Wall assembly with fiberboard?? Considering exterior insulation while siding

[KBforester]

Hello folks,

There is a lot of info online about wall assemblies, but I can't quite find the information I'm looking for. I bought this house a couple of months ago, and started on my first task- removing sketch deck 10' off the ground, on the walkout basement side. It's actually a sunporch and deck, so there is a large square on the side of the house that will need siding. Its old vinyl siding, its cracked and ugly. I'm going to replace it all instead of just a square.... you can see how this is snowballing quickly. 

If I'm replacing the siding on a 40 year old house, why not add exterior insulation? Great. Plenty of information online. I am interested in peoples opinions on insulation if you have them, but the assembly as a whole is perplexing. 

From the interior going out:

1. Drywall (or wood paneling)
2. 6" studs with fiberglass insulation. Pretty sure its craft paper on the interior- will confirm
3. 1/2 OSB sheathing
4. 1/2 FIBERBOARD????
5. Some kind of perforated house wrap.
6. Vinyl Siding 

The only thing I know about fiberboard is its not used much anymore. I'm 38, I've never seen in used in real life before. I've only heard about it as a sheathing accompanies by other bracing, not as a secondary layer. Maybe as an insulation or something? Its black on both sides, I've attached a picture. 

Can I just insulate over it? Or do I need to remove it and the house wrap? 

My plan so far is:

1. Drywall (or wood paneling)
2. 6" studs with fiberglass insulation. Pretty sure its craft paper on the interior- will confirm
3. 1/2 OSB sheathing
4. 1/2 FIBERBOARD????
5. Some kind of perforated house wrap.
6. 2.5" EPS 
7. Strapping for a rain screen + Screws
8. Wood clapboard

I guess since I don't know what the fiberboard does, I'm not quite sure what's going on with moisture management. 

So... long story short: WHATS THE DEAL WITH THE FIBERBOARD, AND CAN  I GO AHEAD AND PUT ON EXTERIOR INSULATION OVER IT? I live in central Maine. 

Thanks! I haven't posted to Forestry Forum in a long time, there are lots of smart people here. 

 

[Don P]

It looks like Celotex fiberboard. It's been about 40 years since I used any. It was meant to have high vapor permeability to let the wall cavity dry, the black asphalt surface was to face out and repel water. If you are using EPS and not XPS it also has good permeability and you are in a heating climate so that should vapor drive to the outside. There is a stack of different "breathable" materials piling up. At some point it ceases to be very permeable. Not a clue if this is pushing the line.