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Retrofit double pane in old sashes?

DougR's picture

A neighbor has one of those fifties living room windows that consists of 12 smaller wood sashes assembled into a giant grid 3 wide by 4 high. One row of 3 are crank-out awning windows and the rest are fixed. Each of the 12 sashes are single pane glass with individual single pane storms held on by clips.

He got an estimate to replicate the whole thing with new double pane units for about $5000. The whole assembly is maybe 10 feet wide by 6 feet tall.

He has two ideas to upgrade what he has now instead:
A- Have a glass shop make up double pane replacement glass (about 1/2 in. thick), remove the interior stops, pop out the single panes and replace them with the double panes.
B- Have a glass shop make up double pane versions of the 12 storm windows.

Cost either way would be about $900 for the glass.

Do either of these ideas seem worthwhile, or do you think it makes more financial sense in the long run to replace the whole works? The sashes themselves are in great shape and the 3 operating sashes would get new weatherstripping as part of the project.

Appreciate your thoughts and experiences. Thanks.

(post #114495, reply #1 of 10)

The glass people will install the glass in the sashes? If so, that sounds like a reasonable approach.

Replacing the storms would also work.

However, I should note that it's a little questionable, given that type of storm, whether insulated glass will be a substantial improvement.

Based on our experience with our 70s house, it would also pay to remove the interior trim and use low-expansion "door and window" style spray foam between the window frame and rough framing. Lots of air leakage through that area.


If your view never changes you're following the wrong leader


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #114495, reply #2 of 10)

Exactly what is the outcome your neighbor/customer hopes to achieve by replacing all this glass?


Have you ever seen R-values for glass units?  Pitiful.  Even double pane units are shockingly low...less than R-5 for 3/4" spacer bar, I think.  If your replacement units are going to be 1/2" overall, single strength on single strength glass, that's what, 3/32" each, so that would be 5/16" spacer bar?  Google the R value of that - I bet you'll be surprised how low the number is.


These past few years they have changed to using "U" values hereabouts to grade windows - I'm pretty sure the U value is the inverse of R value so if you multiply one by the other you get 1.  But it all gets confusing to me - like if it's that simple, why didn't we just stick with R values.


Here's something else to consider - I have tried retrofitting thermal units in sash built for single panes.  You can do it, but it doesn't leave much depth in the rabit for glazing putty (and some thermal seals are not compatible with glazing putty so make sure to ask your supplier).  What I have done is make wood stops that stand proud of the original millwork, but it changes the look significantly. 


Plus, find a glass shop that can get you insulated units with bronze colored spacer bar.  Otherwize that alluminum colored spacer bar you get will reflect a lot of light and stand out like a sore thumb.


Maybe I'm making too much of all this, but I've done a little window retrofitting and these have been some of the things I regretted not thinking about ahead of time. Check back next year and I'll have some other complaints, no doubt!


 


Loren Wallace for president.

(post #114495, reply #3 of 10)

Go look at recent  threads 95896.x (efficiency of storm windows) and 95543.x (insulated glass nightmare).  A really good post in that thread was from a fellow BT'er who did his master's thesis on the fact that 'insulated glass' (95543.126), when all lifetime factors are considers, are MORE costly than even a single pane, way behind 'old fashioned' storm windows. 


IMNSHO, the minimum $$ your neighbor will be 'throwing away' is $900, ya sure dont want to squander $5K!!, you might as well send it to me for beer money<G>.  See 95543.53 for my 'unbiased' opinion on 'insulated glass'.


Seal up any leaks, keep the storm window setup as is and follow storm sash sealing recommendations in posts of 95896. 


Sealing example in mother's house windows in room used just for storage ;  In the winter, I duct tape the inside of the storm sash where they meet the casing, then close the double hung and  tape that sash to the frame. Blue painters tape works good, as it will come off pretty good the next spring. Since the advent of Air conditioning, 90% of the storm sash are left in place all year.  

(post #114495, reply #4 of 10)

I have purchased glass with a discrete, metal, fuzzy gasketed frame, sized to attach to the existing sash with 'L clips' (all available from any glass shop) - it does make a 'dead air' space (a poor mans thermopane) - it is easily removed for cleaning, every couple/three years -


something like that, in conjunction with storm windows gives a triple glazed unit - which might make you think you were warmer -


nothing like curtains or shutters to actually improve the situation -


 


 


"there's enough for everyone"
"there's enough for everyone"

(post #114495, reply #6 of 10)

What you described is what he already has -- poor man's Thermopane. Fairly common for homes built in the Midwest in the 50s, and some of the units are very high quality (which is one reason I'd be reluctant to rip them out and install all new windows).

It's not really clear that replacing the existing glass with IG would be all that much of an improvement, especially if one also did away with these "mini-storms" in the process. More improvement is likely to be seen from working on the window seals, and, as I suggested earlier, foaming around the gap between window and rough opening.

I must say, though, that a prior poster's criticism of IG is pure BS. I suppose down in the tropics it doesn't make much sense, but in places where it actually gets cold you need either IG or storms to avoid an inch of frost on the windows in the winter time. An in our 31 year old house we've replaced exactly two IG sashes, both due to mechanical damage, so the argument that you have to replace them every ten years is nothing but FUD.


If your view never changes you're following the wrong leader


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #114495, reply #8 of 10)

PS: One advantage of the individual per-sash storms over full coverage storms is that they don't have a condensation problem. Unless the sash is somehow defective, it will always seal tighter than the storm, so moisture between will not be a problem (in cold climates).

Of course, the disadvantage (a big one) is that you don't have the storm as a "backup" for poor sealing around the sashes.


If your view never changes you're following the wrong leader


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #114495, reply #9 of 10)

Thanks everyone for your very helpful comments. I think I'm hearing that retrofitting insulated glass in the sashes would be an improvement, but nothing spectacular. Paying extra special attention to weatherstripping the sashes and getting a tight seal on the individual storms will probably get him nearly the same benefit for a lot less money.

Thanks again and I'll pass on all your comments to him.

(post #114495, reply #10 of 10)

Note that the individual storms are probably already pretty tight. He just needs to inspect them and tighten/replace any loose/missing clips, repair anywhere where the frames are bent/warped, etc.


If your view never changes you're following the wrong leader


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #114495, reply #5 of 10)

I don't understand the individual storms, but I would think the best bet would be a single well designed removable storm window over the whole thing.

(post #114495, reply #7 of 10)

  That sounds like a lot of panes to me for a window that size or would pains be a better word. Unless your neighbor really likes the style of the window, I would consider replacing the whole thing with something more attractive and more efficient. The $900 seems reasonable for the glass, but look at all the labor involved, and you still have 3 awning type windows.
     
    For under 5 grand you could find a decent bay or bow type window, and maybe shorten the height to around 5'. There are other window combinations that would also work.  I used 3 large DH cottage style windows in a similar size opening and it looked much better than the picture window and 3 awnings on the bottom. I will see if I can find a picture of it. Good luck.  

   

I started out with nothing....and I still have most of it.