Cracked Houses: What the Boom Built

[Overstreet]

In CMU (concrete masonary unit) construction today, there is rebar in the slab, connected to rebar in concrete "columns" poured within the block (every four feet and at corners/openings), and tied to a lentil (steel reinforce beam around the entire perimiter at the top of the wall. Far superior to the hollow blockwork of the eighties.

Filled cell column rebar spacing  varies with structural engineer and the building. I've seen them in every cell, every other, and greater. A pilaster made from a 16" x 16" block in a normal 8" x 16" wall can make it even stronger but oddly shaped.   More significant would be the bond beam or header beam dimensions that tie all the "columns" together at the top and intermediate beams in tall walls.

Masons are often bad fill cell installers. They tend to use mortar to fill the cells when concrete is called for.  Concrete is higher strength. Mortar is lower strength made to hold masonry together not so much a column.

The truss or rafter connection is often just a toe nail connection in pre-Andrew homes which if the staples on the roof sheathing, often only 7/16 CDX plywood, hold the toenail connections fail and the whole roof structure can peel off a block home in a big blow.  Today's connections have clips at ever truss to tie the roof structure to the bolted plate on top of the CMU wall. .............which relies on a lot of 6# common nails and sheet metal. But we've done pull tests on those connections and found them remarkably strong. Just put enough nails in.   Pre-Andrew clip spacing was 30" centers. which some how became every other truss which might be a 16" or 24" center to center layout. Which none of them measured out to 30" cc.

[Dog Walker]

Another "forever" building method in addition to CMU are ICF (Insulated Concrete Forms) which are frequently used in the coastal high wind zones.  They look like big Lego blocks made of styrofoam that are hollow in the middle and held together with plastic or wire straps.

A wall is assembled like a Lego wall with horizontal and vertical steel reinforcing rods then a small aggregate concrete is pumped into the hollows.  You end up with a 6" thick reinforced concrete wall with two inches of styrofoam insulation on the inside and outside.  Windproof and really high R value.

[Non-RedNeck Westsider]

Another "forever" building method in addition to CMU are ICF (Insulated Concrete Forms) which are frequently used in the coastal high wind zones.  They look like big Lego blocks made of styrofoam that are hollow in the middle and held together with plastic or wire straps.

A wall is assembled like a Lego wall with horizontal and vertical steel reinforcing rods then a small aggregate concrete is pumped into the hollows.  You end up with a 6" thick reinforced concrete wall with two inches of styrofoam insulation on the inside and outside.  Windproof and really high R value.

^^^  This.  I worked on a project last year at Jax Beach that used this method of construction and found it to be considerably advantageous in many aspects - with the sole exception being initial cost.  But I think the residual benefits far outweigh those costs. 

[Non-RedNeck Westsider]

In CMU (concrete masonary unit) construction today, there is rebar in the slab, connected to rebar in concrete "columns" poured within the block (every four feet and at corners/openings), and tied to a lentil (steel reinforce beam around the entire perimiter at the top of the wall. Far superior to the hollow blockwork of the eighties.

Filled cell column rebar spacing  varies with structural engineer and the building. I've seen them in every cell, every other, and greater. A pilaster made from a 16" x 16" block in a normal 8" x 16" wall can make it even stronger but oddly shaped.   More significant would be the bond beam or header beam dimensions that tie all the "columns" together at the top and intermediate beams in tall walls.

Masons are often bad fill cell installers. They tend to use mortar to fill the cells when concrete is called for.  Concrete is higher strength. Mortar is lower strength made to hold masonry together not so much a column.

The truss or rafter connection is often just a toe nail connection in pre-Andrew homes which if the staples on the roof sheathing, often only 7/16 CDX plywood, hold the toenail connections fail and the whole roof structure can peel off a block home in a big blow.  Today's connections have clips at ever truss to tie the roof structure to the bolted plate on top of the CMU wall. .............which relies on a lot of 6# common nails and sheet metal. But we've done pull tests on those connections and found them remarkably strong. Just put enough nails in.   Pre-Andrew clip spacing was 30" centers. which some how became every other truss which might be a 16" or 24" center to center layout. Which none of them measured out to 30" cc.

I'm no engineer, but IMO the typical H-clips used to hold down trusses are probably some of the most poorly designed, over engineered pieces used in home construction.  Your typical H2.5 first is nailed into the side of a double top plate, and unless the installer is taking his time to lay everything out properly (they aren't) the nails are hitting into the weakest part of the wood, aside from the endgrain, and some nails fall into the space between the boards.  And you can blame the installer, but I blame the designer - you have to design to the lowest common denominator.  The straps need to be face nailed into all members in order to utilize the strength of the wood and the need to be designed with a quick intstallation in mind.  They can't expect each clip to be spaced perfectly.  And yes, I understand that this is where the over-engineering comes into play, but once a system fails, it fails.

[Dog Walker]

Cost for ICF walls runs about 10% above CMU per linear foot, but interior finish goes faster and insurance and energy savings will offset the extra up-front cost pretty quickly.

I have one building with this method and will never use another method again.

[Non-RedNeck Westsider]

I was under the impression that it was closer to the 30%-35% higher range....

His cost may have just been project specific - 3 story wall, existing homes on both sides of a narrow lot, at the beach, etc.

[buckethead]

Cost for ICF walls runs about 10% above CMU per linear foot, but interior finish goes faster and insurance and energy savings will offset the extra up-front cost pretty quickly.

I have one building with this method and will never use another method again.

I've done ICF houses before. Far and away superior to all others.

Added note: Styrofoam does not rot. Even CMU will. Especially on the north end of a building where mold can set in.

Little foam dots get all over. The neighbors will complain... really no containing them completely. Not a huge problem, IMO.

[Dog Walker]

My building was only single story and I can see how a three story ICF building would be more than 10% above CMU.  That's a lot of lifts and a really big pump!

[Overstreet]

[/quote]............... but IMO the typical H-clips used to hold down trusses are probably some of the most poorly designed, ................ Your typical H2.5 first is nailed into the side of a double top plate, [/quote]

H-clips that hold the edges of plywood together?....

True that a simpson strong tie, H2.5 nailed to one side of the truss can hit the plates at the joint and be weak. Anything like a H-10 that approaches a saddle is better.  Any of them are relatively cheap compaired to say a sheet of plywood. Load 'em up.  The best connection I saw was a red-iron clip(2) welded to the beam forming a saddle connection through bolted through the truss.  It was a nice picnic pavillian with I'm sure a lot of uplift, not a house.

We did a whole bunch of buildings with welded liteguage framing, 10g top plate with wood trusses and Simpson Strong ties. All connections were screwed or bolted PE designed and many were pull tested. At the time liteguage trusses were three times the price of trusses.

I personnally prefer red-iron and bar joist, but that's another world.