Joined: 20 Aug 2004 Posts: 2946 Location: Portland, Maine, USA
Posted: Tue Jun 30, 2009 10:29 am Post subject: Weatherstripping.
(update: 5/20/14 update link to rolled video)
Weatherstripping limits air flow around the edges of the sashes and is often installed to improved the energy performance of the window.
When creating an energy-efficient home through air sealing techniques, it's very important to consider ventilation. Unless properly ventilated, an airtight home can seal in indoor air pollutants. Ventilation also helps control moisture—another important consideration for a healthy, energy-efficient home with low maintenance and repair costs.
Your home needs ventilation—the exchange of indoor air with outdoor air—to reduce indoor pollutants, moisture, and odors. Contaminants such as formaldehyde, volatile organic compounds, and radon can accumulate in poorly ventilated homes, causing health problems. Excess moisture in a home can generate high humidity levels. High humidity levels can lead to mold growth and structural damage to your home.
The design of traditional double-hung wood windows is highly effective because it has been developed over the past four centuries. One of the aspects of this effective design is air infiltration. A little bit of air is always moving over the edges of the sashes, keeping the wood dry and decay free. Sealing up the edges of the sashes too much limits this drying effect and can lead to rotten sash and frame joints. Some of the window repairs I have done over the past thirty years were needed because they were sealed up too tightly during the 1970s "energy crunch." Can we learn from this lesson and not seal up our remaining original wooden windows with too much weatherstripping? With that said, weatherstripping does SOMETIMES make good sense.
Different types of weatherstripping are used depending on how the edge of the sash meets or moves in relation to other parts of the window:
Sliding, along the sash edge. as with double-hung windows where the vertical stile of the sash slides up and down in the track along the jamb of the frame.
Sliding, across the sash edge. as with double-hung windows where the horizontal top rail of the lower sash and bottom rail of the upper sash meet in the middle of the window; and as in casement windows where the top, bottom and latch-edge meet the frame.
Compression, pressing the sash edge. as with double-hung windows where the bottom rail of the lower sash meets the sill and the top rail of the upper sash meets the header of the frame; and as in casement windows where the hinge edge meets the frame.
Metal, durable, long-lasting
Silicone Rubber, flexible in cold temperatures, somewhat durable.
Plastic, some types such as vinyl are not very durable, and generate pollution and health problems for people where it is produced. Polypropylene plastic and Mylar may be longer lasting.
Traditional Materials: Felt, leather, heavy canvas, cotton and sisal caulking, have been used in the past for weatherstripping. It can be interesting to recreate these when remnants are encountered, though this custom work can be labor intensive. These materials are now considered more "sustainable" and may begin to play a roll in some products and projects.
(see this message in this discussion:
Dorbin Metal Strip Manufacturing Company Inc, Kris Duda, located at 2404 S Cicero Ave Cicero, IL. Phone: 708-656-2333
(they do not seem to have a website, their prices may be significantly lower than Accurate. Call and Kris will email you a catalog.)
Available online at ABSupply:
Accurate Metal Weatherstrip Co. is now out of business. (Nov. 2018)
Fin, Pile & Kerf, or Brushseal: slightly flexible polypropylene plastic backing with a barb that fits into a kerf in the sash, and a plastic Mylar fin centered in a soft fuzzy pile, the pile holds the fin in place, the fin seals out the air
A single touch of paint on fin & pile will ruin it. Complete all painting before installation. This may happen during future maintenance. With all weathering stripping that has a fuzzy pile, I put a permanent sticker in the sash track that says and shows: do not get paint on the fuzzy pile.
Many types of weatherstripping require grooves along the edges of the sashes. Cutting grooves is easily done with a hand-held router. the Bosch PR20EVSK Colt Palm Grip 5.6 Amp 1-Horsepower Fixed-Base Variable-Speed Router with Edge Guide works well.
Fin, Pile & Kerf
At the Video Conference replays you can see Fin & Pile weatherstripping being applied to the edge of the sash:
When a kerf (or groove) must be cut along the edge of the sash, weakening of the sash should always be considered. The kerf is typically 1/16 to 1/8" wide by 3/16 deep. If the sash does not have a cord groove in the edge there is usually plenty of room for the kerf. Also consider if the kerf will weaken the joints significantly. If the sash has a cord groove and is thinner than 1 1/2" there may not be enough room for the kerf between the groove and the face of the sash. Usually there is enough room for the kerf on sash thicker than 1 1/2", although exceptionally wide cord grooves may not leave enough room for the kerf. Sometimes I have filled wide cord grooves with a dutchman and re-cut narrower cord grooves to make room for the kerf. I have also put fin & pile on stops and parting beads.
To fasten spring bronze (both rolled and V) to sash tracks you can use the little bronze nails that come with the weather stripping. The little nails take quite a bit of time to set just right without denting or buckling the weatherstripping. A trim nail punch can help hold the nail then you tap it in with a hammer:
Malco TNP2R Trim Nail Punch
Dave Clark says, "I use Duo-Fast galvanized staples. I found even in this mild humid climate the standard staple rust away, especially on the coast. I have not found the galvanized staples to fail me."
Staples: Galvanized, about $10. for 5,000 count box. Stainless staples are nearly 10 times the cost, and are corrosion resistant but may be too soft to penetrate thicker metal weatherstrips. Use "chisel point" staples, not "divergent point."
"I am now sometimes recommending against highly effective weatherstripping for two reasons. 1. The human body needs fresh air for good health. In the 1970s the death rate from emphysema went up 500%+. What else happened in the 1970s? We hand three 'energy crunches' and started sealing up our buildings. Health experts say that rise in emphysema deaths rates is directly attributable to significant decreases of indoor air quality. 2. The original intent of the double-hung design is to have some air infiltration which keeps the wood dry and decay free. I have seen too many fine old windows rot out from the "seal it up real good" treatment applied in the 1970s.
There are many many other much more effective ways to deal with energy costs and occupant comfort than installing weatherstripping! Air infiltration at all points in the walls including windows can be significantly limited in this type of building with the installation of dense-pack cellulose insulation in the building's horizontal planes (between floors and ceilings), which dampens the 'stack effect' of rising warm air that sucks in air low in the building and pushes it out high in the building.
Why does "no weatherstripping" sound so upside down crazy? Because everyone has been brainwashed by the consumer economy masters and the building products industry. Can we please apply rational thought and our own experience to weatherstripping instead of trusting the corporations and big government whose only interest is grabbing our money?" -- John Leeke, Portland, Maine
Seal up the Interior or the Exterior?
Whether or not the interior or exterior of the window system (storm or shutters, primary sash, interior air panel, interior roller shade, drapes, etc.) should be sealed up depends on the general climate at the building location. Way up north the interior primary sash or air panel should usually be sealed up during the winter, so warm moist air does not get into the system and condense due to the cold exterior air. Way down south the exterior storm should usually be sealed up during the summer, so the warm moist exterior air does not get into the system and condense due to the cooler air-conditioned living space. Sometimes it depends on the micro-climate along a wall (sunny warm south & west, shady cool north & east) or even at a specific window, or what is happening within that building even within a specific room.
According to information newly released at the recent energy conference in Boston, the DoE is now sometimes recommending NOT sealing up the exterior OR the interior in the in-between states with a moderate climate.
As usual, there are no pat answers, and no "one size fits all" in the real world of caring for older buildings. Everything is a balancing act that requires rational thought and spiritual intuition. Steve has it about right: "...just going by the traditional wood storms I have seen and am familiar with..." Forget what other people tell you and pay attention to the real world around you and the people you serve.
In fact, most of what we do to the windows now has a minor effect when compared to how the building occupants of today use the windows and what the occupants of tomorrow will need (what happens when we run low on energy in ten years and can't air-condition our buildings? There will be a lot of unsealing going on, and a lot of cursing for the sealing up we have done.)
Joined: 20 Aug 2004 Posts: 2946 Location: Portland, Maine, USA
Posted: Wed Jul 01, 2009 10:47 am Post subject:
> As you know I am promoting weatherstripping and want to make sure I do
> not cause more problems than I create.
It is OK to promote it, but always with knowledge and foresight about what good it can do and what problems it can cause. To simply promote the most tightly sealing weatherstripping in all cases will lead to some cases where it causes problems.
The edges of the sashes are always left bare wood so the wood can give up its moisture as the air infiltrates past the surface of the edge. The principle issue is that any weatherstripping limits this drying effect, moisture builds up in the wood, and typically the joints (where there is the most moisture), are infected by fungus and decay. Lower sash joints are most affected.
One 'standard treatment' is to fill the weight pockets with insulation. Another is to add storm windows and seal them up real tight to the sill along the lower edge. Both of these plus weatherstripping can lead to decay of the sill and frame jamb joint.
So, in what cases should weatherstripping not be installed? If the windows are important historic material that must be preserved (say an historic house museum), then look for other ways to save energy dollar or to provide human comfort (there are many). If there are windows under eaves where there can be no gutters, then that may be a high moisture situation for those windows and then may need drying air infiltration to keep them rot free. Windows on the north and east get less sun so need more drying by other means, such as less weatherstripping. Where ever you see lower joints rotting out, that is an indication high moisture that may be mitigated by less weatherstripping.
Sometimes we install weatherstripping, but cut it short at the lower joints, especially next to the sill, leaving about 4" of the sash track without weatherstripping. This still gives some drying effect right where it is needed near the sash and frame joints.
Now, you must understand that this is a 'radical' idea that will seem upside-down crazy to most people because they have been brainwashed by the building products industry that if you are not replacing your windows you must weatherstrip the bejezis out of them, even better seal them up with silicone caulk--DON'T DO IT.
So, like everything else, do weatherstripping in moderation. After all, there are many more effective ways energy dollars can be saved and people made comfortable and all of those should be done before any weatherstripping.
What do you think? _________________ John
by hammer and hand great works do stand
by pen and thought best words are wrought
Last edited by johnleeke on Wed Nov 27, 2013 9:54 am; edited 1 time in total
This is getting right down to the heart of it John, to air seal or not to air seal.
Or that is my take on this thread.
I am thinking of a three-legged stool in this situation:
the legs being
resource efficiency-keep the old and reduce land fill deposits
energy efficiency-reduce energy consumption
Health and comfort.
Those are your three legs.
Now we need a seat for this stool and I see that as durability. Whatever we do must be durable.
If we are going to cover the seat with anything I would use moisture management.
With that in mind I want to look at the low hanging fruit and even the stuff on the ground.
For me that is air sealing.
It seems to me that if air sealing wood windows decreases durability that the problem might be something else.
Of course there are several other considerations with climate being the most obvious and than building siting next and finally usage.
Here in a hot-humid climate with 60 inches of rainfall a year we are certainly exposed to moisture.
I see decay and window failure w/o air sealing.
I would like to better understand your position on how we can airseal and maintain durability.
Much thanks _________________ Bill Robinson
Yesterday I was assessing four houses to make a proposal on restoring the windows.
Up to this time I have been looking as a couple of windows at a time.
Here there are 'bout 40 windows.
That is why I am looking for a checklist or worksheet to make future assessments.
So, as probably most practiced window restorers already know there are a few typical places where rot, decay and joint failures typically occur.
IN addition to the locations you have identified as needing treatment I am seeing a gap, literally, where the sill and jamb legs intersect.
This is causing decay in the framing under and here in NOLA the Formosans are not far behind.
This is the durability part of the equation.
I have not gone through all of the threads here---yet...so if you can offer suggestions on how to seal that joint I am ready.
My solution would be to create a correct sealant joint and use a polyurethane paintable sealant to stop the water leak.
I am here to learn so please earn me. _________________ Bill Robinson
Last edited by BillRobinson on Thu Jul 02, 2009 11:46 am; edited 1 time in total
Joined: 20 Aug 2004 Posts: 2946 Location: Portland, Maine, USA
Posted: Thu Jul 02, 2009 11:43 am Post subject:
low hanging fruit and even the stuff on the ground
There is nothing wrong with focusing on windows, but there is much lower hanging fruit to be picked before anything needs to be done with windows. A whole house, or even whole neighborhood approach can be more effective.
A useful problem solving axiom is the closer you get to the root cause of the problem to implement the solution the more effective is the solution.
If the problem is the cost or amount of energy used, then what is the cause of high costs and amounts? Energy loss at windows is a part of it, but moving closer to the cause brings us to the heating or AC unit, this is where the energy is expended. Upgrading to a high-efficiency unit can save far more that anything done at the windows. To get even closer to the cause, go to the supplier of the energy, and negotiate or regulate for lower costs.
So, back to windows, go ahead and seal them up. We just need to be sure to include in our thinking and payback calculations the expense of protecting wood from decay, or the future costs of repairing decayed wood.
Keep in mind that I'm not saying that all weatherstripping causes decay in all cases, I am applying the subtle lessons learned during the last energy crunch. It's interesting to note that the 1970s energy crunch was also associated with economic recession.
The big problem with windows is not loss of energy. It is that, over the past five decades the building products industry convinced the American public that they should simply ignore their windows, let them deteriorate and then replace them with cheap goods. They also set up the expectation in the "public mind" that everyone could live like the wealthy folks who have servants to take care of daily household work, like opening and closing shutter, sashes, curtains, etc. "You can be comfortable just like the wealthy, all you have to do is buy this fancy window (that even includes a window air-conditioner), that does it all, and then forget about your windows." Well, it was just a ruse to sell fancy windows and air-conditioners. Without care the windows rot out, the air-conditioners breakdown, and guess what, you can buy more windows and more air-conditioners. _________________ John
by hammer and hand great works do stand
by pen and thought best words are wrought
Joined: 29 Oct 2008 Posts: 569 Location: Plymouth, Indiana
Posted: Thu Jul 02, 2009 12:41 pm Post subject:
But the problem is not only the cost of energy used.
Comfort has to enter into the equation, regardless of how many sweaters we are willing to wear. I don't think you'll ever win the argument of no weather stripping when the breeze from your window is turning the pages for you on the book your reading. Part of the enjoyment of living in an Historic home is the enjoyment of using it.
I am not an advocate of over weather stripping. I do think appropriate weather stripping should be simple. And in a few places of an old double hung window its crucial.
I think an outside storm window is all important. It automatically protects the windows sash and most of the sill and jamb from the elements and stops most of the wind from entering the home. An outside storm and minimal weather stripping of the prime sashes is the best idea for stopping drafts and protecting prime sashes.
I don't think an interior storm (or insulating panel) is good if left on all year. And when using an interior insulating panel the homeowner needs to be aware that it may very well be creating a dead air space between it and the prime window. I think a dead air space is not good between the prime window and an interior window because it will most assuredly promote moisture accumilation resulting in mold or mildew and rot! I think the prime sashes must have circulation of interior air of the home.
I also think that people need to open their windows more often and enjoy nice days, instead of relying on air conditioning and heat all the time. One of the most common remarks from homeowner when I'm assessing their windows is " You won't need to make that window operable we never use it." I then go into my 2nd layer of my customer on site education, on the value of the engineering of their original double hung windows. Most customers actually listen and some even start using their window how they were designed to be used. When something is not used it starts to deteriorate. The old saying is still true "Use it or lose it"
In what little I have done it seems the tighter (read no rattle) window is much appreciated.
Less rattling when the wind blows and when operating the window.
I have to think that even average windows when new were somewhat secure in their sashes.
maybe not. _________________ Bill Robinson
Doors leak twice as much air as windows. Coupled with the fact that doors also are used more often than windows, you can see why their seals merit careful inspection.
Check for crimped, flattened, or missing weather stripping at the top and sides. You might be able to adjust spring metal by prying lightly on the spring section. Other types probably will have to be replaced.
Feel along the threshold. Air infiltration means you need to seal the bottom of the door as well. And how's the door itself? Warping, an out-of-square frame, or deteriorated caulk around the edges give air a chance to make an "end-run" around even the tightest weather stripping. Examine storm doors, too. Some metal versions have a bulbous gasket along their lower edges; others employ a sweep. Both must be replaced periodically.
Check out any interior doors that open to an attic, garage, basement, or other unheated space. Builders often don't bother to seal these big heat-losers at all. Worse yet, some contractors cut costs by installing hollow-core doors that have little if any insulation value. If that's the case at your house, your best bet would be to invest in the far greater thermal efficiency of a solid- or foam-core door. _________________ Window Air Conditioner Units
Joined: 10 Sep 2007 Posts: 24 Location: Wilmington, DE
Posted: Thu Feb 11, 2010 4:59 pm Post subject: V vs. standard spring bronze & leaky (not Leeke) sash pu
Either I've totally missed it here or it's never really been discussed, but when would V spring bronze be used over the standard spring bronze? Does the V spring bronze cover a wider gap? I would think that the standard spring bronze can be tweaked by running something across the crease causing it to spring more. Perhaps it's just a matter of preference.
Also, a potential client of mine had an energy audit done where the pulleys seemed to be targeted as major air infiltrators. What possible weatherstripping or insulating solutions are out there for this? I've seen pulley covers online but once again feel that the energy auditor is in cohoots with some cheeseball replacement window company. I feel that this may boil down to making the window & weight pocket so air tight that decay and moisture buildup in the future would be an issue.
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