Expert: Richard Taylor, AIA - 3/28/2007

Question
QUESTION: I live in the Kansas City metro area and am looking to replace the existing wood windows on my 30 year old home.  The exterior siding of the home is a masonite sheathing/siding combination with solid wood strips every 16" (I know rot central, but they love the stuff in KC).  Most of the window frames are in good shape, but a few have soft siding spots around the edge of the brickmold.  Replacement windows would obviously be easiest, but for quality I was thinking of doing a full-frame replacement.  

Which brings me to my question... Most modern windows have a nailing flange that should be nailed to the exterior sheathing and tied into the home wrap in new construction and the whole mess is covered with exterior siding.  My house obviously has none of these things.  So, how do I got about replacing the entire frame in this situation?  Do I cut away the siding and install the flange against the studs or install the flange on the siding and use flashing tape/trim/caulk to make thing weather tight?  Also, how does a drip edge, over the top trim piece, work into this system?

Any other candor regarding this topic would be appreciated.  I am handy, but exterior work is very new to me.  

Thanks in advance.


ANSWER: Hi Matt - thanks for your question.

I'm assuming the siding (sounds like board and batten) comes right up to the windows, with no trim boards at the windows.

I'd suggest cutting away just enough of the siding to allow you to install the clad windows with the nailing flange and add a trim board all the way around the window.

That will keep you from having to replace or match up new siding to old.  The trick will be very careful cutting of the existing siding to just the right spot to accept the new trim.

Be sure to properly flash the new windows at the head - that's the cause of most leaks.  The new flashing should be slid up under the old siding and over the top of the window frame.  The new head trim goes on top of that.

Since you'll probably cut through any existing infiltration barrier (Tyvek, etc.) when you do this, you'll want to tape the flanges.  Tyvek, etc. makes products just for that.

Lastly, window size is critical.  Can you get new frames to fit neatly into 30 year old openings?  You may have to compare the cost of custom-sized windows to the added framing and siding work necessary to install standard sizes.  For my money, I'd do the custom sizes (if needed) and skip the extra work.

Hope this helps!

Richard Taylor, AIA
www.rtastudio.com
www.rtaplans.com
www.dontbuyahouseplan.com

---------- FOLLOW-UP ----------

QUESTION: A few follow up questions.  

So to clarify, I cut the siding away, nail the flange to the studs and place a trim piece directly over the flange.  Then, obviously caulk the gaps.  Is there a standard trim width?  Is this trim a basic flat board or what is called "brickmold" or does it matter?  Can one cut away too much leaving the siding without adequate support around the window?  

Lastly, my current windows (wood) have a brickmold pieces that cover the seam between the window and siding.  The existing flashing goes over the head of the brickmold.  In this situation, is the brick mold considered part of the window or is it trim?  You said to bring the flashing over the top of the window frame and the trim piece is place on top.  This doesn't seem consistent with my current window installation.

Thanks again.  

Answer
The trim width will have to be big enough to cover the gap you cut to make room for the flange.  Since you don't have trim now, I'd make it as small as possible.  Most trim boards are 1 x 4, 1 x 6, etc.  Brickmould probably won't be wide enough, and large brickmould would probably be to elaborate for your house.

The siding's attached to the sheathing, so it doesn't matter structurally how much siding you cut away as long at the sheathing is intact.

In your case, the brickmould probably came already attached to the window - so there was no choice but to flash over it.

Richard Taylor, AIA
www.rtastudio.com
www.rtaplans.com
www.dontbuyahouseplan.com