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    Doors in concrete block house

    Doors in concrete block house

    New postby PierreA on Fri Jul 08, 2011 10:58 am

    I'm designing a house made of concrete blocks dry-stacked and filled with concrete. The height of a block is 194 mm; the length is 397 mm. (Hard metric blocks, which are 190×190×390 mm, are not available in North Carolina.) As the minimum height of a door is 2032 mm, I have to make the door rough opening 11 courses (2134 mm) high. I was planning to make the walls 13 courses (2522 mm) high and the door openings 10 courses high until I read this. A 11-course opening leaves one course for the lintel and one course of blocks above the opening. Is this enough or do I have to make the walls 14 courses high? The width of the rough opening will be three blocks (1191 mm).

    Also, since dry-stacking blocks isn't that common, I think I'll have to get custom lintels. The lintels will be 194×194×1588 and I'll need about ten, if the windows are the same width. Should I make them myself or ask the block company to make them?
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    Re: Doors in concrete block house

    New postby Jerry Peck - Codeman on Fri Jul 08, 2011 6:19 pm

    First, before you get much further into the design of the house I suggest checking with the local building department on their requirements for the wall with regard to wind loading and other live loads.

    Dry stacking was something which was tried many years ago and never caught on as the walls simply did not have much strength to resist lateral loads. The dry stacking of the blocks was done and then a surface bonding fiber reinforced plaster was applied to both sides of the dry stacked block.

    You would likely need a lot of horizontal and vertical steel reinforcement in the walls if you dry stack the block.

    I'm at a loss as to why you would choose to go with metric blocks instead of standard modular sized block.

    If you want an energy efficient wall design I recommend you check into ICF (Insulated Concrete Forms) where the ICF blocks are expanded polystyrene (EPS) with plastic separator braces encased in the molded EPS blocks which are designed to hold the horizontal and vertical reinforcing steel which is needed. After the blocks are set and the steel is installed (the horizontal steel is best installed as the walls are stacked up), concrete is placed in the wall cavity to make a solid concrete wall with the foam insulation on the exterior and the interior of the wall. These make quite efficient and well sealed structures. There are special design considerations which need to be addressed when constructing a structure with ICF walls.

    I'm not sure that you have thoroughly thought your design through to the point where you are ready to execute your design and turn it into a full-scale structure. I would like to be of help, but I think you are heading in the wrong direction of both using air for heat transfer and with the dry stacked block.
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    Re: Doors in concrete block house

    New postby PierreA on Sun Jul 10, 2011 12:45 am

    I found this on vobb.com:
    23. How much stronger is a concrete block-built home compared to a wood-built home? Based on industry standards, a concrete block-built home (using regular CMU'S) is 500% stronger than a wood-built home. However, we believe that a VOBB home is much stronger as a result of the interlocking walls and the cavities which are filled with concrete and rebar. (Engineering tests will be completed as needed.)

    I'm using common concrete blocks, not VOBB, but I am both filling them with concrete and rebar and coating them with fiber cement.

    According to http://www.drystacked.com/draw.html, the module size when designing a dry-stacked house is 7+7/8 in, which is 200 mm, which makes the arithmetic a lot easier. I'm also going to add 3 mm to the height, making 197 mm. (The book from the Carolinas Concrete Masonry Association states that blocks can be up to 3 mm bigger than the specified actual dimensions; if they're smaller, I can add mortar.) This means the rough opening width is 1200 mm and the height is 2167 mm minus the sill.

    drystacked.com shows three courses above the top of the door, so that's what I'll use. The first two are the lintel and are poured in place, with rebars above the door. The third is the topmost course of the wall and has horizontal rebars placed all along the wall, which I'll have to place carefully so as not to interfere with the anchor blocks.
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    Re: Doors in concrete block house

    New postby Jerry Peck - Codeman on Sun Jul 10, 2011 5:37 pm

    Pierre,

    I perused several of the pages on those web sites you mentioned in your post and not only are they are geared toward the novice, they contain claims which are exaggerated. One is that concrete block is 500 time stronger than wood frame - in one aspect it might be, but not as an overall for the completed structure.

    Also, they keep mentioning the cost savings of dry stacking over laying the block up with mortar, and then don't tell you to consider the additional cost for all the filled cells they are filling above and beyond what would normally be filled with regular mortar laid up block.

    From reviewing what is on those web sites I would recommend: a) laying the blocks up with mortar; or b) if you are going to fill the walls anyway, then use the ICF blocks I mentioned previously as they will produce a very well insulated house.

    Is a block house stronger than a frame house? Depends. Depends on how each is designed and constructed.

    Does a frame house require more attention to details than a block house? Yes ... but ... if very many of the details are missed on a block house, the strength to resist the wind loads, seismic loads, etc., are lost and you may have a house which is actually weaker than a frame house.

    I'm not trying to discourage you from constructing a dry stacked block house, only trying to open your eyes to some of the things not mentioned by the people trying to sell them.

    One is water intrusion ... a mortar laid up block house will be more moisture resistant than a dry stacked block will be - unless - unless ALL of the cells in the dry stacked block wall are filled with grout, and that adds a significant cost factor which needs to be considered. Water intrusion may not be a big consideration in some areas, like Arizona, but in most other areas it is a big consideration.

    I am just trying to make sure you do all of your homework before beginning construction or getting so far into your project that any changes you make will create re-designing what has already been designed.
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    Re: Doors in concrete block house

    New postby PierreA on Tue Jul 19, 2011 12:12 pm

    I am a novice, so I have a lot of questions! :)

    I'm sure the "500 times" is a typo. It should be "500%", I saw that elsewhere on the site. The ICF site says a few more times - 6.5 or 8.5 times as strong, or something in that range.

    ICF isn't right for what I'm doing as it's insulated on both sides. I need insulation on the outside, but not on the inside. All cells will be filled for thermal mass.

    Wouldn't the cement that is parged on the wall surfaces contribute to moisture resistance?
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    Re: Doors in concrete block house

    New postby Jerry Peck - Codeman on Tue Jul 19, 2011 5:38 pm

    PierreA wrote:ICF isn't right for what I'm doing as it's insulated on both sides. I need insulation on the outside, but not on the inside. All cells will be filled for thermal mass.


    Understood, the ICF would make the thermal mass ineffective.

    Wouldn't the cement that is parged on the wall surfaces contribute to moisture resistance?


    Basically, not much, if at all. Rain, water, moisture all go through the stucco to varying degrees, and either a drainage plane is needed to drain the water down or a system of storing the moisture is needed to allow it to dry out over time.
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