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Question DetailsAsked on 10/9/2015

Does exterior Window trim need to be removed when installing new construction windows on an existing house?

Contractor measured my windows. Indicated he would take off the interior trim, cut out the window and that
exterior trim would not need to be removed to install new construction windows in an existing home. Is this correct, I thought trim always had to be removed, both interior and exterior.

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4 Answers

Voted Best Answer

As you can obviously tell, I don't like the sound of it. Several things I would suggest, if you have a few days leeway to decide:

1) immediately post a NEW question and, to catch their attention, in the title of it (not the details part) say something like this - NewWindowMan and WindowsOnWashington - can you advise me then in the details ask for their input and provide a link to this question. Those two are common contributors to this forum and both are window company owners or managers, so maybe they will give additional advice.

2) By doing what he is saying, you are counting on the existing trim and flashing working perfectly - not generally a good idea, especially if older windows where they typically have NO water seal or flashing and count totally on one caulk joint around the outside for all your water sealing. The issue with that, other than assuming the caulking will work perfrectly (no backup) and requiring you keep up on annual caulk checks and repair as needed (an easy DIY thing if not afraid of ladders), is that if any water gets behind your siding or under any flashing ABOVE or adjacent to the window, there is nothing stopping it from flowing right into that space around the windows and into your walls or house.

3) Below are a couple of details showing how most windows should be installed today - of course, outer flange/flashing/trim varies by window and siding type, but this illustrates how the water seal and flashing direct any seepage back to the outside of the siding -

(in second one, see bottom image on right half of page showing window flashing and sealing details)

Working from the inside, little of this water barrier and none of the seal lapping and overlap can be done, and much of the rest would be done "blind" in the cavity around the window.

4) One other thing - he said there would be a 3 inch gap around the window - so you are losing say 2 to 2-1/2 inches all around (over the normal 1/2-1 inch gap between frame and rough opening) - so on a normal say 30x48 bedroom window that means your existing window would be 1/3 larger than the new one - QUITE a reduction. You might check the other contractor's actual glass dimensions against this guy's - you might not be looking at apples to apples here.

5) And as I said before, check the MANUFACTURER recommended installation diagrams for your windows, not believing what a salesman tells you. I seriously doubt they fail to recommend/require the EXTERIOR water barrier lapping and drainage sill and flashing and such, which you would NOT be getting with this plan. I know I would not allow residential windows to be installed this way except in outer-framed concrete or steel construction where that is a standard install design and the windows (which are actually inserts even in new construction to make them easy to change out) are made to go in that way at times - though still with exterior sealing.

6) If you DO go with this, I would require a detailed sketch showing how they are going to get a watertight seal at the rough opening and drain away any water that gets into the rough opening, and I would also require installation (if you can accept the look) of an overwidth head drip flashing - metal drip edge that is a couple of inches wider than the window outer trim, that catches runoff from above and causes it to free-fall past the window. If installed correctly will catch runoff down the wall, but does NOT do anything about any water running down in the wall. They may claim if that happens it is not the window's fault - which is true, but at any wall penetrations you should take steps to handle any such siding failure BECAUSE you are providing an opening for water to come in.

7) With windows that have an outer trim - like brickmold overlying T1-11 or brick or concrete wall for instance, a high quality caulk job under the trim and around the joint between trim and house can take care of mnost water problems and the proposed scheme MIGHT - emphasize MIGHT - work OK. With a siding that uses joining C or J channel like lap siding, I don't see more than a prayer of it working well.


Obviously, price had to come into the picture here, but I think you may be getting a substandard and possibly substantially undersized product for that cheaper price.

Answered 5 years ago by LCD


I am assuming you are talking the entire window unit, not just the moving sashes which commonly can be installed from the inside, using the existing outer frame.

You went to same school as me - though I have done windoew replacements totally from the outside without touching interior trim, though getting the weather seal into the gap around the window can be tough - and can only be done if the interior trim, is nailed into the drywall rather than the window frame, which is rare and not proper.

I don't think newwindowman will shoots me down here, but in my opinion to replace "prime" or full outer and inner frame windows correctly, you have to install water shield in the rough opening and interfaced and sealed correctly with the house wall water shield and flashing and commonly C or J channels to interface with the siding around the outside - and this CANNOT be done right from the inside. Also, working from the inside you are not going to get proper caulking in the right places.

So - my call - unless I am totally missing something or these are just sash (interior frame and glass) replacements, I think you should be seriously looking at getting a new contractor because he is not going to be able to install them right - basically you are not getting a full "new window" with proper waterproofing and insulation, and the performance of the window will not be as energy efficient as it is rated for because part of the installation will be skipped.

Let me guess - his bid was significantly cheapear than the competition, right ? Maybe now you know why.

I would guess if you went to the manufacturer's website (unless really cheapo windows) you will find that his procedure violates their installation instructions - which might give you cause to terminate him if he is already on board.

Note - if you have contracted with him already and want to terminate, do it quick because he may have ordered the windows already.

Answered 5 years ago by LCD


Thanks LCD.

Actually, these windows are new construction windows and one of the top 5 brands. It is a salesperson from their storefront that came out and measured and when I asked him how he would install, he said take off the inside trim around the windows, cut with a special saw the fame and install. He said their is no need to remove outside trim because there most likely will be a 3 inch gap once the windows are cut out and he can nail into that and seal it with expandable foam and caulk. I have received one other bid from a contractor and he indicated he would have to remove the outside and inside trim and replace with new once the windows are installed.

I'm really concerned about finding the right contractor to do the job correctly. I admit, I'm not an engineer or someone who specializes in this but my gut is doingn flipflops at this point. It's an investment and I don't want to have issues/re do's due to my lack of understanding.

Answered 5 years ago by Guest_92724231


Thank you, have posted the question based on your advice.

Answered 5 years ago by Guest_92724231


IF you wanted, to give them the full picture of your situation, you could (only if you want) post a followup with the URL (page link) for this question, so they could see the detail you provided to me. Hopefully they will look at AL tomorrow and notice this - they (especially newwindowman) have been on here pretty often - basically daily, recently.

Answered 5 years ago by LCD

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