Replies

1. 
   Malcolm_Taylor | Jun 27, 2022 05:00pm | #1

   Boris,

   There are two schools of thought on this. Martin likes to prioritize drainage paths and drying, so he advocated no sealant between the trim and window. Others think stopping water intrusion should come first, and caulk around the window frame. If you are caulking, leave a suitable gap (3/16"). If you aren't, go tight.

   You don't have to worry about trim nails penetrating your flanges, but even though it's quite thin, the flange will cause your trim to lay at an angle. If the trim is being applied directly to the sheathing, you should rabbit out the back so it stays flat. If the trim goes over the cladding or furring, I like to keep the furring off the flange so the wall is co-planar.

1. 
   jamesboris | Jun 27, 2022 05:48pm | #2

   Thanks Malcolm. Especially appreciate the suggestion to keep the furring off the flange. I'd actually prefer to make it tight in this case, but making it tight raises 2 worries for me:
   1) What if the wood or the fiberglass expands a bit (Zone 2A) and causes some binding or other problems?
   2) I feel that rain tends to get into the smallest of gaps, but only tends to get *out* of 3/16"+ gaps... but you deal with much more rain than I do... what do you think?

   Any other downsides to shooting for tight? "Tight" is never as straightforward a word as I'd like when working with wood... largely why I avoid miters on anything exterior ha.

1. 
   Malcolm_Taylor | Jun 27, 2022 06:59pm | #3

   James,

   I've never had problems with expansion - and to be honest I go tight, but do caulk the joint. I just suggested a gap because that's best practice. Even in our wet climate, it's a rare occurrence to have wood expand over the dimensions that you buy it from the lumberyard. Maybe in hot humid regions that differs?

   When I take over as world dictator all miters will be banned, along with half the socket sizes and differing pressure-washer hose connections.

1. 
   jamesboris | Jun 27, 2022 07:09pm | #4

   So you run it tight -- kinda like pic 3 et seq here https://hammerandhand.com/best-practices/manual/4-rain-screens/4-2-top-window/ -- and then run a fillet joint of caulk on the frame itself?

1. 
   Malcolm_Taylor | Jun 28, 2022 12:00am | #5

   James,

   Yes exactly. I've attached a photo showing three windows on my own house, but I'm not sure you can see much.

   
2. Expert Member
   Michael Maines | Jun 28, 2022 08:15am | #6

   I leave about a 1/16" gap, mainly because I pre-assemble the exterior trim but also to allow for expansion since I typically use real wood. My intention is always to go back and caulk it but I rarely do and don't think it's a problem.

3. 
   seabornman | Jun 28, 2022 10:54pm | #7

   I have seen wood window trim expand and cause double hung windows to bind.

1. 
   jamesboris | Jun 29, 2022 07:52am | #8

   I've heard of this too, but there are a lot of variables. For example, I'd think steel or fiberglass frames are less likely to bind than vinyl or wood ones, since the latter expand too. Can you give some specifics on when you've seen this happen, and where? What kind of gap would you recommend? 1/8" maybe? Thanks!

1. 
   seabornman | Jun 29, 2022 08:46am | #9

   Yes. The siding was cedar clapboard. Trim was 5/4 pine. All wood was finished on all sides before installation. Windows were Andersen Narrolines, which have a vinyl wrapped frame and painted wood sash. I ended up routing out the trim where they met.