# Natural Ventilation



## Dr. J (Mar 10, 2010)

I was about to take the Repair Garage Ventilation thread off track, so I thought I would reel it back in and start a new one.

Code references: IMC 401.3 "Ventilation shall be provided during the periods that the room or space is occupied.".  IBC 1204.1 "Interior spaces intended for human occupancy shall be provided with active or passive space-heating systems capable of maintaining a minimum indoor temperature of 68°F (20°C) at a point 3 feet (914 mm) above the floor on the design heating day.

Exception: Interior spaces where the primary purpose is not associated with human comfort."

It is my opinion that the simple version of opening windows for natural ventilation as the exclusive means of code required ventilation is not allowed unless the DP can show how the IBC required temperature in the space is maintained while the windows are open whenever occupied as required by the IMC.

There are options available to the DP such as natural ventilation airshafts with some means of tempering the air, or operable windows with end switches that enable mechanical ventilation when closed and disable it when open, but just plain operable windows is not code compliant.

Note IMC 401.3 does not say "The capability to control ventilation shall be provided..." or "The occupants shall have the opportunity to control ventilation...".


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## Mech (Mar 11, 2010)

Re: Natural Ventilation

I agree.  _ Note IMC 401.3 does not say "The capability to control ventilation shall be provided..." or "The occupants shall have the opportunity to control ventilation..."._

IMC 401.2 requires ventilation, either mechanical or natural.

IMC 401.3 says ventilation shall be provided when the room or space is occupied.

The window, doors, etc. need to be open whenever the space is occupied to be code compliant.


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## vegas paul (Mar 11, 2010)

Re: Natural Ventilation

Ventilation and maintaining temperature are not necessarily inter-related.  Don't assume forced-air heating, for instance.  The requirement for ventilation is for outside/fresh air exchanges - such as required by ASHRAE 62.  The temperature for habitability/comfort could be provided by hydronic, radiant, etc. where no ventilation was provided.  They are potentially two different issues, that are often combined because of forced air systems.


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## klarenbeek (Mar 11, 2010)

Re: Natural Ventilation

Here is what the Commentary for section 402.1 states: "... This section does not, however, state or intend that the doors, windows or openings actually be constantly open.  The intent is that they be maintained in an operable condition so that they are available for use at the discretion of the occupant."

Natural ventilation must be available to the occupants, its up to then whether they use it or not.  A building owner could also choose to shut down the economizer on a rooftop unit, couldn't he?  What happens after the inspector leaves is out of his control.


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## Dr. J (Mar 15, 2010)

Re: Natural Ventilation

@klarenbeek:

So the commentary is making stuff up again, surprise surprise.  Well, maybe not.  _"This section does not, however, state or intend...'_  OK, section 402 does no such stating or intending, but 401 certainly does.  Did the commentary attempt to address how IMC 401.3 "_Ventilation shall be provided during the periods that the room or space is occupied"_ actually means "ventilation shall be provided only during the periods that occupant just feels like it"?

The owner is no more "allowed" to shut off the economizer after CO than he is to put a chain around egress hardware.

@VP:

Agreed, not only can outside air ventilation and temperature control can be through two separate means, in fact the requirements are in two separate codes - M for ventilation and B for temperature.  What is required though is that both requirements be met.

The real issue here is that IMC 401.2 gives two options for ventilation.  In the code, this usually this means the two options result in a similar outcome (spray on fireproofing or sprinklers - either way the result is a more fire resistive building).   How is a mechanical ventilation system, with the heating and cooling capacity to bring in outside air year round equivalent to a natural ventilation system everyone knows will be "off" 80% of the time?

Obviously, allowing operable windows as the only means of ventilation has forever been acceptable.  Just wanted y'all to know this is just one more area of the code that is conveniently ignored, and yet western civilization has not ended.  On the other hand, I believe there are AHJs out there that never really liked allowing "just open the window" in the 21st century, and this is the way to formally deny it.


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## JBI (Mar 15, 2010)

Re: Natural Ventilation

Dr. J - While I appreciate your opinion, I cannot agree with it. It's a stretch at best. Ventilation is provided by the existence of both the operable window and door.

That heat must be provided does not require me to avail myself of it. My son likes his room to be about 55 degrees, anything above 65 and he complains it's too hot. If I want more air, I can open the window or door.


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## RJJ (Mar 16, 2010)

Re: Natural Ventilation

Dr.J I have to agree with this one. I would take note that operable windows and doors are more likely to be closed 98% of the time.

JD: argues about his sons bed room which is not the same as an office or commercial establishment.

I would say that mechanical ventilation in the office is the best source for fresh air. It becomes more productive and affords better fresh air ventilation and more consistent. Once again the code fathers have used the two dart method. Through both at the board and we have a code guideline.

Poor code writing! :roll:

If you provide the proper % of ventilation by either mechanical or operable elements the ahj has no grounds to deny the application as the code exists today. I would ask for chapter and verse!


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## klarenbeek (Mar 17, 2010)

Re: Natural Ventilation

While I don't  disagree that mechanical ventilation is the better option, code allows for natural ventilation.  Section 402.1 does NOT require the windows to be open at all times the building is occupied.  The section itself, not the commentary, says the operating mechanisms need ready access so the openings are readily controllable by the occupants.

If the occupants should not be able to open and close them as they see fit, why would the controls have to be readily accessible to them?

As far as mechanical ventilation, when a thermostat is in the fan auto position on an hvac system, ventilation is only coming in when the system is running.  There are certain times of the year when it might not run much at all.  How am I supposed to be able to keep the building owner from walking to the stat and flipping a switch after I have given occupancy?

Maybe the world IS coming to an end soon--we have an ahj arguing in FAVOR of leniency and common sense.


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## Mech (Mar 17, 2010)

Re: Natural Ventilation

If we got rid of the tight construction requirements and low leakage rates in the energy conservation code, then drafty doors and windows would provide ventilation without being open.   :mrgreen:


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## JBI (Mar 17, 2010)

Re: Natural Ventilation

Now you're just being silly!  :lol:  :lol:  :lol:


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## barlovian (Mar 17, 2010)

Re: Natural Ventilation

Local politics prevent me from doing this myself....but, please, could one of you, an ICC member ask for a formal interpretation?  Can doors be used to provide the required ventilation in climates where temperatures make it unlikely that doors would be used for this purpose?   Can a portion of the required ventilation be met with operable openings, and the rest with mechanical?  Can openings that are not designed for this purpose be used to satisfy the requirement for natural ventilation.  For example, an exterior door with a closer and no hold open? Or, a vestibule opening into a space larger than 3,000 square feet?  Well, it would take 3 pairs of doors to make the 4%, but you get the idea.


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## RJJ (Mar 18, 2010)

Re: Natural Ventilation

Most of us at one time were ICC members! :lol:  Now we are just black sheep. I would send in the question, but I am on the sh** list. :lol:  :lol:

Mech: just where are you in PA? Pm me please! East is a large area.


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## Builder Bob (Mar 18, 2010)

Re: Natural Ventilation

AND I thought Firefighters were bad about what ifing..........The codes are a minimum. In natural ventilation, it is up to the occupants whether the heating system is capable of operating at 68 degrees three feet above teh floor when the windows are open.

Point blank.....The codes are what we can enforce in black and white (with a whole lot of grey/ gray areas......)

In the Sunny South, we pretty much could care less about a heating system at 68 degrees when it is 105 degrees in the summer...... Old school natural ventilation required the ability to cross ventilation with houses being built on crawl spaces.

What is differnet about this concet in forcing mechancial ventilation that the requirement for residential fire sprinklers? For sake of arguement, both will drive the cost of housing up.


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## Uncle Bob (Mar 18, 2010)

Re: Natural Ventilation

I'm moving, a bit grouchy and pooped (not strong enough to open a book); but, I believe you will find that "natural ventilation" refers only to openable windows.

Now that "Unusually Tight Construction" has been deleted from the 2009 I-Codes (no such thing anymore); after the fire sprinklers are firmly entrenched in the code requirements, openable windows will become the next code violation.

Note: emergency escape through windows will no longer be required because the required sprinkler and alarm will provide sufficient time for occupants to evacuate the building.  You will be required to provide emergency escape route instructions on the door of all sleeping rooms.    :roll:

Uncle Bob


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## Dr. J (Mar 18, 2010)

Re: Natural Ventilation



> Section 402.1 does NOT require the windows to be open at all times the building is occupied.


  But 401.3 does - conflict/most restrictive and all that.





> As far as mechanical ventilation, when a thermostat is in the fan auto position on an hvac system, ventilation is only coming in when the system is running. There are certain times of the year when it might not run much at all.


"Fan Auto" on a t-stat is illegal if the system is the source of mechanical ventilation.

IMC 405 "_Mechanical ventilation systems shall be provided with manual or automatic controls that will operate such systems whenever the spaces are occupied. Air-conditioning systems that supply required ventilation air shall be provided with controls designed to automatically maintain the required outdoor air supply rate during occupancy._"

The only way to make a "Fan Auto" switch legal would be to override it somehow with occupancy sensors to sense all areas served.  Otherwise, this should be rejected by inspectors.

This is my point.  How can natural ventilation by means of operable windows only (AKA NO ventilation for 4-6 months) possibly be equivalent to what is required for Mechanical Ventilation?


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## RJJ (Mar 18, 2010)

Re: Natural Ventilation

Dr.J It can't be equal! It is not equal!


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## klarenbeek (Mar 22, 2010)

Re: Natural Ventilation

So a warehouse with a 10x10 office with a door and operable window to the outside requires mechanical ventilation???  Remember, an office is an office no mater how small.

Nowhere in the code does it say natural and mechanical ventilation have to be equal. All section 401.2 says is ventilation must be provided by either natural or mechanical means, not that they have to be equal. 401.3 then says it must be provided. By choosing natural ventilation, you then go to section 402 to see how to provide it. The windows have to be OPERABLE during occupied times.  They can't be locked when occupied.

As far as "conflict/most restrictive and all that", that is section 304.2.  It applies to conflicts between manufaturer's installation instructions and the code, not percieved conflicts within the code.

If you would apply confict to just items in the code, Section 405 comes close to contradicting itself.  A mechanical ventilation system can have either manual OR automatic control, but an air conditioning system (which is a mechanical system) used to provide ventilation has to have automatic controls only.  According to this, a stand alone HRV can run off an on/off switch, but one tied in with the hvac system can't.

Most (if not all) thermostats come with a fan on/auto setting option. A contractor could jumper the contacts so the fan runs continuous and simply remove the jumper before I'm even out of the parking lot.  I've seen it done. I check the minimum outdoor air setting the system will be at when the fan is running, and walk away.  I've got bigger fish to fry.


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