Insulating ISBUs for Fun and Profit… YOUR OWN!

10 Jan

As the New Year (2011) starts to rear it’s ugly head, I have a few ISBU projects that are demanding a LOT of attention.

So, I’m gonna reach into the mail bag and answers some email.

Here goes:

Trey said (for about twenty pages… Oy.. we have another “Ted”);  🙂

RONIN, I love your website. I have just finished reading all of your archives and your book. Great stuff. I even followed your comments on ADVRIDER [Editors note: link deleted].

Oh my, I think I am a stalker. : )

Yes… you are. You’re a stalker. 😉

Right about now… I suspect I’m being “buttered up”… 😉

1. Is there a way to be notified when someone post a comment to your blog? I have found that your answers to the comments are very insightful and straight to the point.

Not at present. The format we’re using doesn’t incorporate user notification of new comments.

The blog format is going to change sometime in the first Quarter of the new year (2011).

2. It seems like you have a few different websites dealing with ISBU. Can you provide a list of them?

The two primary ISBU sites are:

Renaissance Ronin and

The other blog I contribute to regularly is “The Bubba Effect” –  which is a “family survival” blog.

3. Previously you said that you can use furring strips and welded L brackets on the outside and then spray SPF and then attach your siding. However, if you use nails or screws to attach the siding isn’t that creating a thermal bridge where the screw goes through the siding, spf and furring strip? Is it okay because the bridge created by the screws are so small?

Note first that each location and climate demands a offtimes different solution.

First, to clarify:

I said “Angle Iron” – NOT “L Brackets” Those are two entirely different animals.

It’s true that the dimensional lumber you use in conjunction with SPF (complete with mechanical fasteners – nails/screws) will create some thermal bridging. It is “minimal” but it will indeed create a “thermal bridge”. It WILL be measurable.

In temperate climates like Los Angeles, it’s not really an OMG issue. In places like Montana and Wyoming (or even worse…) it can be a “major league” big deal.

A work around is to actually apply your SPF or Rigid Foam (PolyIso) to the container and then embed or attach 2x4s (24″OC) into (or on top of) that insulation base to create both an air-space and a thermal break. Then use fasteners (I like screws as they don’t come loose in heavy weather) to attach your siding into those 2x4s.

This will also help your siding “breathe”, keeping it dryer.

4. Based on comments regarding how inexpensive Rigid Polyiso Foam Board is couldn’t I use it on the outside and then apply Tyvek House wrap to prevent air and moisture infiltration?

[editor’s note; link deleted – not current]

Trey goes on to say: Of course, I would do more research than simply buying from the first website I come across, but wouldn’t using foam board and tyvek house wrap be an effective and inexpensive alternative assuming that you properly seal the tyvek wrap with the appropriate tape?

Sure. That works.

And if you can find an insulation liquidator (you can find them regionally) with sufficient inventory you can get a really good deal on rigid insulation boards and save yourself the “headaches” that come with SPF application altogether.

You CAN commonly find “Rigid Foam (PolyIso) Seconds” that are VERY affordable. In fact, it’s the direction I send many families that supplement SPF with rigid to build up R-Values affordably.

The seconds are usually just panels with creases in the foil or chips in the sides or corners. Most are extremely usable. Note also that this is NEW product, not stuff scavenged out of a dumpster on a build site.

Rigid PolyIso is essentially closed-cell foam. So, you’ll still get the vapor and moisture a barrier benefits as well as the r7.5 value you seek. However, you’ll have to seal all the joints in between each board. I also shoot some SPF into the gaps, just to make sure everything is tight.

Using Rigid Foam boards is more time consuming… but if you got the rigid foam cheap, it’s definitely worth it.  It’s easy to handle, easy to apply and it’s almost “idiot-proof”.

If you insulate in this manner, MOST (YMMV) building inspectors will still insist on housewrap being applied over the foam.

Here’s a good example;

I constantly hear from building families (where zoning actually applies in the first place) that the yardstick they’re being bludgeoned with is based on the 2003 International Building Code.

The 2003 IBC  calls for; “a “water-resistive barrier behind the exterior veneer” consisting of flashings and a “weather-resistant sheathing paper” lapped at least 2 inches horizontally and 6 inches vertically.”

It specifies asphalt-saturated felt that weighs at least 14 pounds per square and complies with ASTM D226. Note and understand that most unrated No. 15 felt paper sold at lumberyards (which are actually confusing as they weigh closer to 7 pounds per square) do not meet this requirement.

It should also be noted that some contractors will try to use this same 15 pound felt if they think they can get away with it. It’s a no-no!

Nearly all the plastic housewraps (Tyvex, Typar, etc…) have been submitted to the model code authorities and accepted as substitutes for ASTM rated No. 15 building paper.

You’re gonna have lots of options.

If you are building in an area that follows the Model Energy Code (MEC);

Builders will be required to either install a “vapor-permeable housewrap” on the exterior or seal all the penetrations in the building by using some combination of polyethylene, caulks, and gaskets on the interior. Yes. You will.

5. I live in San Antonio and we have some pretty bad soil here. Just about everyone uses slab foundation here.

He goes on to say; Of course, once I build I will consult with an engineer. There are alot of local websites that say contractors use slab foundations here because it is cheaper. However, you recommend pilings. Does having to create a floor framing in the typical stick home cause pier & beam and piling foundations to be more expensive than slab foundations? And if this is the case, do you recommend pilings because with an ISBU home the floor framing is already present in the ISBU steel? (Boy, I hope that made sense)

I commonly recommend pilings (where possible) because they are easily constructed by hand (using Sonotubes and rebar), are easily placed in “homeowner supplied holes” and require much less in the form of actual  “site prep.”

But… in some cases, it’s just not practical.

If set on slabs (our current ISBU-based Multimedia project outside Houston is a good example) care must be taken to engineer the slabs effectively. Your engineer will carefully define what you require.

If I’m shooting an ISBU slab, note that I also like to insulate the footings. 😉

6. I have seen you say that you can build an ISBU home for as low as $28 sqft, but your average is around $40 to $50 sqft (If I am wrong on the numbers, please forgive) .

Trey continues: However, I have also hear you say that this does not include the land (obviously) and foundation. Does this number leave other costs out as well? I am just trying to get an idea of the different costs involved.

Many of my families are building structures based on ISBUs for right around $50 a square foot if they are both REALISTIC and CAREFUL.

Inflation bites everywhere and that cost is rising.  Note that this is for “structure” and doesn’t include land costs, the foundation, appliances, HVAC, or “tweeks”.

I’ve seen builds run as low as $25 a foot, but we’re talking about constructing “structural shells”. More will be spent to make them actually livable.

Realistically, I advise families seeking to build “spartan ISBU homes” to think about construction numbers that range between $50 and $75 a square foot, just to be safe.

7. What does your typical family pay for foundations? I understand there are a lot of variables involved. I just wanted a ballpark figure.

You’re kidding, right? 😉 That’s far too general a question to answer accurately.

Trey closes: Thanks, for all you do. You know if you would finish your book I wouldn’t have to ask you so many questions. 🙂

Books don’t write themselves, especially technical books (where people will try to crucify me on every page) that talk about “groundbreaking” subjects. (Pun Intended). 😉

P.S. You should really put some more ads on your website I wouldn’t mind clicking on a few ads to help you out.

I’m trying to keep the site ad-free. Honest.

P.S.S. I will save my other 20 questions for future posts. It will give you something to look forward to. ;)

You do that and I’ll blacklist you. TED gives me enough headaches. 😉

Stay tuned.

Note that no insulation was harmed during the creation of this post, but Trey probably shouldn’t try to stamp out any “paper bag fires” burning on his porch for a while. 🙂


3 Responses to “Insulating ISBUs for Fun and Profit… YOUR OWN!”

  1. Trey C. January 12, 2011 at 10:05 pm #

    Thanks for the detailed post Ronin. You rock!

    By the way I have decided to limit my questions to one every two weeks. How does that sound?

    Um… that question doesn’t count 🙂

    Have a good one

    • ted yrizarry January 14, 2011 at 7:06 pm #

      Don’t worry Trey…I will take up the slack as much as possible. Least I can do for letting Alex bash away at me! Gotta reign him in a little sometimes! 😉

      • Trey C. January 17, 2011 at 12:57 am #

        Well Ted, just in case I get blacklisted I am going to send my questions to you and then you can ask him. 🙂 Just don’t tell Ronin. LOL

Comments are closed.