Home depot sells this and I was wondering if it sounded right? 3/4 in. 4 ft. x 8 ft. R5.0 R-Matte Plus 3 Insulation. So ten sheets would be 7.5" thick (8" realistically) and give me R50? They list a 1/2" sheet with R3.2, which scaled to 3/4" would be R4.8 so it's pretty close. If so then I'll post up my wall structure diagram and would appreciate feedback on it...

Here is the link to the website...

3/4 in. 4 ft. x 8 ft. R5.0 R-Matte Plus 3 Insulation

Yes- all polyisocyanurate insulation runs ~ R6-6.5/inch. And that's the aged R-value- it's about R7/inch when brand new. It's R will change somewhat with temperature, more than spray polyurethane, IIRC but not as much as EPS (bead board.)

It can be bought at lower cost in thicker sheets and with various facers fiberglass/foil etc. Rather than stacking up 10 sheets of 3/4" to get ~ R50, try 2 layers of 3.5" or 4" goods, sold as roofing insulation through commercial construction distributors, not orange or blue box stores. It's been successfully used as insulating wall sheathing for high-R structures as well, eg.: A double-layer of 2" iso on the exterior of a 2x6" framed wall with spray cellulose delivers an R45-R47 clear-wall value on a wall less than a foot thick. (To get the same R value in a double-studwall with all cellulose would take ~15" or more with sheathing & siding & interior drywall included.)

TY Dana1 I appreciate it! I'm mostly a forum lurker and you always give good advice! What I'm looking at is using shipping containers for construction of very basic housing. Essentially just simple boxes, no weird shapes or angles. Using google sketchup I've been building the structures piece by piece looking for ways to keep it simple and estimate material costs.

I am in central Florida (zone 2) and the goal or course is an airtight, sustainable and dependable house. I chose to start with shipping containers as a base to re-use them, strength, and cost. I plan to insulate on the interior of the container, and leave the exterior steel untouched, except for paint. This is what I have been playing with...



The right side and top are the container walls, the left side is partially cut away into the main area of the home. From the exterior to the interior there would be the container steel, 8" polyiso board, 1/2" OSB, 2x4 stud wall, drywall. I plan to make the steel shell airtight, then once that is done, insulate with the polyiso, sprayfoam the weird/tight spaces, and build the interior stud wall. I know your going to ask, the reason for the OSB is that instead of trying to make the drywall airtight, I will make the OSB airtight. Then I can run the utilities inside the studs without (I hope) as many worries. From what I've calculated, the OSB doesn't add very much the material costs, and I believe would solve a lot of problems with future airtightness...

This will be a family built home, which is why I'm trying to keep it so simple yet still functional, form isn't even being factored in :) Considering it will be me (6' computer geek), my ex-wife/best friend (5'2 95lbs soaking wet), my son (11yr old geek), ex-wife's daughter (2yr old), ex-mother-in-law (the man hater), and my mom (bad hip and knees) living there, I think I'll end up doing most of the work, so simple is good...

And don't ask for any back-story on all that it'll make your ears bleed...!

A question for Dana1 "try 2 layers of 3.5" or 4" goods"

How would you attach the second course of insulation and then attach an outer covering, vinyl, stucco or whatever? Just curious!

Sorry, I reread the post and read 2 layers of 2" that is doable with nails!

John

Air-tight OSB is fine. You might consider using 1x or 2x furring through-bolted to the steel for much of it rather than a full 2x4 studwall, to save interior floor space. The bolts would add some thermal bridging, but since it isn't structural- it only needs to hold up the OSB & insulation- the steel carrys the structural load, so you don't need many. You'd have to thin out the insulation a bit behind electrical boxes to fit them into the shallower space, but the hit in overall thermal performance would be quite small for such a small amount of square footage (square inchage? :-) )

If it's in direct sun it'll be worth using a high solar-reflectivity high-emissivity "cool roof" paint (see http://www.coolroofs.org/index.html ) on the exterior of all that steel (particularly on the top) which will cut the sensible cooling load measurably. Designing it for minimum east/south/west glazing with appropriate overhangs & exterior shading counts too (big time).

Don't forget to insulate the floor too. Heat gain through the floor would likely be pretty small, but heat loss through a steel sub-floor during the winter could make for some pretty miserable barefoot mornings. R7 would be about the minimum for comfort but going with something like R10-R15 might be more optimal from an energy use point of view. (This LA Passivehouse used R16.5 under a slab, but that was fairly well earth-coupled- you'll most likely be at grade, running both higher & lower temps than that VERY well insulated house: http://www.greenbuildingadvisor.com/blogs/dept/green-building-news/passivhaus-finds-home-bayou-state If you're going for that sort of energy use level you may want to consider insulating under the cargo can as well, not just interior.) Using XPS or EPS instead of iso would give you better floor loading capacity, and you'd need a 1/2"-3/4" OSB/ply subfloor, but the insulation & subfloor could esentially float- it won't need sleeper-joists- just a few attachments per sheet of subfloor to keep the shifting under control would do.

JohnyH: 5" nails may not be the best way to go either. Foam board construction adhesive can be used for assembling the insulation, but there needs to be something more structural than the insulation supporting the siding. Typically with stick-built structures with thick exterior insulation 1x furring is used to trap the insulation to the building, through-screwed into the studs, and the siding nailed to the furring, leaving a 3/4" rainscreen gap between the siding & insulation (or housewrap, depending on how the designer stacked it up.) The thicker the insulation and heavier the siding, the more screws would be needed to handle the load. (Fiber-cement siding is a lot heavier than vinyl, etc.) But nails would almost surely pull over time on any sheathing insulation thicker than ~ 1.5".

Sorry it took so long to respond, running a business consumes more time than I ever thought it would!



Anyways, the main idea behind the 2x4 stud wall was ease of building. I wanted to attach to the exterior steel as little as possible. Also pretty much everybody is comfortable with 2x4 walls, nobody is going to look at it cross-eyed and wonder what is going on. I'm already scared of the inspectors freaking out because I'm using containers, I don't want to give them anything else to bother me about. Also I figured it would be quicker and easier to build by myself or with one or two people helping. I can build an 8' section at a time, put it in place and secure it, then build the next section.



Currently the easiest way to describe the home is a pyramid shape. There will be two rows of five 20' containers spaced 40'(ish) feet apart. Then on top of those spanning the empty area will be five 40' containers. Then a 40' container on each open end. This will leave me with a totally enclosed steel shell, once I finish welding it all up of course. The central area will have a stained concrete slab, and the containers will be welded to steel pilings and be up off the ground about 1'. The area under the containers will be sealed and insulated (from both the inside and outside environments). The one thing I can't seem to get a straight answer on is whether I should insulate the slab. I would like to use the earth to help keep the house cool, and figured 1600sqf of exposed ground coupled concrete could help. Some people tell me it would give me more to cool, and other people tell me it would help cool the house.



For the container floors I thought of just laying down 1" of foam board and then 3/4" decking. OR just pouring 1.5" to 2" of concrete and staining it to match the main slab. I've seen another person use the concrete floor idea and have to say it looked really nice and came out pretty cheap.



The roof will be painted with a cool-roof coating and the exterior walls will be painted a light color. I also plan on building a shade roof. Essentially just an inexpensive corrugated or steel roof on stilts 2' to 3' above the top of the containers to keep direct sun off of them. This will also be painted with a cool-roof coating. It will be open on all sides to allow normal airflow to remove any heat between the shade roof and container roof. Although I can't think of any way to keep it from blowing away in a hurricane, I'll just make sure it's inexpensive enough to not worry about it :-)

Posted By Quarantine on 11 Oct 2010 03:14 AM




Currently the easiest way to describe the home is a pyramid shape. There will be two rows of five 20' containers spaced 40'(ish) feet apart. Then on top of those spanning the empty area will be five 40' containers. Then a 40' container on each open end. This will leave me with a totally enclosed steel shell, once I finish welding it all up of course. The central area will have a stained concrete slab, and the containers will be welded to steel pilings and be up off the ground about 1'. The area under the containers will be sealed and insulated (from both the inside and outside environments). The one thing I can't seem to get a straight answer on is whether I should insulate the slab. I would like to use the earth to help keep the house cool, and figured 1600sqf of exposed ground coupled concrete could help. Some people tell me it would give me more to cool, and other people tell me it would help cool the house.



For the container floors I thought of just laying down 1" of foam board and then 3/4" decking. OR just pouring 1.5" to 2" of concrete and staining it to match the main slab. I've seen another person use the concrete floor idea and have to say it looked really nice and came out pretty cheap.

If I'm understanding this correctly, you'll have a central section that is slab on grade, about a foot below the bottoms of the containers(?).

In central FL deep subsoil temps are ~75F- pretty close to conditioned space temps, but you still probably want to insulate under the slab if you're going for R40+ walls & roof. The thermal mass of the slab itself it probably sufficient for dealing with the diurnal temp swings, and if insulated, you won't be heating/cooling the thermal mass of the earth with your mechanical systems should you choose to run the house at a temp different from earth temp.

If you don't insulate with more than R5 (1" of XPS) between the steel and the subfloor you'll have a significant thermal short-circuit around all of that wall & roof insulation for both hot & cold exterior air.  Insulating under the container (between the steel and the ground) would help some, but not nearly as much as you might hope for, since steel is a pretty-good thermal conductor.  Detailing for as much thermal break as possible between the steel and the conditioned space will be critical for maintaining thermal performance. The heat gain/loss of an R50 wall with a big steel heat-sink penetrating it will be dominated by the qualities of the heat sink, not the insulation.