Exterior fastener selection in PNW coastal area
I am having hard time figuring out what type of fasteners to use on the exterior of the house in a marine 4c environment (Puget sound area in WA) from the corrosion protection perspective. The fasteners in question are fiber cement siding nails and furring strip screws. After reading Simpson’s Fastening Systems document (C-F-2017) it looks like 316 stainless steel or HDG A153-C are the only recommended options. I somehow doubt that most of the houses in the area follow these guidelines. I think the answer to my question would be easy if I could find guidelines on what constitutes marine environment as far as corrosion protection goes. Obviously, waterfront location would be the case where salty mist is usual occurrence, but 1 mile away from waterfront and 500′ up on the hill doesn’t get that much salt. Here is one interesting source of the information on the subject: https://pomametals.com/salt-air-inland-distance-for-metal. They indicate that salty air is definitely a factor as far as 100 miles away from the coastal areas, but to what degree?
I am considering using Simpson’s SDWS screws for the furring strips that have “Double-Barrier proprietary coating that provides a level of corrosion
resistance that is equivalent to hot-dip galvanization (ASTM A153, Class D)”, but then they indicate that screws with this coating not to be used in the marine environments.
Joseph Lstiburek’s analysis on his retrofit project indicates that epoxy coated screws are as good as SS ones (Foam Shrinks, and Other Lessons https://www.greenbuildingadvisor.com/app/uploads/sites/default/files/foam-shrinks.pdf), but does that conclusion apply to marine environments as well?
Perhaps I am overthinking this, but in my mind it seems to be a valid concern to ensure that siding nails don’t fail before the siding does. Any thoughts on this would be greatly appreciated.
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Replies
Vlad,
The builders around you are probably using what the builders up here on Vancouver Island use. Both the furring strips and concrete-based siding get air-nailed with HD galvanized nails. The furring with a framing nailer, the cladding with something like a Bostich siding nailer.
Over the years you will see a bit of white corrosion on the heads of galvanized nails if they are exposed, but no diminution of structural strength.
If you want to use screws for the furring, I'd suggest deck screws with a coating rated for ACQ contact.
Malcolm,
Thank you for your prompt reply. I was hoping you would offer your opinion since Vancouver Island is almost within line of sight from where I am. I'll feel much better using HDG nails since as you've indicated that is a common practice around here. The reason I am going with the screws for the furring strips is that I have 3" of exterior insulation under them, so nails won't work in my case. I probably won't find deck screws long enough for this either, but I believe both HeadLok and SDWS are rated for ACQ, so either one should work.
Vlad,
On waterfront lots I see a lot of corrosion on exposed metal like light fixtures, door hardware, chimneys, but not fasteners which are embedded in (and protected by) siding or framing. The ones that fail in those situation are common nails that are either continuously wet, or exposed to something like ACQ.
Headlock, or SDWS make sense for that much foam, although I wonder if you could get by with something less expensive like GRK R4's?
Good luck with your build!
Thanks Malcolm, all good points.
316 stainless is probably about the most corrosion resistant stainless alloy you’ll find used for regular things like fasteners. “Real” hot dip galvanized fasteners are ok, but not nearly as good. Hot dipped galvanized fasteners are the dull grey ones, not the shiny “flash” galvanized kind which will NOT last.
Personally, I’d use the 316 stainless fasteners for anything exposed, and anything likely to get wet at times. For the long screws holding up your furring strips, you could save a bit and use the hot dipped galvanized screws since those should be pretty well protected.
I don’t really trust the coated (epoxy, any polymers) screws as much as the stainless or galvanized fasteners, but I don’t have a lot of long-term experience using them, either.
Bill
Bill,
I share your feelings about fancy screw coatings. But those will be behind siding and won't see much moisture. I agree that 316SS is the only bullet proof option, but those fasteners are much more expensive. To Malcolm's point even siding nails should be fairly protected too with blind installation method. So, HDG siding nails will probably last for the lifetime of the siding. Having said that, after I've posted my original question I found out that I can get SS nails from a big box store for $100. Seems like saving $50 or so is not worth the risk.
Yeah, $50 is cheap insurance.
I wouldn’t really expect the galvanized fasteners to fail outright, with a structural failure, but I’d be worried about the possibility of rust streaks running out where you could see them. I’ve seen that happen sometimes in the past. Rusty streaks on the visible part of the siding under each blind nail isn’t good. Stainless is the safest option.
Bill
If you can find a fastener store that will sell to the public, you can save a lot on large quantities of Simpson nails.
Hi Vlad
We did a 2" exterior insulation project near Vancouver. We attached the furring strips alternating between standard 5" ACQ screws and 4.5" Headloks (we found the latter much cheaper than the GRKs). We alternated simple to save money as the screw costs really add up and our siding was lightweight Cedar and short lengths of heavier corrugated metal. The Cedar and trim was however all attached with stainless.
Quin,
What do the screws for a project like that end up costing? Fasteners used to be an incidental expense you didn't really thing about, but large quantities of structural screws must add up.
Malcolm,
Here are my estimates in USD for the furring strips installation. I have about 140' of 10' tall exterior walls. I figured I would need a bit less than 600 screws. DHC Supplies sells a bucket of 600 5" SDWS screws for $292.75 plus shipping. diyhomecenter.com sells a bucket of 250 5" Headlok screws for 141.49, so three buckets (750 screws) would be $424.47 and free shipping.
I find roofing deck screws the cheapest ($.10 to $.20 each) when looking for long truss headed ones. Bonus is they are stock at local roofing suppliers.
Hi Malcolm
I can't actually recall. But you are absolutely right fasteners really add up. We had 6" of exterior rigid foam on the roof too that needed to get attached via furring strips with GRKs and those cost a fair bit. Rang around all the commercial suppliers and roofing places to source the best price as even small price differences add up.
Kind regards
Thanks Vlad and Quinn for weighing in on costs.
Quinn,
Thank you for sharing details from your project. I've also settled on using HeadLok screws. This green building stuff ain't cheap :)
316 stainless is for marine salt water applications
303 or 304[or 18-8] stainless is the more common generic 'stainless'
specing 316 will do nothing but raise costs
I prefer stainless[over galvy] because it does not bleed on unfinished cedar etc
316 is also a little harder than 304. I wouldn’t say “316 is for marine salt water” though, but it is best for that application. 316 is more corrosion resistant than 304, regardless of application. Anytime you’re working with a material that is going to react with the metal a fastener is made of, 316 stainless is going to last the longest.
For a typical siding application though, I agree than 304 and 316 will probably both hold up about the same, but the OP is in an area subject to salty air so the 316 will be the better choice.
I’d stay away from 303. 303 is much worse than 316 or even 304 for corrosion resistance. 303 is commonly used for stainless steel electrical plates and if you’ve ever worked with those, you’ll know how easily they can be stained.
Bill
Just to go back to the OP's original question. I agree that for cedar and other wood siding stainless steel makes sense, but he is using cement-based siding, and his lot is a mile inland. If galvanized fasteners aren't robust enough, we have a lot of more pressing problems on the exterior of houses than the siding. Decks and ledgers are routinely built with galvanized fasteners in load-bearing situations. The standard fastener for all exterior use, except where there are cosmetic concerns, are galvanized ones. Unless we see some failures, i'm not sure why that should change.