Metal Interlocking Weatherstrip (draft)

ATBagala · **Posted:** January 25th, 2012, 1:40 pm

Number:
Status: [ ] submitted work method, [x] proposed treatment standard, [ ] final treatment standard
Update: 2/15/12
Author: Marc Bagala
References: Metal Interlocking Weatherstripping: Ordering and Installation Guide, Marc Bagala
Contributors:

Title of Treatment: Interlocking Metal Weather-strip for Double-Hung Windows
Class of Treatment: [ ] Maintain, [ ] Stabilize, [ ] Repair, [x] Upgrade, [ ] Exception
Type of Treatment: [ x] Traditional, [ ] Contemporary, [ ] Conservation

Condition to be Treated:
Air infiltration around window sash. Sash that are difficult to move in window openings.

Description:
Metal interlocking weather-strip (MIW) is a traditional method of stopping air infiltration around window sash. It increases the energy performance of traditional windows, improves comfort by eliminating drafts, results in an easy to operate window, provides an aesthetic means of weather-stripping and is extremely durable. MIW is often found still functioning well where it was installed over 100 years ago. This standard is for adding weatherstrip windows that do not have it.

Typical Procedure:
1. Mark and trim (if necessary) both upper and lower sash to allow proper tolerance for weather-strip between jamb and sides of sash.
2. Slot upper and lower sash on three-sides, excluding the meeting rail side.
3. Modify the upper and lower meeting rail to accept weather-strip.
4. Attach weather-strip to upper and lower meeting rails.
5. Hang the upper sash in the window opening, with sash cords and weights complete.
6. Cut upper sash weather-strip to size.
7. Place upper sash weather-strip at the head and sides of the window jamb.
8. Nail upper sash weather-strip in place.
9. Install parting bead.
10. Hang bottom sash in window opening, with sash cords and weights complete.
11. Cut bottom sash weather-strip to size.
12. Place bottom sash weather-strip in the sill and sides of the window jamb.
13. Nail bottom sash weather-strip in place.
14. Replace interior stops.

>>15. Install wheel covers, if desired, to stop air infiltration in the wheel area.

Materials:
• 8 pieces of interlocking metal weather-strip
• Weather-strip nails
• Sash cord
• Parting bead

Quality of Results

Best Work: Windows work in an unhindered fashion and go up and down smoothly in the window opening. Meeting rails meet properly and lock together tightly. Weather-stripping covers the entire perimeter of the sash. Air infiltration is eliminated or significantly reduced.

Adequate Work: Window is moderately too tight or too loose in opening. Meeting rail weather-strip requires pressure to lock.

Inadequate Work: Window binds in window opening, or fits too loosely in opening. Meeting rails do not meet correctly. Gaps in weather-stripping allow air infiltration.

johnleeke · **Posted:** January 26th, 2012, 2:51 pm

Marc & Ann, thanks for submitting this method. I like the concise, yet detailed, way you present it.

Here is an initial suggestion:

On steps 5 and 10:

>>5. Hang the upper sash in the window opening.<<

I'd like to edit that by adding a mention of the sash cords and weights:

5. Hang the upper sash in the window opening, with sash cords and weights complete.

Is that accurate?

johnleeke · **Posted:** January 26th, 2012, 2:56 pm

The photos are excellent.

I notice that they are 300dpi (which is good), but they are 1.2" x 1.7" in size. Can you provide the same photos with files that are larger, say 3" x 4"?

ATBagala · **Posted:** January 26th, 2012, 3:14 pm

Hi, John,

Re: steps 5 and 10, yes, that would be accurate. Thanks.

I'll get back to you re: the photos.

Ann

Martin Muller · **Posted:** February 29th, 2012, 11:42 am

Thoughts on Metal Interlocking Weather-stripping (draft) portion of “The Standards Document.”

By Martin Muller

My compliments on including the “traditional” metal interlocking weather-stripping in the proposed standards document.

The following thoughts are based on my experience (15 years) with metal interlocking weather-stripping as encountered in existing situations here in western Washington (mainly Seattle, but also in surrounding areas). I have extensive experience repairing this system as well as adding it to existing windows.
I have used both Pemco and Accurate Metal Weatherstrip products. Currently I use the Accurate product, with slight modifications. I locate the meeting rail hooks at the bottom of the meeting rails rather than in the center (as shown in their diagrams) since that is how I always find it in original installations. Second, I use the corrugated strips on all three sides of the sashes, rather than using a mixture of flat (header & sill) and corrugated strips (jambs).

A few thoughts:

- Under Class of Treatment mark “Maintain” “Repair” as well as “Upgrade” to reflect that repair of existing (but missing or damaged) weather-stripping is included in the standard.

- Under Description I think it is fair to increase from 50 to 80 the age at which this product is still found in good working condition.

- Typical Procedure:
General) At what gap dimensions does installation of this product becomes advisable? I would suggest we incorporate some hard numbers. I typically suggest this option if the play (side-to-side of either upper or lower sash or in-and-out of mainly the upper sash) between sash and jamb is equal or greater than the gap required to install the weather-stripping.
For the side-to-side play I use the following guideline: Since the products I use is 1/16” thick, I typically use 3/16” or more play as a guideline. Allowing for thickness of two strips plus some play (1/32” – 1/16”on either side).
If after addition of the side strip the side-to-side play is more than 1/8” recommend installing filler strips between the jamb and backside of the weather-stripping to reduce the “opening” to no more than 1/16” wider than the sash.
For the in-and-out play I typically recommend installation when the play exceeds 1/16”.
Step 2) Placement of grooves/ribs. Grooves in the sashes should be cut into the sash closer to the parting bead, rather than to the outside face of the upper sash and inside face of the lower sash.

Step 4) Specify 3/4” nails, zinc-coated when using zing weather-stripping or brass-coated when using brass weather-stripping, to avoid usage of nails that will rust. Specify nail spacing: 2” – 3” apart along length of meeting rail hooks and within 1/8” of the end of the hook at each end. Make holes in weather-stripping material either using an awl or pre-drill, and set nails using nail set so nails are close to flush with the hook surface.

Step 5) Often the groove for the weather-stripping runs close to or through the edge of the knot hole in the sash (especially in 1 3/8” sash). When using the traditional knot-in-hole method for attaching the sash cord, I find that in a few occasions the knot will interfere with the top of the weather-stripping rib (during closing). For that reason I don’t use a knot, I tuck the end of the cord deep enough inside the knot hole so it cannot interfere with the weather-stripping rib and secure it there with a nail, then one or more nails to attach the cord in the cord plough (to carry the weight). Perhaps discriminate between “Adequate” treatment = knot, “Best Work” treatment = the fastened-with-nails treatment?

Step 6) How to determine the length of the side strips? In older installations I typically find the upper side trips extending 1” – 2” below the bottom of the closed upper sash. Especially in shorter upper sash (less than 1/2 opening) this helps avoid the sash running off the rib of the weather-stripping when opened fully.

Step 8) Specify nailing spacing. One nail immediately above the pulley (to avoid the weather-strip flaring out and cutting into the sash), one nail immediately below the pulley, and one nail at the very bottom of the strip (in the section exposed beneath the closed upper sash). Depending on opening width, 3 – 5 nails in the top strip (enough to avoid sagging of strip). Nails should be placed in between the corrugation of the strips so nail heads don’t touch the sliding sash sides.

Step 11) Specify length of side strips and meeting of corners (see above). Lower sash side strips should not be visible above the top of the sash in the closed position. Side strips should be angled at bottom to match sill pitch.

Step 12) Include a note to slightly bend the bottom weather-strip rib to align it plumb (with the lower sash bottom groove) when the sill is angled.

Step 13) Side strips nailed at bottom within 2”-3” of sill, at the top within 1/4” of the top. By nailing the bottom and one side strip prior to hanging the sash, one side strip can be nailed through the center at the top. By following this procedure only the last strip (the other side) will have to be nailed through the very side (with the lower sash in place).
Question: In looking at the second photo; are you using a side strip that is wider than the sash (for instance 1 ½” for a 1 3/8” sash)? Does that explain what I think this photo illustrates: nailing the side strip next to the sash (behind the interior stop)?
Again, specify number of nails for the sill strip, also specify whether nails are on the inside or the outside of the rib. I have seen both treatments. I favor nailing on the outside because it prevents any gaping between the weather-stripping and the sill. Should “Best Practices” include caulking the front edge of the bottom strip (between sill and metal)?

Nowhere is there a discussion of the corners where vertical and horizontal strips meet. In my opinion “Best Practices” should include crimping the ends of the horizontal strip ribs, mitering the ends of the vertical strip ribs, and opening up the mitered corner so the strips overlap in the corners. “Adequate Practices” could then be specified as either completely mitered corners or abutting the vertical strips to the horizontal strip. “Inadequate Work” would be specified as gaps at the corners where these strips meet.

johnleeke · **Posted:** February 29th, 2012, 2:23 pm

Martin, thanks for pitching in here at the Collaborative, and for you detailed comments here. Your northwest regional experience, and experience with more than one brand of this type of weatherstrip will be useful here.

You suggest:
>>Under Class of Treatment mark “Maintain” “Repair” as well as “Upgrade” to reflect that repair of existing (but missing or damaged) weather-stripping is included in the standard.<<

This treatment is specifically for adding weatherstrip to windows that do not have it. I have added a statement in the description to make that clear.

It is possible, and perhaps even good, to have treatments on the maintenance and repair of this type of weatherstrip. If you would like to submit one or more, you can learn how here:
viewtopic.php?f=23&t=150

>>- Under Description I think it is fair to increase from 50 to 80 the age at which this product is still found in good working condition.<<

And I have seen this type of weatherstrip doing well after 100 years. I'll change that to "50 to 80 years", and stretch it out further if anyone else confirms that there are typical cases where it has actually lasted longer.

I'm hoping Marc and others will chime in on your other detailed comments.

johnleeke · **Posted:** February 29th, 2012, 2:30 pm

As editor, I'm inclined to remove the Step 15:

>>>>15. Install wheel covers, if desired, to stop air infiltration in the wheel area.<<

because it does not relate directly to the weatherstrip treatment.

Installing wheel covers could be submitted as a separate treatment and standard.

johnleeke · **Posted:** February 29th, 2012, 2:31 pm

I think a final step needs to be included for testing and adjusting for smooth operation of both sash.

johnleeke · **Posted:** February 29th, 2012, 3:22 pm

As editor, I'm working on what words to use to name this type of weatherstrip, keeping in mind that we cannot promote specific products in the final standards document, and so want to avoid using specific product names and marketing phrases.

Here is a list of the various manufacturers and their product names:

Interlocking Weatherstrips, Accurate Metal Weatherstrip Co.
Interlock Weatherstrip, Pemko
Rib Strip, Dorbin
Interlocking Metal Weatherstripping, West Coast Weatherstripping

Here are some possible names:

Metal Rib, this is what I have always called it.
Ribbed Metal, this is what Bob Yapp calls it.

What do you call this type of weatherstrip?

Bob Yapp · **Joined:** May 9th, 2011, 8:39 am **Posts:** 58

Martin Muller said, "- Under Description I think it is fair to increase from 50 to 80 the age at which this product is still found in good working condition."

I would take it even further Martin. The house I'm restoring now has this system, same that I use today, and it was installed in the 1890's to windows made in 1859. I also see it in my old milwork catalogues from the 1890's.

WPSC

Metal Interlocking Weatherstrip (draft)

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