Window sill question
February 14, 2011 11:19 AM   Subscribe

There is air coming under the window sill.

Just moved into a new place. Underneath the window sill I hear a strange noise like boiling water. It's the wind from outside, and some is getting underneath the window sill.

Comparing it to another window sill, the problem one is not 100% against the wall, it's about 1 cm away.

Before I approach the building company to fix this, I'd like to know the acceptable way to fix this, rather than the quickest/cheapest way.

Would sealing it with silicone on both sides be an acceptable fix?, or is the only acceptable fix taking out the window in my apartment and refitting the sill?

I am also slightly worried about water getting under there somehow and it freezing or creating damp.
posted by devnull to Home & Garden (12 answers total)
Based on my own experience, silicone caulking would work perfectly well for a gap of only 1 cm. But of course, the surfaces must be very dry for the silicone to adhere. You can also use acryllic caulking compound, which is not as completely waterproof as silicone but which can be successfully applied to surfaces that you cannot get completely dry.
posted by grizzled at 11:30 AM on February 14, 2011

Expanding foam insulation would be my choice, as it's designed to fill gaps around windows. But don't use too much - it does say on the can that it expands!
posted by caution live frogs at 11:31 AM on February 14, 2011

Expanding foam can make a mess real easy, and it is very hard to clean. For a gap that small, caulk will work fine, and it will be easier to use.

If you do not own a caulk gun, they make single use caulk containers. Just use your finger to get it in there nice and tight.

It might be helpful to watch some DIY videos about caulk - though, caulking a gap is very simple.
posted by Flood at 11:51 AM on February 14, 2011

Response by poster: Thanks for the answers so far. I'm surprised that everyone is agreeing on not taking the window and window sill out! Is there really no disadvantage to caulk or expanding foam?

(The company who built the apartments will be doing this and paying for this thankfully, not me.)
posted by devnull at 11:54 AM on February 14, 2011

An apartment I used to live had some windows like that. Rain or dampness were never an issue (ymmv), but it was always letting in cold air. If you pay extra for heat, I would ask your landlord or building maintenance to take a little bit out of rent to cover additional heating costs until they can fix it.

FYI, hold a small candle under the windows to scope out which windows have this problem. If it flickers, air is getting through.
posted by raztaj at 11:57 AM on February 14, 2011

Wait - is this new construction? Is this window newly installed?
If it is new, and the window is that drafty, then you should be worried about more than just the window.

I am a contractor. When installing a new window, making sure it is sealed tight is the very point of the job. If they installed a new window, and forgot to caulk under the window sill, then you are not dealing with some seriously shoddy work. And in my experience, once guys start slipping on a job, the whole job is compromised.

That said, caulking is still probably the best solution for the construction company.
posted by Flood at 12:02 PM on February 14, 2011

Response by poster: It's a new build.
posted by devnull at 12:05 PM on February 14, 2011

Expanding foam is better at filling large gaps (and thus would be my choice here), but it's incredibly sticky until it dries, and is easy to make a mess if you're not used to working with it. Caulk doesn't work well for large gaps, but it's easier to work with. Those are the tradeoffs you're looking at. Regardless, anything that stops the air flow will improve the situation.

On preview, I agree w/Flood that this doesn't bode well for general construction quality.
posted by jon1270 at 12:05 PM on February 14, 2011

Caulk and/or foam can be messy, but there's not much real downside. It's just that the cost of ripping out the window frame is so much greater than the extra heating cost. (Your comfort & tolerance for whistling are of no concern to them, honestly.)

I just did something very similar to the door into our garage. The gaps are so big that fiberglass insulation simply fell out, so I shoved it back in, then sprayed in expanding foam. NOTE: there's regular expanding foam, and then there's a formulaiton that expands slightly less. Get this, so you can avoid having the strong stuff tear your windowframe apart as it flexes its mighty thews.
posted by wenestvedt at 12:06 PM on February 14, 2011

Since you ask, there is no significant disadvantage to using caulking compound, but I will note that if you use silicone, paint does not adhere to silicone once it has hardened, so whatever color you have used is the color you are going to have. But that is a very minor concern. White silicone generally looks fine in most situations.
posted by grizzled at 12:43 PM on February 14, 2011

Until they fix the problem, you can use clear packing tape to cover up the gaps and keep the draft out. It works surprisingly well, and it won't leave a sticky mess behind (like duct tape would).
posted by ErikaB at 1:26 PM on February 14, 2011

I've been dealing with this myself -- some very shoddy (rehab) construction, as Flood notes. It's par for the course in this building I own.

Basically, I have four materials I use. Fiberglass batts, trimmed to size; caulk backer (foam rope); low-expanding "windows and doors" foam (so it won't distort the frame); and silicone caulk. I stuffed fiberglass in where I could using a screwdriver and putty knife, and used expanding foam where I couldn't. Small gaps were closed using the backer. On top of that is nicely beaded caulk.

Depends on if you pay for the heat whether you want the actual gap between the front and back caulk filled. More R-value.
posted by dhartung at 5:11 PM on February 14, 2011

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