Retrofit - replace glass only single pane to double pane

Ask replacement window questions & get answers!
Post Reply
Message
Author
plp
Posts: 3
Joined: Mon Jan 05, 2015 9:46 am

Retrofit - replace glass only single pane to double pane

#1 Post by plp »

Hello there,
It might have been discussed already… I spent little time on searching for it on the forum, so do not bash me, please.
My problem is as follows.
House was built in 1982. It appears windows are still original. Currently I have double hung, all wood, single pane with storm windows/screen. They are warm (frame, not glass!!), not leaking air, and look still good. Frame is still stiff, not bent anywhere or such.
Since it is MI (today outside is -15C – sorry, I am a metric guy) I get significant condensation on the glass inside (even with the storm windows in place). In order to minimize it I thought about new windows, but the lowest quote is roughly 4k. With windows matching our current exterior and interior it is another 50% more. Therefore, an idea of retrofitting double pane into current frame came to my mind.
Initially I made a “double pane” myself – I simply cut a sheet of glass and secured it from outside in the frame. Result – much warmer glass and condensation cut by about 80%.

I found double pane (made to order) Low-E. It costs roughly 65 USD per piece (a piece is 32”x24”) and I have 12 of those pieces plus a pair of 32”x16” at 42 USD… so we are talking about 850 USD plus taxes and misc. Labor is an extra 22/piece if I want them to replace the glass.

So here we come to a question – shall I replace the glass only and keep the old frames or go for a whole window? Is it OK for the window frame? It will hold the extra weight (I got one “retrofit” done, and it works OK – will stay in place when open). But I wonder, as someone told me that the frames will go bad and the double pane will start leaking within a year or so (it was one of those “quote guys”).

Some additional data.
Today in the morning I measured temperatures in the two rooms (the regular one and the test one with “new glass”). I used infrared thermometer.
Outside is -15C, wind 15 km/h. Inside the rooms is about 19C. All temps are in C.
Wall: 17.1, frame 14.5, glass 3.8 (about half way condensation – that is 12”, similar upper sash)
Wall: 17.4, frame 14.5, glass 9.5 (some condensation – that is 3/4” on the lower sash, upper minimal, less than 1/4")
The product I would be getting is Synergy Series by VPI Quality Windows. U-factor 0.30, SHGC 0.22 (for their window – I am not sure about the glass itself).

Please advise.


EDIT:
the total thickness of the double pane is 3/8", if it matters.

User avatar
HomeSealed
Posts: 2996
Joined: Mon Feb 15, 2010 3:46 pm
Location: Milwaukee, Madison, SE Wisconsin

Re: Retrofit - replace glass only single pane to double pane

#2 Post by HomeSealed »

Lot's of variables to consider here, may or may not be worth it.

A few off the top of my head:
- $22 per window for installation!? That can't be right. You are retrofitting double pane glass into single pane sashes. That will require some finagling, including new glazing beads.
- The balance assemblies in the original windows are not meant to hold this added weight. May work in one, may not work in others, may cause premature failure in others.
- If the job is professionally done, it CAN work, just a matter of if it will be a wise investment when all is said and done. Superior sealing storm windows with Low-e may be a better choice for efficiency. Also, 50*F glass at about 5* exterior temp is not too bad.
-30+ year old windows likely have some issues even if on the surface everything looks "ok". If these were much older, there would be some reasons to preserve/recondition (old, dense wood, architectural and design considerations) but from 1982 that would not apply.

On the condensation, is that primarily in the interior of the main window, or on the storm? In most cases, (similar climate here in WI), we see that moisture/frost accumulate on the storm since the air leaks out through the prime unit. If on the interior of the prime unit, that means that they probably are sealing pretty well, but also may indicate excessive moisture in the house. If your primary motivation is to eliminate the condensation/frost, there are many ways to do so. At an interior temp of 69*F, and a glass temp of 49*, that puts your RH at about 49%. That's a bit high, particularly if you'd like to see less condensation at 5*F exterior temp. The number of threads on condensation on this board is nearly endless, so that would be worth a look as well. If you have an appetite for a comprehensive technical explanation, look for responses from Oberon who always adds a great contribution.

I guess if you are looking for a yay or nay one way or the other, I'd say nay in favor of either replacements or new storms as a better investment when all is said and done.

plp
Posts: 3
Joined: Mon Jan 05, 2015 9:46 am

Re: Retrofit - replace glass only single pane to double pane

#3 Post by plp »

Thanks for your input.
HomeSealed wrote: - $22 per window for installation!? That can't be right. You are retrofitting double pane glass into single pane sashes. That will require some finagling, including new glazing beads.
- The balance assemblies in the original windows are not meant to hold this added weight. May work in one, may not work in others, may cause premature failure in others.
22 is per opening, so that would make 44 per window. Sorry for confusion.
Is there a way to tell if the window can or can't support the extra weight?
HomeSealed wrote:- If the job is professionally done, it CAN work, just a matter of if it will be a wise investment when all is said and done. Superior sealing storm windows with Low-e may be a better choice for efficiency. Also, 50*F glass at about 5* exterior temp is not too bad.
-30+ year old windows likely have some issues even if on the surface everything looks "ok". If these were much older, there would be some reasons to preserve/recondition (old, dense wood, architectural and design considerations) but from 1982 that would not apply.
How can one tell if the job is professionally done? Is there a way to tell the frame is or is not OK?
In the retrofitted window I see a fresh clear silicone bead on the inside (simply glued to the same place where old glass was) and on the outside is a lip (kind of seal - I am not sure how this strip is called) securing it. The lip/seal slides into a rim in which an old "seal" was.

50*F glass is the double pane with the storm OPEN. The single pane is 35 or so withe the storm sealed. The gap between storm and window is about 2.5" what from my knowledge would be a poor air pocket allowing great convection. Hence, I dropped sealing storms in the first place.
HomeSealed wrote:On the condensation, is that primarily in the interior of the main window, or on the storm? In most cases, (similar climate here in WI), we see that moisture/frost accumulate on the storm since the air leaks out through the prime unit. If on the interior of the prime unit, that means that they probably are sealing pretty well, but also may indicate excessive moisture in the house.
Inside. Storms are clean.
From thermal camera it looked like windows did not loose much of heat.

Excessive moisture could be a case here as yesterday the temps were around +32F (outside) and dropped overnight to +5F. Therefore, RH inside is too high for outside temp and for sure condensation is expected.
I do want to get rid of condensation since it is a great place for mold grow... and some windows have signs of it.


Sure, I will look into Oberon's posts.
Thanks again.

User avatar
HomeSealed
Posts: 2996
Joined: Mon Feb 15, 2010 3:46 pm
Location: Milwaukee, Madison, SE Wisconsin

Re: Retrofit - replace glass only single pane to double pane

#4 Post by HomeSealed »

Pricing makes more sense, still seems somewhat low though. Admittedly it is not a service that I offer so for a company that specializes perhaps they are able to make a buck at that price due to improved efficiency. Regarding the weight, probably the easiest way to tell would be to add weight to each panel to simulate the increase (tape some washers to the glass or something along those lines). That said, I can say with a fair amount of certainty that modern balance systems are sized appropriately to the weight of a given window. The new weight would likely exceed what is ideal for proper operation.

The "securing strip" is the new glazing bead. On the existing installs it would be hard to determine the quality of the job without seeing it, but going forward finding a company that specializes in this sort of thing would be the best way to insure proper installation should you decide to go that route.

If I'm correctly understanding that the condensation is your main concern, I'd recommend addressing that area first and then reassessing the situation. You can buy a cheap hygrometer at most hardware stores.
Do you run an Aprilaire or have window treatments closed a lot? Those are two common issues that can return quick results.

plp
Posts: 3
Joined: Mon Jan 05, 2015 9:46 am

Re: Retrofit - replace glass only single pane to double pane

#5 Post by plp »

HomeSealed wrote:Pricing makes more sense, still seems somewhat low though. Admittedly it is not a service that I offer so for a company that specializes perhaps they are able to make a buck at that price due to improved efficiency.
that's a local glass/window repair store. It is a small shop with good reputation.
HomeSealed wrote:Do you run an Aprilaire or have window treatments closed a lot? Those are two common issues that can return quick results.
No, no humidifier in the house.
Today's morning RH was at 55% at 19C if the hygrometer tells the truth.
Windows treatment - there are some, but open during a day.

I will take some pictures of the windows so you will see what exactly is happening.

User avatar
HomeSealed
Posts: 2996
Joined: Mon Feb 15, 2010 3:46 pm
Location: Milwaukee, Madison, SE Wisconsin

Re: Retrofit - replace glass only single pane to double pane

#6 Post by HomeSealed »

55% RH is a bit higher than ideal, particularly at that temp. Have you had weatherization work done on the home? That is a pretty high reading for a 1982 built home with no humidity added.

On the window treatments, the overnight hours are going to be the most critical. Much like the balance in humidity between interior comfort and less condensation, with window treatments you want to balance privacy with allowing warm interior air to circulate across that glass. If you can open some of those partially overnight you should notice some improvement.

User avatar
TheWindowNerd
Posts: 2216
Joined: Fri Apr 17, 2009 3:05 pm
Location: SE PA & NJ; DFW/Metroplex

Re: Retrofit - replace glass only single pane to double pane

#7 Post by TheWindowNerd »

What is the seal failure warranty on the new IGU's?
If less than ten years I would not do it.
3/8" is the IGU OD? very thin.

Post Reply