I need advice on how to rebuild 2 exterior walls of an add on room to my
house. The room is technically just an enclosed portion of a porch. Due
to
poor contruction, the walls are severely water damaged. . . .
Professional assessment is 38,000$ or more but it makes true walls and
brings the room up to full specs as a bedroom code (rases floor and all
sorts of things). This is beyond us financially.
. . .

Advice on how to handle adding the missing exterior wood then the
'waterproofing layer' is what we need.

This estimate for constructing a "bedroom to code" may be helpful
in making up your mind what you really want. Do you need another
bedroom (insulated, with electricity etc.) or would a screened porch
meet your needs? This depends on where you live, temperatures
and duration of summer and winter etc.

Thanks for the reply!

What we have is what used to be a roughly 40ft wide, 11ft deep enclosed
porch all along the back of the house (wall up 3ft then screened). About
10ft of it at the outer corner was later enclosed replacing the screen with
plexiglass. The condensation on the plexiglass caused it to rot down the
lintel in the enclosure. The rest of the remaining open porch is just fine.

I don't need an extra bedroom. My use for the space was a summer playroom
and some extra bookshelves. In winter, we just closed the door and ignored
the room except the things stored in it.

If you want a rule of thumb, it is that you must remove all water-
damaged material (because any you leave behind is likely to
infect what it touches, i.e. sabotage your reconstruction. Rule

Yes, we take that as a given.

#2 is that you must decide whether (2a) you want to keep the
weather out: in which case you need siding and caulk to do so,

Ths seems what we need.

or (2b) you do not mind occasional damp, OK if the porch is so
built that rainwater runs off fast and the structure dries out
thoroughly (like my own winterized porch.) But you must
first decide whether you want a genuine "indoors" room or a
conveniently roofed outdoor space.

The porch does get wet in heavy rain but dries out fine. The enclosed part
is raised about 1/2 inch higher and water never reaches that high or even
near that corner due to the mild grading of the porch slab (designed to
drain to the other side of the house, a level shows a very mild consistant
grade).

I suspect we need to find out more about building codes and building permits
before we can start any actual exterior work.

xxcarol