attic in detached garage after spray foam

[goldenboy9r]

Just had the garage sheetrocked after spray foam installed. I also put a 12K btu mini split in the space. I installed some OSB in the garage attic this weekend and noticed it was very hot up there and the humidity felt high. It felt like it needed some venting and air movement but would seem odd venting it since the whole idea of foam is to not vent. Anyone else had the same issue?

The temp in the conditioned space is 73. Garage is 20X22. Cheapo indicator from wal mart put in the attic says 85 and 69% humidity but felt a lot more hot and stuffy up there.

Any ideas?

 

[930dreamer]

I'd think the garage still needs some sort of venting?

 

[Cobra5150]

Attic needs to be vented. It's the venting from the interior to exterior you want to prevent.

 

[volleyball]

What kind of foam? how thick?
Foam generates lot of moisture curing. Did it have time to dissipate?

 

[Dustball]

Attic needs to be vented. It's the venting from the interior to exterior you want to prevent.

Not with spray foam applied to the underside of the roof decking. Doing so turns the attic into conditioned space and no venting is needed.

To the OP- read this article to see if your attic has any of these defects- http://www.energyvanguard.com/blog-...bid/25546/4-Pitfalls-of-Spray-Foam-Insulation

 

[volleyball]

That articles is for a certain area,doesn't know if it applies to the OP because again we have no idea where the property is located.
As far as cobra talking about venting, it didn't imply to the exterior, it was interior circulation.

 

[LB-1911]

The OP resides in the Houston area.

http://www.garagejournal.com/forum/showpost.php?p=3859539&postcount=1

 

[goldenboy9r]

What kind of foam? how thick?
Foam generates lot of moisture curing. Did it have time to dissipate?

6" open cell on roof. 4" walls

Correct. Im in Houston

 

[volleyball]

What are you using as a vapor barrier? You don't seem to have one

 

[goldenboy9r]

What are you using as a vapor barrier? You don't seem to have one

Are you supposed to put a vapor barrier then foam?

 

[MN4x4]

Your situation may be normal. Think of it this way:

Warm air rises. Regardless of how large or small your space is, it will be warmer at the ceiling than at ground level.

Assuming that your foam is doing it's job - and there's no indication from your post that it isn't - you may need to 'stir up' the air so it mixes, and - based on outside air temps - you may also need to condition the space - i.e., heating or air conditioning. Just because your space is now insulated doesn't mean that it is necessarily warmer or cooler than before. But it SHOULD mean that it's easier to get it to the temperature that you want it at.

Make sense?

 

[volleyball]

open cell foam is not a vapor barrier.

 

[ADSR]

open cell foam is not a vapor barrier.

yes it is. it just has a lower R value.

 

[volleyball]

Not at those thickness

 

[ADSR]

Not at those thickness

6"? 3" passes code here for OC VB.

 

[Orionrising]

open cell foam is not a vapor barrier, closed cell is. If the space is not conditioned, power ventilated with a air exchanger, or dehumidified, and there is closed cell foam water vapor will rise to the attic and be trapped.

 

[ADSR]

open cell foam is not a vapor barrier

Yes, it is. I should know. I only build houses and buildings for a living.

Try and google it

 

[ADSR]

double post

 

[Lewisthepilgrim]

Check this out...

according to IRC "In all but Climate Zones 2B and 3B, the IRC requires air-impermeable insulation in
direct contact with the underside of the roof deck. A combination of an air-impermeable insulation and air-permeable
insulation directly below it is permitted."

You are i zone what 3? Still might be a good idea.....

"The IRC also prohibits a vapor retarder on the attic floor of conditioned attics so that any moisture that may
build up in the attic can dissipate into the house."

This is a GREAT READ http://www.energycodes.gov/sites/default/files/documents/cn_unvented_attic_assemblies.pdf

 

[MN4x4]

I think you missed this statement:

"Note that the additional rigid board insulation is not required if air impermeable insulation is installed in direct contact with the underside of the roof sheathing."

 

[volleyball]

Lord and I disagree, the OP needs to search and decide for himself. There is a builder in his area that has lots of youtube videos about home building. I found him with a link through Fine homebuilding magazine

 

[Trey T]

spray foam seems impermeable to me unless you cut the outer layer.

I'm not sure if the OP trim/cut his foam at the ceuiling or not, but usually people always trim/cut foam at the wall frame. When you cut the foam, that's no longer a vapor barrier bc the foam can absorb moisture now.

If you ever cut a cured spray foam open, you will see that there's a lot of porosity.

open cell foam is not a vapor barrier, closed cell is. If the space is not conditioned, power ventilated with a air exchanger, or dehumidified, and there is closed cell foam water vapor will rise to the attic and be trapped.

Yes, it is. I should know. I only build houses and buildings for a living.

Try and google it

 

[ADSR]

Lord and I disagree, the OP needs to search and decide for himself. There is a builder in his area that has lots of youtube videos about home building. I found him with a link through Fine homebuilding magazine

Well, there seems to be a lot of mixed info on the subject. I'm not saying you're wrong. OC will pass here as a VB.

That being said, i would never in a million years use it on my house. We use CC foam whenever in budget. There is a big price difference.

 

[readhead]

I'm guessing the mini-split is not conditioning the attic. If that is the case all you are doing is collecting heat and humidity in the attic. Some kind of ventilation will be required to cool the attic.

 

[volleyball]

I wonder if the moisture problem has cleared up? It may just have been the sun had warmed the air but not the ground and it was cool in the space.

 

[Orionrising]

First they key word in those codes is conditioned spaces. Conditioned spaces have powered ventilation and humidity controls, which are key to preventing mold


From Icynenes website:

Does the Foam entrap moisture?


Icynene’s closed-cell spray foam insulation products are able to reject bulk water and block mass transfer of moisture that may cause mold.

 

[goldenboy9r]

spray foam seems impermeable to me unless you cut the outer layer.

I'm not sure if the OP trim/cut his foam at the ceuiling or not, but usually people always trim/cut foam at the wall frame. When you cut the foam, that's no longer a vapor barrier bc the foam can absorb moisture now.

If you ever cut a cured spray foam open, you will see that there's a lot of porosity.

The roof was not cut. Only the walls were trimmed so that sheetrock could be applied.

 

[goldenboy9r]

I'm guessing the mini-split is not conditioning the attic. If that is the case all you are doing is collecting heat and humidity in the attic. Some kind of ventilation will be required to cool the attic.

You are correct. Mini split only cooling below the attic.

 

[zcar751]

If you are only cooling below attic, then the attic space will be hot an humid in the summer. After all you are in Houston. On the bright side it will be cool and humid in the winter.
By insulating the attic ceiling your create a thermal barrier between you roof and ceiling which will lessen your thermal load on your interior space making it easier to cool. Your best bet would be to put a dehumidifier up in the attic.

 

[volleyball]

If you have a ceiling below the foam and the area is sealed, it will be hotter or cooler but more humid.
a couple of vents in the ceiling to allow air to circulate will allow the moisture to equal the space below the ceiling

 

[JakeKohl]

If you have a ceiling below the foam and the area is sealed, it will be hotter or cooler but more humid.
a couple of vents in the ceiling to allow air to circulate will allow the moisture to equal the space below the ceiling

I've always wondered about that. I got foam quotes when building my 2 story garage and they wanted to foam the underside of the roof decking. I had installed mini-splits up and downstairs so there wouldn't be any air movement up there... I asked about what to do with ventilating the attic space and they said I didn't need to but they couldn't explain how moisture would be able to leave or equalize. Now, I'm no expert, but I was really uneasy with their answers and decided to go a more traditional route.

 

[TEXACMAN]

I am an HVAC tech , we love the spray foamed attics! Usually in the summer it is 120 degrees but with foam it is around 80. The foam basically seals your home completely off from outdoors , no attic ventilation , defeats purpose. Some homes are too tight and they do have a powered ventilator sucking in outside air into conditioned space but it heats or cools the air , basically another mini hvac unit. As far as your location , that is one of the most humid places in Texas! Lol! If you keep having moisture issues you may have to put a dehumidifier in your attic to remove it , watch for mold growth! As far as venting ceiling to garage area , just remember you will be adding extra heat load to HVAC equipment and it may not cool your garage then.

 

[volleyball]

If you say the under roofs are cooler than others, part of that is the A/C system doing its job. So adding vents will not overload the system. Cool doesn't rise. Were you talking registers?
Now if the ceiling was removed, there would be a bit more of a load.

 

[bd8134]

Goldenboy9r, maybe you should get some additional insulation added to what you already have, you have a lot more hot weather than us in MA. Don't put outside vents in your attic, you will be wasting all that money you paid on insulating your attic. Ask a few local spray foam installers for their opinion.
I had 9.5" of open cell sprayed in our attic on the roof deck with an ignition barrier in the house and thermal barrier in the garage, sprayed on top. Our attic is not much different in temp, winter or summer than the house temp. I read some people having an ac supply in the attic, we do not. Our ac units are also in the attic.
Our attic used to have the traditional soffit and ridge vents and I also added a gable fan at one time. That used to switch on at 100 F and on hot days would run all day, I am not sure it made any real difference.
The foam has made a great difference to comfort and our heating / cooling bills. Our house is very tight now so I might consider putting in an HRV or ERV.

 

[volleyball]

It is venting in the ceiling, to the conditioned space, not to the outside. That would be illogical.

 

[bd8134]

Putting vents in the ceiling to the attic would most likely make the situation worse.
Stale, moist, dirty air is not something you want trapped up there.

 

[volleyball]

Putting vents in the ceiling to the attic would most likely make the situation worse.
Stale, moist, dirty air is not something you want trapped up there.

Not putting vent from work area to above is what will trap that air you are avoiding.

 

[bd8134]

I have not seen a recommendation for putting vents in a ceiling if the attic is also not conditioned by an ac vent. I could be wrong. I have no ceiling vents in my garage and would never consider adding them.

 

[bgarrett]

A small attic vent can still be a good thing to let heat out and possibly draw in cooler air

 

[James_B]

I'm very interested in this topic.

We have an enormous 40' x 30' attic space in our 100+ year old farm house. The attic is completely unobstructed except for a single brick chimney stack, and there are 4 dormer windows (one on the North side, 2 on the East, and 1 on the South) set into the roof line. It's too useful a space to waste, but being uninsulated, it's freezing in winter and stifling in summer.

We'd like to spray foam insulate it and turn it into useful living space, but we keep getting conflicting opinions on what we should and shouldn't do when it comes to dealing with venting of the space. We have no problems venting the space to the outside in the Summer, but we are loathe to vent any of the house heat outside in the Winter.

Here's an almost 360 degree panorama of the space (and yes, the chimney stack is leaning over and is not vertical).


(The thumbnail image links to a 4.3MB, 12815 x 1469 pixel image)