Reuben's Home Inspection Blog


Reuben's Quick Tip: Caulk Doesn't Belong Here, Part II

Last week I blogged about not caulking at the base of storm windows, which is a simple no-brainer. Another place that should never be caulked is the space between the siding and the flashing above a window; this piece of flashing is often referred to as drip flashing, drip cap, or head flashing.  Caulking this opening shut is a very common defect, even on new construction.

Caulked head flashing

Why not caulk here?  The head flashing at the window provides a drainage plane for water that could potentially get in behind the siding; the head flashing allows the water to drain out above the top of the window.  If the space between the flashing and the siding gets caulked shut, where will water go?  It will get trapped behind the siding and potentially cause damage to the home.

Some siding manufacturers already require this space to be left open, such as fiber-cement siding manufacturers.  Unfortunately, this detail isn't spelled out in any window installation instruction manuals, or if it is, I haven't found them yet.   I also haven't found any vinyl siding manufacturers that specifically say "don't caulk here".  For fiber-cement siding, it's an installation defect.  For just about any other type of siding, including vinyl, it's a 'best practice' not to caulk here. 

Don't caulk head flashing

Just wait though... I'm sure that the manufacturers of windows and other types of siding will catch up on this detail soon enough, and they'll start explicitly telling you "don't caulk here".  Installation instructions for windows are getting longer and more specific every year.  Case in point: about ten years ago, Windsor Windows published a one page installation sheet; today it's aten page installation manual.  Did the windows change significantly?  No.  Manufacturers are just doing their part to help prevent failures from improper installations.

Is this really a defectWell, technically no, not on all installations.  It's not a defect until the manufacturers put it in writing or it's specified in the building code... but it sure isn't wise.

Reuben Saltzman, Structure Tech Home Inspections


Comment balloon 35 commentsReuben Saltzman • November 16 2010 06:04AM


Didn't know that - seems that everyone wants everthing caulked these days. Thanks for the post.

Posted by K.C. McLaughlin, Realtor, e-PRO, Homes for Sale - Cary, Raleigh NC (RE/MAX United) over 8 years ago


From a one-page instruction sheet to a ten-page manual - that tells you something about the intricacies of installing windows. The "do not caulk here" verbiage also needs to be included.


Posted by Claudette Millette, Buyer, Broker - Metrowest Mass (The Buyers' Counsel) over 8 years ago

Hard to mandate common sense Reuben.  But hey, isn't that what duct tape is for?



You knew that was coming, didn't you...?     ;)

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 8 years ago

K.C. - that's exactly it.  Caulk has it's uses, but it doesn't belong everywhere.

Claudette - I agree, the manufacturers need to start specifying this.  I think it will be coming soon.

Jay - ha!  Well done.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 8 years ago

Very good point. Thanks for the tip.

Posted by Surprise Arizona Realtor Jim Braun Sun City Grand Active Adult Communities, Surprise AZ real estate Phoenix West Valley (Coldwell Banker Residential Brokerage Jim Braun Sun City Grand Az ) over 8 years ago

Ruben, it seems logical to caulk it to seal the open space. A good point where logic doesn't prevail. Thanks for the tip.

Posted by Michael Setunsky, Your Commercial Real Estate Link to Northern VA over 8 years ago

Great tip Ruben,  I would have most certainly caulked that area.  It's good to know in case I ever get near a caulking gun.

Posted by Mike Leibel, Associate Broker - REALTOR® (CIR Realty - Condo Specialist) over 8 years ago

Great info, and great series.  These all make sense, but I can tell you that I have seen hundreds of windows that are caulked between the flashing and siding.

Posted by James McGary (Agents Set Free, Inc) over 8 years ago

Reuben, I think some people go for the the "neat look" over "what works"-----every time.

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) over 8 years ago

Good post and information Reuben. Thanks for getting this and other good tips out to us on AR.

It's appreciated.  Please keep the help/tips coming.

Patricia/Seacoast NH & ME

Posted by Patricia Aulson, Realtor - Portsmouth NH Homes-Hampton NH Homes (BERKSHIRE HATHAWAY HOME SERVICES Verani Realty NH Real Estate ) over 8 years ago

Good info. Not sure I would have ever paid attention to the area above the windows.

Posted by Dustin McClure (Mossy Oak Properties Outdoor Realty) over 8 years ago

Reuben - Great Post and always funny to see how people try to fix stuff... How about Duct tape? Just

Posted by Robert and Lisa Hammerstein -201-315-8618, Bergen County NJ Real Estate (Keller Williams Valley Realty) over 8 years ago

Jim - thanks for reading.

Michael - that water needs to get out somewhere.

Mike - I hate to say it, but I've been guilty of doing that myself before I knew better.

James - you and me both.

Charles - that's especially true with your point about caulking between tiles and tubs.

Patricia - thanks, glad to help.

Dustin - now that you know, you'll start seeing it everywhere.

Lisa and Robert - I think duct tape would do a much better job of allowing water to drain here than caulk would :)

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 8 years ago

Well Reuben, I'm going to have to relay this to my DIY boyfriend who is pretty sure that caulking works for all problems.  I can't tell you how many items on our property have their equal weight in caulking!

Posted by Dee Bundy, Helping You Make Colorado "Home" (Fort Collins Realtor @ C3 Real Estate Solutions) over 8 years ago

Interesting Reuben. Definitely need to make a note of this. Thanks.

Posted by Denise Hamlin, Broker/Owner, Helping Happy Clients Make Smart Choices (Cardinal Realty ~ 319-400-0268) over 8 years ago

It certainly would be much simpler if you diagram was just included with every window.  People have a hard time reading, but they love looking at pictures.  

Posted by Simon Mills (Mills Realty) over 8 years ago

A good example of why people should keep warranties for everything they install into/onto the home. Much easier to hand a binder to a contractor than to try and remember these things. Also nice to have to hand over to a buyer...shows that the homeowner was responsible.

Posted by Leslie Ebersole, I help brokers build businesses they love. (Swanepoel T3 Group) over 8 years ago

Danielle - I don't think he's going to like me much after reading this!

Denise - thanks.

Simon - wouldn't it?  I'm pretty sure you'll start seeing this same diagram a lot more.

Leslie - great point.  Hopefully that stuff will be digital soon, and we won't have to worry about holding on to a stack of paperwork.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 8 years ago

From my framing days, one of my favorite window installation instructions was the big red decal on the nail flange at the top of the window that stated:


This, of course meant that we were not to nail the top flange to the window opening header in case the header sagged / moved.  However, after the windows were secured, we would take the decals off and put them on our pneumatic nail guns as a reminder.

Posted by Mike Weber, 40+ years in Northern Colorado (Keller Williams Realty Northern Colorado) over 8 years ago

I really like your blog!  I'm not sure I posted in the comments when you blogged a few weeks ago about the need for an inspection with new construction, but I placed a link to your blog from my FB page.  That blog was so extensive and educational that I hoped some readers would find it and be awed as I was.

Keep up the good work!  You are awesome!

Posted by Kate McQueen, Tailored service for your real estate needs! (CB&A Realtors) over 8 years ago

Oh!  Forgot to mention -- I used to sell doors and windows at a large well known retailer and learned some good stuff while there.  But windows are sometimes more complicated than people think, at least for people that are not in a construction/inspection type of trade.

Posted by Kate McQueen, Tailored service for your real estate needs! (CB&A Realtors) over 8 years ago

Mike - that's a great idea for the manufacturers to put that warning on the windows.  It's tough to get that one wrong.

Kate - thank you so much!  My wife used to work for Pella windows, and I actually learned a few things about windows from her during that time.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 8 years ago

Just found your blog. Great information! It seems like the homebuilders I come across either use caulk on EVERYTHING for no rhyme or reason or simply don't use enough caulk on anything. Leaving caulking off under the flashing seems so intuitive when you see the diagram of how it is supposed to work.


Posted by Thomas Miller over 8 years ago

Thanks for the tip, I did not know that.  I always enjoy learning new things from the HI's standpoint.

Posted by Justin Dibbs, REALTOR® - Ashburn Virginia Homes for Sale (Pearson Smith Realty) over 8 years ago

Thomas - thanks, diagrams certainly help.  I wanted to construct a model window for this one, but it would have just taken too much time.

Justin - thanks, glad to help.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 8 years ago

The installation manual has probably gotten longer due to complaints from consumers because of what are installation defects, not manufacturing issues.

Posted by James Quarello, Connecticut Home Inspector (JRV Home Inspection Services, LLC) over 8 years ago

Reubs:  my dad just mentioned that drip cap should never be caulked, which no one had ever mentioned to me before.  I hadn't read it on any installation isntructions either.

So I did a Google search for "Should the drip cap be caulked to siding" and what comes up?  Your outside blog!  Here's a screenshot of the results below.

Once I saw it was your blog, I was instantly convinced of the errors of my ways.  We'll stop caulking the drip cap to siding joint and be sure to flash the top of the drip cap.

Do you have any recommendations for proper flashing with the short PVC drip cap that is sold?  Door & window tape?  Or door & window tape over metal flashing?

Drip cap caulk search results


Posted by Jeremy Wrenn, C.O.O., Winslow Homes (Winslow Homes) over 7 years ago

Nice!  It's all about the long tail searches, my friend :)

My preference would certainly be door and window tape over metal flashing.  Here's an excellent slideshow showing how it should be done -

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 7 years ago

Reuben, we don't have a brake machine to make metal drip cap, and we've not found a supply locally, so we use the PVC drip cap instead.  The PVC drip cap doesn't really have a tall profile (only 11/16" tall, East Coast profile 197) to go behind the siding, which is why we have been caulking it.  We've caulked it to keep the water out from behind the siding, as 11/16" of an inch is not much protection.  The 188 profile, which is 1-1/16 tall isn't available locally, but isn't much better.  (Everyone only sells the aluminum drip edge, for going under shingles.)

That's why I was envisioning having to add metal flashing, with tape at the sheathing.  But even with that, the metal flashing wouldn't really have much lip to cover on that EC197 profile.  So until we can find a supplier for the metal drip cap, I think we'll have to keep caulking the siding to drip cap to keep water OUT from behind the siding.

Your thoughts?

Posted by Jeremy Wrenn, C.O.O., Winslow Homes (Winslow Homes) over 7 years ago

Different types of construction require modification to typical "common sense" details.  Vinyl  "J" channel would require a bead of caulk as Jeremy touches with his comment.  If you do wood shingle application where an air gap is left behind the shingle with a drainage plane you would need flashing of some sort and no bead of caulk.  Water would certainly channel its way back behind "J" channel in any installation as shown in your picture and I would focus more on the fact that the "J" channel pictured is installed incorrectly in my book.

Posted by Brian almost 7 years ago

Brian is correct and you are very likely incorrect calling out no caulk in that specific installation in the photo.  Furthermore, if you go to any major name brand window manufacturer, that area above the window where J-channel finishes the vinyl siding to the window it is often called out as a 3/8" maximum gap with backer rod and sealant your window installation instructions as it could void warranty if you install it incorrectly.  It is typical to seal around vinyl windows as shown because vinyl moves, expands and contracts far more than any other type of window with hot and cold weather temperature fluctuations.  My own vinyl windows installed on my home with vinyl siding and J-channel have a bead of sealant to prevent moisture from tracking back under the j-channel and wicking up behind the siding.  The J-channel is installed very much the same as you would flash-tape a window where the bottom is installed and then the sides with the top peice of J-channel being the last and the ends cut long to cap off the side peices of channel and allow positive drainage of any water that drains down the siding to the top of the window.  I have seen where they used housewrap tape to seal off the top of the J-channel to create a path or positive drainage plane behind the siding because moisture does condense behind the siding...not quite sure if it's correct to do so but the concept with vinyl siding installations using J-channel makes sense to me to create a positive drainage plane over the top of a window or door.  Remember, not one person be it inspector, homeowner, installer, or engineering professional has every single answer out there to every single construction detail.  I would caution anyone who installs a vinyl window to follow Reuben's quick tip because you could "potentially" create a problem or even void your windows warranty if you do not follow the manufactuer's installation instructions..."""ALWAYS READ YOUR WINDOW MANUFACTURER'S INSTALLATION INSTRUCTIONS AND GUIDLINES"""  This very detail is often always covered.   So, to propery address this issue and Reuben's quick tip I write: "When properly using "drip flashing" in the correct manner in the building industry you never caulk the path of positive drainage in the drainage plane.  Be sure to check your installers credentials and be certain that they are properly licensed and insured to do such work as your home is the single most biggest investment you will make."

Posted by Lee almost 7 years ago

Jeremy - revisiting this thread made me realize I never answered your question from last year.  I don't have any great advice to give you on that East Coast Profile drip cap; the only time I ever see anything like that is on really old houses.  

Brian - every authority on this matter that I've ever spoken to and everyone teaching classes on this subject has always specified no caulk above the drip cap, no matter what type of siding is being installed.  

Lee - can you show me a window installation manual that specifies caulk above the drip cap?

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 7 years ago

I have to revise this blog.  I said that the detail of omitting caulk at the top of the window isn't specified in window installation manuals, but it really is.  In fact, it's specified right in the manual for 2008 Windsor Windows, which I included a link to in this post - .

Look at step 7 in the installation instructions; these are non-siding specific instructions, and they specify leaving out sealant at the top of the window in their diagram.  The text also says 

B) After you complete the siding or wall exterior, apply backer rod and 100% neutral cure silicone sealant between the window frame and siding material on both sides and sill.

I added the underline.  

I'm certainly not claiming to be an authority on this matter; I'm only repeating what every authority on this matter says, and I'm re-iterating what manufacturers specify in their installation instructions.  

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 7 years ago

Pella very clearly details this but they also have a clause to cover themselves in this can be interpreted many different ways and is often a gray area in any discussion.



Posted by Lee almost 7 years ago

My siding guy says this...Why not caulk the top and caulk the side and bottom?  If the water should wick back behind the siding from the top J-channel being left open then the caulk on the side and bottom will retain moisture around the window like a bag if there are any voids.  He says they install siding with a positive drainage plane over the top J-channel and thus caulk the J-channel according to the Pella detail.  He said that drip cap flashing is only required when trim is applied to the window that would be likely to rot and need to be protected same for wood windows and even more specific details that need not apply to vinyl window installation.  He jokingly said "when a vinyl window rots because of moisture apply drip cap flashing.  He has been doing this for almost 40 years and never had an issue with inspectors or Pella reps visiting the site.  I am a  designer and understand the many, many different details that require drip cap flashing and this one has always been a gray area...I just would not be so quick to take a photo and call it wrong if it was a gray area where there are manufacturer's that support that detail.  I am going to bow out of this post now and felt I would question this specific detail with my two pennies worth of experience.

Posted by Lee almost 7 years ago