MICF stands for Masonry ICF or Masonry Insulating Concrete Form.
It is a stay-in-place ICF form system where the shells of the form are CMU instead of Rigid Insulation.
Rigid Insulation is layered against the inside face of the exterior or both CMU shells.
The shells are assembled in place with dovetail shaped plastic tees that also accept 1/2" pvc crossties.
The key to using CMU shells as concrete form walls in a labor saving manner is the plastic tees.
They have a shim built into them so that the 3/8" gap between shells is maintained by the tees.
This allows the shells to be snapped together with no mortar while maintaining proper spacing.
Imagine the PERFECT House Wall Envelope!
Cost efficient - Use standard Materials you can find at any Home Improvement Box Store.
Eco-Friendly - A concrete wall and CMU and Plastic are all recycling Friendly.
Healthy for Occupants. - Concrete & CMU walls do not emit dangerous vapors to indoor air.
Energy efficient - Continuous layer of any brand of rigid insulation slows energy flow thru wall
Energy efficient - Thermal mass of concrete wall to the interior acts as energy battery.
Energy efficient - Solid Concrete wall prevents flow of air thru wall.
Energy efficient - PVC pipe crossties limits thermal bridging thru rigid insulation.
Safety & Performance - CMU and concrete exterior and interior ensures Fire Safe Construction.
Safety & Performance - Concrete Wall as Structure can resist high wind events, floods, earthquakes.
Comfort & Performance - Concrete lined with rigid insulation will result in a quiet house.
Durability - Concrete Wall will last 3 Times Longer than Wood Walls.
Sustainability - A longer lasting house does not have to be rebuilt or update every 50 years.
Low Cost Labor - Mortar Free Joints result in Masonry Construction that requires less Skill to learn.
MICF - Only two special parts required, Green Plastic Tee Connector, Masonry Shells w/ Dovetail Channels.
Simple Solution for a Better House Wall!
The Breathing Wall Advantage:
My stay in place concrete wall system was inspired as an inexpensive concrete wall form system
to protect homeowner from high wind events such as happened in Joplin. But it is also a system
that has all the components of the perfect wall system to balance insulation with moisture management and thermal mass.
You might ask, "Why is this system with cmu shells as the forms, layered with insulation only against the exterior shell, any better than current ICF concrete form systems with two rigid insulation shells, one on the interior and one on the exterior?" Isn't it common sense that two layers of insulation are better than one!
I would ask you to think outside the block. (sorry for the pun)
Old historical buildings constructed of an exterior and an interior layer of stone with stone rubble between the two layers have lasted hundreds of years and as it turns out
these walls are also ok at keeping in the heat. So lets examine how these walls perform so well and how can we keep the good properties of these walls while improving on the deficient properties of stone walls.
So what properties do we want to keep and what properties do we want to improve on?
One advantage of a stone wall is that they can breath. The mortar joints are porous and vapor can move slowly through the mortar joints and eventually into and out of the building, but in a controlled slow manor. These stone walls and their stone rubble centers have a high moisture mass. What does this mean?
The Stone Wall ACTS as a SPONGE! a big Sponge. When rain hits a stone wall the stone can absorb that rain. You would normally think of this a a bad thing. But you are thinking inside of the block. Old historic buildings with thick stone walls usually do not have problems with moisture
penetration that reaches the interior finishes. This is because the walls are so thick and can absorb so much water that the walls have enough water capacity to store the rain water in the stone wall sponge before it reaches the interior finish. If your sponge was not big enough to
hold all of the water then the water would start to stain and mold the interior finish. Think of a large sponge that is big enough to absorb a bowl of water but when you use a small sponge the
sponge can not absorb all the water and starts to drip because it is saturated.
The key that makes stone walls successful throughout the years is that they have high moisture mass to absorb rain water and humidity to prevent those damaging elements from reaching the
interior finishes. But the key to a successful sponge is that you need to dry the sponge out.
The stone needs to BREATH. Before water sealers existed, stone walls were built and lasted hundreds of years even though mortar technology was not as good back in historic days. I would
contend that water sealers have caused more problems with stone walls then they have solved.
The stone sponge wall should have the moisture mass to absorb water during rain and high humidity events. The stone sponge must then have the chance to dry out once the sun and drier weather returns. Just like a regular sponge needs to dry out after use or the sponge becomes useless, so
must the stone sponge dry out by breathing otherwise it becomes useless.
The most damage to stone walls occurs when moisture remains in the mortar joints and then that moisture freezes. This breaks the bonds inside the mortar and it then no longer has tension strength. When you can take a pencil and scrape out mortar between brick or stone, this damage
is usually caused by excess moisture that freezes while inside the mortar.
Inside of the mortar are air pockets that you can not see. When moisture freezes in mortar or brick or concrete, it first expands into these air pockets. So there can be some moisture in the masonry during freeze thaw cycles as long as the expansion does not exceed the capacity of the
air pockets. The key is to construct a stone or masonry wall that has enough moisture mass so that the moisture density is low enough to allow for the air pockets to absorb the expansion. The
key is to construct a stone or masonry wall that can dry out enough before the moisture freezes.
The key is to construct a wall that breaths.
Sealing a stone or masonry wall can cause more problems than it solves. You must completely seal the wall so no moisture can get into the mortar. Moisture can actually get trapped inside of the masonry that leaks into a half complete sealing job. That moisture can then be trapped inside of the wall by the same sealer. When the moisture freezes the mortar joints can turn to oatmeal.
Stone walls also have a high thermal mass. In short they are not so bad at keeping your house warm. The mass of the stone absorbs the energy produced inside of your house. This mass acts as
a temperature battery that is trying to even out temperatures around it. At the same time the stone is a good conductor of energy. This means that energy can be conducted to the outside air
faster than through insulation materials. You have to take the good with the bad.
Or Do YOU?
What if you could have a wall that breaths like a stone wall? What if you could have a wall that
has high moisture mass like a stone wall? What if you could have a wall that has a high thermal
mass to the interior to act as a battery for your heating or cooling system? What if you could
have a wall that has a continuous layer of rigid insulation to the outside to reduce conduction
of your stone wall? What if your rigid insulation had plastic pipes and joints through it that
allows your wall to pass through vapor but separates the thermal mass from the exterior shell?
I would say that you would have all the advantages of a stone wall plus the advantages of an insulated wall. I would say that you have a high moisture mass, high thermal mass, highly
insulated, breathing wall system.
What is another advantage of a stone wall? It has high weight mass and high compressive strength. A wall with high mass is harder to blow over. The wind must accelerate more weight. While this is good for a high wind event it is bad for a seismic event. When an earthquake accelerates the large mass of a stone wall it takes more force or strength in the wall to slow down that acceleration after the quake changes directions. Stone walls have low tension strength so resisting its own mass
that has been accelerated in an earthquake is a problem.
But what if your stone wall could be reinforced with steel to increase the tension strength of your stone wall? That is what
a concrete wall is. It is a reinforced, high compressive strength, high mass wall that has tension strength. You can combine
all of the strength advantages of a stone wall with all of the tension strength advantages of steel.
So you can have a stay in place concrete form system that has a high moisture mass, high thermal mass, high weight mass, reinforced concrete center formed by two layers of cmu shells with all the advantages of a stone wall plus tension strength, insulate only to the exterior of the concrete wall to counter the high energy conductivity of the concrete, while retaining the high energy conductivity to the interior so that your wall can act as a battery for you heating or cooling system, at the same time the insulation has paths to allow for vapor flow so that your wall can act as a moisture battery to store and release the rain before it reaches the interior finishes.
So would you rather have a 2x6 wood stud wall that has insignificant moisture or thermal mass and molds at the drop of a hat, or would you rather have a well insulated concrete wall made with stay in place cmu forms? Would you rather have a wall that is constructed on individual sticks that are connected together with puny steel pins (nails), or would you rather have a wall that is formed in place as one member? No wonder the test for resisting tornadoes is firing a 2x6 out of an air cannon. Where do those 2x6 members come from?
Would you rather have an ICF wall where your thermal battery mass of the concrete center is insulated from your heating or cooling system, or would you rather have an MICF system where the thermal mass is only insulated to the exterior?
Would you rather have an ICF wall where your exterior rigid insulation is exposed to the soil allowing for insect infestation? or would you rather have CMU block protecting your rigid insulation from insects?
Would you rather have an ICF wall that snaps together so tightly that moisture is permanently trapped inside your concrete wall, or would you rather have an MICF system where your concrete wall can breath and dry out and absorb water and dry out and breath?
So think inside the block in a new way. Combine the advantages of a proven old technology (stone wall), retain the properties that worked so well, while combining those properties with modern insulation and reinforcing technologies to come up with the perfect wall system.
MICF - Breath!
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Advantages of MICF:
Let us review the advantages of Masonry Insulated Concrete Form wall system as compared to a house where the walls are constructed of 2x4 wood framing at 16” centers:
Air Flow – Differences in interior and exterior pressures in a house result in air and vapor moving through 2x4 construction as plywood to stud connections are not capable of stopping air flow. MICF is filled with concrete and while moisture and air can still move through concrete the rate of movement is slowed down.
Continuous Insulation – In 2x4 construction the insulation is placed between the wood studs. The wood studs act as thermal bridging to let energy into or out of your house. MICF has a continuous layer of rigid insulation that is only interrupted by plastic pipe cross ties. These plastic cross ties transmit less energy through the insulation.
Mold – In 2x4 construction the dew point can occur inside of the wall. With condensation present and a food source available (organic 2x4 studs) mold can form inside of walls. Masonry shells, concrete, rigid insulation, pvc pipe, plastic connectors are all inorganic and will not provide the food for mold to grow.
Wind Resistance – 2x4 wall construction is assembled with nails. These connectors are easily compromised in high wind events. The 2x4 studs then become flying projectiles. MICF is a continuous concrete wall system that can resist high wind events.
Thermal Mass – Concrete and masonry have high thermal mass that can absorb the energy of a houses heating and cooling systems acting like a temperature battery to even out daytime and nighttime temperatures.
Moisture Mass – Concrete walls can act as a sponge to absorb moisture. Your HVAC system can be sized smaller to remove the moisture from the air as the concrete wall will even out that demand over a 24 hour cycle.
Sound Absorption – A layer of masonry, a layer of rigid insulation, a wall of concrete, another layer of masonry, a quiet home. Need I say more.
Insect Infestation – The rigid insulation is shielded by a layer of masonry. Unlike ICF and 2x4 construction where insulation and wood are easily accessible to the exterior grade.
Longevity – The design life of a wall system constructed of 2x4 wood studs would be considered to be ½ or less of a wall system constructed of a concrete wall.
Fire Resistance – the interior and exterior layers of MICF are masonry protecting the plastic parts from any fire exposure. 2x4 wood studs are fuel for fires.
Structural Support – 2x4 wall systems are generally only used to support wood floor and roof systems. MICF can support wood floor and roof systems, but can also support new floor and roof systems that may evolve to meet future energy and construction practices.
Normal Masonry Safe Rooms must be hidden as a small bathroom inside of a house because they are uninsulated. Since MICF are stay in place concrete forms
with a layer of insulation, you can extend the safe room (250mph hurricane) to include a security room (170mph hurricane) to the exterior walls of the house.
Now your important documents and possesions can be protected up to a f3 hurricane while your family can be protected up to a f5 hurricane.
The roof of your security room would be a 6" concrete slab. The rest of the first floor and the second floor can be standard wood framing. The master
bedroom on the second floor would have a concrete slab floor. The security room would be non-combustable construction and could be used as an office or
den where items can be protected from fire. If you opt for an upgraded security door on your den the room could double as a secure room against intruders.
Links to More MICF Connector Ideas
Cast in Place Concrete Lintels
Round Corner in 12 Inches
Combine 2 Shells and Cube It
Dead Weight Soil Retaining
Replace Steel beam w/ Cast Concrete Beam
Masonry Structural Insulated Panels, M-SIPS
A Better Flexible Masonry Bond Beam
Let's Get Artistic with MICF
1/2" PVC Crossties: Let the Air Flow!
Poured in Place Prestressed Concrete Wall
ZigZag Running Bond Control Joints
Eyebrow Concrete Pilaster / Column!
Air Insulated Concrete Wall
Jump ideascale Perfect House Wall
NCMA PHX Slideshow