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Old 11-28-2015, 01:51 PM   #1
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Old home - crazy plan?


Hi!

I have an 1860 farmhouse of some historical significance. Nothing is insulated, at all. The 2nd floor is essentially unfinished...3' kneewall, and the roof. The home is post-and-beam, and everything is in good shape. Partial fieldstone basement has been spray foamed, so it is pretty dry down there.

I want to build in the 2nd floor. I can look down in that knee wall right now, and see my sill 8 feet below. Now, if I truss the 2nd floor and create finished space and insulate it (4" of foamboard or Roxul), with its own vapor barrier, but do NOT insulate the 1st floor walls, what happens?? I can't figure out if I should close off the top of the wall, or leave a bit of a gap so moist, warm air can escape into the new 'attic' above my construction...which could be gable-vented if appropriate. If I closed the wall top, won't that cause condensation and moisture on the sheathing (which will be cold...)?

I've talked to a few others about this - I'm not doing it to go 'high efficiency', but just to grab some warm air and hold it for comfort. We heat with wood; the uninsulated 1st floor isn't a big deal to us. I don't want to spend $10k to save 1 or 2 cords/year. I don't want to pump in dense pack & ruin the historic plaster, or spray foam, etc. etc., and this is all going to be DIY.

So I guess, has anyone here done this, how and why did they do it, and is my 'plan' crazy, or does it just need some fine-tuning?

Thanks!

Plan I have so far, nothing started yet:

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Old 11-29-2015, 06:39 AM   #2
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What is the construction of the 1st floor walls? What is the exterior sheathing and construction type?
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Old 11-29-2015, 06:58 AM   #3
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Hi Windows,

Post and beam framing (so wall cavities tend to be quite wide)...from inside to out, 1st floor is plaster, air space (6"?), sheathing boards, probably tar paper, original clapboards...then a "foil blanket" and the old asbestos siding they probably put on early 1960s.

The main question is how the dynamics change if I totally close the top of the wall, which you can see down into from the 2nd floor at the current time. I wonder if the sheathing stays warm enough so no worries - or if I will create a condensation problem for myself!

Thanks,

Knee wall with an interior board removed:

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Old 11-29-2015, 07:14 AM   #4
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I would be concerned about that as well. It's likely that the foil blanket isn't vapor permeable and the walls are staying dry via convective air movement. I would be sure to leave a space for that air to still move up.
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Old 11-29-2015, 07:23 AM   #5
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My thoughts exactly! the gap where floor meets knee wall is really only about 1.5", and I plan to leave that. Build 2nd floor per usual (vapor barrier on inside etc). So hopefully that dynamic will stay the same...moving moisture out of the wall cavity. This makes it impossible to install soffit venting, though.

I am concerned about if I have to install a gable vent. There is none now, but this 2nd floor is 16' high, has lots of air volume. If I halve that by making new 8.5' ceiling, might have a spot to catch condensation above my new work. I figured I'd install the vents, and would have house wrap on the OUTSIDE of my new walls just as a vapor precaution (to stop "out from in" migration).

I'm thinking of this sort of like how someone might do a gambrel, in a way. Does this make sense? <see drawing above>

Thanks!
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Old 11-29-2015, 08:11 AM   #6
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If I felt the way you do, I would go with your drawing. I think you will maintain enough air flow to protect the first floor cavities.

But, I would investigate whether plastic is the right choice for the vapor barrier. I'm not sure it is considered the right thing to do anymore.
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Old 11-29-2015, 08:41 AM   #7
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+1, Colby. Any idea how i can figure out how much gable vent to provide?

I'll look into the right barrier method...
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Old 11-29-2015, 08:49 AM   #8
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I have to disagree.
That's balloon wall framing.
Those walls are open all the way to the crawlspace or basement.
They act like a chimney in a fire.
Around here you could not even buy insurance until the top and bottom of those walls where fire blocked.
Going to have to be done anyway when insulation is added.
100% sure that attic was even designed for living space?
Add a bedroom and it opens up a whole can of worms with the building, zoning and health dept.
Main concerns are septic, egress window sizing, and a big deal is floor joist sizing and spacing.
If the joist are over spaned, over spaced, under sized there's going to be damage to the ceilings below.
In your area at least R-40 to R-50 is called for in the ceiling, without some major changes there's just no room the way it's built now.
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Old 11-29-2015, 09:27 AM   #9
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What code? I live in a very rural area.

That's post and beam, not balloon framing. The sill at the base is 8" square, and there is no communication with the basement - altho, yes I do understand - should a fire start in the wall, there is no firestop. Again, this is how they built them, and as we can see, retrofitting them can destroy the home by trapping moisture. Insurance was a-ok with this construction.

The part up here you're not seeing is the 'nana room' - there is a framed in and plastered room in 1/2 the 2nd floor, it's been there for 150 years. My construction will be lighter than this. This is listed with the town as a liveable bedroom already, by the way - doing what I plan won't change that a bit. Home-owners are allowed to do their own work here.

I'm working with an 'old home experienced' carpenter to determine loading and such, anyway.

This is a better pic across the space. Like the creosote? Old homes..:
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Old 11-29-2015, 06:01 PM   #10
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If the basement is spray foamed, it should probably have been blocked out previously.

I would do just as you are planning with some rigid foam to complete the thermal break from the exterior and allow that middle floor to vent/dry to the outside via convection. It isn't going to dry through the foil barrier at this point.
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Old 11-30-2015, 05:54 AM   #11
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Quote:
Originally Posted by Windows on Wash View Post
If the basement is spray foamed, it should probably have been blocked out previously.

I would do just as you are planning with some rigid foam to complete the thermal break from the exterior and allow that middle floor to vent/dry to the outside via convection. It isn't going to dry through the foil barrier at this point.
Makes perfect sense. By using rigid foam, do you mean "sheathing" the back side (cold side) of the trusses I will build? Instead of using house wrap...then insulating the 'bays' with something like Roxul? I see the point, that prevents the framing from acting as a thermal bridge...

Safety: I would think that them foaming the fieldstone basement, all exterior walls and penetrations, and extending up onto the subfloor gives some measure of fire safety (which here, simply means more time to jump out the window! Of which there are 3 on 2nd floor) 70% of the housing stock in my state is of this vintage, and few can retrofit to the degree that an engineer would say the home now meets modern standards. $50k isn't generally available, nor are qualified builders to help. These places are not modern - they are antiques. Mine is a nice one - you should see some of the others in the area! Joe is correct in pointing out concerns, of course! Many places you'd be in deep doo doo without an engineer, architect, licensed GC, 20 permits, town council, oodles of fees and permissions...that is why I moved from a more built up area...if you can't DIY, you are in BIG trouble. 25 years in the trades, as a restoration painter/glazer, but cautious about insulation...
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Old 11-30-2015, 06:47 AM   #12
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Yes on your first point.
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Old 11-30-2015, 07:06 AM   #13
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Quote:
Originally Posted by joecaption View Post
Add a bedroom and it opens up a whole can of worms with the building, zoning and health dept.
I don't know how it works in your area but where I am at it only opens a can of worms for the building department. Around here adding a bedroom to a residential home isn't a zoning issue and the health department doesn't nose around residential unless your running a day care center or a catering business.
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Old 11-30-2015, 02:35 PM   #14
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Quote:
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I don't know how it works in your area but where I am at it only opens a can of worms for the building department. Around here adding a bedroom to a residential home isn't a zoning issue and the health department doesn't nose around residential unless your running a day care center or a catering business.
I grew up in MA (sadly), and it's exactly like that. I worked the trades from 17 yrs. old til 30, then moved to Maine. Not like that up here, at all!! You have to do what makes sense and will protect your property, of course, and COULD have insurance issues...good warning, but a lot of the nation still is free to do with their property what they will.....their loss, though, if they don't do due diligence to make sure it's not going to mold up in a few years! That's why I'm checking my thinking on this, before going in with a carpenter to build in trusses - he probably won't have the knowledge that everyone on here does! Carpentry, yes....insulating - dark art for most (me too). Tons of people have 'built in' their old homes like this, since the 60s, up here. But most close it all up with fiberglass, and we know that can rot & attracts rodents...

I'm not adding anything (well, maybe a 1/2 bath up there, LOL), the bedroom counts right now and the other space will just be storage. They lived in here all thru the years, the last 150 of them - there are wood stove hookups all over....3 per chimney, ha ha (bad bad bad). I have one big stove on the 1st floor, stainless liner, that's it (actually to code). So I will need to insulate up there to catch some of the heat. Probably put in floor grates, too...

Windows - I see what you're getting at, thank you - good idea.
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Old 11-30-2015, 03:03 PM   #15
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If you wanted to insulate the walls you could go with Styrofoam breads and blow them in the wall from up stairs. You could use a shop vac, just take the filter out and do a little modification and use that to blow the insulation in the walls. Check out the video.

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