I am doing a new addition to my home and have been speaking to contractors and reading online about the differences between concrete block and poured wall. I have found some reference articles explaining the differences but am still a little unsure. It is a budget addition and although I understand the importance of the concrete portion of the building I want to make sure I spend my money wisely.

Question 1. What are the opinions on the financial differences between a Poured wall, and a steel reinforced concrete block wall? I am sort of looking for a percentage difference in price.


Question 2. What is the opinion on the real life differences in the stability of the two walls.

Also the interior will be a recording studio so the transmission level is also key.


Thanks for the help

Steve Mabee
audiokat1@yahoo.com

 

I don't know if your a talking about below grade or above grade, so here goes -

BELOW GRADE
1. For a basement, the costs are about the same. For a square box basement, poured will be cheaper. If you are talking about some corners or offsets and changes in height or stepped footings, block will be cheaper. Poured walls ar very difficult to pour plumb and square (carpenters hate sloppy poured wall contractors since the problems during pouring do not show up until the next day and are hard to fix). You can analyze both to death and the difference will probably be less than the cost of different fixtures in a bathroom. The strength of the walls can be whatever you need since both are designed to meet the same codes and loads.

2. Stability for the two would be the same since both would probably use the same footings. The block wall will probably be thicker (8", 10" or 12"), so it is easier to get greater flexural strength (bending resistance) unless you use thicker poured wall. Both walls are designed as reinforced structural elements. Both can crack due to shrinkage. The shrinkage of a poured concrete wall is greater.

3. For a recording studio in a basement, sound transmission is not important for an exterior wall. If you use interior walls, there is no question that block would be cheaper for the same sound transmission. For acoustics, I would imagine that you would rely on surface treatments. For an uncovered wall, the block wall would have slightly better acoustic proerties.

ABOVE GRADE
If you want the value of a concrete structure above grade, both poured and block would be vastly superior to wood construction. Masonry and concrete block are the preferred and most common types of construction in the developed countries. Wood frame and straw bales represent a smaller part of the construction. They are more common in undeveloped countries.

1. ICFs (Insulated Concrete Forms for poured walls) provide excellent thermal properties, but are more expensive than block. Concrete block are much more economical for above grade, especially if interior walls are considered.

The strength of both would be equal. Both very economically meet the FEMA requirements for resistance to wind driven objects (tornado, hurricane). Only very specilized, unconventional, costly construction using wood can do this. The both perform better than wood for seismic resistance and in flood areas.

2. Stability and strength of both methods are equal, since they both are designed to the same structural requirements. Two to four stories are the normal for concrete masonry. Building up to 25 stories are commonly constructed using 6" thick block walls with no structural steel or concrete frames.

I hope this gives you some onformation of both types of residential construction. Obviously local economics governe the details of the costs.

Dick

 

Dick,

Thanks allot for the help. I am newbee to contruction but becuase of a limited budget I am forced to do as much learning as possible to act as the GC. The strucure is going to be fully above ground. The plan is a 700 Square foot two story addition with the first floor as concrete and the second framed out.

You mentioned the acoustic transmission being roughly the same becuase in a below grade it is of course under ground. What do you know about above grade? I would imagine there would be less transmission with the poured walls but if I read your explanation correct you said that above grade poured walls would be more expensive.

As for acousic treatment I am not to worried to much since the interior will be framed out.


Thanks again for the help.

 

Sounds like a good hurricane structure if there are no flyng obects above 8 feet up. You would be back in business a day or two after the water goes down.

For rigid walls, the sound transmission generally is related to the mass of the wall. A normal unfilled 8" block wall wall has an STC (Sound Transmission Coefficient) of about 50. Filling it with sand or grout raises it to about 53 or 55 which is many, many times better (the scale is logarithmic). You probably would be in the range of 53 to 55. It is very difficult to get above 55 unless you take extra-ordinary measures and an unlimited budget. Special high density concrete block could be used (similar to x-ray protection), but are costly and impossible to get in smaller qualtities.

To give you an idea, a wood frame is about 40 to 45 STC, depending on whether it has staggered studs or not. Fiberglas gives a minimal contribution, since the wall can act as a drum. Wood walls can be improved somewhat by hanging sheet lead. and using costly acoustic panels that you are probably familiar with.

Doors, windows and corners raise the cost of poured concrete because of the opemings and the need for additional bracing to keep the unsymetrical structure plumb, square and level during pouring.

I would suggest looking into precast concrete floor slabs with a 2" topping between the concrete and wood sections.

Dick

 

Dick,

This may be an absurd question but do you happen to know what I can expect to pay for a concrete slab with concrete block walls? I know that there are a million different variables so feel free to not answer, I am simply doing a rough budget outoine and was trying to get a rough figure for that part of the buildout.

I suppose I am also trying to figure in general what is involved with building such a structure. I have searched the web for general concrete/foundation terminology but haven't found anything incredibly useful yet.

Here's the info I have:

Building size: 34x22
Slab Size: I suppose 8'' less(?)
Wall height: 12'
The grade is nearly flat.
Location: Nashville TN

Of course I will be leaving this to a professional I am just trying to get educated enought to screw things up. : )



Thanks again,

Steve

 

I am not able to give you any accurate prices for your area. You would be best to contact a contractor and explain that you need some budget figures. Since you don't have a great deal of information, do not expect anything accurate - its just a budget estimate.

He will ask you some questions that will make you think a little more about what you want.- That is good. He may be able to point you toward someone for drawings and addressing the code issues.

If the 12' height is for the sound proofed level, I would suggest 12" concrete block walls filled with dry sand. No problem with the height and filling with sand is effective and a lot cheaper than the concrete and the cost of forming and bracing a 12" high wall. 12' of concrete puts a lot of pressure on the forms and separates the men from the boys in placement and form quality.

If you are really serious about cutting sound transmission, I would seriously think about holllow core precast panels (probably 8" thick) for the roof. They can handle the span easily and will transmit a fraction of the sound that any wood system would, and you can eliminate any interior walls or columns.

You will have to address the code provisions for frost (I think you have that in Tennessee). You may end up with a 4" slab floating between block stem walls sitting on a footing below the frost line.

Dick

 

I have heard before about the precase panels. Are those in replacement of the floor joists? Is it quite a bit more expensive than lumber?


Steve

 

They are more expensive. Precast hollow core concrete panels are commonly used for floors in other countries that build two story homes with concrete or masonry walls. Some progressive builders use them for the first floor to acheive a basement without columns. A wood frame structure is not suitable for the concrete panels.

If you are serious about sound control, they are your answer. Usually, they are 3 to 4 feet wide and cut to the span length you need. They range in thicknesses from 6" to 20", depending on what is needed. The most common thickness is 8" since it fits well within most building module dimensions. An 8" plank will be adequate for your spans. They are placed with a mobile crane.

Dick

 

What do you mean by this? If were to use this as the ceiling/fllor for the second level would it be difficult to attch framing for the second level?

Thanks,

Steve

 

It is done every day. Use anchors, Tapcons or ramset (22 caliber powere nailer). - Just a detail.

The big picture is the cost and precticality of your addition.

Dick