Should I and how should I properly caulk exterior windows?

October 8, 2009 7:31 AM

I'm a fairly new home owner in the midwest. So, we can see some pretty harsh winters. I'm trying to prepare my house for the coming winter, and I noticed that there is no caulking on the outer edges of my windows where they meet with the siding. This may be a dumb question, but should the windows be caulked? More inside.

It's an old home with aluminum siding. The windows are relatively new (my best guess is that they were installed within the last 10 years).

Browsing the web, the majority of sites suggest caulking around the windows. However, I did come across an article that suggested that caulking isn't always necessary depending on the windows and siding. Plus the fact that there is absolutely no caulking there now makes me wonder why the window installer chose not to do so. Laziness, inexperience, or maybe it really doesn't need it. Maybe it could pose a problem for moisture to get out (as the article suggested). So, I just don't know if I should do this, and that's why I'm posting this question.

To properly maintain my home, should I caulk between the exterior window edge and the siding? If so, will any exterior caulking do? Would a picture help or is my description adequate?

posted by Swede78 to home & garden (8 comments total)

The windows were probably caulked (or installed with construction adhesive) after being shimmed for being level, at the area where they join to the wall framing. The real test is if you are getting any cold air intrusion around the window frame. You can test this in a number of a ways, including use of a fan-door (basically just a panel that can be fit into an external door frame, with a couple of electric fans that can pull air out of the house at a good rate), or just wait until cold weather. Use a candle all around the window frame to feel for cold air leaks, using either a fan-door or the cold air that will be trying to seep into the warm house. Also, look for ice and condensation buildup on interior surfaces of windows (a little being OK if the shower has been running, or the house if full of people giving off condensation, but interior ice buildups almost always mean a cold air leak).

If there is no cold air leaking in, additional caulking isn't going to help anything. If there are cold air leaks, caulking at the point you're concerned about is the wrong place to try to fix it. In that area, the siding will typically move a little, expanding with heat, and contracting with cold, and caulking will just tend to make the window trim push away from the siding. You'd want to remove either interior or exterior window trim, and caulk the window to the frame with expanding foam sealant.
posted by paulsc at 7:45 AM on October 8

You can candle for drafts at any time, the air doesn't have to be cold.

If you can determine the manufacturer of the window, you might contact them. They may recommend against caulking externally for various reasons.
posted by Lyn Never at 7:55 AM on October 8

Well, wouldn't you want caulk there to prevent water from entering between the siding and the window? Even ignoring the issue of cold air getting into you house, if you get water in there and it freezes, the expanded ice will wreak havoc on your window frames and siding. And then you'll have many more problems than merely cold air coming in.
posted by dfriedman at 7:57 AM on October 8

A good rule of thumb is to caulk where different materials meet. It may not have been caulked because they wanted to allow for expansion and contraction of the siding. The caulk should be flexible enough to allow for some expansion.
posted by Gungho at 8:26 AM on October 8

All of the sealing around the window is done prior to the siding being installed, as can be seen in this diagram.

The wall underneath the siding is considered a drainage plane, where any water that gets past the siding will be transferred down the plane and away from the house. It needs to be able to escape at the bottom of the window, so if you caulk around it, leave that part open.

A pan flashing is an element installed below every window and door designed to collect and direct any water that may leak through or around the opening back out to the exterior. As such the sealing of the window or door assemblies into the rough opening (through the use of membrane flashing and/or sealants) should be made at the jamb and head of the window, however the sill should be left free to drain to the exterior.
posted by orme at 9:09 AM on October 8

I'm also a fairly new homeowner in the midwest too. Last year we put up something like this window insulation kit. Basically it was a sheet of plastic that is stuck along the edge of the window which is supposed to catch cold air coming in. Ours always fill up with air, so I assume they're helping at least a little bit.
posted by chndrcks at 12:26 PM on October 8

As long as you leave the bottom uncaulked, I see no problem with caulking the top and sides.

chndrcks- you are supposed to use a hairdryer to shrink the material so it looks nice and doesn't make noise and doesn't fill with air.
posted by gjc at 9:14 PM on October 8

Thanks for all the responses. I've tested for leaking air, which thankfully is not an issue. There is no air rushing in around the windows. I will try the insulation kit as chndrcks suggested to save on energy costs. I've also heard that bubble wrap works well and is easier to put up.

Like dfriedman, I'm more concerned about water getting in. There seems to be some contradiction in people's answers. Kind of what I found when I searched various websites. Some say to do it, some say don't bother, it won't help. Thanks to some of the posts of how windows are installed, and the fact that air is not leaking in, I will assume that my windows were properly installed. I just hope water is being transferred away.

I've tried to examine other people's houses while I walk my dog. It seems that most of the houses in my area do not have anything between the siding and windows. So, I'm really leaning towards not caulking around them. I don't want to do it without knowing it will definitely benefit my house. I think I'll try to contact the manufacturer as Lyn suggested, and see what they have to say. Thanks again.
posted by Swede78 at 9:51 AM on October 13