Opinions on Hardie Board Siding
In the northwest we deal with a ton of moisture but also increased threat of fire in our longer hotter summers. I sided the shed in beveled cedar clapboards (included a rainscreen detail). I love how it looks, but it seems that the most pragmatic choice for my upcoming house is hardie board siding for both durability and fire resistance.
1. Does anyone have any complaints or hesitation or warnings about installing hardie board siding?
My preference visually would be the vertical board & batten look…
Still working through how I’ll detail that over vertical 16 inch o.c. framing…I know you can install blocking in the framing but that increases thermal bridging…was hoping I could install 1×4 horizontal furring strips on top of sheathing & housewrap, then attach vertical hardie boards to that…
The thing that bothers me about this is that the horizontal furring strips ruin the rainscreen effect behind the boards. I have an air gap but water could potentially collect and sit on the furring strips instead of running out of the wall cavity, right?
2. Any ideas for how to get the rainscreen effect behind vertical boards, without excessive complexity or framing?
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Just use vertical furring, one on each stud. This is what we have. If I was building a single story house, I wouldn't hesitate to do it again. The panels are no fun to lift to a second story.
Just to clarify, Hardie doesn't make boards for vertical installation. The vertical board and batten look is achieved with 4' wide panels (8-10 feet tall), and covered by battens every 16" (or whatever your stud spacing is).
Trevor. Good info. This what I am planning: I will be using 3" EPS, on top of tyvec covered sheathing, on top of 2x4 framing on my home reno project. On the exterior of the EPS I am planning 1x4 furring on 16"c. Hardieboard Prevail panels 'Installation Requirement' sheet calls for a 'water resistive barrier' on the outside of the EPS below the furing strips. Is this necessary? Did you do this? Surely the barrier will trap moisture within the EPS and not allow for vapour movement to the outside wall? This could be a serious problem in the cold climate of Alberta, Canada. Your thoughts would be most welcome. Thanks!
Mike,
WRBs are typically somewhere between 25 and 80 perms. So although there is no reason to have one on each side of the foam, there is no danger of trapping moisture. They are designed to stop bulk-water intrusions, but allow water-vapour to pass through.
My wall construction is dissimilar to yours, so that particular issue did not come up. I'm guessing that the requirement for a WRB beneath the furring strips is general and does not presume there's another WRB behind a layer of EPS. If that requirement is in fact specific to that exact wall construction, then I don't know why they want that. I'd call their tech support and ask for clarification and reasoning.
Hardie and the like are sort of floppy, are they not? Depending on the width of the boards, you will could have spans of material that are not supported from impact, etc.
You could use one of the netted cedar breathers maybe? Or corrugated, horizontally ran material like this.
https://www.bestmaterials.com/detail.aspx?ID=22797&gclid=CjwKCAiAx_DwBRAfEiwA3vwZYpW3ORRw-ZMScQthEhnrfSKMumOHi4QLFEgZtstZLm_uMh0ajEL5phoC26MQAvD_BwE
Maybe you could cheat with wood vertically on the studs then the plastic horizontally arranged to optimize the fastening purchase.
Hardie prob has warranty rules, however.
Hardie's instructions are for fastening at stud intervals (up to 24"). No support between studs (or furring on top of studs) is required. 4x10 panels are floppy in transport; once fastened, you have to try pretty hard to break one, even at 24" spacing.
I would assume that flat against the sheathing the flex isn’t an issue but if someone were to go with a rain screen and have spaces of 16” w w/0 direct support behind, would that be an issue?
No issue. Rain screens are allowed per the installation instructions. I have a 1.5" rains screen on 24" spacing. While I'm sure I could break a panel, I'm equally sure I'd injure myself doing it.
Since this thread was originally posted, I decided to go with a continuous exterior layer of mineral wool (rockwool comfortboard 80) which is 1.5 inches thick.
I spoke with Hardie Panel, and they said in this situation, the panel requires 1.75 inch thick furring strips, because it requires 2 inch siding nails.
So the installation I was considering would leave the siding more than 3 inches away from the house. Also, adding 1.75 inch vertical furring strips over all studs, and having such a cavernous seeming rainscreen gap, annoys me. However, Trevor seems to have done it....was that over some other exterior continuous insulation?
The screws to secure the furring strips through the 1.5 inches of rockwool are fancy and long fasteners (1.5+1.75+1 = 4.25 inches min). Then I have to purchase the additional lumber for the bulky furring strips, and work out the window details at that added depth.
I had been set on vertically oriented siding, but I know the 4x8 hardie panel will be awkward to handle & install. This added information is inclining me to consider hardie board instead. With hardie board, I was told that 3/4 furring strips are adequate, but elsewhere I am seeing that 1 inch embedment into studs are required, so wondering what thickness furring strips I can get away with. Does anyone here have experience with that?
I am definitely sold on the rainscreen idea. The assembly will be 2x6 wall, plywood, WRB, 1.5 inches rockwool mineral board, furring strips, and then hardie panel or hardie board.
I guess the difference is only an inch thicker, but an inch can add a lot of complexity and aggravation, and I can imagine there will be other cascading effects from having such a thick assembly.
I look forward to hearing from anyone with experience dealing with adequate furring strips over rockwool mineral board insulation, for hardie board. THanks!
Paula,
My house has no external continuous insulation.
Hardie's best practice guide has conflicting information on the matter of fastener length for panels in particular. In the section on rain screens, it says:
"When attaching panel siding products over wood furring, the typical fastener used is the 6d common 50mm (2 in) long nail. This fastener is going to be the shortest fastener approved for fastening panel siding products into wood, therefore the furring must be a minimum of 43mm (1 11/16 in) thick to achieve the same values as CCMC..."
The second sentence contradicts their own fastener specification a couple of pages earlier, which allows for the following into wood studs:
-0.118x0.267x1.5" 4d common nail
-0.118x0.267x2" 6d common nail
-0.091x0.221x1.5" ring shank siding nail
I would ask them to explain that discrepancy; the corresponding sections in the guide for Hardie Planks has no such discrepancy, which allows for 1.25" roofing nails into either studs or furring strips. Assuming you could use the 1.5" nails, that still means 1 1/16" furring, compared to the 3/4" furring you could use for the planks.
Rigid mineral wool is somewhat squishy. If you use 3/4" strapping, you have to adjust each screw individually to get the strapping flat otherwise your siding will be wavy. With 2x lumber on flat, this is less of an issue.
Unless you are in wild fire area, I would stick to either unfaced EPS or permeable poyiso. With that you can nail up the siding directly through the foam. If you want a rain screen you can use either thin strips of 3/8 ply as spacers or one of the drainage mat (ie Slicker Classic). Either option would probably less than 1/2 the cost of the mineral wool setup for same R value.
Hardy-Panels with Hardi-trim on a rain-screen, all at 16"oc. The big problem is finding a trim nailer that likes going through that much cement board without pre-drilling.
Paula,
I have vertical 4x10 Hardie Panel on my home (Just as Trevor described). We nailed it to vertical 1x3 furring strips, 16 O.C. It would take no time at all to nail on some battens every 16", hiding the seams.
Martin Holladay (if my memory serves me correctly) has encouraged people not to worry about horizontal strapping under siding. This might even be a good thing in fire country? (Although, I read recently that studies have shown that a 3/4" vertical rain screen generally doesn't cause a "chimney effect" during a fire.)
If the horizontal strapping is keeping you up at night then you could alway install a bumpy house wrap like Hydro Gap, Tyvek Stucco wrap, or cedar breather under the strapping- offering a small space for drainage. Horizontal Coravent could also work. Adding a layer of Mineral Wool "boards" as exterior insulation/fire protection might also provide a drainage surface given its porous composition under furring strips.
I am in a wildfire prone area (long hot summers of Oregon), and I prefer the mineral board because I can rest easy during the rainy wet winters (moisture won't get stuck in wall)...
I am wondering if Akos' comment (which I can't seem to reply to directly) implies that the foam board products are less fire-resistant than the mineral board.
Thank you Trevor for that summary of the fastener specs from Hardie. I find their literature much harder to decipher than the Rockwool installation manual, which is amazing (more pictures, less numbers though).
If I were to rip 2x4's length wise to get a 1.5 inch thick furring strip (1.75 or so wide), then I could fasten through 1.5 inches of mineral wool batt, and I guess go for 1 inch embedment into the studs? That would still be 4 inch screws just to get furring strips installed. But with the advantage that there'd be less flexing and a flatter surface to attach panels to.
If I went with the 5/16 thick hardie boards, then the 3/4 furring strips that I was told is ok, doesn't compute with the allowed 1.25 inch nails - 5/16 thick board. That would leave 15/16 on the nail which exceeds 3/4 inch of furring strip. Hmm.
I thought the Hardie planks were half inch, but I could be wrong.
There's a limit to the depth of message nesting, that's why there's no reply option to some messages. The workaround is to reply to the message it was in response to.
Foam is definitely not more fire resistant than mineral wool, which is virtually fire proof.
The purpose of the rain screen gap is so that it dries out. There shouldn't be any issue using foam behind the rain screen.
There is no point in ripping the 2x4, just use it as is. I would not go down to 3/4" with rigid mineral wool as the adjustments are too fussy (fine if DIY but gets expensive you are paying for labor).
I would comb through the Hardie specs a bit more, there are generally different amount of embed specs for siding when installed with ring shank nails. This should let you install most of their products over 1.5" thick furring.
The general idea is whatever embed specs the siding calls for when installed directly over studs, you need to provide the same amount of wood for your furring strips.
Don't forget lot of the siding is nailed up through two layers, so for clap board use 2x the siding thickness when back calculating embed.
Akos hit on the key point here. I'll go into more detail since I happened to look into this issue recently.
The procedure for calculating the required thickness of the furring strips is described on page 117 of the Best Practices Guide: "The specific ESR 1844 & 2290 fastener must be installed into a material that has the same or better holding power than that specified in the ESR 1844 & 2290 and with the same penetration as the ESR 1844 & 2290 fastener."
If you look at ESR 1844 you'll find a dizzying array of fastening options. For any one of those you have to figure out how much of the fastener would be in the stud, and then use that as the thickness of the furring strip.
Technical Bulletin 19 has a useful worked-out example of this. See Step 6 on page 11 in particular. They show that a 1 1/4" fastener would have 3/4" net penetration into the stud. Therefore they use a 1x4 furring strip.
I recently chose an assembly very similar to yours for our house: sheathing, WRB, Rockwool, furring strips, and board and batten using HardiePanel. I chose horizontal furring strips only, as I tend to agree with Martin and others that much of the benefit of a rainscreen can be achieved simply by having a reservoir of air behind the siding. An important caveat, though, is that I'm in a place that only gets about 19 inches of rain a year. So a rainscreen is not considered essential here. I might be more concerned if I were in rainy place like the Pacific Northwest.
@Akos, I'm unable to reply to your previous comment:
"Unless you are in wild fire area, I would stick to either unfaced EPS or permeable poyiso."
Any particular reason you should use unfaced EPS in this case?
Unfaced/paper faced insulation is somewhat permeable.
This bit of permeability allows for a some outward drying. If you have sufficient rigid insulation for condensation control, the permeability of the foam is not an issue. None the less, permeable foam makes the assembly more robust.
Here's the hardie tech bulletin #19 ...
https://www.jameshardie.com/JamesHardieMainSite/media/Site-Documents/TechnicalBulletins/19-jh-over-advanced-framing-or-continuous-insulation.pdf
...that details applying hardie over continuous insulation (including mineral wool). I am in Eastern WA and this summer am planning to do 2" mineral wool with a rainscreen detail (1x4") with hardie panel with batten strips 16 OC. It's interesting to hear hardie when spoken to said the furring strip needs to be beefed up to 1.5" because it looks like the tables work out in their literature to be 1x4 or 0.75 x 3.5".
Also, check out the Victoria illustrated guide to R22+ effective walls construction guide...
https://www.victoria.ca/assets/Departments/Planning~Development/Permits~Inspections/Example~Plans/Illustrated-Guide-R22-Effective-Walls-In-Wood-Frame-Construction.pdf
...page 17 shows Fastener tables and minimum strapping size for foam vs. mineral wool per different cladding weights. Hardie panel, as heavy as it seems, falls under the light weight cladding category. Their strapping min. says 3/8 x 2 1/2".
Did I miss something??
Hi Mountain Cabin,
I saw that publication #19 also, and found it hard to decipher. Will have to re-read. Each page seems to be sending you to a different page before you can finish the sentence.
The question I have for you first is what fasteners? Between furring strips and through mineral wool to the framing first? And then from the hardie panel to the furring strip? Or are you doing one fastener all the way through to studs to hang the hardie panel?
I guess if you go with the thin furring strips then you are obligated to have fasteners that go all the way back to the framing. Maybe this is a way to simplify. Others are saying that 1x4 strips will flex and result in a non-flat plane for hardie panel. I think you can back screws out or push in to create a flat plane, although it sounds finicky!
I have called hardie tech/installation support 2-3 times and gotten slightly different information different times. Not sure if they were assuming things and I didn't give enough information? I'm piecing all the elements together slowly.
I will be DIYing this project with another person's help. Mountain Cabin, are you worrying over the door/window detailing yet? I loved the Rockwool installation guide. Also this:
https://hammerandhand.com/best-practices/manual/
I will definitely check out the other products that Chris D mentions--thanks for the tip.
Thanks all!
Hey Paula,
I am also a DIY'er. We kind of did things out of order with our windows. We just installed new ones last November but thankfully I thought ahead enough for the windows to be installed with windowbucks so hopefully there's much issue for us when we get to this point.
I also get confused by the docs and will re-read but it seems like the 1x4's should be fine. I think it mostly depends on the wood furring species you use + the fastener depth to hold the furring strip in place. I am not talking about the depth of the siding fastener but the fastener to hold the furring strip. There's an equation in both links I sent, even the hardie one, which talks about furring fastener length and how to arrive at it.
Although this doc https://www.nrel.gov/docs/fy15osti/63186.pdf is probably the best mineral wool install reference I've come across. It gives great detail in just about every situation. I would love to chat more offline about our projects since they seem to be in similar climates and similar material choices. Let me know if you want to connect!
-Zach
Yeah, Mountain Cabin, I'd love to connect and discuss siding details. Not sure how to make that happen without putting information on this forum. Do you?
Akos said "There is no point in ripping the 2x4, just use it as is. I would not go down to 3/4" with rigid mineral wool as the adjustments are too fussy (fine if DIY but gets expensive you are paying for labor)."
Well I'd love to avoid fussy, but it is my own labor, not paid. Ripping a 2x4 would be a way to spend 1/2 the money on lumber. I guess I don't have a sense yet whether nailing onto a 1.75" wide strip would be a challenge. Probably less so with clapboards than panels.
Looking at hardie clapboard siding installs in my area, the nailing is sometimes blind (under the following course) rather than through two layers, as people are suggesting here. This means a thicker than 1x furring strip might be needed after all. I like the traditional way of nailing 1/3 of way up the board so as to allow for movement in each board. I don't mind the visible nail heads-they'll be painted over.
Mountain Cabin, where did you source the window bucks, or did you make them yourself?
If you haven't bought anything yet, and are doing a DIY (if that may void any Hardie warranty), also look into Nichiha and Allura panels if they are available at your local yards. There may be some significant cost savings over paying for the Hardie name.
Hey Paula,
I've installed a lot of Hardie (a few houses a year) mostly over 3" or rockwool IS board and strapping/rainscreen and have never had a problem. I live in Vermont.
A few tips.
use 1x4 not 1x3s (we often are residing and use the old siding/trim when possible (need wide boards for corners)
align your screws vertically in the strapping so that when you string the wall for straitness its easier to adjust (shims help keep the strapping out when needed) it is finicky but it works. Use epdm washers to hold rock wool in place before stapping. window bucks are nice guides too.
for what its worth i tried the allure panels (just once) in a soffit situation and did not feel they were as strong as hardie - they sagged a bit
Good luck. ~Brad
Hey Brad,
It sounds like Paula is saying some Hardie techs have suggested using 1.5" thick furring by 4". What wood species are your 1x4s? What is your fastener wood penetration and screw type you're using on top of your 3" mineral wool? I myself am planning a 2" mineral wool install and seems like people recommend different stud wood imbedment requirements. I was planning on a 4 3/4" fastenmaster headlok screw but they seem to only make a 4 1/2" and 6" screw (2" stud imbedment + 2" for insulation + 3/4" furring = 4 3/4" ). Any thoughts? Thanks.
Hi Mountain Cabin. Great info in the Victoria, BC, link you provided. Thanks. I noticed that they recommend 3/4" x 4" ripped plywood for furring strips. That's the first reference I've seen to using plywood. They say it will reduce the possibility of splitting and I'd also think that the cladding attachments may be more secure. But...that's a lot of ripping! Do you think plywood's a good idea?
Mike,
Once rain-screens were added to our building code for coastal areas here in BC, lumberyards started stocking pre-cut 1/2" and 3/4'" plywood strips. They work well applied directly over sheathing or foam, but i think might be too wavy with mineral wool boards. I don't know if it's worth using plywood if you have to rip them yourself.
The photo shows plywood strips set into J-shaped perforated flashing:
Here's an article on errors in installing fiber cement siding:
https://www.jlconline.com/how-to/exteriors/common-siding-failures_o
I don't seem to have taken a picture, but there is a style of siding i'm seeing around my area where strips of hardie panel that are about 12-16 inches wide are mounted horizontally, with flashing between, creating sort of a modern look. It seems easier to install than 4x8 sheets.
I'll try to get a picture of it, in case it's not being done elsewhere. Sort of a modern look.
Thicker furring strips to minimize fussing and guarantee a solid siding job seems worth it, even thought it pains me to buy 2x4's instead of 1x4's for furring strips. Ripping the 2x4s to be about 1.5x1.75 seemed like a good compromise to save lumber.
Hardie markets their Reveal system which is a flashing/reveal gap system that sounds like what you're talking about, but I have no idea if it's a commercial-only product with a high price tag. People could be using standard Z-flashing instead, like would be done at horizontal panel edge joints.
What do the vertical joints look like on the 12-16 inch horizontal installations that you're referring to? That may shed some light about whether it's a coordinated system (like Hardie Reveal) or not.
When is season II going to air? I'm enthralled by this as I'm setting my brain cells into exploring where to go with siding on a new build.
For what it's worth, I'm in zone 4c (the BC stuff is applicable).
Perhaps off topic but since you want to install vertically and already have a cedar outbuilding (a beautiful choice for your environment) have you considered Cedar siding in Shou Sugi Ban finish? This is fire/insect/rot resistant and lasts an incredible long time. You can find these claims on line and I was skeptical when someone I know sided with it because here in very rural Montana we are no stranger to house-wildfire interface and use a lot of exterior rockwool also. Long story short (and purely anecdotal info) he had a fire go through and the Shou Sugi Ban siding with steel roof survived well but a nearby cedar sided building (painted exterior/steel roof ) burned to the ground.
Thinking about your J. Hardy application...what would be wrong with using something like Cor-A-Vent’s SV3 or SV5 for your horizontal rain screen application? It drains vertically when applied horizontally and is marketed more for insect control in a rain screen but might work as the screen itself. I have no experience with it however so is worth researching yourself.
Serendipitously Eric Whetzel linked to his experience with Shou Sugi Ban today in another thread. Like all Eric's blogs it's worth a look.
https://kimchiandkraut.net/2019/09/21/shou-sugi-ban-siding/
Malcolm, that is a different look than what the guy I saw did. He charred the wood, brushed the char with a large nylux powerbrush made by Makita. He then stained a color and wiped it off before sealing it with either oil or varnish. I’m not sure which but it had no shine to it. It was striking from a distance and even better as one got closer.
The longevity of the finish, and even whether you want to touch the boards, relies on sealing the surface and regularly re-coating. That's not a lot different from any other wood finish - which to me begs the question as to what the advantages are.
A second issue is that the present popularity among designers for black houses is already waning. Like any fashion its best to have some way of altering the building once the trend has moved on. Black painted houses can change colours. With Shou Sugi Ban you are stuck with it for the life of the cladding.
Wow, my neighbor who helps me build sometimes, mentioned this as a possible solution to some moldy boards that are looking ugly. He suggested using my propane torch to char them. Said this is sometimes done in Alaska? Apparently he saw someone char the lower portion of plywood sheathing to prevent rot, and the plywood lasted 20 years (usually the first part to fail).
I think I'll mess around with this on some scraps of fir and cedar, and see how it looks. I was set to use hardie siding, but maybe I should consider this. BTW cedar would cost me 3x as much as hardie, for siding, per my rough estimate. Also labor intensive! But no icky hardie dust.
Thanks for weighing in, Malcolm and Wannabe :)
p.s. update: I decided against the continuous exterior insulation (detailing too complicated for my time frame/attention span/budget). I found another way to meet the code requirements for extra energy efficiency...air sealing and a heat recovery ventilator...which I am sure I'll be posting questions about shortly.
Paula, I think if it is mold that concerns you then I think there are better ways to approach the problem. Mold needs food (the wood), the correct temperature (obviously you have that) and moisture to flourish. It is the water you can work on to control the most easily in your application by ventilation, better rain screen, better flashing above the wood to handle bulk water ect. Not knowing your specific problem I can’t even surmise how to advise and be of help. I have had huge success just doing my due diligence to dry things out but always use a shotgun approach to the treatment of rot because I take anything degrading my hard won building project very seriously. You can spray the product Boracare on your problem and then sprinkle additional boric acid on it. Wear a mask and keep pets and children away from it. Mold does not like it you lowered the ph of the wood. I personally used a solution that works even better than this product but unless you want to go to the trouble of mixing it I won’t waste your time going into that. Personally, even though I wannabegreen I favor “treated” wood near soil or any place moisture is a suspected problem. I know it nasty to our earth and I feel a little guilty each time I use it. If moisture is a problem however then there has been a failure in design or in the building process. If you do not tackle the problem of moisture no amount of Shou Sugi Ban finish will solve the problem. At best it may only slightly extend the wood’s useful life or keep mold from appearing very soon. In Japan there is a temple made of Japanese Red Cedar finished with the Shou Sugi Ban finish. It is well over 100 years old and is doing fine. It has no mold that one could visually see. (All building have some) Just because it has this finish does not mean the builders didn’t keep in mind how to avoid moisture AND this did not mean the caretakers of the building just ignored routine inspection and maintenance. This method is just one way to approach wood (especially cedar, fir and pine.) I don’t know if heat from the burn would affect the glue in the plywood in your case either. I just want to be clear so you are not disappointed. I made the suggestion about this finish only because of an outbuilding already cladded with cedar. I guess I’m a little OCD but I feel one building should fit or compliment the other. I also give bonus points to people who build structures that look as though they belong in a particular environment. This often involves using materials native to the area. Sometimes these materials are less practical or are more expensive but just plain right for a particular application. When one builds the first thing one learns is there are a lot of trade offs! Even though we try for perfection, there is no perfect building. Some are just better than others.
Andy
Hi Andy,
The moldy boards in question were left in my driveway covered by a tarp (my bad). Then the rain started and I went back to my teaching job and left them there for a month (months?). When I pulled the tarp back I had a nasty surprise.
I have mixed up a formula of baking soda, tsp and washing soda that creates a low ph spray. I have used it before when plywood started showing signs of mold or mildew. It stains the wood which of course doesn't matter on framing or sheathing.
Recipe here
https://www.practical-sailor.com/blog/homemade-mildew-preventers-that-really-work
I have a lot more 2x6's than I need for framing interior walls. I have some exposed floor joists and these are just too ugly to show, unless the burning treatment makes them magically a lot more attractive. Of course if I remove too much material I'm compromising the strength of the lumber.
Alternatively I can rip these to 2x4 and then use in framing interior walls, and buy prettier wood for exposed joists...
But yeah, I am getting mold/mildew on my studs too. I went around and sprayed the worst spots with my magic mix and it seems to have helped. The house will have doors and windows in a few weeks and then I can run a dehumidifer and dry the place out.
Paula T, I have a home brew for insects/rodents/mold that I make also. Part of it I learned from a master boat builder and the antifreeze portion actually stabilizes the wood if you make enough applications on it to really soak it in.
50% Ethylene Glucol antifreeze
28% borax
22% boric acid
Heat mixture outside or in well ventilated place and allow to cool. Pour solution in to sealed garden sprayer. Wear mask and spray moldy areas (or even light rot) in stud bays or other wood with coarse spray. Allow to soak in and repeat. Dust with Boric acid. Keep away from pets and children. Close wall ASAP. Kills bugs and mold. Messes with reproductive capability of mice but won’t outright kill them.
Andy