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Condensation on windows


mgbinspect
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Tom,

I tried hard to find the original thread we had discussed this particular subject and instance on, but was unsuccessful, which is probably just as well since I believe it had become a drift from the original subject.

I had the good fortune of stumbling upon this inspection and the photos while addressing a wood boring exit hole in a joist (most likely present before the joist was ever installed in the home), which is holding up a closing. Wheee... Termite guys must be hungry!

All that being said, here is a rather unusual observation - not the condensation on the windows, but rather the apparent cause.

The condensation was present on only the windows in the front elevation of the home, which had brick veneer. The condensation was limited to the perimeter of each of these front windows. The windows had never been caulked and there were considerable gaps around all of them between the vinyl window frames and the brick.

I hypothesized that the gaps were permitting cold air to enter around the windows keeping the glass at the perimeter of each window chilly, which was easily confirmed by a touch of the hand to all surfaces near the perimeter of each window opening.

Below are supporting pictures. Photo 38 actually shows a small gap in the interior sealant along the window frame and some minor mildew and discoloration on the painted wood surface. There was actually condensation on the vinyl window frames around the perimeter, which was impossible to demontrate in photography.

Of course, this is independant of any discussion regarding the source of the moisture or if it is excessive.

Just curious to see if you or others in the brain trust agree or disagree with this theory.

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I'm with Michael in that the condensation is likely the result of sealing (draft) issues but I'd like to add the possibility of a significant issue with internal negative pressures.

Sometimes the negative pressures developed can be a more significant contributor to a moisture intrusion problem than the sealing of wall openings.

Marc

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I have found that an infrared thermometer to be a very helpful tool for tracking down stuff like this. First know your spot ratio, then hold your thermometer at approximately that distance from the center of the glass from inside. Pull the trigger and note the surface temp, then slowly sweep out to the jamb stopping briefly at each change in material, again noting the temps. The center of the glass should be the warmest temp on the window, or within a few degrees of it. The glass will get cooler as you get close to the edge, but that is a high performance spacer system so not too much cooler. The weather stripping should be the coldest temp, but from your pics I would suspect that the joint between the window and the extension jamb is a very similar temp if not colder. It doesn't matter what the temps are, but they should all be within a range of about 5 degrees or so. Any variance greater than that wll steer you towards the problem area and you can ignore the rest.

A simple test for Marc's theory would be to unlock the window. If the condition is localized humidity and poor air flow the condensation will clear quite quickly, if it's negative pressure it will get worse as the surfaces cool. Careful observation for say 30 -45 seconds should be enough to see a change in the surface condition, it will move slowly like watching your windshield defrost when the heater finally warms up.

That is a crappy install, and I'd guess that there are several problems. Mid grade windows with mediocre performance numbers, missing caulk at the brick, likely improper or missing flashing at the nail flanges (or missing flanges altogether), insufficient insulation around the window. Your best bet would be to pull the trim off one and check it out.

Tom

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That is a crappy install, and I'd guess that there are several problems. Mid grade windows with mediocre performance numbers, missing caulk at the brick, likely improper or missing flashing at the nail flanges (or missing flanges altogether), insufficient insulation around the window.

Tom

I think that sums it all up pretty neatly, and that was my thinking as well. Voids in the insulation really has to be a player...

Thanks for finding and responding to this, Tom.

Marc - good point.

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I've also seen condensation on the inside of dual-pane thermal windows and all caulking/sealing "appears" to be OK.

In some cases it has been more prevalent at windows where the 2-inch blinds are kept fully closed and completely dropped to the sill.

I've noted, over the years, that keeping the blinds fully closed can still be OK, but lifting the blinds off the sill an inch or two will allow more air circulation behind the blinds and minimize some of the condensation collection.

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If the bulk of the air leaks are indeed at the perimeter, the cheapest and easiest fix is to pull the interior trim and fill the voids with low expanding spray foam (not great stuff, unless they'll be happy with non operable windows), and a polymerized exterior caulk. I like NPC Solar Seal, and would choose clear for that task, but OSI Quad would work well, or any of the polyurethanes out there. Silicone doesn't bond well to vinyl and when it fails will be impossible to remove from the brick, none of the other sealants will stick to silicone so fresh silicone caulk every two or three years will be your only option. I have yet to see a butyl compound that doesn't become brittle and crack, I have no use for them.

Of course, fixing the air infitration won't do anything for missing or botched flashing details, but you already know what's involved with popping off that veneer to get at those. Here's hoping they're high and dry!

Tom

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I have found that an infrared thermometer to be a very helpful tool for tracking down stuff like this. First know your spot ratio, then hold your thermometer at approximately that distance from the center of the glass from inside. Pull the trigger and note the surface temp, then slowly sweep out to the jamb stopping briefly at each change in material, again noting the temps. The center of the glass should be the warmest temp on the window, or within a few degrees of it. The glass will get cooler as you get close to the edge, but that is a high performance spacer system so not too much cooler. The weather stripping should be the coldest temp, but from your pics I would suspect that the joint between the window and the extension jamb is a very similar temp if not colder. It doesn't matter what the temps are, but they should all be within a range of about 5 degrees or so. Any variance greater than that wll steer you towards the problem area and you can ignore the rest.

Tom

You know, I have a great little infrared thermometer, that I really need to get in the habit of using more extensively than I do.

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