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Robert Eckerle Posted: Nov 17, 2012 08:45 AM	HVAC configuration with spray foam attic insulation Hello, I am building a small home in south Alabama and using 7.5 inch of open cell foam sprayed on the under side of the roof deck. I have a serious design issue with my HVAC and county building dept codes. I am not using a conventional forced air system, but Using Mitsubishi mini split HVAC system this configuration of individual room AC units has no ducts in the attic, so conditioning the attic area is a problem. My original plan was to place vents in the ceiling so air could flow through from the living area to the attic area.The building dept says NO VENTS in the ceiling. But the county building dept codes require the attic to be conditioned and DO NOT allow vents in the ceiling the mini split AC system is not designed to put a unit in the attic, and would be an unnecessary expense.adding more problems. If you have HVAC equipment in your attic the code requires a barrier coat on the foam for a fire code. my roof is 5 on 12 with a center height of about six feet, so my attic is not a large area I had assumed with ceiling flow through vents the attic temps would be a reasonable variable of the living area temps What is the proper configuration of a sealed attic using individual room HVAC units ?
Bryan Kwater Posted: Nov 17, 2012 06:53 PM	Why not just vent the attic and spray the foam directly on the flat drywall ceiling? Direct applying foam to the roof is a better option, but it may not be the best option in your case.
Mark Mouton Posted: Nov 18, 2012 04:12 PM	If you have can lights, these are somewhat openings to the attic. Also,a pull down staircase. Maybe a couple of access attic openings in out of the way places,(pantry or closets) with perforated, I'm sorry, not perforated wood, but 3/4'' plywood.(We call it semi-conditioned,just control moisture) I also notices Icynene has an open cell foam that doesn't need Intumescent Coating. There's more than 1 way to skin a cat.
Robert Eckerle Posted: Nov 19, 2012 06:19 AM	Why not just vent the attic and spray the foam directly on the flat drywall ceiling? Direct applying foam to the roof is a better option, but it may not be the best option in your case. Several reasons to not foam the the ceiling and vent the attic 1. the house is framed, gables sheathed solid with no vents, soffits are sheathed solid. this is common now in hurrricane areas 2. Hurricane winds Homes with ridge vents,gable vents and soffit vents have a tendency to allow too much pressure into the attic, in some cases causing excessive damage to ceilings,windows,floor covering etc Keeping the wind pressure out of the attic is a priority so, non-vented, solid soffits,solid gables
Robert Eckerle Posted: Nov 19, 2012 06:29 AM	If you have can lights, these are somewhat openings to the attic. Also,a pull down staircase. Maybe a couple of access attic openings in out of the way places,(pantry or closets) with perforated, I'm sorry, not perforated wood, but 3/4'' plywood.(We call it semi-conditioned,just control moisture) I also notices Icynene has an open cell foam that doesn't need Intumescent Coating. There's more than 1 way to skin a cat. good idea no flow through vents gets me a CO, and after the BI is finished and gone I can refit the attic access solid plywood covers with vented covers. BUT, the requirement is for conditioned attic airspace So, we still need to address this issue with the mini split system
blomberginsulation Posted: Nov 19, 2012 10:12 PM	As we live in missouri and you in alabama, I realize there are completely different building codes. Here, whether the ac/heat system is in the attic space or not the attic space once unvented and foamed becomes "conditioned" as is. Are they requiring you to pump air into the attic space? Heat rises, and once you have foam directly to the roof deck, there is no need for concern of warm air in the attic space from convection. What exactly are they specifying you are to do?
Mark Mouton Posted: Nov 20, 2012 07:28 AM	Are they saying you have to blow conditioned air into the attic? Will every room in your house(bathrooms, walk-in closets, etc.) have air directly blown and returned from them? (I think?)If you have access holes open into the attic space from the living area, you will be semi-conditioning the attic area. I do not believe exact temperature control is required in the attic, but more of a moisture controled environment(try and keep it dry). With the air conditioner running in the summer months, you will lower moisture levels in the whole house area that is seperated(sealed) from outside. It will also draw moisture from the attic area to the dryer air in the living area. You could put a fan in the attic at the the attic opening just blowing to move air around (once or twice a year) for a day or two. You could also go in and inspect the attic area. I'm convinced by sealing the attic from outside conditions, it will be closer to to living area conditions because you have it(attic) opened to the living area through openings in the ceiling. Let me finish by saying, I am not 100% sure of everything. I try to take a common sense approach. If what I am saying spurs contriversy, so be it. I am out to do whatever is the right thing to do and will listen also.
Robert Eckerle Posted: Nov 20, 2012 07:43 AM	I'm sorry, I thought I made it clear what the problem is The code requires a HVAC duct blowing conditioned air into the attic space The Mini Slit system has no such configuration to accommodate the code
Mark Mouton Posted: Nov 20, 2012 08:38 AM	Could I ask why the code officials will not allow a vent(hole) into the ceiling? Can you not have access to the attic?
Robert Eckerle Posted: Nov 20, 2012 10:37 AM	Could I ask why the code officials will not allow a vent(hole) into the ceiling? Can you not have access to the attic? you can have a solid access hatch in the ceiling , but it can't have vent holes in the hatch door not sure why they won't allow the flow through vents in the ceiling, I think it's some type fire code that applies to the foam. will confirm after I sit down and meet with the Building dept
blomberginsulation Posted: Nov 21, 2012 10:01 AM	are there any can lights installed into your ceiling? I uinderstand the fire code issue with air drawl to the attic space but open can lights with no insulation over the top is the same as, especially if they are not sealed in any way. Ceiling recepticles will pose the same issue. So to simplify, unless you have no light fixtures in your ceiling which is doubtful, then they have no argument with an open vent going to your attic to condition it.

Author

Comments

Robert Eckerle

Posted: Nov 17, 2012 08:45 AM

HVAC configuration with spray foam attic insulation

Hello,

I am building a small home in south Alabama and using 7.5 inch of open cell foam sprayed on the under side of the roof deck.

I have a serious design issue with my HVAC and county building dept codes.

I am not using a conventional forced air system, but Using Mitsubishi mini split HVAC system

this configuration of individual room AC units has no ducts in the attic, so conditioning the attic area is a problem.

My original plan was to place vents in the ceiling so air could flow through from the living area to the attic area.The building dept says NO VENTS in the ceiling.

But the county building dept codes require the attic to be conditioned and DO NOT allow vents in the ceiling

the mini split AC system is not designed to put a unit in the attic, and would be an unnecessary expense.adding more problems. If you have HVAC equipment in your attic the code requires a barrier coat on the foam for a fire code.

my roof is 5 on 12 with a center height of about six feet, so my attic is not a large area

I had assumed with ceiling flow through vents the attic temps would be a reasonable variable of the living area temps

What is the proper configuration of a sealed attic using individual room HVAC units ?

Bryan Kwater

Posted: Nov 17, 2012 06:53 PM

Why not just vent the attic and spray the foam directly on the flat drywall ceiling? Direct applying foam to the roof is a better option, but it may not be the best option in your case.

Mark Mouton

Posted: Nov 18, 2012 04:12 PM

Robert Eckerle

Posted: Nov 19, 2012 06:19 AM

Why not just vent the attic and spray the foam directly on the flat drywall ceiling? Direct applying foam to the roof is a better option, but it may not be the best option in your case.

Several reasons to not foam the the ceiling and vent the attic

1. the house is framed, gables sheathed solid with no vents, soffits are sheathed solid.
this is common now in hurrricane areas

2. Hurricane winds
Homes with ridge vents,gable vents and soffit vents have a tendency to allow too much pressure into the attic, in some cases causing excessive damage to ceilings,windows,floor covering etc

Keeping the wind pressure out of the attic is a priority

so, non-vented, solid soffits,solid gables

Robert Eckerle

Posted: Nov 19, 2012 06:29 AM

If you have can lights, these are somewhat openings to the attic. Also,a pull down staircase. Maybe a couple of access attic openings in out of the way places,(pantry or closets) with perforated, I'm sorry, not perforated wood, but 3/4'' plywood.(We call it semi-conditioned,just control moisture)
I also notices Icynene has an open cell foam that doesn't need Intumescent Coating.
There's more than 1 way to skin a cat.

good idea

no flow through vents gets me a CO, and after the BI is finished and gone I can refit the attic access solid plywood covers with vented covers.

BUT, the requirement is for conditioned attic airspace

So, we still need to address this issue with the mini split system

blomberginsulation

Posted: Nov 19, 2012 10:12 PM

As we live in missouri and you in alabama, I realize there are completely different building codes. Here, whether the ac/heat system is in the attic space or not the attic space once unvented and foamed becomes "conditioned" as is. Are they requiring you to pump air into the attic space? Heat rises, and once you have foam directly to the roof deck, there is no need for concern of warm air in the attic space from convection. What exactly are they specifying you are to do?

Mark Mouton

Posted: Nov 20, 2012 07:28 AM

Are they saying you have to blow conditioned air into the attic? Will every room in your house(bathrooms, walk-in closets, etc.) have air directly blown and returned from them?
(I think?)If you have access holes open into the attic space from the living area, you will be semi-conditioning the attic area. I do not believe exact temperature control is required in the attic, but more of a moisture controled environment(try and keep it dry).
With the air conditioner running in the summer months, you will lower moisture levels in the whole house area that is seperated(sealed) from outside. It will also draw moisture from the attic area to the dryer air in the living area. You could put a fan in the attic at the the attic opening just blowing to move air around (once or twice a year) for a day or two. You could also go in and inspect the attic area.
I'm convinced by sealing the attic from outside conditions, it will be closer to to living area conditions because you have it(attic) opened to the living area through openings in the ceiling.
Let me finish by saying, I am not 100% sure of everything. I try to take a common sense approach. If what I am saying spurs contriversy, so be it. I am out to do whatever is the right thing to do and will listen also.

Robert Eckerle

Posted: Nov 20, 2012 07:43 AM

I'm sorry, I thought I made it clear what the problem is

The code requires a HVAC duct blowing conditioned air into the attic space

The Mini Slit system has no such configuration to accommodate the code

Mark Mouton

Posted: Nov 20, 2012 08:38 AM

Could I ask why the code officials will not allow a vent(hole) into the ceiling? Can you not have access to the attic?

Robert Eckerle

Posted: Nov 20, 2012 10:37 AM

Could I ask why the code officials will not allow a vent(hole) into the ceiling? Can you not have access to the attic?

you can have a solid access hatch in the ceiling , but it can't have vent holes in the hatch door

not sure why they won't allow the flow through vents in the ceiling, I think it's some type fire code that applies to the foam.

will confirm after I sit down and meet with the Building dept

blomberginsulation

Posted: Nov 21, 2012 10:01 AM

are there any can lights installed into your ceiling? I uinderstand the fire code issue with air drawl to the attic space but open can lights with no insulation over the top is the same as, especially if they are not sealed in any way. Ceiling recepticles will pose the same issue. So to simplify, unless you have no light fixtures in your ceiling which is doubtful, then they have no argument with an open vent going to your attic to condition it.

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