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Adding Exterior Window Trim


Our house was build back in 1999 by the previous owner/general contractor who did not put exterior trim around the windows. As such, the steel siding butts up near the window (3/16" gap) on all sides. No caulking is used and I'm not sure how/if the window is flashed. I'm fairly confidnent the house is wrapped.

We now would like to add trim to the windows but I'm not sure how to undertake the project. I know that I would have to cut the siding out in the area around the window where we would add the trim. What would I do between the trim and the window frame? Between the siding and the trim. Is there a special procedure to construct in order to keep water out...thanks in advance...j

Re: Adding Exterior Window Trim

if you want to add trim to the windows after the fact your going to have to have a very steady hand to cut the siding back for the siding to fit. you should allow for the width of the trim plus an 1/8" which allows for caulking

as for the application of teh trim, if it were me i would use a roll of 4" blueskin or vycor and run that on the house wrap over just up onto the window frame but not so much that it will be visable once teh trim is on. from there i wouild set the trim into a bead of caulking at teh window, from there install a aluminum head flashing to seal the top of the window. after that use a color match caulking to caulk the siding to the new trim

Re: Adding Exterior Window Trim


Thanks for your great input! A couple of followup questions:

1. Any ideas on how to cut the steel/aluminum siding? I was originally thinking of a cirular saw with a carbide tip blade. However, I think it would be easy to keep line but cutting depth would be a problem.

2. As prevoiusly stated, there is currently no caulk where the siding terminates the fram of the window. Additionally, I don't see an existing head cap. If I hold off on this project for a year, should I caulk at the siding/window frame around each window? Is this standard practice? Thanks again...j

Re: Adding Exterior Window Trim

To answer your questions:

1. You can use your circular saw to cut metal siding. I would prefer a blade made for cutting metal (available everywhere for a few bucks). The blade height can be adjusted on the saw, so that you don't cut too deep. Don't cut the house wrap. Use caution and cut in a straight line.

2. Yes, you should caulk and seal the window frame.

Here is another idea: if you want a wood trim, it's fine. But you can use composite trim which will have better resistance to weather conditions, with less maintenance.

good luck.

Re: Adding Exterior Window Trim

for cutting the siding you can use a few different tools, just depends on what you feel most comfortable with. a circular saw with a metal cutting blade, a recip saw or a mini grinder

another option for trimming the windows is to cut out the siding to allow for trim first, insted of putting hte trim in first, you can install furring strips using pt lumber first which is about as thick as the siding itself, then from there install the composite trim and fasten it to the pt. this will create a similar effect as j-channel for vinyl and clean things up a bit. it will also hide any ugly cuts from cutting the siding. just be sure to use bluesking and plenty of caulking to seal things up so no water gets in

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