ZIP, AdvanTech, OSB, and Plywood.
ZIP, AdvanTech, OSB, and Plywood
Hi
What are people’s preferences/experiences when it comes to these products in the two following locations?
Roof Sheathing – Vented attic, with metal standing seam over top. Also what underlayment would you use with each?
Wall Sheathing- Inside to out lay-up is ½” drywall (hopefully fairly airtight) (possibly a membrane required by building inspector), 2”x4” studs, ½”sheathing taped (3M) (air barrier), 2 layers of 3” used fiberglass faced polyiso (6” total) Tyvek (WRB), horizontal ¾” furring strips, vinyl board batten siding.
Note:The polyiso (used from roofing) has a thin paper/fiberglass coating, not sure this is considered a fiberglass facing?
I know there are articles with info also, which I don’t mind links because I might have missed some, but I like firsthand experiences or preferences was costs a big factor? What would you guys use/why.
I plan to live here 50+ years, so I wanted the house to stand the test of time.
Thanks for any input, framing starts June 1st!!!
Dave Zone 6
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Replies
Dave,
I think any one of the 4 sheathings you listed will last 50 years, assuming that you catch any roof leaks promptly, and assuming that your wall flashing is detailed properly.
Fyi....ZIP Sheathing is an OSB w/WRB product embedded in it so it's not intended to require the additional expense of hanging housewrap (i.e. Tyvek) or some other WRB unlike your other options.
Matt Risinger did a YouTube video on sheathing. I think you'll find it informative.
Here's my Advantech anecdote. For three years, we've had a piece of half inch Advantech acting as a placeholder for our eventual stone step outside the front door. While under a roof, it's been exposed to the weather, often wet and snow covered. Not a bit of delamination or other deterioration.
Martin
Yes the details are very important, which I assume is why I will be asking more questions the closer the start date gets, looks good in the drawings, doesn't always transfer to the job site.
What do you think of ZIP under a metal roof? I've heard mixed reviews, some saying you still need a underlayment , which seems like an extra expense if the ZIP is already WRB?
Thanks,
John,Thanks I don't think I've seen that one yet. One detail I forgot to mention is the windows are outies.
So that is why the Tyvek.
Stephen, good to know, I have heard it stands up to the weather very well. Did you use it in your build?
Dave,
Here is a link to a relevant article (in case you didn't see it): Wall Sheathing Options.
Huber (the manufacturer of Zip) tells customers that you don't need roofing underlayment if you use taped Zip sheathing on your roof. Since roofing underlayment is a code requirement, I would check with my local code enforcement official to make sure that the official agrees before deciding whether it makes sense to skip the underlayment.
Thanks Martin
Yes I guess its is another question for the code official, Do all this research, with the possibility of getting shutdown by the "man".... I'll add that to my list.
Would certain underlayments be more durable under a metal roof, I assume the metal "moves" under thermal conditions. Would it be enough to wear through the ZIP coating? I never played with ZIP.
I think most of us would want plywood if the budget and weather would cooperate.
The OSB is great for the budget does not like to get wet for very long.
For the subfloor I like the AdvanTec if you think it will get rained on.
For the walls I like the Zip if you care about air sealing your walls.
For the roof I like plywood, the advantage of the Zip is how fast you can make it weather tight and how much more wind it will take than tar paper. I think the plywood holds nails better and stays flatter.
Walta
I would think if you use Zip for your wall sheathing and polyiso over that, you will need a drainable surface between the two ora WRB on top of the polyiso. Otherwise, water that gets past the polyiso will not evaporate or drain away easily
My framer installed 5/8" zip on the roof, the advantage being immediate dry-in (a few drips here and there). I helped them install a metal roof over synthetic underlayment and HT ice and water. The synthetic underlayment was cheap. I wouldn't trust the zip sheathing to be an ice and water barrier and I'm not sure the zip tape could resist the direct heat on the back of the metal roof.
Thanks ,Joel .
I trying to compare doing plain OSB with the synthetic underlayment or peel and stick, with just ZIP.
The ZIP is already a premium so you would think you could get away with nothing on the ZIP., as they show on their site. No ice or water protection needed it's built into the product they say.
We use fir plywood for wall sheathing in our double stud houses since moisture has been observed in these type of assemblies, and fir plywood is one of the best in terms of dealing with moisture, whereas OSB will disintegrate. (ZIP is OSB with paint) We also use Advantect - nearly impervious to moisture - on the two surfaces that may encounter substantial moisture - subfloors and roofs.
Dave: Our entire house is sheathed with Advantech. Our builder uses it instead of cdx, because he often can't get decent plywood and he likes Advantech's agility to get wet without any probems. We taped the joints with 3M 8067 flashing tape.
Stephen, Did you use Advantech on the roof also?
I like the idea of Advantech, I also heard it is tough to get decent plywood. which is still a premium price.
I still haven't got back pricing on Advantech, so I could be in for sticker shock!!
The 3M tape seems best bang for the dollar.
Plain OSB seems like your asking for future possible issues.
Bob, I think plywood will be my back-up if Advantech price is unreasonable, if I can't get good quality plywood, it will be OSB with some sort of coating (blueskin, etc.)
Thanks both of you for the input.
Dave: Yes, we used it on the roof as well.
Dave,
Be sure to Google the phrase "high temperature metal roof underlayment" before committing. Sample the sales pitches and costs and be sure to check with local code or at least what the local inspector will demand. In my area it is mandatory for metal roofs to have high temperature stick down underlayment from eave to peak. The detailing on metal roofs is quite a lot more varied than I would have believed so be sure to talk to more than one installer. Don't be fooled by the "I always do it this way" attitude.
Also, check your insurance companies attitude toward metal roofs. In some areas subject to high fire risk, some insurance companies do not consider them a Class A roof. The issue is embers getting caught in pockets and/or the capping details allowing direct entrance to the ridge line vents. The details for shedding rain don't necessarily work with blowing embers. Guess who lives in such an area.
Some other things to consider when looking at metal roof choices aside from the fact they get blazing hot in the sun. The expansion/contraction rate, the noise factor during rain or hail, and repairability should all be considered in addition to cost. Screw down metal is the least cost and most repair friendly, but often will have issues with the gasketed screws. The constant cycling will work them loose over time which means going up on the roof to tighten them periodically. I chose clip style standing seam, it is mid cost and still repairable. The clips are screwed to the decking and the metal is (mostly) free to slide on the clips which in theory eliminates the thermal cycling levering on the screws. I will never know since the screws are hidden. Full on rolled standing seam is premium cost and a one way install. The seams are theoretically water tight which is not true of screw down or clip seam.
If you have low pitch roofs the seam height can be a driving factor depending on snow load and how well the heat flow through the roof is managed. One other thing to know about metal roofs is melting will occur no matter how well the roof under it is insulated. Mine are about R-54 and the sunlight drives the melting 100% of the time. So far careful planning has not led to any ice issues that cause problems, but the north side is especially vulnerable to build up from run off from the 2nd floor roof which does catch sunlight. The run-off from the 2nd floor roof is also the one big boo boo we live with. The dripping from the eaves 8' above the metal roof over the kitchen is rather trying at times even if the roof plane is nearly 18 inches thick. Gutters are not sensible in our environment, ice will build up and tear them off.
So far the hail has not been an issue, but we seldom see any over 1/2". The gauge we chose is thicker than many screw downs, so just be aware if hail is an issue in your locale. Last thing. The outie windows will require the very best tapes or liquid sealers. Tyvek will not cut the mustard. I used Henry Blueskin on the entire house and their tapes for all penetrations. I was very pleased with the stickiness even in low temps and since I still haven't done my 1st level window sills inside, I can attest that there is no leaking anywhere. My windows are technically middies due to the outsulation placement, but functionally outies when considering the water management on the envelope. Anyway, seal and detail the windows meticulously.
Thanks for the info Roger.
I am looking at the clip style roofing, not screw down. The roof pitch is 8/12 down to a 4/12 wrap around porch, so it should all work fine. The Tyvek is my WRB over the 6" exterior foam and if detailed correctly should work fine, the windows are outies with boxes.
Why your concern???
Hi Dave B,
Sorry not to respond sooner, my country internet was out for a while. I worry about windows and water due to a paranoia I developed over the years fixing rotting windows for myself and others. I can't see the details of your planned window installations so I must guess and warn accordingly. On my own Santa Fe-esque design which is wide open to the elements I went with the Blueskin WRB on the sheathing and sealed the window boxes with the Henry tapes in addition. I have two drainage plains behind a synthetic stucco over foam finish. I have made every effort to keep water out, but failing that, provided as many barriers to infiltration as practical. Water is persistent and very patient, taking advantage of any gaps to wick into places you don't want it.
The outie window boxes I used actually 2x8 stock set outward of the main wall framing. The front edges are set back about 3" shy of the overall finished wall plane, and slightly short of the outermost drainage plane. Drip edge profiles above each window and shaping of the foam around the windows is first line against driven rain. If I experience a barrier failure that manages to get to the primary drainage gap, I still have the blue skin and an entirely sealed box to keep the water out of the framing. I even got so anal that I put small ledges on the blue skin above the window boxes to direct bulk water sideways around the opening. Hopefully, water will never get any where near that far in.
That said, my current understanding of your wall details suggests a need to more closely consider water entry points. I have not experienced repairs on vinyl board and batten style siding so I may be way off base, but the more common lap siding I have dealt with has lots of opportunities for water entry if not detailed carefully. (and even if done carefully) The expansion factor for vinyl is quite large and the edge channels by necessity are deep and not a tight fit. Even in a vertical orientation the water staining observed suggests driving rain and/or wet snow is making in past the siding edges in fair amounts. The channels and j-strips around windows also show dirt and algae staining that I take to mean water has been present. While washing a house with vinyl siding, I found the window trimming details a bit less than encouraging. A garden hose is perhaps a bit more aggressive than a driving rain, but it was revealing to see how the water eventually found its way behind the siding to slowly dribble out behind the starter strip at the bottom.
You have mentioned horizontal furring strips mounted over Tyvek and 6" of foam which infers long screws. Having dealt with the same long screws, they require some skill to set accurately and a miss will leave a long track through the foam layers to your sheathing. Even a properly set screw offers a track path for bulk water. The condensation issues will be determined by local humidity levels and duration of same. Where I am it is dry most of the year with low annual precipitation. (The screws by the way do conduct heat from inside the envelope quite well. The ones holding down my roof nailbase foam panels make little melted dot patterns in light snow dustings.) The horizontal furring strips will form a catch point for any water driving past the seams of the siding. The long screws will provide access through the WRB. I am not sure the polyiso you have is really completely water resistant. I used some for interior walls and noted the black paper acts and smells like it is an asphaltum/fiberglass paper. Suggest you take a scrap and put a big wet car washing sponge on a horizontal piece and see if any water makes it through. I would also suggest doing the same with a piece of tyvek laying on cardboard to see if contact water makes it through. Bulk water can behave differently when infiltrating compressed layers of materials such as you have with your furring-tyvek-fiberglass paper sandwhich points.
My major concern overall is the one water barrier which you will be poking many holes into. The window trimming details for the vinyl are another critical point, unless your plan calls for very deep overhangs on all sides. Taping the window flanges to the Tyvek won't do much good if the wall above is secretly admitting water above all the tape. The window boxes really need the tops to be bullet proof. A slight backward pitch on the top will help water to pool and track in ways that would be very difficult to cure after the fact and hugely expensive to repair if discovered only after the damage is done.
I do hope you won't think I am merely being a pointless Cassandra. I too built for the next 50 years even though I won't make it that far. Hopefully, the kids will inherit a house that is at least salable if they decide not to live in it.
One other point I forgot to make on the metal roofing - some suppliers can roll the panels out on site like seamless gutter, some are limited to maximum lengths which may be shorter than your longest roof run. Be sure to know which they can do. Some rollers can also make the pans wider or narrower to fit the roof better or for simple aesthetics. Beware that very wide pans may "oil can" which just means pop and hump in the heat. Also the Kynar finishes seem to do pretty well here in the extreme sun, but they do fade eventually. We went with a locally popular raw metal finish which rusts to an earthy oxide color. Seems odd, but here the life is 40 years for sure and most likely much longer based on existing examples.
Hope this isn't too much to drop on you at once, but as you note - framing starts soon.
Thanks for your input Roger,
As for your concerns, the one that worries me a little is the fact that water could make it past the board&batten vinyl siding and then sit on the horizontal furring strips and weep it's way along the screws to the inside of the wall assembly. Although I'm not sure how you could prevent this?
The one thing going for me is that the house has a wrap around porch that is 7' deep. There is only one section 30' long that does not have a large overhang.
The window boxes I still need to detail, I have looked at some suggestion here on this site.
The roof is pre-made clip style "standing seam"
@Dave.
Don't worry about water migrating via nails into the interior of your home. Besides when putting up B&B with a rainscreen it should, imo, ideally utilize a cross hatch pattern where the B&B is attached to horizontal strapping which is then attached to vertical strapping which is attached through the exterior insulation into the sheathing/framing. You'll have plenty of airflow behind the cladding to encourage drying.
https://hammerandhand.com/best-practices/manual/4-rain-screens/4-6-horizontal-rain-screen-battens-vertical-siding/
John, thanks for the link.
I didn't really want to do that method as it's adding another layer,(longer screws, more lumber) but I may depending how paranoid I get about water. I guess I could do the vertical furring out of thinner material as it's only there to give a gap for water to fall. There will still be 3/4" material on top of that for the siding to attach to and have plenty of air movement for drying potential.
Always more to think about, never done.
Dave, if you are looking for some cheap plywood to make furring spacers to space out your strips enough for a drying space, there is a company in Peterborough that sells 1/4" plywood scraps from their manufacturing processes for next to nothing. The pieces are only 5 feet long, but if they are just spacers they should work fine. I can send you an email with the contact info for the guy I know there if you want.
Thanks Yupster, send me the link when you can.