House insulation and house wrap

[rjwassink67]

We would like to start building our own house in about 5 years. We are on the edge of zone 5a and 6 (NorthWest PA). Our interior insulation will be mineral wool r23, then 1/2 plywood sheathing. Here is where the debut comes in. I would like to put 3/4 rigid board insulation on the outside to help with thermal bridging and to help as an air barrier. Questions on house wrap.
1. If we put it on under the rigid board, it helps get any inside moister away from the sheathing, but you're letting the outside moister further in. If you put it on over the board your stopping the outside moister before it gets to the rigid board keeping it further away from any wood, but could inside moister get trapped between the sheathing and rigid board? Should you do 2 layers? It's relatively cheap right, about $300 to do a house? Why not do one over and one under the rigid board.
2. Last question, we are probably using vinyl siding (least maintenance). Use furring stripes to create an air gap or does vinyl siding have enough airflow to create a good drying situation?
Thank you everyone!
Ryan

 

[Snobdds]

Just skip all your steps and use Hubert's Zip system that has sheeting,poly foam insulation, and a air blocker on the same board.

Once you figure all the time it takes to put all the different materials on...Zip's are faster and better.

Vinyl...hate the stuff. I had a rental house done with it...big mistake. It has about a 10-12 year life span. Plenty of other stuff on the market today that is much better at not that much more money. When it comes to siding...it's too expensive in labor cost to replace to save $2.00 a square foot now.

 

[buckeyefarmer]

Vinyl lasts forever if you dont beat it. Probably used on over 95% of new houses.

 

[RedNeckRacin]

Before you get carried away with the foam board, I would look at the energy savings difference vs the cost. From the research i did, there wasn't much savings past r-21 wall insulation. I just built a house in Zone 6 in Clearfield County. I also did 7/8" sheathing and tyvek on the exterior of the house under a mid-grade vinyl siding. Don't use cheap siding.

 

[RNeumann]

Your thought process isn’t flawed nor is it flawless. The permeability of the wrap, plywood and rigid aren’t really working together. The rigid is the “trap” and where the building wrap goes doesn’t change that.

I’d check out this website. I’ve learned a ton! Building Science Corporation | Consulting & Architecture

I ultimately went with OSB, house wrap with desired perm rating, 1” Roxul in the field (I have 1 3/8” window flanges so no mods needed) and 1” rigid around the areas that get trim- windows, corners etc. The Roxul can breathe unlike the rigid. So far so good. I’m in zone 6- North Idaho.

BTW- blown cellulose provides a little better real world envelope R value. They can do the lid and walls.

 

[rjwassink67]

RedNeck - I agree with the r value and cost. I would like to get more of an air barrier with it. I also agree with the vinyl, spend a little bit more money on it. I just want something I can install and forget about it. My parents installed some 25 years ago and no problems, they are not easy on it.

snodbbs - I have read the zip is inconsistent and you have to be carfully how tight you screw it around widow and door openings. I have spent a decent amount of time reserching it, because I think it is a good product. I would rather have my sheathing up tight against my wall studs.

 

[rjwassink67]

Your thought process isn’t flawed nor is it flawless. The permeability of the wrap, plywood and rigid aren’t really working together. The rigid is the “trap” and where the building wrap goes doesn’t change that.

I’d check out this website. I’ve learned a ton! Building Science Corporation | Consulting & Architecture

I ultimately went with OSB, house wrap with desired perm rating, 1” Roxul in the field (I have 1 3/8” window flanges so no mods needed) and 1” rigid around the areas that get trim- windows, corners etc. The Roxul can breathe unlike the rigid. So far so good. I’m in zone 6- North Idaho.

BTW- blown cellulose provides a little better real world envelope R value. They can do the lid and walls.

I have spent a lot of time on that website. For me its very difficult to navigate and find what your looking for. Most of the time I get there by google searches.

I am worried about the cellulose settling.

 

[Jchonline]

RedNeck - I agree with the r value and cost. I would like to get more of an air barrier with it. I also agree with the vinyl, spend a little bit more money on it. I just want something I can install and forget about it. My parents installed some 25 years ago and no problems, they are not easy on it.

snodbbs - I have read the zip is inconsistent and you have to be carfully how tight you screw it around widow and door openings. I have spent a decent amount of time reserching it, because I think it is a good product. I would rather have my sheathing up tight against my wall studs.

Inre Zip around windows, does this help? Matt is a builder in the South, but some of this should apply.

 

[RayfromTX]

I really like Matt. There is so much to not like about Matt's videos. He gets really convinced that products will work as they are advertised and then the failures happen and he gets convinced that this other product will perform the magic that is promised. This video shows some of that. He talks about peel and sticks being teased as really being stick and peel. Then he talks about how this new zip tape won't have those failures but it is even worse in reality. Tapes and goops are usually short lived. Zip wall isn't air tight and it is compromised by the fasteners. Painted plywood isn't a drainage plain for the ages. There are other examples in this short video.

The expert trainer in the video is shown driving screws right down through the pan he just created. The failures that we see over and over aren't just poor workmanship. In many cases it is products that are used just as the manufacturer recommends. This pan isn't a pan, it is an illusion and the window installation will trap water in the compromised pan. Matt knows a lot about marketing but he still has much to learn about building science. Products are no substitute for knowledge.

I am criticizing Matt's videos which isn't really fair. He makes great videos. The one he did on my site was adlib and he got 80% of it right. He has great presentation skills. He needs to learn the science and then he wouldn't fall for the sales pitches. I would recommend that y'all do the same.

Here is the bottom line take away for a subject that simply can't be covered by internet forum posts. Every sentence is backed by decades of painful lessons. These products won't save you. They will fail and they won't perform the way you are counting on them to. I can tell many stories of this in my long career doing custom residential. If you aren't sure, and I mean absolutely positive that you know what I'm talking about and how to keep water out of your buildings in all it's forms then do yourself a big favor. Keep your roof lines simple and flash properly and use overhangs to keep the walls and windows from getting wet because windows leak either soon or later. Use real pans and real head flashings. Nailing fins are a mistake. Under no circumstance should you minimize the overhangs for a nicer look or minimize the roof pitch because a product will protect you. The manufacturers are selling you a bill of goods. The condos that you see going up with no overhangs and balconies everywhere are going to be the next leaky condo crisis with billions of dollars in losses.

The good news is that the knowledge is available to both understand the problems and build buildings that perform exceptionally well and can last virtually forever. The materials we need are available and the methods are affordable. Matt even does some videos that show some what I'm referring to but it just isn't quite ready for publication and yet ready or not he has published 500 videos! He told me he has only removed a couple for being obsolete. All the rest are still floating around out there.

Rjwassink67- The good news for you is you still have lots of time to learn. You can learn first about the physics of heat air and moisture. Learn about the second law of thermodynamics. Don't be intimidated by it. This is no more complicated than understanding tractors. I'm really happy that you want to understand the best way to build your house. Approach it from how moisture in all 4 phases are a threat to your buildings and then how building science can help you to understand the risks and failures and then the understanding of how water moves will inform the methods for managing it. I got involved 18 years ago because in my lifelong quest to build better buildings I decided to figure out how to build a smarter house with complicated systems that managed these issues, kind of like our cars and washing machines and air conditioners. I soon learned that what is required to build better buildings is to understand the issues and then build simple walls and roofs, etc with the right materials in the right place so that the solutions are passive and durable and logical. Enjoy the journey but beware of the sales pitch.

 

[PILOON]

I very much like Canexel for cladding, reasonably priced and very resistant.
Under that there is a product that combines foam and tentest (beaverboard) that is used under the house wrap, I like that!
Completely sealed interior vapor barrier is an absolute must.
For wall bracing there is nothing like the metal 'T's' for the structural corners, forget plywood or strand oriented 'presswood' and go the tentest/foam board.
For all windows/doors foam the gaps.
Spend the bigger $$'s in the ceiling insulation as that is where you lose the most heat.
I repeat, tape seal all vapor barrier joints.