Plexiglass cover for inside of windows?

[Brian W Evans]

I am thinking about ways to better insulate my shop, which is a 3-car garage. I have 5 windows, each double-pane, but no storms. I can feel a significant amount of cold air near the windows and am thinking about cutting some plexiglass to cover the windows, probably with some weather stripping around the edges to create a seal on the molding. My concern is that there might be a condensation buildup in there and I might get mold or otherwise damage the windows with moisture. I would probably attach the plexiglass with bolts that screw into t-nuts embedded in the molding so that I could take the plexiglass off in the warmer / moister months.

Thoughts on doing this?

Thanks.

[Harry Murray]

Why not try the shrink wrap window insulation first? It would be quick, easy and show you if there is merit from an insulation point of view. It would also be easy to see if you are creating a condensation problem.

[Jim Becker]

Brian, I use 1/8" thick plastic to essentially do the same thing in the 250 year old portion of our home. I don't believe that the windows date back to the 1750s like that portion of the building does, but they are very, very old and I don't want to "replace" them. They don't open, either, so the plastic was a good solution to be able to provide additional sealing for air infiltration. I didn't use Plexiglas, however...I used Lexan. For your shop, I'd suggest the same because unlike Plexiglas, Lexan doesn't shatter. I attached with 5/8" screws and because the window frames are uneven, I did use a bead of clear silicone to adjust for that. It's worked for about a decade now to keep drafts non-existent from the glass.

[Adam Herman]

i built 1x2 on edge wood frames for our skylights, and used foam weatherstrip along the edge to the drywall, 1/4 polycarb panel. drilled small holes in the drywall and used rivit to slid in the hole and hold the panel up. really reduced the cold air rolling down from them.

[Doug Garson]

Sounds like a good idea, I wonder if adding some desiccant packs like these would help with the moisture concern.
https://www.amazon.ca/Dry-Premium-Indicating-Silica-Packets/dp/B01N1MTT2A/ref=sr_1_6?ie=UTF8&qid=1513464568&sr=8-6&keywords=desiccant+packs

https://images-na.ssl-images-amazon.com/images/I/51XFd4SyruL._AA218_.jpg

[Dan Rude]

I have thought of this too. Except my issue is my regular double pane insulated windows I installed 20 years ago.. I am always getting build up of moisture on them that freezes, then I get the mold. :( It is a constant battle here in the upper Midwest. This year I am making mini storms using screen frame stock. I am going to put the shrink plastic on them and see how it works. If I get new windows or build I will skip the wood or vinyl and get the fiberglass windows and triple pane. Dan

[Lee Schierer]

I would check to insure that the gaps between the rough opening and the window frame is properly insulated. When I remodeled our family room I was amazed at the gaps around the window that were just covered up by the window casing. A little minimal expanding "Great Stuff" worked wonders on the drafts by the windows.

[Tim Bueler]

It's possible adding a piece of plexi, or better yet, Lexan as Jim suggested, will actually help eliminate condensation problems by creating the extra air space. Condensation occurs because you're hitting the dew point at that particular location. Much of the new superinsulation building technology deals with moving that location to a point where it isn't harmful. You could try Lexan, in some removable configuration on the inside of one window, and maybe the shrink wrap idea on another window to see where you get the best performance.

[Bill Dufour]

I have heard that adding such extra layers can overheat the glass and crack it in summer? Especially a problem with older stained glass windows. I do not know if this is really true or just a old story. Certainly in summer the windows interior space can easily be over 150F or higher which is just 30F over the air temp.
I have no idea of the thermal expansion of wood vs glass or plastic.
Bill

[Brian W Evans]

I would check to insure that the gaps between the rough opening and the window frame is properly insulated. When I remodeled our family room I was amazed at the gaps around the window that were just covered up by the window casing. A little minimal expanding "Great Stuff" worked wonders on the drafts by the windows.

I put the casings up on these windows, so I know there is insulation in there. Thanks.

[Wade Lippman]

I have thought of this too. Except my issue is my regular double pane insulated windows I installed 20 years ago.. I am always getting build up of moisture on them that freezes, then I get the mold. :( It is a constant battle here in the upper Midwest. This year I am making mini storms using screen frame stock. I am going to put the shrink plastic on them and see how it works. If I get new windows or build I will skip the wood or vinyl and get the fiberglass windows and triple pane. Dan

I had the same problem. Went away when I paid better attention to the humidity in the house.

[Brian W Evans]

It looks like I'm going to try the shrink-wrap stuff this winter. I checked out the price of Lexan - $183 for a 4' x 8' sheet (1/8" thick) was the best I could find. I'll need three sheets, so that's a lot of cash, especially at Christmastime.

Thanks for all of the input. I'll post results if I do end up doing something like this.

[Jim Becker]

Brian, I bought the Lexan I used at Home Depot...they had pieces large enough for the windows I needed to cover. I don't remember the cost, however.

[sean meltvedt]

Brian, if you put the plexi on the outside of the window, it will reduce the likelihood of condensation since the vapor seal (the window seals) is closer to the warm inside. This is assuming your relative humidity inside the house is reasonable.
Regardless, the air gaps will gain you insulation value (approx .5 R value in still air if I remember correctly, so your plastic sheet would gain you an additional 1 R value)
Merry Christmas
Sean

[Steve Peterson]

Old books about house building would describe ways to create dual pane windows. They recommended to seal the inner layer completely and let the outer layer vent to the outside. The reasoning is that colder outside air holds a lot less moisture than the warm inside air. There is a lot less chance for condensation this way.

[Peter Kelly]

I am thinking about ways to better insulate my shop, which is a 3-car garage. I have 5 windows, each double-pane, but no storms. I can feel a significant amount of cold air near the windows and am thinking about cutting some plexiglass to cover the windows, probably with some weather stripping around the edges to create a seal on the molding. My concern is that there might be a condensation buildup in there and I might get mold or otherwise damage the windows with moisture. I would probably attach the plexiglass with bolts that screw into t-nuts embedded in the molding so that I could take the plexiglass off in the warmer / moister months.


Thoughts on doing this?


Thanks.What size windows? Ikea has some decent cellular cordless shades that aren't terribly expensive.

http://www.ikea.com/us/en/catalog/products/50381484/
http://www.ikea.com/us/en/catalog/products/10290631/

The TRIPPEVALS blackout ones keep things a bit cooler in the summer as well.

[Brian W Evans]

What size windows? Ikea has some decent cellular cordless shades that aren't terribly expensive.

http://www.ikea.com/us/en/catalog/products/50381484/
http://www.ikea.com/us/en/catalog/products/10290631/

The TRIPPEVALS blackout ones keep things a bit cooler in the summer as well.

I actually have those on some windows inside the house and they do help a surprising amount. My concern for inside the shop is that they will gather dust and also that they are quite fragile. Part of my thinking about the lexan is that it will offer some protection for the windows from me maneuvering large pieces of lumber around.

Thanks for the idea.

[William Sonnier]

I just built 36 frames out of 1x2 select pine and installed .030 marine grade vinyl in them for our screened porch. They made a big difference!!! Wouldn't be difficult to make some to cover your windows. We ordered the vinyl on line and paid about 9.50 a yard.

[Brian W Evans]

William, thanks for the idea - I had never heard of that stuff before but it is definitely a possibility. How did you stretch it tight over your frames?

[William Sonnier]

I ran a 3/4" rabbet on all my stock and mitered the corners, then glued and nailed them. Primed and painted then stapled the vinyl in the rabbeted area. We would start on one side with three staples in the center of the frame, then start stapling the other side with a few staples while my wife pulled the vinyl. We then moved to the middle of say the left side side and stapled towards one corner while pulling the vinyl tight. We worked from the middle to the corners and managed to get the vinyl pretty tight. We used .030 vinyl, but the .020 might be easier to work with. We ordered it from Marine Vinyl Fabric.com and they will send you small samples to get a feel for how thick the different sizes are. I will rip some strips to cover the rabbeted area and staples. I also used a pneumatic stapler from Harbor Freight that shoots T50 staples. Used a coupon and paid about 20 dollars and worked great. I was also able to use the nose on the stapler to put some pressure on the vinyl to help pull it a bit tighter as I stapled it. Overall, it takes just a little practice to get really good results.