Hi,
We’re experiencing a problem at work that I’m hoping someone can help me with. I work at an apartment complex built in 1952. They are townhouse style apartments with a brick exterior on the ground floor and a combination brick and siding on the second floor. Unfortunately they were never insulated when they were built so we had them insulated this summer. It was blown in from the interior on the ground floor and from the exterior from the second. Now that it has turned cold we are starting to experience some of the interior walls and ceilings getting so cold they start to get condensation on them. The problem is where the interior wall intersects with an exterior wall and has only happened on the first floor. The insulation company says that this should stop after we have the attics sealed and additional insulation blown in up there. That is scheduled in the next couple of weeks. I don’t understand how attic insulation would affect the walls on the first floor. I would greatly appreciate any explanation or thoughts as to what could be happening.
Thanks
Tom
Replies
It is a little curious, and hard to say with any certainty without knowing a lot more about the construction of the building and its layout.
It is possible that you could be getting cold air coming down interior walls if the walls are not sealed to the attic space, but you wouldn't expect to see this affecting the bottom floor unless the walls were balloon framed -- very unlikely, especially for interior walls.
So my primary suspicion would be that the walls are not getting any colder than normal, but rather the humidity is higher than previously. This could happen because of the inherent air-sealing characteristics of cellulose (I'm assuming that the insulation is cellulose?), and significant interior moisture generation that previously was being "vented" through the leaky walls.
The other possibility (perhaps equally likely) is that the heating systems are not running as much as previously, so naturally cold areas of the building are getting colder than normal. The areas near wall intersections could be worse than elsewhere because insulation was not blown into these areas very well (if at all). (All the wood in typical wall intersection of the era didn't leave much room for insulation.) (Note that this hypothesis would be dependent on the style of heating and distribution of heating elements. A poorly designed forced air system or a hydronic system with poorly distributed radiators would be worse.)
Or it could be a combination of these factors.
In any event, I can't see how having installed insulation could make any part of a building actually colder, given the same amount of heat being supplied inside.
(Is it possible that the "condensation" is actually moisture leakage due to the exterior work?)
Good puzzle
First, what type of insulation was blown into the walls? Dry, dense-packed cellulose? Something else?
What you're seeing may be interior moisture condensing that used to be able to leave the building, but is now less able to leave because airflow in and thru the walls is now restricted. It makes some sense that this would occur at an interior partition because the blown-in may not have filled the three-stud channels where the partitions intersect, so those are the coldest areas. Same applies to the rim joist.
By filling the wall cavities you may have made the frame more vulnerable to moisture from the brick. Insulating against the inside of a masonry wall is a known risk and has to be done correctly. If the brick was previously drying to the interior the insulation may inhibit this.
Some things I would recommend. One, use infrared imaging to inspect all areas for insulation fill. I bet you will find missing areas, and those will be cold / condensation-prone areas. Two, pick up some thermo/hygro USB dataloggers and start monitoring interior temperature and RH inside some of the units--you want 50% or less at 68 degrees as a basic guideline. Third, get a moisture meter and see what you can learn about the MC inside some of the walls. This kind of testing and inspection might best be assigned to some type of specialist. What area of the country are you in?
I assume the windows are not double pane? Where in the country are you located? How cold is it getting nights? How many units total are involved?
If you're getting "significant" condensation on double-pane windows then the humidity is probably a bit on the high side.
More specifically:
During a cold snap it's probably "normal" with standard double-pane units to get condensation covering 1/2 the lower sash when curtains are closed.
It's also "normal" (during a cold snap) to have maybe an inch of condensation in the corners and along the bottom of the lower when the curtains are open.
More condensation than what's described above would suggest too much humidity in the unit.
(Do the furnaces have humidifiers? If so, they may need to be turned down after insulating, depending on the type of humidistat control.)
Based on the other information provided, I tend to think that you've increased the sealing and haven't done anything about exhaust fans/ventilation. Sealing and ventilation have to be considered simultaneously. Even though your intent was insulate, not seal, sealing may have occured.
What is the common wall between units? Are two walls separated by an air gap exposed to the ambient air or is it a true common wall?
The corner is going to be thermally your weak point as others pointed out, so with increase humidity, you will find condensation.
With a tenant that cooked a lot ... no wonder. Did they use a range hood fan? Is it vented to the outside?
You've done well by insulating ... follow through and check your exhaust fans ... they need to ven to the exterior and do a good job.
Sounds like maybe a stud bay got missed or not filled all the way. That happened to me. I had cellulose blown in from the exterior and for whatever reason, one of the bays got missed completely. (it's below a window too).
That spot on the wall will get condensation on it on a REALLY cold day/night (like when it's -20 and we have one of those lovely 40-50 mph winds).
I know it got missed because I had put an "after construction" outlet box in there for some CAT5 wiring and I had enough slack to remove it and fortunately have small arms. stuck it in there and there's NO insulation in that bay at all.