Concrete home construction

[Paddy]

Highbeam,

I have done a little searching on Thermal mass and insulation. Found a neat site devoted to research on the topic. One paper in perticular that caught my eye compared 4 concrete and foam isulation methods;

Ext foam/concrete int
Ext concrete/foam/concrete int (my choice)
Ext foam/concrete/foam int (ICF)
ext concrete/foam int

Each configuration is simulated in 10 climate regions. Summary; foam on inside walls performed lowest and concrete on inside performed highest.


link to this overall website; Thermal Mass Discussion Forum

The paper can be found under "View presentations' at the botom. The paper is called; Calculation of Energy Benefits of Application of Thermal Mass in Residentail Buildings - Methodology

Be carefull, you can spend all day on this site!

 

[dfkrug]

The roof has no gable ends to speak of so maybe that helped it stay put.

Yes, hip roofs could survive; gable roofs were doomed.

The other reason that some roofs stayed on and some did not is the
quality of the top plate to roof connections. Post-mortems of
hundreds of failed newer stick-framed structures (mostly in FL in the
90s) showed that simple toe-nailed connections did not hold the
roof on. Simple truss-to-top plate connections were better, but not
enough. Codes changed to require steel strapping that extended
down the walls and in some cases, over the roof.

In ICF construction, the top plates on the walls are bolted to cast-in
connectors, similar to those used for foundations. Trusses or rafters
use steel connectors to this very secure top plate. Gable roofs of
all-ICF construction to the roof apex is also very strong.

Of course, the ultimate roof diaphragm is a concrete slab....

 

[Paddy]

dfkrug,

I agree, nothing like a concrete slab with conecting rebar to the walls. I plan on having short half walls so it will be safe to use the roof as a patio.

I have seen other photos where homes with concrete walls survived just to wall height. I think, if it had just gone all the way up!

 

[_RaT_]

Yes, hip roofs could survive; gable roofs were doomed.

The other reason that some roofs stayed on and some did not is the
quality of the top plate to roof connections. Post-mortems of
hundreds of failed newer stick-framed structures (mostly in FL in the
90s) showed that simple toe-nailed connections did not hold the
roof on. Simple truss-to-top plate connections were better, but not
enough. Codes changed to require steel strapping that extended
down the walls and in some cases, over the roof.

In ICF construction, the top plates on the walls are bolted to cast-in
connectors, similar to those used for foundations. Trusses or rafters
use steel connectors to this very secure top plate. Gable roofs of
all-ICF construction to the roof apex is also very strong.

Of course, the ultimate roof diaphragm is a concrete slab....

I remember framing my first project, a 4 plex. I was a bit suprised even though I knew nothing, at how little connection there was between the top plate and the ceiling/roof joists. Toe nailing, a little freeze block and that was it, we did not even use plywood on the walls, just led in bracing. Out here in CA, we have many Simpson type brackets to attach and create seismic panels, some seem a bit silly, but the rafter connection brackets make alot of sense. For me, ICF is the start of the future. There is so much more to "R" value then what you read on the bag of fiberglass insulation. Remember, with open insulation like fiberglass R13, R19 etc. measurements are static conditions where air movement is minimal at best. Put fiberglass on a vaulted ceiling and its R value will go down. Same in a walls. ICF pretty much eliminates many of those issues.

 

[bugstruck]

Ext foam/concrete int
Ext concrete/foam/concrete int (my choice)
Ext foam/concrete/foam int (ICF)
ext concrete/foam int

Each configuration is simulated in 10 climate regions. Summary; foam on inside walls performed lowest and concrete on inside performed highest.

Haven't checked the link out yet (I will though) but I would have guessed the all foam exterior to be the best. The thermal sink (concrete) is against the most evenly regulated thermal envirionment (inside) and acts a a buffer or delay to exterior temp swings. My guess anyhow? The only better place for that thermal mass could be inside the exterior walls?? I know that is often done on passive solar but I'm not aware of anyone intentionally putting thermal mass on the inside of the home in a conventionally controlled envionment. Not sure if it would be of real benefit or not. Seems it might though.

 

[_RaT_]

Haven't checked the link out yet (I will though) but I would have guessed the all foam exterior to be the best. The thermal sink (concrete) is against the most evenly regulated thermal envirionment (inside) and acts a a buffer or delay to exterior temp swings. My guess anyhow? The only better place for that thermal mass could be inside the exterior walls?? I know that is often done on passive solar but I'm not aware of anyone intentionally putting thermal mass on the inside of the home in a conventionally controlled envionment. Not sure if it would be of real benefit or not. Seems it might though.

Chris, I think you hit the nail head on, dead smack square in one swing.

 

[Paddy]

Rat/Bugstruck,

Internal thermal mass is very good when solar is used. It seams here in Indiana, when it's cold it's also cloudy

In some of the studies listed above, no insulation on the outside was best because of big daily temp varriations, Southern CA and AZ. In these cases, the goal is to "flip the temp cycle". That is to have the heat of the day being dumped in to the home as the cool of night comes. One main issue is timing. If your timing/ Thermal mass is to great, you can have the heat of Yesterday dumped during the heat of the following day. This will double your heat! Even in cases where the outside temp never gets below inside temp, the temp cycle flip is still good because the heat pump is pulling cooler air across the coils at night when the load hits.

Do check out the paper I reccomended, really neat material

 

[bugstruck]

Rat, I'm far far away from any mechanical guy so that was just a lucky guess based on some observations of construction types over the years. As for hitting the nail.... I'm a Carpenter before anything else, and before pneumatic nailing took hold, so I'd better Very interesting discussion here. I'm learning a lot from this thread and the links. Pretty humbling as there isn't a whole lot I haven't seen or experienced in the construction arena. Nothing the expert makes though, that's a rule I try to remember. I do favor the concrete home constuction idea for the reasons expressed here. If I do another home, that or timber frame is what I'd be inclined to go with. Now if you blended the two and did it well, that would be rather unique. I need to park that thought though or I could be distracted for hours...or days

 

[bugstruck]

Paddy, That is a very interesting description you gave on the CA and AZ locations. Makes a lot of sense. So is the ideal position of the insulation and the volume of the thermal mass inclined to vary from one geographical location to another? I think that's what I got out of that.

I'm the student on this one. I did poke around that link and there is a bunch of info as you said. I'll read some more over the weekend.

 

[_RaT_]

Rat/Bugstruck,

Internal thermal mass is very good when solar is used. It seams here in Indiana, when it's cold it's also cloudy

In some of the studies listed above, no insulation on the outside was best because of big daily temp varriations, Southern CA and AZ. In these cases, the goal is to "flip the temp cycle". That is to have the heat of the day being dumped in to the home as the cool of night comes. One main issue is timing. If your timing/ Thermal mass is to great, you can have the heat of Yesterday dumped during the heat of the following day. This will double your heat! Even in cases where the outside temp never gets below inside temp, the temp cycle flip is still good because the heat pump is pulling cooler air across the coils at night when the load hits.

Do check out the paper I reccomended, really neat material

Thanks Paddy, great info.

 

[Paddy]

Bugstruck,

Yes location, location location. Oh and time of year! And that is the core of the problem. The configuration that is best in Fall will not be optimal in 96 deg Summer with high humidity. The best design is the one that benifits more days per year than another design. I saw a report where a caution was placed on a design where it was so efficiet that the AC never runs, too much humidity.


When I first started seeing ICFs, I liked them but as I thought about it did not make sence. How can they claim supper insulation and effective high thermal mass? If that insulation is doing such a good job, the thermal mass isn't going to be exposed to much heat. ICFs are definately better than standard frame construction. I also don't like the foam inside and out. They say you can stuco the outside but once a baseball hits it, you got a nice dent. With the concrete on the exposed sides, I would have stuco on the outside and a thin layer of plaster on the inside. Both sides would have a textured look

 

[Highbeam]

"The only better place for that thermal mass could be inside the exterior walls?? I know that is often done on passive solar but I'm not aware of anyone intentionally putting thermal mass on the inside of the home in a conventionally controlled envionment. "

Big herkin masonry chimneys that are within the envelope offer an effective thermal mass that you can warm up with the fire.

 

[_RaT_]

Bugstruck,

Yes location, location location. Oh and time of year! And that is the core of the problem. The configuration that is best in Fall will not be optimal in 96 deg Summer with high humidity. The best design is the one that benifits more days per year than another design. I saw a report where a caution was placed on a design where it was so efficiet that the AC never runs, too much humidity.


When I first started seeing ICFs, I liked them but as I thought about it did not make sence. How can they claim supper insulation and effective high thermal mass? If that insulation is doing such a good job, the thermal mass isn't going to be exposed to much heat. ICFs are definately better than standard frame construction. I also don't like the foam inside and out. They say you can stuco the outside but once a baseball hits it, you got a nice dent. With the concrete on the exposed sides, I would have stuco on the outside and a thin layer of plaster on the inside. Both sides would have a textured look

You must be thinking of a one coat acrylic stucco. Why not do a 3 coat? That is the standard for better quality. With anchors every 8, you have better and more options to anchor whatever material you decide to use. I have yet to see an ICF that says "this is the overall R value" that their product has. Nudura makes the claim only on the actual foam, but that thermal mass will effectively add to that. The super insulation quality you must be refering to comes into play in more ways then meets the eye. No wall pockets, no header pockets, no studs which will drop the entire wall R value well below that of the insulation, no air infilitration flowing through the wall significantly reducing the effectiveness of conventional insulations. Reducing humidty, if it is a problem in your area can very easliy and effectively be accomplished without an AC and at less cost. I would much prefer a situation where I do not run my AC as frequently. While ICF will decrease your cooling costs, you still will probably have a conventional ceiling system. You won't get away from some AC with ICF and one thing you can count on, electricity will increase in price! Count on most areas of the US going to a progresive rate, the more you use, the base rate will continuie to escalate. Plan and be prepared.

 

[dfkrug]

The whole issue of thermal mass effects of various types of concrete
house construction has been beat to death in the ICFWeb forums. It
would be interesting to see the real word performance of a system that
utilizes no interior insulation. There is, of course, tons of real world
data on ICF performance with insul on both interior and exterior of the
forms.

Don't forget that in overall performance of an all-concrete house you
have to take into account the so-called thermal siphoning effect of a
large portion of the exterior walls being below grade. Virtualy all houses
will benefit from basements as part of a monolithic concrete house.

On the subject of stucco exteriors, that is a big one, too. The newer
thin-coat polymer-modifiied stuccos used by themselves over ICFs can
be easy to damage. Conventional stucco (Portland-based) over steel
lath, 7/8" thick is extremely durable. Unlike in stick frame construction,
conventional stucco over ICFs require no weep screeds, no expansion
joints, and no paper-backed lath. On my house, I used the 3-coat
with top color coat. Some systems now employ convention scratch and
brown coats with a polymer top coat, which yields more color choices
and a waterproof seal.

 

[Paddy]

dfkrug,

The web site I listed has good data performed by a lab endorced by the DOE for concrete inside and foam outside. Also Concrete/foam/concrete. In the study these two are conpared to ICFs.

I would not consider an "all concrete home". I plan a concrete/foam/concrete method. In this case the exterior concrete is isolated from the inside concrete except the ties that join the panels. The concrete floors/roof only rest on the inner concrete walls, again to isolate. There would be some exposure from the bacement level.

Can you reccomend a ICF discussion board?

 

[dfkrug]

dfkrug,


Can you reccomend a ICF discussion board?

I am no longer an active participant myself, but try
ICFweb.com

It is commercial, but ICFTalk includes forums from users, designers,
and explorers. It has been thru many changes as the industry
has matured and I do not know how good it is now.

 

[Paddy]

dfkrug,

Thanks for the link, I'll check it out. I like your ending statement, "I used to be an engineer, but now I get to build things." . I was a carpenter that moved to engineering. Back injury I have always felt my experince as a carpenter made me an engineer, not the book work.

 

[bugstruck]

"The only better place for that thermal mass could be inside the exterior walls?? I know that is often done on passive solar but I'm not aware of anyone intentionally putting thermal mass on the inside of the home in a conventionally controlled envionment. "

Big herkin masonry chimneys that are within the envelope offer an effective thermal mass that you can warm up with the fire.

I didn't think of that. Yes they do work much better than an exterior wall location. Had a central chimney in one of my childhood homes. Best conventional heating fireplace I ever saw. Probably was a net negative heat loss during fire-up at least. The baseboard heat didn't crackle much whan that was stoked up for more than a few hours though. I was old enough to notice that it hardly ran at all. But then the home was only about 1300 SF and the fireplace was exposed masonry front, back, and one side. The back got pretty toasty too.

A friend of mine has (2) woodstoves in an 1100 +/- SF home. Only runs one unless it's approaching zero and blowing. Maybe twice a year. Amazing how easy they are to heat at that size. Small stove in the basement about runs you out of the entire home. Burns it day and night and only goes through about 3 cords of mixed hardwoods a season. I think we are eventually headed back to smaller and even more energy efficient homes and the big builders are missing the boat. They make too much sense not too, high land prices or no. Cookie cutter that combo and you could make some coin. People would line up - even in this market IMO. Particularily in this market.

I forgot to mention.... He has aluminum sliding windows, 1970's vintage, no storms, and T-1-11 directly over 2 x 4 studs. R-11 insulation and half the main floor is true cathedraled ceiling that's 2 x 8's (thin) with a massive stone fireplace on the outside wall and some more poor glass either side. He doesn't like the baseboard electric bills. He told me 4 years ago his total electric could go to around $200.00 a month on a cold month. So he went to wood at $100.00/ cord at that time. He has no idea the value in that little place. Frees him up to live a very comfortable life on a modest income. Big boat, beach home, and the like. You'd think he knocked down 200K+ a year. Not at all.

 

[dfkrug]

I was a carpenter that moved to engineering. Back injury I have always felt my experince as a carpenter made me an engineer, not the book work.

It always seemed to me that if I did the research and then designed
something to meet a need, then I was missing out on a big part of
the creative process by not getting to build the product. This is true of
widgets, systems, software, or buildings. There is a place for theory and
a place for application.