Good Evening All –
I’m working on a small kitchen extension for the wife . Since it’s our place, I’ve been trying to use heavier materials like 2×6 walls, 12″ oc floor joists, extra insulation, etc.
On the walls, I have 3/4 ply, with 1/2″ polyisocyanurate over that. I had planned to wrap that with Tyvek, but got to wondering if that’s redundant. (The poly will be taped on seams and siding will be 1/2″ by 6″ pine clapboards.)
Any thoughts?
Don K.
EJG Homes Renovations – New Construction – Rentals
Replies
One of the cities I do alot of work in wants two layers of water protection ie, tar paper, Tyvek, fanfold etc.
Family.....They're always there when they need you.
Okay, so your answer is that it is redundant, but maybe not a bad idea in some people's opinion... I appreciate your input.
Not sure if I'm going to follow the "plans" or not. Redundancy can be a good thing, but that Tyvek is about $80.00/roll. :-)
Don K.
EJG Homes Renovations - New Construction - Rentals
80 bucks a roll may seem expensive now, but will it seem like so much if you end up with water intrusion and expensive repairs?
I thought about that too.
As insurance, it's a one time thing. Could also use tar paper, which is cheaper - then I need to put more holes in the insulation. Don't like that either.
Don K.
EJG Homes Renovations - New Construction - Rentals
"Could also use tar paper, which is cheaper - then I need to put more holes in the insulation."Your exterior finish will be lap siding? Apply the tar paper with some tape and you won't need to put any holes in the foam insulation board. Of course, you will be placing a nail every ~16" horizontally and 6" vertically with the siding installation, but that's practically unavoidable.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
I'm not knocking redundancy, just stating what i've been told.
Sometimes I agree with redundancy. I some times like redundancy.
Family.....They're always there when they need you.
In Virginia it's redundant as a wind barrier, but may be worthwhile as a rain barrier.
I don't really think Tyvek is but a Weather Resistive Barrier (WRB) is absolutely necessary.
You can use Tyvek, felt, Grade D paper, Typar, etc. Some of the foams *can* work fine as a WRB but you're typically relying on adhesives heavily in some areas.
For instance, how will you flash your window head jambs with no WRB? The only way I know is to apply tape to the head nailing flange/drip cap. If the bond ever fails, you have a nice trough to catch water and direct it onto the window head jamb.
There are systems out there that rely heavily on tape and adhesive, I'm just not willing to jump on that wagon yet.
Jon Blakemore
RappahannockINC.com Fredericksburg, VA
If you've got water intruding to the housewrap or felt or whatever, I think you've got bigger problems than a WRB is gonna solve.
So you feel you can trust vinyl, cedar, or fiber cement siding to stop all water intrusion.My observation makes me feel uncomfortable with that.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
Forgot to include a picture. (Sorry about the size.)
Don
Hi Jon-
I hadn't really thought about the window flashings when I posted. Probably would have when I started setting the windows. :-)
In this one, the casings are going to be old style wide wood, not plastic. We're duplicating the originals. And, actually, two of the three are going up against a 12" piece of trim under the eave, and there's a 13" overhang. The third and last window is going under a porch roof so head flashings likely wouldn't have been too big a deal.
If you look at past experience here, we don't need any flashing at all. This place is over 100 years old by my guess, and when I opened the wall, there was neither head flashing nor any evidence of water intrusion. I've found that lapped siding is a pretty good water shed- at least most of the time.
I do know that those times I've used the sticky sealants, especially on foam, they held. You know what I mean, when you get half way across the piece and decide you want to peel it back and move it up "just a little bit". It's not happening...
Don K.
EJG Homes Renovations - New Construction - Rentals
If it were me, I'd do Tyvek, then whatever rigid foam you want. Is the polyiso foil faced? I'm not sure I'd use foil faced.
Josh -
I've used the foam faced polyiso in the past, and I like it. I have found it to be easy to work with and it does a good job. Only once did I have an issue with it, and that was condensation where I used it on a ceiling near can lights.
Here, one reason that I want it is because of the heat and sun. I'm hoping that it will help reflect some of the hot sun and keep it cooler inside. Summers get hot.
Why do you not like it?
Don K.
EJG Homes Renovations - New Construction - Rentals
I've read that it is a complete vapor barrier, 0 perm. I've also read that close cell spray foam has a low enough perm that it's a vapor barrier as well, so my opinion might not be that well founded.
Don,
Tar paper seems , if properly installed, and that's key, to have stood the test of time. So many different products out their that are great, but installed wrong, don't do what they purport to do. The concept of "house wrap" still I find baffling.
You wrap the structure in it, tape it and seal all the seams, then when the structure gets sided, poke thousands of holes in it securing the siding, defeating the purpose of how its marketed, not to mention that if it see's much sunlight before the siding goes up (very common) it's shot. But at least the seller of the house can say it has "house wrap." Which is cheaper than tar paper, but people have the misconception is superior.
WSJ
I'm with you on the housewrap concept. It's not something I feel I truly understand. But, what little reading I've done seems to support it's use.
(I still prefer tar paper.)
Don K.
EJG Homes Renovations - New Construction - Rentals
How about making a rainscreen wall, skipping the housewrap? The taped, foil-faced polyiso will be your drainage plane.
Cut furring strips from 3/8" plywood and attach them with screws though the foam, into the sheathing and studs. Nail siding to them, then they can drain and breathe on the back.
The furring would help prevent tape failure especially if you can line up most vertical seams under the strips. Use a good, wide tape such as the Nashua 330 "extreme weather" foil tape (http://www.covalenceadhesives.com/SearchProductsDetails.aspx?ID=579).
The goal is to add life to both your clapboards and your paint job, compared to nailing wood siding directly against housewrap. Plus you won't have the risk of bulk water getting trapped behind wrap.
Prime the siding on all 4 sides. Use window screen at the top and bottom to exclude pests, or install cor-a-vent SV3 (3/8") siding vents.
Detail drawings at:
http://www.coravent.com/siding-vent-sv-3.cfm
Tom -
That's an interesting scenario. It kind of fits into my thinking. Unfortunately, I am matching existing walls on 2 sides and the 3/8 plywood design pushes the new siding out too far. It was designed for the siding to be flat on the foilfaced - other than the paper.
I might use that one on the next design. Thanks for something else to think about. :-)
Don K.
EJG Homes Renovations - New Construction - Rentals
>> I am matching existing walls on 2 sides and the 3/8 plywood design pushes the new siding out too far.Yes, that's something to consider about a rainscreen wall.
They are great in theory but they do force you to bend your thinking around details like wall thickness and flashings. I had such a system almost complete before I got up to a dormer
and realized, hmmm, the installed furring is gonna interfere with the flashing upturn on the metal roof we're about to install. Now what?The solution I came up with involves tearing out the 7/8" furring and replacing with a layer of Huber Zip wall sheathing (7/16") over the foam and before the metal. New furring cut from the same Zip panels will go above the upturned roofing, to arrive at the original thickness (7/16 x 2 = 7/8). Now, that triggered a new round of learning about how the Huber Zip panels work.This is a conservative business, for good reason.