Looking into buying this house that was built around 1900. From the photos, it appears that there is a layer of shiplap underneath the siding. Is there any way, barring ripping all of the siding off and re-sheathing and wrapping the house, that I could go about insulating? I've read a bit about insulation and moisture problems, and the idea that you need the vapor barrier seems to be somewhat disputed (according to this article the sheetrock ends up behaving as a vapor barrier). It also appears that this structure has some lateral bracing, so the sheathing may also be overkill. So what would be the most efficient way to insulate? just pack the walls with insulation and seal for air leeks? Get some closed cell foam panels and cut to size? Experience would be appreciated.

Also found this interesting article.

enter image description here

  • Since the walls are open staple the insulation up. I would not remove the old siding as it looks to be in good shape from the inside. I have remodeled several turn of the century homes and have found it easier to gut the inside than mess with the outside and it is impossible to get the quality of wood that is on the outside unless you just won the lottery.
    – Ed Beal
    Dec 25, 2017 at 0:07
  • thanks, also, I'm not sure that is the siding, I think it is the layer of lap board that is below the siding, but I'm not absolutely sure
    – user379468
    Dec 25, 2017 at 0:08
  • On the old places there was a sub level This 2 layer is incredibly strong, the actual siding is usually cedar or redwood and at that time most of it was clear no knots or very few.
    – Ed Beal
    Dec 25, 2017 at 0:12
  • 1
    Who's project got abandoned after the historic interior was gutted? What climate? What's the outside look like? Lead paint?
    – Bryce
    Dec 27, 2017 at 2:49

3 Answers 3


Ahhh...the good ‘ol days. We didn’t worry about much: 1) single top plate, 2) top plates not lapped at corners, 3) no headers in non-bearing walls, 4) no hold downs, 5) is that a floor above those ceiling joists? 6) that beam on the left with just a single stud under it probably doesn’t mean anything either.

If you live in a high wind area or a high seismic zone, you may want to put some clips on those ceiling/roof joists, add a hold down or two, check your anchor bolt sizes, etc.

You can’t follow the “prescriptive path” for energy compliance requirements with those 2x4’s. You’ll need 2x6’s or add some rigid wall insulation, extra ceiling insulation or install a super efficient heating system...all of which requires a ton of calculations.

BTW, do not install plastic sheeting vapor barrier on the inside of the walls, unless you live at the North Pole.

You’ll need to Solve some of these issues to get a Building Permit. You are getting a Building Permit, right?

  • hahahaha building permit? by rigid wall insulation, do you mean closed cell foam? like cut and cobble method? seen it where people are putting a 1" gap between the outside and the foam. 2x6 s? just ot have a cavity larege enough for fiberglass ?
    – user379468
    Dec 26, 2017 at 14:44
  • 1
    If you’re too smart for a Building Permit, then you’re probably too smart to understand 1) why you need double top plate, 2) window headers, 3) posts under beams, 4) hold downs, etc. The reason we vent the attic is because of the Dew Point and air space on the outside of the attic insulation. So, we fill the stud space so there’s no air space (and thus no need to vent the stud space) in walls.
    – Lee Sam
    Dec 26, 2017 at 16:17
  • 2
    @LeeSam smart or not, consider he's looking at buying historic wood. It's tight grain first growth timber, not termite ready home depot lumber. 118 years of standing up argues that perhaps the double top plate was not really needed. But insulating it? That could cause this home to rot in just a few years.
    – Bryce
    Dec 27, 2017 at 6:05
  • 1
    @Bryce Yeah, look at all those houses out there that develop rot in 2 years after installing insulation...I’m sure it’s not from 1) improper placement of vapor barrier, 2) leaky roof, 3) lack of moisture barrier... Darn that crazy insulation. Oh, and termites like that original growth lumber just as much as that “termite ready Home Depot lumber”, whatever that is...(You’ve got to explain that remark.) so, the moral of your story: “You’ve suffered without insulation for 100 years, so you should continue suffering.”
    – Lee Sam
    Dec 27, 2017 at 6:51

Your options more or less come down to:

  • Spray foam, trimmed to the stud bays, then sheetrock
  • Fiberglass, probably UNFACED without the vapor barrier.

I don't recommend cellulose. While cheaper it retains too much moisture given probable other problems.

Really you appear to need local help, as there are a dozen other concerns that come before insulation here. If it's 118 year old wood siding outside, you don't really want to mess with it. And for that matter consider contacting a local historical society... you may run into some vintage photos of the place and be able to add vintage touches.


I agree with the article, but insulate to suit you and let the house do what it's always done...on a smaller level. To air-seal breezy siding, go for spray or rigid foam. This way, the siding still does its breathing and drying like it always has and no moisture gets into the stud bays, but you get comfort.

If spray or rigid foam is too expensive, then batts are perfectly fine. However, to stop the drafts you must have vapor barrier and it must be against the shiplap. Why? Because, batts only work in dead-air space and breezy siding will destroy fluffy insulation's R-value instantly and completely.

For between floors, I do the vapor barrier on the bottom...heat rising takes moisture with it. For exterior masonry walls, I do the vapor barrier on the inside...keeps moisture to a minimum and any that gets it is sucked up by the masonry and bled right out. You saw above what I do with breezy exterior walls...it kills all drafts and convection that draws moisture into the wall.

I've never had the slightest problem, mold, dampness, rot nor wet-bug attraction...potato bugs, silverfish, etc. For the structure, the house was built right and has the joists lined-up with the studs, but you may want to replace your almost worthless joist bridging with homemade or purchased IBS2000's, they make a huge difference (see - IBS2000 Fix for Bouncy Floors https://www.youtube.com/watch?v=dTf-pGj6zoU AND How to Fix Bouncy Floors https://www.youtube.com/watch?v=R_OF9KgWhzI

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.