If I'm understanding you correctly, they're installing Tyvek directly to the studs with no sheathing between and then intend to nail siding to the framing members? I guess it could be done, but I would never sit still for that in my build. A combination of sheathing and Tyvek provides a much better protective barrier. In addition, having the Tyvek attached directly to the studs means that it is unsupported between the studs and more prone to damage and penetration before and during siding installation. I suspect that they are trying to save money by cutting a big corner here.

As for the insulation, old insulation in good shape does not have to be replaced, but I would want to be sure that all the wall cavities were filled to the full stud depth.

It's time to meet with the contractor and let him know you're not satisfied with this. If you are paying for it, you should expect to have it done right.

What is the new siding?

Is all of the window & door trim being replaced?

I'm not positive what the new siding is. The old siding was redwood, and it's possible that we are using redwood for the new as well, but I'm not positive. All of the windows and doors have been replaced - all new doors and windows (not sure what you mean by "trim").

Did you decide to replace the siding after the doors & windows were installed?

If so, that explains why no plywood sheathing is being used. The plywood would need to have been installed before the doors and windows (ideally). As long as you're replacing wood siding with wood siding, you're good. (The new siding on the Tyvek over studs has to be structural, IOW's. No vinyl lap siding, etc.)

Why did you rip off the old redwood siding?

Trim--the frame around the windows & doors. Wood, vinyl, etc.

Is this a Do-It-Yourself project?

I think you are saying there were bare studs behind the original siding. That was sometimes the case In a mild climate and the lateral bracing was provided by let-in diagonal bracing. You need to tell us if that was the case and be sure the bracing is there; its required by the building code..

You should be talking to the general contractor to see what it would cost to add some kind of sheathing board like plywood, OSB, Huber Zip system or foam board). The zip system doesn't require Tyvek homewrap which is a plus. If the contractor is not responsive you will need to hire someone like a "home inspector" to advise you.

Do you have a written construction contract? Does it describe the work to be done? That's usually required by state law. Remove the names and post the work description here. You need to act quickly.

I don't think we have enough information from the OP to fully understand what's being constructed.

Generally speaking, solid panel sheathing is applied to the exterior face of studs for all perimeter walls (and some interior walls if additional shear or lift capacity is required for the design). The exception may be Zip system sheathing where this is included as part of the Zip paneling.

As RES describes, some older framing used let-in diagonal bracing which is not as good as ply or OSP (or Zip) continuous panels.

"...Last minute we decided to replace all the old wood siding on the house..."

Well...in that case you should do things properly and install the ply or OSB panels or Zip system.

Good luck with your project.

That wouldn't fly around here, mild climate, but windstorm area. Our home has wood framing, wrapped 100% by OSB sheathing, then tyvek, then Hardie.

Seems it never rains in southern California ...

"Seems it never rains in southern California ..."

There may be a song in there....................................

This is all bass ackwards. If the siding is being replaced, and there's no sheathing underneath, the windows have to come out. The sheathing is applied directly to the studs, and covers up to the edge of the window rough openings. Not Tyvek. Then the windows can be properly installed and flashed correctly against the sheathing. The original post seems to describe a recipe to rot out a house in a single rainy season.

Where did you find this "contractor"? Are why would anyone ever get rid of original redwood siding to begin with???

I wonder if the OP has any idea of the cost of genuine redwood siding...?

I doubt you could even buy red wood siding anymore. My sister bought a 60 year old home and reconfigured some some windows. Tried to find some redwood siding to fix some areas. Couldn't find any. They managed to salvage and piece together some they had to tear off. Siding in pristine condition, even in areas that should have rot because it was touching concrete stairs for 60 years. Just needs a little scraping and fresh paint.

Maybe California has more redwood available but Minnesota it's rare. I hope the redwood siding was salvaged it would be a shame for it to end up at the dump.

Many decades ago, it was plentiful and relatively cheap because we were indiscriminately chopping down ancient forests. Today it's available, but somewhat pricey (maybe $10-$20/sqft, uninstalled) from managed redwood forests. It's beautiful stuff, with great properties as a building material, although I suspect it's not quite as good a quality today compared to old growth trees. But I'm glad we are not able to do this anymore:

The original siding was cracking, damaged, etc. It is being replaced with cedar siding. This is not a DIY - it’s a massive, down-to-the-studs reno. Under the original redwood siding there was black paper. The house is 60 years old, and we live in Los Angeles. And that’s right, it rains like six times a year here.

And W’s, we decided to replace the siding after the new doors and windows were installed. And there are lots of windows.

*yes, not W’s

"...it’s a massive, down-to-the-studs reno..."

Then do it properly. Use plywood, OSB or Zip sheathing.

Save the redwood for something. It's valuable. Then take out all the windows and start over with the proper sheathing.

Jerri-

If there was tar paper under the old siding, I presume there was some kind of board sheathing under it? If so, did that get torn off, too?

I agree that redwood and cedar should be cherished, reused and maintained. As for the sheathing, it could be more complicated. As long as the frame is structurally braced and there is blower door proven airtightness, then having no structural sheathing could arguably be better, it depends on the details.

The Arctic Wall developed by CCHRC seems to perform well and the main argument for not using OSB or plywood is that it can trap moisture.

It's doubtful most projects are going to have the necessary attention to detail for this and there is a strong case for insulative sheathing in building climate zones 4 and colder. For all climates the Zip product is appealing because it's so easy to make an effective air barrier, the most overlooked yet important fundamental of a building shell. Unlike structural or insulative properties, airtightness is easy to measure and improve.

Frame homes with siding but without sheathing were not uncommon before the 1940s.

Dissecting an 1835 home. Siding directly onto the timber framing.

Here's Fine Homebuilding's guide on how to properly insulate such homes while retaining the siding.

One option for retaining the old siding while providing water-resistant insulation and a rain control layer.

But once the siding is being replaced, modern methods would be more energy efficient and weather resistant.

Somehow your siding person thinks the black tar paper underneath the original siding can be improved upon by using Tyvek. He may be right about that. But he's letting that small improvement overshadow the fact that neither would be acceptable today without sheathing. Remove the Tyvek, add sheathing as if it was new construction and then Tyvek.

When cedar siding s installed over plastic house wraps, or Zip panels, the wrap and panel manufacturers recommend the cedar siding be back-primed. Although the manufacturers don't make recommendations, it should also be done for asphalt saturated felt.

OP......it's obvious you did NO research on what you were doing!! 'So the old siding was removed, and tyvek paper went up... directly onto
the framing. IS THIS NORMAL? On the addition (new construction), the
tyvek was put on top of plywood.'

I would think after the 'old' siding was removed, everything else is new. Everything from then on should be to 'current' codes. What do the inspectors say??

"IS THIS NORMAL?"

We ask this all the time................................

I'm not aware of a residential building code that requires structural panel sheathing except when its called for to resist seismic and/or wind forces. For a house in a low risk zone, let-in diagonal bracing is allowed and the inspector would have required it if it was not present.. However, a weather resistive barrier (Tyvek, etc.) is required.

A building inspector is not the person to rely upon for good design choices or workmanship; he/she represents the city/county instead of you and is concerned with public safety and the next coffee break.

The thing that is scary to me is the words "We're doing a huge reno & addition". It should have been obvious from the start that such a project needs a qualified designer to represent and protect the owners in the design and construction phases.

You get what you pay for, pay me now or pay me later .... all the tired old cliches apply.

I hope the OP was able to stop the work and get someone on site to advise her. I suspect this issue is just the beginning of the problems.

I appreciate the helpful and constructive input - not quite loving the judgies though. I will reiterate this important detail: replacing the siding on the existing house was not a part of the original plan. It was an after thought, and as some have noted, the plywood is not necessary to pass inspections. I have a licensed and competent general contractor building my house - not a bunch of smack heads I picked up on skid row. We live in sunny LA, and I think he was trying to save us money by not doing the plywood. And it is my understanding (from various contractors I have spoken to) that there is more than one proper and correct way to build a house. So everyone please calm down, and remember what your mama told you: if you don't have anything nice to say, then shut it down.

One more observation. I live in earthquake country, and so do you. I want my house to be as structurally sound and cross-braced as possible. Sheathing is one of the things that accomplishes this.

We are also in the LA area doing a reno and addition on a 1948 house. Without knowing the details, it seems we have some similarities. Our house had redwood inside and outside and we ended up having to get down to studs because we added more openings. Do you have a lot of interior shear walls? We had to put shear walls in the exterior walls and install sheathing before wood siding in the plans. Wonder why it is different for you.

I suspect the OP's house has some wind bracing somewhere; we just haven't been told about it. Photos would have solved that problem.

All exterior walls of a house act along their length to resist the wind forces transferred to them by upper floors and roofs. When portions of those walls are reinforced with what the building codes call "wall bracing" (diagonal boards or structural panel sheathing), they are called "braced walls".

When additional bracing is required at interior walls due to unusual conditions, like too much glass, they're designed by an engineer and called "shear walls" although they do essentially the same thing as exterior braced walls do, interior shear walls will usually be shorter and require additional design and construction in order to transfer the forces all the way to the ground since there might not be a foundation wall below it.

IMO the reason some members have reacted in a critical manner is that seeing an exterior wall built without bracing seems ridiculous and it is. I'm sure the walls are braced somewhere, either by another part of the house or by diagonal bracing but we just don't know about it. An interior shear wall would not have been built in lieu of exterior wall bracing.

Like so many threads here, the OP gave us a fraction of the information and we grabbed it and ran with it.

In the majority of cases, shear walls are designated with specially designed footings/ foundations, tie down connectors to tie the wall framing to the footings/foundations, with specially designed sheathing and a specified nailing schedule. In many cases there will be specified connections for the roof framing at the top of the shear wall, and connections between the second floor and first floor framing. It doesn't matter if the shear walls are perimeter walls on interior walls; they are all designed the same for the same purpose.

It's also common that plywood or OSB will be called for the roof sheathing to act as a structural diaphram.

In other words, shear walls and roof diaphrams are much more than nailing some plywood or OSB panels at the corners of a house. And this sort of design is why the older let-in diagonal bracing may no longer be sufficient to resist lateral and wind forces.

I agree with RES that we got only a bare partial of information from the OP, which is all too typical of many postings here.

But one thing is very clear: in light of the OP's comment of a major remodel, the existing and new construction involved should be designed for lateral forces which are common in California.

Ok, so you need to know that there's a difference between the existing structure and new construction.

Current code generally requires diagonal bracing that consists of exterior sheeting or let-in bracing. Local codes may be much more restrictive if wind, earthquakes, etc are an issue.

Some older homes (1910 - 1920's that I'm familiar with) were built with lath on the interior of the perimeter walls that was a full 1" thick, tongue and grove, that provided excellent diagonal bracing when covered with plaster. They had no diagonal 1x boards as sheeting under the exterior cedar siding - just tar paper.

Your local building codes will determine if you need OSB or similar sheeting when replacing the siding. Doing so does improve the structural performance of the house and improve the appearance of the siding. However, HardiPlank siding, for example, is manufacturer approved for installation over open studs (that were covered with Tyvek or similar). Know that if you remove the plaster/lath from the interior perimeter walls you MUST provide diagonal bracing regardless of what is permitted by code if that plaster and lath is the source of the diagonal bracing.

If you are keeping the existing door and window frames, adding sheeting will create additional challenges - but they can be addressed.

As for cedar siding, it has a lifespan of about 50-70 years. I'm sure there's some that's lasted longer, but general rule is that by the time it's 50-70 years old it's time to go. In addition, anything that old is coated with lead based paint. Removing the siding allows one to fix insulation, structural issues, water issues, lead paint issues, etc. I'm a big fan of coming back with the appropriate HardiPlank siding (generally that's smooth and not textured) with the correct reveal.

So, to answer your question:

1. Check manufacturer's instructions on installation over open studs.

2. Check local code on re-siding over open studs

3. If there's no other diagonal bracing besides the 1" lath and plaster on perimeter walls, consider if the plaster and lath will be removed in the future. If yes, then you must sheet the exterior before siding - even if code would allow you to re-side without sheeting.

4. For the best structural performance of the home, and for the best appearance of the siding, you want to sheet the exterior of the home with OSB or similar.

In summary, you may not be required to sheet the existing structure, but it would be a very good idea to do it anyway.

That's exactly how I plan to rewall my potting shed. No sense on a shed to put down sheathing, then wrap, then the exterior siding, since the insulation with go inside and interior paneling over that. And.. it's just a shed.