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Stainless steel flashing for exterior basement insulation


I'm looking to insulation a basement on the exterior with 4.5" EPS. This is a retrofit application. It's in Halifax, NS, Canada (zone 6 I believe).

I'm looking at stainless steel L flashing with drip edge. Stainless for durability and appearance as the house is about 1000ft from the sea and we get a fair amount of rain even in the winter. We also get a fair amount of snow too. :)

(1) What is the minimum gauge of stainless steel you guys would recommend? The 2010 Canadian building code requires a minimum of .33mm (13 thou) for galvanized steel for flashing. That's thin for galvanized. It doesn't say anything about stainless. One good link from SSINA ( says you can use a thinner gauge stainless than galvanized.

(2) How do you join the flashing end to end? Does each piece have to be mechanically fastened to each other or can I use sealant to seal the seams between pieces. How do you account for expansion in the joining?

(3) What is a good method of adhering the flashing to concrete. We don't have termites in Nova Scotia but there are carpenter ants. I'd like to use it as a bug guard as well by attaching it to the top of the concrete wall. Again this is retrofit so I can't insert it under mud-sill.



Asked by Wesley Manning
Posted Thu, 03/27/2014 - 14:28
Edited Thu, 03/27/2014 - 19:45


14 Answers

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Basic overlap joints is what most do this way. As to thickness, you just need to be thick enough to deal with oil canning... Go to where you are buying it.. and sample.

Go to a home or contractor that you like the install and copy. I have done so my whole career. Ask and yee shall receive.

As to stainless, I am now a user of it for dock hardware on the lakes around the Adirondacks. The first part of a dock to go is the hardware. The wood can last the way we build 2-5 times as long as the hardware.

Answered by aj builder, Upstate NY Zone 6a
Posted Thu, 03/27/2014 - 20:42

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Wesley: will be looking forward to the info you can find here and there ..
I'm in center Quebec and we also have problems with "rading" carp-ants
( because they have only so short time to thrive )
And still looking for a suitable ant/bug flashing at bottom of insulation/walls ...

Do you wish extend the SS flashing pass the 4.5" EPS ?

Answered by Jin Kazama
Posted Thu, 03/27/2014 - 22:13

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There are several reasons why stainless steel flashing is rarely used. Unlike copper, it can't be soldered in the field. (It's possible to weld stainless steel, but it's tricky, and I've never heard of stainless flashing being welded in the field.) It's also hard and difficult to cut.

Answered by Martin Holladay, GBA Advisor
Posted Fri, 03/28/2014 - 04:49

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Thanks for the answers guys. I maybe should do a little bit more research before posting.

FYI: I talked to a sheet metal shop. They never go under 24gauge because SS or galvanized crinkles on them. Stainless steel is about twice the cost of galvanized from what they quoted me. It was just over $600CAN for 125feet of 2" x 5" L 24gauge flashing vs about $300 for the same galvanized.

Yes I want to extend the SS past the EPS to do a drip edge. I just got a quick quote on L flashing to get an idea. I will update this thread on what I find out. It will be a few weeks before I figure it out.

Thanks. I thought about copper but thought it would have been more expensive. I thought wrong. I called the sheet metal shop back and copper is actually a bit cheaper. Is copper compatible with cement? I'd like a adhere the flashing to the cement to provide an insect barrier.

Answered by Wesley Manning
Posted Fri, 03/28/2014 - 10:21
Edited Fri, 03/28/2014 - 10:22.

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Q. "Is copper compatible with cement?"

A. See this article posted on the website of the Copper Development Association (a group that doesn't want to see any failures when copper is used improperly): Is There A Problem With Embedding Copper Tube In Concrete?

Answered by Martin Holladay, GBA Advisor
Posted Fri, 03/28/2014 - 10:42

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How could concrete be a problem to coper if you are going to use adhesive/caulking ?

Is copper cheaper than galvanized ? what is the guage they would use ?

Answered by Jin Kazama
Posted Fri, 03/28/2014 - 13:00

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About insect, i have hard time finding a recommended "shape" for "flashing " against ants over google.

Any hint as to what kind of shape makes it impossible for carp ants to crawl pass the flashing ?

Answered by Jin Kazama
Posted Fri, 03/28/2014 - 13:05

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Caulking is not perfect so I want to be careful. They didn't specify a gauge for copper they talked about ounce. I forget now what they told me for ounce.

I don't think there is a recommended shape. The barrier is only meant to prevent the bugs from sneaking into the wood from the insulation. It forces them to the outside where you can see them so you know you have a issue. For termites I heard others on this forum say they are somewhat deterred by daylight but I don't think its the same for carpenter ants.

Answered by Wesley Manning
Posted Fri, 03/28/2014 - 14:21

Helpful? 0

What do you mean caulking is not perfect? nothing is..but don't you only wish for the flashing to be correctly positioned and caulked here ?

There must be a specific shape/dimension that carp ants cannot cross phisically.
Usually if the colony cannot easily reach ground to nest, they do not set there.
Don't worry ..they have no problem going around in daylight at all :)
( i've been infested more than once, and they do love EPS )

Answered by Jin Kazama
Posted Fri, 03/28/2014 - 14:47

Helpful? 0

Jin, I deal with Carpenter Ant infestations in houses here all the time. They will bypass any base flashing and find another route into the structure. I have never seen a successful mechanical way to stop them. Treating with borate spray, such as Boracare, is the way to go.

Answered by Malcolm Taylor
Posted Fri, 03/28/2014 - 22:20

Helpful? 0

In the past when we used a 50 year galvanized flashing, we had them break the inner flange down (at least an inch for anchors) a bit under 90 degrees so water drips outward and the outer flange downward a bit more than 90 degrees so the drip edge (half inch) is outwards. I've used a peel and stick type window flashing on the inner flange (to go against cement, seal and hold it in place). Then it's easy to lift up the 4-6" flashing and screw to the wall. Overlaps are about 2" and you can hardly see them when looking down the wall.

I'm sure SS will work and look fine as well. We use a lot of it on our fire truck builds along long edges/corners. You can choose brushed, polished or plain. S/S is also a low conductor which is nice.

Answered by Paul Kuenn
Posted Sat, 03/29/2014 - 08:27

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Just being paranoid. I don't want the copper to touch the concrete. I think though a peel and stick membrane would work for that.
I found another GBA article on ants: I think you seen that one.
Here's another article on carpenter ants from a pest control company:

Thanks. I may go with copper. For SS can you cut 24gauge with aviation snips? Wondering how you would do inside an outside corners? Just curious.

I wanted to do both a bug guard (J channel) and z flashing for the wall. They'll get expensive with copper or SS. Wondering if I can have a very small z flashing that drips on the J channel if the J channel slopes down? That doesn't feel right though.

I was doing wiring lath with surface contact cement so maybe I can bring that up to cover top of foam. That would provide barrier for the ants. Some more thinking to do.

How about a rust proofing paint or coating over aluminum or galvanized? I may look into that. More labor intensive but I could do that myself.

Answered by Wesley Manning
Posted Tue, 04/01/2014 - 14:37

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I've actually used a great local Heating/cooling outfit that was able to order the width of stock and use their brake (machine for bending long pieces... sorry, I used the word "break" above). They did 10 foot long sections for me. S/S is a pain to cut/slice as it is very malleable.

Answered by Paul Kuenn
Posted Tue, 04/01/2014 - 22:53

Helpful? 0

Wesley, If the flashing is just for insect control I wouldn't use an L flashing. I'd use perforated stainless steel bent to a U. That's what we use here in BC for rain screen base flashing whether there is foam or not.

Answered by Malcolm Taylor
Posted Tue, 04/01/2014 - 23:15

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