Condensation inside walls of insulated steel building

Started by Alan Gage, December 09, 2013, 01:47:08 PM

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Alan Gage

I believe I'm getting some condensation inside the walls of my newly constructed shop. Over the past couple weeks I've noticed some wet spots along the floor, right along the wall, and it appears to be coming from the inside of the liner steel. The shop has been heated to 45 degrees all the time and then bumped up to 55 when I'm there working. Outside temps were in the 30's when I first noticed it and in the low single digits last time. I noticed some wet spots on Saturday but they were dried up by Sunday and I saw no new ones. The weather outside was pretty much the same both days (COLD!).

The shop is stick framed with 2x6 studs and fiberglass insulation. The inside walls and ceiling are steel and the outside will be steel too (though at this point it's still just house wrap until spring comes). The purlins the inside liner steel is attached to were set into notches in the studs so no air gap between the insulation and liner steel. The attic has R-60 cellulose with vented soffits and ridge cap.  The footings and slab are also insulated with rigid foam.

No vapor barrier was installed in the walls or ceiling. Perhaps this was a mistake. After some research it sounds like maybe I should have. I'd never worked with steel before and was used to sheetrock where it was easy to seal all the joints to make an effective area barrier. Not so much with steel. I also figured that since there was no water supplied to the shop and that it's main purpose was just a wood shop that there wouldn't be much moisture floating around in the first place.

I popped up into the attic and didn't see any frozen condensation up there, either on the roof or the trusses. Had an infrared temp gun and the temps in the attic varied from 7 degrees to 20 degrees (the gable wall the sun was hitting).

I have noticed that it doesn't feel as dry in the shop as it does in my house. Could this be from the relatively fresh concrete? If that's the case is there any luck that after this year the problem will go away.

I'd hate to remove all the liner steel (would mean undoing electrical and dust collection ducts) and installing a vapor barrier but it could happen. Since the outside steel (except the bottom 3') isn't installed yet I could do some exterior foam on the outside to hopefully keep the wall cavities above the dew point but that extra couple inches will goof up the soffits, doors, and overhangs.  Another thought I had would be finding a way to seal the wall/floor and wall/ceiling transitions as that must be accounting for the vast majority of the air leakage.

Any thoughts or ideas?

Alan

Redoverfarm

Alan I don't think you can cure the situation without a vapor barrier toward the warmer side of the wall.  Most steel buildings usually spray foam the interior walls  and ceiling or use a insulation w/barrier on ceiling.  Being it is a steel interior wall it has surfaced much faster than drywall but both would have the end results of a ruined wall.  Although time consuming you might want to consider pulling off the steel and sealing a vapor barrier on the warm side. 

I have seen numerous steel buildings w/o insulation in the ceiling and it is like walking in a rain forest when the temps are right.  Even though you insulated the walls there is still air allowed to meet the tin and the same effect only it is not dripping but running down the sheet to the floor.


MountainDon

How about spray foaming the interior steel walls from the outside?  Come spring.

The fact that the concrete is relatively fresh might be exacerbating the issue but the main thing to remember is steel will be first to collect condensation.
Just because something has been done and has not failed, doesn't mean it is good design.

MountainDon

OOPs I re-read and see that fiberglass has been placed in the wall cavity. 

Removing the exterior steel and applying the correct thickness of rigid foam on the exterior and then the steel might be the solution. The foam will keep the inside of the walls above the dew point when the building is heated.

Just thinking out loud, so to speak.
Just because something has been done and has not failed, doesn't mean it is good design.

akwoodchuck

"The lyf so short, the craft so long to lerne."


Alan Gage


rick91351

Proverbs 24:3-5 Through wisdom is an house builded; an by understanding it is established.  4 And by knowledge shall the chambers be filled with all precious and pleasant riches.  5 A wise man is strong; yea, a man of knowledge increaseth strength.


Alan Gage

Thanks for the responses. I'll have to chew on this over the winter since nothing will be happening until spring either way. I'll monitor the situation and see what the humidity is in the shop. Perhaps it's quite a bit higher than normal due to the curing concrete.

A couple things that seem a little strange:

I've only noticed the water on the west wall, which catches the afternoon sun and would, I'd think, be the warmest wall and least prone to condensation.

It seems to be running down the inside of the liner steel (it's leaking out on top of the box base starter strip) and I'd expect that with insulation in the walls the dew point would be somewhere in the middle of the wall since the inside of the steel should be warm (same temp as the inside of the shop) and that the vapor wouldn't condense until it met cooler air closer to the outside wall. So is the insulation just getting so soaked that it's wicking the moisture back to the steel? If that's the case I'd expect to see a steady damp edge along the sill plate from moisture running down rather than just an occasional spot coming down the inside of the steel.

Or maybe I'm just trying to convince myself I don't have a big problem. :)

Alan



akwoodchuck

How old's that slab? Less than a year, it's probably not fully cured yet....any insulation under it? I won't even ask about vapor barrier ;D  If you want a "scientific" way to check the humidity inside your shop, just heat it up, and bring in a cold beer out of the fridge....if condensation beads up on it, you might have some moisture issues.

https://store.extension.iastate.edu/ItemDetail.aspx?ProductID=5062
"The lyf so short, the craft so long to lerne."

Alan Gage

The slab was poured in September and has foam underneath as well as the edges.

Checked the humidity in the shop last night when I was out there working and it was 31%.  Checked it in the house and it was 22-24%.

I'd say there's certainly some extra moisture out there, presumably from the concrete, but how much that's contributing to the issue I don't know. Checked around the inside of the building again last night and didn't see any more signs of moisture.

Alan

rick91351

Allen are you using the shop all the time or rather is you radiant heat going all the time or most of the time? 

Just wondering if you left it on for a few days if it would not lower the humidity in there enough to stop the condensation.   
Proverbs 24:3-5 Through wisdom is an house builded; an by understanding it is established.  4 And by knowledge shall the chambers be filled with all precious and pleasant riches.  5 A wise man is strong; yea, a man of knowledge increaseth strength.

Alan Gage

I keep the building at 45 all the time and bump it up to 55 when I go out to work (a few hours every evening and all weekend) so it's been staying fairly warm. I've wondered, assuming the extra moisture is being caused by the curing concrete, if a hotter shop would make it better or worse? Perhaps with higher temps the concrete would give up more moisture. I'll raise the temp for a few days and see what happens.

Alan

Don_P

Another thought, is the west end a gable or an eave? Is there a gutter? Is there any correlation between precip and the moisture a day or 2 later?

... and your house is too dry! find the drafts, you're heating outdoor dry air. A psychrometric chart would give the dew point... or AK's method, I like that, but with wood heat we're running above 40% in the house, the shop is not excessively moist.


MountainDon

Quote from: Alan Gage on December 12, 2013, 09:28:08 AM


Checked the humidity in the shop last night when I was out there working and it was 31%.  Checked it in the house and it was 22-24%.

You have no idea how much water we have to run through the humidifier to attain numbers as high as those at our normal indoor temperature.
Just because something has been done and has not failed, doesn't mean it is good design.

Alan Gage

Quote from: Don_P on December 12, 2013, 03:57:56 PM
Another thought, is the west end a gable or an eave? Is there a gutter? Is there any correlation between precip and the moisture a day or 2 later?

... and your house is too dry! find the drafts, you're heating outdoor dry air. A psychrometric chart would give the dew point... or AK's method, I like that, but with wood heat we're running above 40% in the house, the shop is not excessively moist.

West wall is an eave with 2' overhangs and no gutters yet. There's been no precip other than some very light snow and it doesn't seem to correlate to when I'm seeing moisture inside.

I suspect I'm in a bit drier climate than you. My house is pretty tight and should be much tighter than the shop (without outside air hooked up and windows closed the wood stove starves for air) and I'd say my inside humidity levels are higher than normal around here. My mom runs a big humidifier 24/7 and when I was over there last night she was in the upper 20's for humidity inside the house. So I'd say the shops humidity is elevated a bit but I don't know if it's enough to cause any issues or not. My hope is that it's up just enough to push it over the edge.

I checked the dew point earlier based on the shops temp. and relative humidity and it was around 25 degrees.

Alan

Alan Gage

Well it's been 3 more winters and no signs of condensation after that first one. So I guess I'm going to lay most of the blame on the concrete and lumber.

Alan