Seal Interior and Exterior Casings (final)

Controlling the movement of air and heat through windows.
bobyapp
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Joined: April 25th, 2011, 11:17 am

Seal Interior and Exterior Casings (final)

Postby bobyapp » January 18th, 2012, 6:19 pm

Author: Bob Yapp
Contributors:
References:
Title of Treatment: Seal Interior and Exterior Casings
Class of Treatment: [ ] Maintain, [ ] Stabilize, [ ] Repair, [x] Upgrade, [ ] Exception
Type of Treatment: [ ] Traditional, [x] Modern

Condition to be Treated:
Gaps between the field of the wall and the exterior sill & casings and interior casings and related trim parts.

Description:
All exterior and interior trim is sealed to the field of the walls with a sealant to limit air infiltration.

Typical Procedure:

1. Inspect all gaps related to the exterior and interior trim around the window to determine areas that needed to be sealed to prevent excessive air infiltration.

2. If trim is loose re-nail it to tighten it to the window frame and the field of the wall. Pre-drill old wood to prevent splitting.

3. If gaps are wider than 1/4" insert backer-rod into gap and position slightly below adjacent surfaces.

4. Caulk all gaps and joints identified as potential air infiltration points.

Materials:
• Sealant, paintable, acrylic latex with silicon
• Nails, #8 hot dipped, galvanized, exterior casing
• Backer-rod

Quality of Results:
All loose trim and siding around the window opening, interior and exterior, is nailed tightly. All areas were caulked neatly where air infiltration could occur.

Best Work:
All interior and exterior trim and siding fastened tightly, so the wood is not cracked or split. All caulking done neatly and cleanly in lines with straight edges and with no stray smears or glops of sealant.

Adequate Work:
Minor splits in wood that is re-nailed with hot dipped, galvanized, exterior casing nails. Minor splits are caulked. All caulking done fairly neatly but not perfect.

Inadequate Work:
Lots of trim and siding not re-nailed or caulked. Large gaps filled with caulking and no backer rod. Not all gaps caulked to stop air infiltration around the window opening. Un-coated steel nails or drywall screws used to secure trim.

oculus
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Joined: May 18th, 2011, 12:15 am

Re: Seal Interior and Exterior Casings (draft)

Postby oculus » February 7th, 2012, 12:30 am

Sounds good to me. Would you change the type of caulk used if the siding was stained or natural?
Amy Harrington McAuley
Oculus Fine Carpentry, Inc.
http://oculuswindow.blogspot.com/
oculuswindow@gmail.com

"Opportunity is missed by most people because it is dressed in overalls and looks like work"-T.Edison

BirminghamPoint
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Re: Seal Interior and Exterior Casings (draft)

Postby BirminghamPoint » April 12th, 2012, 12:29 pm

Not sure if this is the right place to bring this up, but if you're going to be tightening up and air-sealing interior & exterior casings, and therefore limiting air infiltration in the wall assembly within the vicinity of the window frame, shouldn't a prerequisite to doing this be ensuring that the window is properly flashed? If you're going to be significantly reducing or eliminating the drying effect of infiltrating air, you'd want to make sure to prevent water/moisture from getting in, as much as possible. Windows on very old homes were not always flashed.

johnleeke
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Re: Seal Interior and Exterior Casings (draft)

Postby johnleeke » April 12th, 2012, 1:41 pm

Not sure if this is the right place to bring this up,...


John, if you thought of it here, then this is right place.

...shouldn't a prerequisite to doing this be ensuring that the window is properly flashed?


Possibly. Certainly, the need for sealing and flashing should be determined. The detail of whether or not a window is already flashed could be determined during the preliminary assessment. The Standards current include a method on Condition Assessment Documentation (draft):
viewtopic.php?p=536#p536

and a topic on Window Project Organization, to make sure the assessment happens:
viewtopic.php?p=358#p358

If you're going to be significantly reducing or eliminating the drying effect of infiltrating air, you'd want to make sure to prevent water/moisture from getting in, as much as possible. Windows on very old homes were not always flashed.


This is an excellent point. I am always railing on about how the air infiltration is an original feature of these old window systems that functions to keep the wood dry and limit decay.

It is very possible to seal up the windows too much, as some of us learned back in the 1970's energy crunch and the repairs we had to do just five and ten years later. Even in today's contemporary practice, some of the historic window specialists are on the "Seal It Up As Tight As Possible" bandwagon.

I think this standard needs to have a couple of qualifying statements, probably in the Description section, that cover the purpose and effects of this treatment:

==> adding the purpose of keeping liquid water out, yet allowing liquid water to drain out when it does get in

==> considering the benefits of the drying effect of infiltrating air, and assuring that the sealing up allows for enough drying effect to assure the long-term durability of the wood, especially at the lower joints of the frame, which might be dealt with at the sash weatherstripping that is not involved in this treatment of sealing up around the casements.

Also, the regionality of this treatment might be considered. I have seen the detail in Florida, Georgia, Alabama and Texas where the clapboards run underneath the exterior casing, leaving rather large (1/2" to 5/8") triangular gaps. Some water must get in there during a rain storm, but right after the storm the dry air whistles in there drying everything out--clearly functioning for a century or more without decaying. Is there flashing under there keeping the wall structure dry? Would this treatment of sealing up those gaps be an advantage or dis-advantage over the long-term?

And, we need to keep in mind that these Standards are not specifications. Someone on each project still has to determine what should and should not be done.
John
Standards Co-Founder
Standards Editor

http://www.HistoricHomeWorks.com

BirminghamPoint
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Re: Seal Interior and Exterior Casings (draft)

Postby BirminghamPoint » April 12th, 2012, 11:24 pm

Hi John. I see your point. We're not putting together a specification, so we're not going to prescribe specific steps to be taken beyond the standard treatments themselves. I suppose that, wherever a treatment might potentially cause a problem, we'd include a caveat to that effect, and possibly cite the condition assessment portion of the standard, if applicable. But it's up to users of the standards to determine if that concern is actual in their particular case, and how to deal with it. I think that's reasonable.

All of that aside, however, I gotta say that the issue of air sealing window frames and casings and making them airtight and potentially impacting the wall's ability to dry itself out is actually a deeper problem than it might at first seem. For example, you stated that an objective would be to do an adequate amount of air sealing, but not air seal too tightly. Which in principle seems reasonable, but how does one know what's the right degree of air sealing? Even were I to directly measure the before/after infiltration rates at some particular window, through out the air sealing process, how would I know what to aim for? 60%? 85% 90%? And even if I could reduce infiltration by some predetermined percentage, I still don't know if I haven't affected the air flow through the wall in some manner that would result in some area of the assembly not quite drying. My point is that there's really no good answer for this. (I merely point all this out as food for future thought or discussion; not as something for inclusion within the standard, necessarily... :-)

johnleeke
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Re: Seal Interior and Exterior Casings (draft)

Postby johnleeke » April 13th, 2012, 7:14 am

...the issue of air sealing window frames and casings and making them airtight and potentially impacting the wall's ability to dry itself out is actually a deeper problem than it might at first seem.


I fully agree that too much sealing up (and other practices like adding vinyl siding and insulation to exterior walls of wooded structures) can cause moisture buildup in the wall. The deeper problem, I would say it's a critical issue, is that there are many people working on these old places who don't know this. They don't understand how the earlier building technology operates to keep the walls dry, with air infiltration, the inner volumes of air in the stud spaces, etc.

...how does one know what's the right degree of air sealing?


I've never seen the kind of funding needed to objectively study this and come up with empirical numbers and rules. (Well, there was one case, the Warner House, Portsmouth, NH, where we had a Getty Foundation grant of huge proportions to study moisture over three years. I wrote a brief article about it for Old House Journal, Detecting Moisture, May 1996 (http://tinyurl.com/767odu3). The house is open to the public so I suspect the full moisture report is available, two 3" binders.)

I depend on my own experience from the 1970-90s, and make subjective judgements based on deteriorations I have seen, some of which I caused myself with too much sealing up. I now frequently recommend not sealing up as tight as possible. For example, when weatherstripping sashes, not weatherstripping the the bottom 4" of the lower stiles, so there is air infiltration to keep the sash and frame joints dry.

Or, not weatherstripping at all, or not sealing up around the casing boards. In one case, here in Maine, a client was getting ready to seal up a house that was never occupied in the winter, and did not have plans to occupy it in the winter. The house had stood for 150 years with just the right amount of air infiltration and zero deterioration due to moisture buildup. In the end they did not seal it up.
John
Standards Co-Founder
Standards Editor

http://www.HistoricHomeWorks.com

BirminghamPoint
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Re: Seal Interior and Exterior Casings (draft)

Postby BirminghamPoint » April 13th, 2012, 3:45 pm

Thanks so much, John, for both the convo and the link. I really appreciate it!


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