspector says cannot have windows, unless we have no egress windows and use fire rated windows. The inspector says they are "imagining a line in between these buildings, which would be 2' on either side, they are saying they draw it down the middle.  These houses will be in a condo regime, with a horizontal property regime.  I am under the impression, I measure from one of the walls over to the other building which is 4' which clears me.... I can't seem to get past this issue....


FIRE SEPARATION DISTANCE. The distance measured from the building face to one of the following:

1. To the closest interior lot line; or

2. To the centerline of a street, an alley or public way; or

3. To an imaginary line between two buildings on the lot.

R302.1 Exterior walls.


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## SCbuild (Aug 13, 2021)

SCbuild said:


> I have attached my site plan here. We intend to build several houses on 1 lot, separated by 4' between houses, this 4' would be an easement.   Building Inspector says cannot have windows, unless we have no egress windows and use fire rated windows. The inspector says they are "imagining a line in between these buildings, which would be 2' on either side, they are saying they draw it down the middle.  These houses will be in a condo regime, with a horizontal property regime.  I am under the impression, I measure from one of the walls over to the other building which is 4' which clears me.... I can't seem to get past this issue....
> 
> 
> FIRE SEPARATION DISTANCE. The distance measured from the building face to one of the following:
> ...


If the code said they draw it down the middle between the 2 house, I would understand, but it doesn't say that...


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## Joe.B (Aug 13, 2021)

Isn't that what #3 says?


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## SCbuild (Aug 13, 2021)

Some people have said the imaginary line is whatever your architect, hoa, and civil engineer draw....In this case, they have the lines drawn at the base foundation of each house...Which means we would measure from those lines over which is 4'


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## Joe.B (Aug 13, 2021)

So one building has 0 clearance to lot line and the other has 4 feet? Or are you saying that measured from either building has 4 feet clear and your imaginary line is wherever you want it to be?


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## SCbuild (Aug 13, 2021)

Joe.B said:


> So one building has 0 clearance to lot line and the other has 4 feet? Or are you saying that measured from either building has 4 feet clear and your imaginary line is wherever you want it to be?


The lot lines are drawn around the foundation, the measurement is measured from right angles from the wall the code says.....If you measure from building 1 to building 2, it's 4'. If you measure from building 2 to building 1, it's 4'. I was told the architect/civil engineer/ surveyor draw that imaginary line.


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## steveray (Aug 13, 2021)

You typically measure on both sides of the property line....

Imaginary line...Not lines....


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## SCbuild (Aug 13, 2021)

steveray said:


> You typical measure on both sides of the property line....


Then why does the code say it is measured from a right angle from one wall. If I do that, then I measure over and it's 4'. If I do that to the other side, it's 4'.


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## Joe.B (Aug 13, 2021)

By that logic I would say each building has 0 separation then, but that's not the point. When dealing with an "imaginary lot line" in regards to fire separations then I agree with Steve, a single imaginary line equidistant between the two buildings. Since so much of code is up to interpretation it only really matters what your local AHJ has to say, everything else is just opinions. Since that's often the point of threads here I offer my opinion. I think the idea of an imaginary lot line is that theoretically someday down the road the property owner could decide to do a subdivision creating a real lot line and the building needs to be designed as such. If you only have 4 feet between the two buildings then you have 2 feet to the imaginary line and all fire protection would be designed to the standards in section 302. Just out of curiosity, how many buildings on this single lot. Another interesting interpretation is the use of the residential code vs. building code for this, but I'd have to know more about the project, and state laws may be different over there. Again all just opinions...


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## Joe.B (Aug 13, 2021)

SCbuild said:


> Then why does the code say it is measured from a right angle from one wall.


Which section are you pulling that from? It might be talking about measuring something different, but I'd have to read that section to give you any opinion on that interpretation.


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## Joe.B (Aug 13, 2021)

Both the IBC and IRC (CBC/CRC for me) have the "fire separation distance" definition you shared in the original post, and as Steve pointed out it says "line", not "lines" and it is purely used for determining separation requirements. R302.1 is applicable if the building (or buildings) are designed using the Residential code. Check out IBC 705.3 in case your project actually falls under IBC, it's much more clear.

*705.3 Buildings on the Same Lot*

For the purposes of determining the required wall and opening protection, projections and roof-covering requirements, buildings on the same lot shall be assumed to have an imaginary line between them.


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## SCbuild (Aug 13, 2021)

Interesting. There are 5 houses on this lot.


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## mtlogcabin (Aug 13, 2021)

2018 IRC will permit unlimited openings and non rated exterior walls if you have over 6 feet between the buildings and install a fire suppression system i the buildings


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## SCbuild (Aug 13, 2021)

mtlogcabin said:


> 2018 IRC will permit unlimited openings and non rated exterior walls if you have over 6 feet between the buildings and install a fire suppression system i the buildings


Good to know, thanks. 

Still doesn't get me where I need to be sadly. These need to be 4' apart. I guess I could use fire rated windows with no egress


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## cda (Aug 13, 2021)

SCbuild said:


> Good to know, thanks.
> 
> Still doesn't get me where I need to be sadly. These need to be 4' apart. I guess I could use fire rated windows with no egress



Or no openings


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## Glenn (Aug 13, 2021)

How to measure fire separation distance is questioned so often, that I took a clip from one of my webinars (heavily edited to be shorter) and put it on youtube.  I hope this helps.


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## SCbuild (Aug 13, 2021)

Glenn said:


> How to measure fire separation distance is questioned so often, that I took a clip from one of my webinars (heavily edited to be shorter) and put it on youtube.  I hope this helps.


Thank you! I am going to PM you


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